Common Radiation Path for Acquiring Particle Information by Means of Direct Image Evaluation and Differential Image Analysis

Abstract

Device for determining information which is indicative for a particle size and/or a particle shape of particles in a sample, wherein the device comprises an electromagnetic radiation source for generating electromagnetic primary radiation, an electromagnetic radiation detector for detecting electromagnetic secondary radiation which is generated by an interaction of the electromagnetic primary radiation with the sample, and a determination unit which is adapted for determining the information which is indicative for the particle size and/or the particle shape based on the detected electromagnetic secondary radiation, wherein the determination unit is adapted for selectively determining the information firstly by means of an identification and a size determination and/or a shape determination of the particles on a detector image which is generated from the electromagnetic secondary radiation, and/or for determining the information secondly from temporal changes of the electromagnetic secondary radiation between detector images which are generated at different detection points in time.

Claims

1. Device for determining information which is indicative for a particle size and/or a particle shape of particles in a sample, wherein the device comprises: an electromagnetic radiation source for generating electromagnetic primary radiation; an electromagnetic radiation detector for detecting electromagnetic secondary radiation which is generated by an interaction of the electromagnetic primary radiation with the sample; and a determination unit which is adapted for determining the information which is indicative for the particle size and/or the particle shape based on the detected electromagnetic secondary radiation; wherein the determination unit is adapted for selectively determining the information firstly by means of an identification and a size determination and/or a shape determination of the particles on a detector image which is generated from the electromagnetic secondary radiation, and/or for determining the information secondly from temporal changes of the electromagnetic secondary radiation between detector images which are generated at different detection points in time.

2. Device according to claim 1, further comprising at least one of the following features: wherein the determination unit is adapted for determining the information from the detector image which is generated from the electromagnetic secondary radiation by dynamic image analysis, and wherein the determination unit is adapted for determining the information from temporal changes between the detector images by differential dynamic microscopy.

3. (canceled)

4. Device according to claim 1, wherein the determination unit is adapted for performing both the first and the second determination of the information for at least one pre-givable sub-range of particle sizes in a range between 100 nm and 20 m.

5. Device according to claim 4, wherein the determination unit is adapted for performing the determination of the information for particle sizes above the pre-given sub-range of particle sizes only by the first determination and/or for performing the determination of the information for particle sizes below the pre-givable sub-range of particle sizes only by the second determination.

6. Device according to claim 1, further comprising at least one of the following features: wherein the determination unit is adapted for using the same electromagnetic radiation source and/or the same electromagnetic radiation detector for the first and the second determination of the information, wherein the determination unit is adapted for using at least partially the same detector data which are detected by the electromagnetic radiation detector for the first and the second determination of the information, and wherein the determination unit is adapted for calculating and outputting a difference between particle sizes which are determined according to the first determination and particle sizes which are determined according to the second determination.

7.-8. (canceled)

9. Device according to claim 1, wherein the determination unit is adapted for performing the determination of the particle size exclusively according to the first determination above a first pre-givable size threshold value and for performing the determination of the particle size exclusively according to the second determination below a second pre-givable size threshold value, wherein the first size threshold value is larger than or equal to the second size threshold value.

10. Device according to claim 1, further comprising at least one of the following features: wherein the determination unit is adapted for performing the determination of the particle size exclusively according to the first determination below a first pregiven concentration threshold value of the sample and for performing the determination of the particle size exclusively according to the second determination above a second pregiven concentration threshold value of the sample, wherein the first concentration threshold value is smaller than or equal to the second concentration threshold value, and wherein the determination unit is adapted for determining information with respect to a viscosity of the sample from the first and from the second determination of the information with respect to the particle size.

11. (canceled)

12. Device according to claim 1, further comprising: an electric field generation unit for generating an electric field in the sample; and wherein the determination unit is adapted for determining the information which is indicative for the zeta potential of particles in the sample based on the electromagnetic secondary radiation which is detected in the sample when the electric field is present.

13. Device according to claim 12, further comprising at least one of the following features: wherein the determination unit is adapted for determining the information which is indicative for the zeta potential from temporal changes between detector images which are generated from the electromagnetic secondary radiation at different detection points in time by differential dynamic microscopy, wherein the electromagnetic radiation source is adapted for emitting the electromagnetic primary radiation in a pulsed manner, and wherein the device further comprises a primary beam forming optics between the electromagnetic radiation source and the sample, wherein the primary beam forming optics is adapted for collimating the electromagnetic primary radiation in parallel with respect to an optical axis.

14.-15. (canceled)

16. Device according to claim 1, further comprising: an imaging optics between the sample and the electromagnetic radiation detector, wherein the imaging optics is adapted for imaging the electromagnetic secondary radiation on the electromagnetic radiation detector.

17. Device according to claim 16, further comprising: an adjusting mechanism which is adapted for adjusting the imaging optics between different optics configurations for receiving detector data for the first determination of the information and for receiving detector data for the second determination of the information.

18. Device according to claim 17, wherein the adjusting mechanism is a revolver mechanism.

19. Device according to claim 17 or 18, wherein the adjusting mechanism is adapted for adjusting a first imaging optics for the first determination, which first imaging optics has a smaller numerical aperture than a respective aperture of the second imaging optics for the second determination.

20. Device according to claim 19, wherein the first imaging optics comprises or consists of a telecentric optics.

21. Device according to claim 19 or 20, wherein the second imaging optics comprises or consists of a microscope-objective.

22. Device according to claim 1, further comprising: a sample container which is accommodating the sample and arranged to intersect incident electromagnetic radiation generated by the electromagnetic radiation source.

23. Device according to claim 1, wherein the determined information which is indicative for the particle size and/or the particle shape comprises a particle size distribution and/or a particle shape distribution.

24. Method of determining information which is indicative for a particle size and/or a particle shape of particles in a sample, wherein the method comprises: generating electromagnetic primary radiation; detecting electromagnetic secondary radiation which is generated by an interaction of the electromagnetic primary radiation with the sample; and determining the information which is indicative for the particle size and/or the particle shape based on the detected electromagnetic secondary radiation wherein the information is selectively determined firstly by an identification and a size determination and/or a shape determination of the particles on a detector image which is generated by the electromagnetic secondary radiation and/or the information is determined secondly from temporal changes of the electromagnetic secondary radiation between detector images which are generated at different detection points in time.

25. A non-transitory computer readable storage medium, in which a program is stored for determining information which is indicative for a particle size and/or a particle shape of particles in a sample, which program, when it is executed by a processor, is performing or controlling the following steps: directing an electromagnetic radiation source to generate electromagnetic primary radiation that is emitted in a direction to interact with a sample; detecting electromagnetic secondary radiation which is generated by an interaction of the electromagnetic primary radiation with the sample; and using an acquisition device to determine information indicative of a characteristic of a particle size based on the electromagnetic secondary radiation; wherein the information is selectively determined firstly by particles on a detector image which is responsive to the electromagnetic secondary radiation, and/or secondly from temporal changes between detector images which are generated at different times.

26. (canceled)

27. Device for determining information which is indicative for a zeta potential of particles in a sample, wherein the device comprises: an electromagnetic radiation source for generating electromagnetic primary radiation; an electric field generation unit for generating an electric field in the sample; an electromagnetic radiation detector for detecting electromagnetic secondary radiation which is generated by an interaction of the electromagnetic primary radiation with the sample in the electric field; and a determination unit which is adapted for determining the information which is indicative for the zeta potential based on the detected electromagnetic secondary radiation; wherein the determination unit is adapted for determining the information which is indicative for the zeta potential from temporal changes of the electromagnetic secondary radiation between detector images which are generated at different detection points in time.

28. Device according to claim 27, comprising at least one of the following features: wherein the determination unit is adapted for determining the information which is indicative for the zeta potential by differential dynamic microscopy, wherein the electromagnetic radiation source is adapted for emitting the electromagnetic primary radiation in a pulsed manner, wherein the device comprises, a primary beam forming optics between the electromagnetic radiation source and the sample, wherein the primary beam forming optics is adapted for collimating the electromagnetic primary radiation in parallel with respect to an optical axis, and an imaging optics between the sample and the electromagnetic radiation detector, wherein the imaging optics is adapted for imaging the electromagnetic secondary radiation on the electromagnetic radiation detector.

29.-31. (canceled)

32. Method for determining information which is indicative for a zeta potential of particles in a sample, the method comprising: generating electromagnetic primary radiation; generating an electric field in the sample; detecting electromagnetic secondary radiation which is generated by an interaction of the electromagnetic primary radiation with the sample in the electric field; and determining the information which is indicative for the zeta potential based on the detected electromagnetic secondary radiation; wherein the information which is indicative for the zeta potential is determined from temporal changes of the electromagnetic secondary radiation between detector images which are generated at different detection points in time.

33.-34. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In the following, exemplary embodiments of the present invention are described in detail with reference to the following figures.

[0047] FIG. 1 shows a device for determining information which is indicative for a particle size of particles in a sample and for determining a zeta-potential of the particles according to an exemplary embodiment of the invention.

[0048] FIG. 2 shows a schematic illustration for evaluating detector images by means of differential dynamic microscopy according to an exemplary embodiment of the invention.

[0049] FIG. 3 shows an image structure function for a 70 nm large PS-latex particle in water, recorded by a 10 microscope objective with a numeric aperture of 0.25, obtained by means of differential dynamic microscopy.

[0050] FIG. 4 shows a result of an evaluation according to a measurement with differential dynamic microscopy at 46, 70 and 100 nm PS-latex particles by means of the cumulants method.

[0051] FIG. 5 schematically shows the diffraction of light at a grating, wherein an angle of the first diffraction order depends on the wavelength of the incident light and the grating constant g.

[0052] FIG. 6 shows an image structure function for a 500 nm large PS-latex particle in water, recorded by means of a conventional 40 microscope objective with a numerical aperture of 0.6, obtained by means of differential dynamic microscopy.

[0053] FIG. 7 shows a device for determining information which is indicative for a particle size of particles in a sample, according to an exemplary embodiment of the invention.

[0054] FIG. 8 shows a device for determining information which is indicative for a particle size of particles in a sample, according to another exemplary embodiment of the invention, wherein a horizontal measuring cell for suppressing disturbing influences is provided, for example particle sedimentation or forming temperature-induced flows in the measuring cell.

[0055] FIG. 9 shows a schematic block diagram of a device for determining information which is indicative for a particle size of particles in a sample, according to an exemplary embodiment of the invention.

[0056] FIG. 10 shows a device for determining a zeta-potential of particles of a sample, according to an exemplary embodiment of the invention.

[0057] FIG. 11 shows a schematic block diagram of a device for determining a zeta-potential of particles of a sample, according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0058] Same or similar components in different figures are provided with the same reference signs.

[0059] FIG. 1 shows a device 100 for determining information which is indicative for a particle size and/or a particle shape of particles in a sample 130 and for determining a zeta-potential of the particles, according to an exemplary embodiment of the invention.

[0060] The device 100 comprises an electromagnetic radiation source 102 which is configured as a pulsed laser, which is adapted for generating pulses of electromagnetic primary radiation 108 (here optical light). The electromagnetic primary radiation 108 is directed to a sample container 126. The sample 130 to be examined (for example particles which are contained in a liquid, in the order of magnitude of micrometers, for manufacturing ceramics such as titanium dioxide) flows through the sample container 126 which is configured as a flow-through cuvette in a flow direction which is indicated by arrows 132 while interacting with the electromagnetic primary radiation 108, wherein thereby the electromagnetic primary radiation 108 is converted in electromagnetic secondary radiation 110. The flow of the sample in the sample container 126 may optionally be prevented by valves 133 and 134 prior to a measurement. Furthermore, the sample container 126 may be adapted such that the flow through cuvette is replaced by any arbitrary cuvette, in order to examine sedimentation properties of the sample 130 or in order to exclude any sample change, for example. An imaging optics 118 between the sample 130 and an electromagnetic radiation detector 104 (for example a two-dimensional camera such as a CMOS-camera or a CCD-camera) is configured for imaging the electromagnetic secondary radiation 110 on the electromagnetic radiation detector 104.

[0061] The device 100 comprises a uniaxially slidable adjusting mechanism 120 (see double arrow) which is configured for adjusting the imaging optics 118 for receiving detector data for a first determination (the reference sign 112) of the information and for receiving detector data for the second determination (see reference sign 114) of the information. The adjusting mechanism 120 is configured for moving a first imaging optics 124 in the optical path between the electromagnetic primary radiation 108 and the electromagnetic secondary radiation 110 for the first determination 112, which first imaging optics 124 has a smaller numerical aperture than a second imaging optics 122 which is moved in the optical path between the electromagnetic primary radiation 108 and the electromagnetic secondary radiation 110 for the second determination 114. The first imaging optics 124 is a telecentric optics. The second imaging optics 122 is a microscope-objective. In this manner, the imaging optics 118 can be adapted with respect to the respective evaluation principle.

[0062] The electromagnetic radiation detector 104 serves for detecting the electromagnetic secondary radiation 110 in form of two-dimensional detector images which are generated by an interaction of the electromagnetic primary radiation 108 with the sample 130.

[0063] The detector data which deliver a two-dimensional image of the sample 130 are supplied to a determination unit 106 which is configured as a processor, for example, which is configured for determining the information which is indicative for the particle size based on the detected electromagnetic secondary radiation 110. More precisely, the determination unit 106 is configured for determining the information firstly (see an evaluation path which is designated with reference sign 112) by means of an identification and a size determination of the particles on multiple single detector images which are generated from the electromagnetic secondary radiation 110, and for determining the information secondly (see evaluation path which is designated with reference sign 114) from temporal changes between detector images which are generated from the electromagnetic secondary radiation 110 at different detection points in time. In other words, in the device 100, the size determination of the particles can be performed by means of a selectable procedure or by means of two complementary procedures. The determination unit 106 is adapted for determining the information from the single detector images which are generated from the electromagnetic secondary radiation 110 by means of dynamic image analysis (DIA) (see reference sign 112). The determination unit 106 is further configured for determining the information from temporal changes between the detector images by means of differential dynamic microscopy (DDM) (see reference sign 114).

[0064] The determination unit 106 in particular is adapted for performing the first (see reference sign 112) and the second (see reference sign 114) determination of the information for at least a part of a range between 100 nm and 20 m, i.e. twice. In this range, both determination methods are sensitive and deliver information due to the complementary underlying physical principles, which information is not determinable by the respectively other determination method.

[0065] The determination unit 106 is further adapted for performing the determination of the information for particle sizes above 20 m only by means of the first determination (see reference sign 112) and for performing the determination of the information for particle sizes below 100 nm only by means of the second determination (see reference sign 114), since the respectively other determination method in the mentioned particle size ranges is not sufficiently sensitive.

[0066] A control unit 150 receives the detector data from the electromagnetic radiation detector 104 and forwards them for further processing in one or both branches (see reference signs 112, 114). Detector data may also be stored in a database 152.

[0067] As storage medium, both computer readable storage media and/or storage media can be used which are formed by programmable logic circuits, for example field-programmable-logic-gate arrangements (FPGA), microcontrollers, digital signal processors (DSP) or the like. These storage media may be directly integrated in the device 100.

[0068] For the first determination (see reference sign 112) of the particle size distribution, i.e. the detection of particle sizes and/or particle shape directly by means of a camera image, the detector data are forwarded to a particle recognition unit 154 which, by means of methods of image processing (for example pattern recognition based on reference data), recognizes single particles on the single detector images. The identified particles are forwarded to a parameter determination unit 156 which is assigning the recognized particles to a size and/or a shape.

[0069] For the second determination (see reference sign 114) of the particle size distribution, i.e. the detection of particle sizes indirectly by generating camera difference images and deriving the particle sizes from a Fourier-analysis, the detector data at first are transferred to a difference image determination unit 162. The difference image determination unit 162 determines the respective difference images from the detector data which are recorded at different points in time. The determined difference images are subjected to a Fourier transformation in a Fourier transformation unit 164. An averaging unit 166 is averaging the results of the Fourier transformation. A parameter determination unit 168 then determines, from the results of the determination, the size distribution of the particles.

[0070] A combination unit 170 can combine the results of the both determinations according to reference signs 112 and 114. The results of the analysis may then be displayed to a user on a display unit 180.

[0071] The device 100 in addition comprises an electric field generation unit 116 for generating an electric field in the sample 130, wherein the determination unit 106 is configured for determining the zeta potential and the electric charge of the particles, respectively, of the sample 130 based on the detected electromagnetic secondary radiation 110. Controlled by means of the control unit 150, a voltage source 177 of the electric field generation unit 116 can apply an electric voltage between two opposing capacitor plates 179 of the electric field generation unit 116. The arrangement of the electrodes 179 should be positioned such that the field lines of the electric field run normal to the propagation direction of the electromagnetic primary radiation 108. In the case that the sample 130 additionally is moving in a direction which is normal to the propagation direction of the electromagnetic primary radiation 108, the electrodes 179 shall be arranged such that the field lines are aligned normal to the flow direction of the sample and normal to the propagation direction of the primary radiation.

[0072] More precisely, the determination unit 106 is configured for determining the zeta potential and the electric charge, respectively, of the particles from temporal changes between the detector images which are generated from the electromagnetic secondary radiation 110 at different detection points in time, i.e. by means of differential dynamic microscopy. For determining the zeta potential from the detector data, the latter are supplied to a zeta potential-determination unit 190 which can then forward the result of the evaluation to the display unit 180.

[0073] Dynamic image analysis (DIA) is a method which is based on the photography of moving objects. The use in the particle characterization is enabled by the development of very rapid cameras and by the combination with pulsed light sources. Rapid cameras are advantageously in order to be able to measure many particles in a short time due to reasons of statistic. A pulsed light source further enables recording very fast-moving particles without a moving blur occurring.

[0074] Differential dynamic microscopy (DDM) can be performed by means of a commercial optical microscope which illuminates the sample by means of a non-collimated white light source. The data analysis however is not based on the evaluation of the images of the particles, but on the evaluation of the temporal changes of the structures in the image. Thereby, the diffusion velocity and indirectly the size of the particles can be determined. The method is not limited by the optical limit for the resolution of a single particle.

[0075] Using non-collimated white light is possible, since in DDM not the entire scattering vector |Q| is included in the calculation, as it is usual in DLS, but only the projected scattering vector q is included in the calculation and this is independent from the incident angle and the light wavelength. The latter can be seen as an advantage of DDM with respect to DLS, since simulations have shown that for small scattering angles (<20, corresponds to forward scattering) the difference between q and |Q| is negligible.

[0076] FIG. 2 shows a scheme 200 for evaluating detector images 202 by means of differential dynamic microscopy according to an exemplary embodiment of the invention. The procedure of a DDM measurement and evaluation which is described in the following is schematically illustrated in FIG. 2.

[0077] The particles in the liquid are photographed by means of an electromagnetic radiation detector 104 which is configured as a high-speed camera, i.e. intensity values I are recorded in dependency from the spatial coordinates x, y and the time t. By subtracting respectively two images (see reference sign 162) difference images 204 are generated. The time difference t between the detector images 202 to be subtracted is varied. Thus, a whole series of difference images 204 is obtained which contain the information about the dynamic of the system. The intensity in the difference images 204 is given by:

I(x,y;t)=I(x,y;t+t)I(x,y;t)

[0078] Subsequently, the difference images 204 are Fourier-transformed (FFT(I(x,y;t)).fwdarw.F(q;t)), see reference sign 164, wherein thereby Fourier transforms 206 are obtained. Since the Brownian molecular motion is stochastic, the Fourier transformation delivers a rotational symmetrical image. F(q;t) can thus be integrated over the azimuth-angle.

[0079] After performing the Fourier transformation, an averaging is performed, see reference sign 166, wherein thereby averaged Fourier transforms 208 are obtained.

[0080] The Fourier transformation can be imagined as a decomposition of the object in refractive index gratings 500 with a different grating constant g, see FIG. 5. The relationship between the projected scattering vector (=grating vector) q and the grating constant g is given as following: q=2/g.

[0081] The so-called Fourier performance spectrum, also referred to as image structure function 210, is given by:

D(q,t)=(|F(q,t)|.sup.2)g(q,t)

wherein g(q,t) is the intensity-autocorrelation function as it is also known from the DLS theory.

[0082] FIG. 3 shows D(q,t) for 70 nm PS (polystyrene) latex particles in water, recorded by a 10 microscope objective.

[0083] Thus, from D(q,t) for example by means of the cumulants-method (see Koppel, Dennis E. (1972), Analysis of Macromolecular Polydispersity in Intensity Correlation Spectroscopy: The Method of Cumulants, The Journal of Chemical Physics 57 (11): 4814), the particle size can be calculated: FIG. 4 shows a result of an evaluation according to a measurement with differential dynamic microscopy at 46 nm, 70 nm and 100 nm PS-latex particles by means of the cumulants-method.

[0084] Due to a DDM measurement, measuring data at different q-vectors are already present. The result thus corresponds to a multiplicity of single DLS experiments which were performed at these q-vectors (=scattering angles).

[0085] Conventional methods for determining particle sizes have disadvantages which can be overcome by the inventive measuring principle:

[0086] The measuring range of the dynamic image analysis (DIA) is limited towards below by the optical resolution limit. This constitutes a significant disadvantage compared to competing technologies, for example static light scattering (SLS).

[0087] Polydisperse samples which contain particles below the optical resolution limit, cannot be entirely characterized a means of DIA. The small proportions of the size distribution function get lost.

[0088] The particle concentration in DIA is limited due to the condition that overlappings of particles on the recorded images are highly improbable. It is not possible to distinguish random overlappings of the particles from aggregates. The limit for the particle concentration which is still measurable depends on the used imaging optics, the used detector and the particle size itself.

[0089] By means of dynamic image analysis (DIA), only that parts of the particles can be recognized which have a significant difference in the refractive index with respect to the solvent. For example, strongly swollen polymer shells (steric stabilization) remain invisible.

[0090] DIA delivers a static image of the particles. Dynamic processes, for example a diffusion motion or an electrophoretic motion are not accessible.

[0091] In order to at least partially overcome these disadvantages, exemplary embodiments of the invention have been developed:

[0092] In the context of the present invention, it has been figured out that DIA and DDM almost have identical requirements concerning the measuring geometry and can thus be implemented in the same device. Also the periphery which is required for the operation of the measuring device is highly similar.

[0093] By a combination of the technologies, the measuring range with respect to the particle size can be significantly enlarged. While DIA is limited with respect to small particle sizes by the optical resolution limit (smallest particles which are still measurable should be at least ca. 100 nm large), DDM is able to measure far below (for example up to ca. 20 nm). With respect to large particles, DDM is limited by the diffusion motion which, with increasing particle size, becomes slower and thus more difficult to measure. The upper measuring limit for DDM is ca. 10 m particle size. The reason for this limitation can be explained as following. Until a particle having a size of, for example, 10 m diffuses a distance which is detectable by means of optical imaging, in fact multiple seconds may pass. When the measuring times are such long, it becomes difficult to exclude disturbing influences, for example sedimentation or vibrations.

[0094] By the relatively large overlapping in the measuring range between DIA and DDM (for example ca. 500 nm up to 10 m), the following advantages result:

[0095] While in DIA an image of the particle is directly evaluated, DDM is an indirect method in which the diffusion velocity is determined from an image. For ideal dispersions of diluted smooth spheres it is expected that the both determined diameters are matching. If, in experiment, discrepancies between the both results occur, this can be interpreted as effect of a deviation from this ideal behavior. Therefore, from the combination of both methods, valuable information about non-ideal behavior can be obtained. In the following, a concrete example is described:

[0096] In examination by means of DIA and DDM, sterically stabilized particles can lead to different results. The optical contrast of the swollen polymer shell this extremely low compared to the contrast of the particle core. Correspondingly, DIA delivers the core diameter as a result. For DDM, the situation is fundamentally different. The diffusion behavior is determined by the thermal energy and the flow resistance. The effective diameter in this case is the core diameter plus twice the thickness of the shell.

[0097] Since the shell is moving with the particle, the shell effectively decelerates the diffusion. From the combination of DIA and DDM, the thickness of the polymer shell is experimentally accessible (R.sub.DDM-R.sub.DIA). Neither DIA nor DDM can deliver this information on their own.

[0098] In real samples, compositions with very different particle sizes are often present. Many methods for particle size determination cannot determine the correct distribution of particle sizes from such compositions. For example, dynamic light scattering DLS is disturbed by low concentrations of large particles (for example aggregates or dust). Then it is no longer possible to determine the particle size of nano-particles, also when they are present in a substantially higher concentration. A substantial advantage of DDM with respect to DLS is that there is not such a strong sensitivity with respect to large contaminants in low concentration. In the course of data evaluation, in DDM respectively two images which are recorded at different points in time are subtracted from each other. Very large particles only move extremely slow and thus disappear from the difference image. The contribution of the small particles which diffuse rapidly and therefore have significantly moved in the time between the both records is not influenced by the large particles. Thus, DDM allows measuring small particles besides very large particles. For DIA, nano-particles indeed are outside of the measuring range. However, large particles are recognizable very well. By the combination of DIA and DDM, a complete characterization of samples with nano-particles and low amounts of large particles results. This would not be possible with one method alone.

[0099] For DIA, it shall be ensured that the particles in the image are not overlaying each other. This can be achieved by a respective dilution. The size determination in samples with high concentrations of particles is problematic. How high the concentration of the particles is exactly allowed to be depends on the selected imaging optics, the detector and the particle size. In contrast, DDM operates well at high concentrations and reaches its limits at low particle densities. The limitation towards high concentrations is determined by the condition of the quasi-ideal dilution in the Stokes-Einstein-equation. The combination of both technologies thus enlarges the concentration range in which it is able to measure correctly.

[0100] Usually, the Stokes-Einstein-relation is used for calculating the particle radius R from the diffusion coefficient D (with a given viscosity of the solvent, the Boltzmann constant k.sub.B and the absolute temperature T):

[00001]$R=\frac{k_B.Math.T}{6.Math..Math..Math..Math..Math..Math.D}$

[0101] The method of micro rheology however uses the Stokes-Einstein relation in another form. It determines the viscosity of the solvent from the diffusion coefficient:

[00002]$=\frac{k_B.Math.T}{6.Math..Math..Math..Math.R.Math..Math.D}$

[0102] However, for this purpose it is necessary to add particles with a known size and thus to possibly change the sample. By the combination of DIA and DDM it is possible to directly determine all required input parameters. While the particle size can be directly taken from the images (DIA), the diffusion coefficient can be determined via DDM. The precondition is only that particles (of unknown size) are present in the overlapping range of DIA and DDM.

[0103] FIG. 7 shows a device 100 for determining information which is indicative for a particle size of particles in a sample 130, according to an exemplary embodiment of the invention.

[0104] In order to be able to eliminate the above mentioned disadvantages of the DIA technology by means of a combination with DDM, the technology combination can be used which is shown in FIG. 7.

[0105] The measuring arrangements for performing DIA and DDM are very similar, both technologies can commonly use a majority of the components of the device 100, or even the entire components. The measuring arrangement in form of the device 100 consists of a light source as electromagnetic radiation source 102 which sends a light beam as electromagnetic primary radiation 108 along an optical axis 702, a beam forming optics 700, a measuring cell as sample container 126 which contains the sample 130 to be examined, an imaging optics 118 and an image sensor as electromagnetic radiation detector 104. The inlet window and the outlet window, respectively, of the measuring cell are designated with the reference signs 704 and 706, respectively. The beam forming optics 700 serves for a beam expansion and collimation, respectively, in order to cause a sharp image. It can be taken from FIG. 7 that the optical path length which is required for the electromagnetic primary radiation 108 passing the sample container 126 is very short, in order to avoid falsifications of the size determination of particles which are located in close proximity to the inlet window 704 and the outlet window 706, respectively. It can be further taken from FIG. 7 that the imaging optics 118 is formed by two collecting lenses 708 between which an aperture 710 is arranged (alternatively, also an aperture-less lens system is possible). The imaging optics 118 can be adapted such that it maintains the image at the position of the electromagnetic radiation detector 104 permanently equally large.

[0106] With regard to the light source which is most suitable, DIA and DDM have practically identical requirements. Both technologies also operate with coherent and polychromatic light. However, for suppressing disturbing interference artifacts in the images, an incoherent or only very weakly coherent light source is preferred. Since usually there is no reason for recording DIA images in color, also using a monochromatic light source is fully sufficient in many cases. Actually, monochromatic light has many advantages. For example imaging errors which are caused by chromatic aberration can be avoided and the relation between the projected scattering vector q and the actual scattering vector |Q| is then distinct (except of an angle dependency). With regard to a good adjustability of the optical setup with a high resolution capability at the same time, a wavelength is preferred which is as short as possible but which is still within the spectral range which is visible for the human eye. Also using a pulsed light source, as usual for DIA, does not constitute a problem for DDM and actually is an advantage, respectively, since also in DDM only snapshots have to be made.

[0107] A further improvement with regard to the quality of the recorded images is achieved in DIA by using a collimated illumination. The beam forming optics 700 thus is aligning the light beams which are coming from the electromagnetic radiation source 102 in parallel with respect to the optical axis 702. This manner of illumination is also an advantage for DDM. Since there are no more light beams which obliquely impinge the object, the relation between the projected scattering vector q and the actual scattering vector |Q| is distinct (except of a wavelength dependency).

[0108] Differences with regard to the requirements of the setup of DIA and DDM devices are most notably present in the imaging optics 118. Since DIA is a method in which particles are directly measured by means of the images, perspective falsifications as they occur in conventional entocentric (and also pericentric) optics shall be avoided, if possible. Thus, particles shall appear equally large independent from their distance to the imaging optics 118. Although DIA is also possible with conventional optics, therefore often so-called telecentric optics are used for imaging the particles on the detector. However, exactly these telecentric optics often have a low numerical aperture NA (especially when it is a bi-telecentric image) which constitutes a limitation for DDM with respect to the accessible q-range and the resolution. DDM-comparison measurements with three different objectives (40 microscope objective with NA=0.6, 10 microscope objective with NA=0.25, 8 telecentric objective with NA=0.09) have shown that the 10 microscope objective is most suitable due to its optical parameters (magnification, NA and light intensity).

[0109] The reason for this can be imagined again with the decomposition of the object in periodic refractive index gratings 500. The NA of an optics limits the optics with respect to the angle under which a light beam can still enter the optics and contributes to the optical image. FIG. 5 schematically shows the diffraction of light at a refractive index grating 500, wherein the angle of the first diffraction order is dependent from the wavelength of the incident light and the grating constant g. Since each grating scatters the incident light, depending on the grating constant, to a certain angle (see FIG. 5; only the first diffraction order is regarded here), the NA also constitutes a limitation in the grating vectors g which can still be received and, due to q=2/g, also in the projected scattering vectors q. If it is desired to cover a scattering vector range which is as large as possible by means of DDM, using an imaging optics with high numerical aperture is suggested.

[0110] However, whereby is the q-range shown in FIG. 3 and its resolution in a typical DDM measurement further determined? In order to be able to clarify that, the magnification M (with M>1 for a magnifying image and M<1 for a reducing image) of the imaging optics, the size of the pixel array-detector (assumption: square with m pixels side length) and the size of the pixels located thereon (square with an edge length S.sub.P) have to be known. Under the assumption that the imaging optics is matched to the pixel array-detector, in other words the pixel array-detector is illuminated by the optics over the entire diagonal, the field of view F at the side of the object, which can be still imaged by the imaging optics on the detector, is resulting to:

[00003]$F=\frac{m.Math.S_p}{M},F=F_m.Math.F_m$

[0111] Since the q-vector is given by q=2/g, and the smallest possible grating in the image has to comprise a grating constant of two pixels, q.sub.max is given by

[00004]$q_{\max }=\frac{2.Math..Math..Math.M}{2.Math..Math.S_p}=\frac{.Math.M}{S_p}.$

For FIG. 3, with a pixel-edge length of 14 m this results to: q.sub.max=2.24 m.sup.1. However, q.sub.max in FIG. 3 is slightly larger than 3. The discrepancy results from the diagonal of the Fourier-transformed image, which diagonal is larger than the width and the height, respectively, by the factor {square root over (2)}. Thereby, the correct value results: q*.sub.max=q.sub.max {square root over (2)}=3.17 m.sup.1. Measuring data concerning q-values which are larger than q.sub.max should not be used for evaluating, since they do not contain useful information about the image. The smallest possible q-value now results to:

[00005]$q_{\min }=\frac{q_{\max }}{m}=\frac{.Math.M}{S_{p.Math.m}}=2.8.Math..Math.{}^{-3}.Math..Math.{\mathrm{.Math.m}}^{-1}$

at an image width of m=800 pixels.

[0112] From the previous considerations, the following can be concluded:

[0113] The usable q-vector range in the context of the here described theory is limited towards above by the NA of the objective. That is, the scattering vector can be maximum so large that the first diffraction order of the corresponding grating can still be recorded by means of the optics.

[00006]$q_{\mathrm{upper}.Math.\text{-}.Math.\mathrm{limit}}=\frac{2.Math..Math..Math.\mathrm{NA}}{N.Math.}=/\mathrm{for}.Math..Math.N=1/=\frac{2.Math..Math..Math.\mathrm{NA}}{}$$\left(N.Math..Math.\mathrm{.Math.}.Math..Math.\mathrm{diffraction}.Math..Math.\mathrm{order}\right).$

[0114] The usable q-vector range in the context of the here described theory is also limited towards above by the magnification of the imaging optics and the pixel size of the used detector

[00007]$q_{\max }=\frac{.Math.M}{S_p}.$

[0115] The last issue shows that an optics with a larger magnification makes a larger q-range accessible. However, it is also to be considered that the used optics is able to resolve the effective pixel size

[00008]$S_{p.Math.\text{-}.Math.\mathrm{eff}}=\frac{S_p}{M}$

and can transfer such small structures with a sufficient contrast as well. This can be read from the modulation transfer function of the optics.

[0116] For the example of FIG. 3 with NA=0.25 and =430 nm, restriction 1 would deliver a crupper-limit=3.653 m.sup.1 and restriction 2 would deliver a q.sub.max=2.244 m.sup.1. Thus, the NA of the optics would not be the limitation in this case, since the q-range is already stronger limited by the selected magnification and the size of the detector pixels. However, it is to be considered that a large q-range is not always advantageously, since not at all q-values useful data are measured. The optics and the detector should be selected such that only one q-range is recorded, if possible, in which the measuring data are useful. FIG. 6 shows an example for this. FIG. 6 shows an image structure function for a 500 nm large PS-latex particle in water, recorded by a conventional 40 microscope objective with a numerical aperture of 0.6, obtained by means of differential dynamic microscopy.

[0117] The recorded q-range is in fact large due to the strongly magnifying objective, but useful measuring data are only present for a small q-range (for this measurement is q.sub.max=8.98 m.sup.1).

[0118] With respect to the measuring method DDM, in the following additional considerations shall be described:

[0119] Smaller particles are moving faster compared to larger particles, thus they lead to a significant difference signal in the DDM difference images. The mean distance s which a particle was moving away from an initial point in a certain time T can be expressed as the root of the mean square displacement (MSD): {square root over (MSD)}={square root over ((s.sup.2()))}={square root over (2D)}. Thus, in order to be able to measure larger particles by means of DDM, very small displacements should be measured.

[0120] When regarding sections along the dt-axis (these curves are proportional to the intensity correlation function) in FIG. 3, it can be noted that these curves for certain q-values, when the difference times dt (dt corresponds to the above mentioned distance time t which has passed between two subtracted images) are large, are transitioning in a plateau. This plateau means that each correlation between the single images which were used for the difference image has been lost. Only when the curves are transitioning in a plateau, the characteristic decay time T and in the following the particle size can be calculated from them. The q-dependency of the decay time is known from dynamic light scattering and is given by: =1/(D.sub.mq.sup.2), with D.sub.m being the mass diffusion coefficient of the particles. It should also be paid attention that the measuring duration and thus also the decay time t which is maximum available for the difference images is adapted to the particle size (for larger particles it should be measured longer).

[0121] Particles in the Rayleigh limit constitute so-called phase objects, therefore they are less scattering in the forward direction compared to larger particles. With decreasing particle size, the influence of the particles on the difference images decreases and at any time it gets so low that it disappears in the detector noise and thus cannot be evaluated anymore. The amplitude of the image structure function D(q,t) for small q-values is proportional to q.sup.4.

[0122] FIG. 8 shows a device 100 for determining information which is indicative for a particle size of particles in a sample 130, according to another exemplary embodiment of the invention, wherein a horizontal sample container 126 and a horizontal measuring cell, respectively, for suppressing disturbing influences, for example particle sedimentation or forming temperature induced flows in the measuring cell, is provided. The horizontal orientation of the sample container 126 is enabled by an arrangement of deflecting mirrors 800.

[0123] Since the particles for a size determination by means of DDM are allowed to be subjected only to the Brownian molecular motion, for large particles it can be an advantage to configure the measuring cell and the sample container 126, respectively, horizontal as shown in FIG. 8, for example. The influence of sedimentation and also the generation of undesired flows by temperature gradients (as they can be caused by a laser, for example) is reduced in this manner.

[0124] In the following, considerations with respect to a DDM measurement in and of laminar flows are explained.

[0125] If the diffusion motion is superimposed with a directed laminar flow, the particle size determination by means of DDM is possible as well. However, the rotational symmetry of the Fourier-transformed difference images I(q,t) is broken and integrating over the azimuth-angle is therefore not allowed anymore. Only data which result from a motion perpendicular with respect to the laminar flow shall be used for the DDM evaluation. A majority of the recorded measuring data thus cannot be used for the evaluation and the signal-to-noise ratio is correspondingly worse and more measuring data should then be recorded, respectively.

[0126] DDM cannot only be used for determining the particle size, but also for measuring the flow velocity of a suspension, for example. The flow which is superimposed to the Brownian motion leads to a strip pattern in the image structure function which can be evaluated with respect to the strip distance and in this manner the flow velocity can be determined. Since the cause which is generating the flow is not decisive for the flow measurement, for example also the electrophoretic mobility can be measured by this method. From the electrophoretic mobility of particles, then also the zeta potential of the particles can be calculated. By means of DDM it is also possible to measure both particle size and zeta potential.

[0127] Usually, for DIA multiple telecentric objectives are used, in order to cover a sufficiently large measuring range. Small particles should be magnified (typically 10-15), in order to be still recognizable on the pixel-array detector, whereas very large particles even have to be optionally imaged in a reduced manner (typically by the factor two). In order to make a reproducible exchange between different optics as comfortable as possible, for example an optics revolver can be placed at the location of the imaging optics 118 which is shown in FIG. 7 and FIG. 8. Exchanging the different optics can be performed manually or automatically.

[0128] As already mentioned, not using a telecentric optics, but a conventional microscope objective with high NA may be an advantage for DDM. This may also be mounted in the optics revolver.

[0129] FIG. 9 shows a schematic principle arrangement of a device 100 for determining information which is indicative for a particle size of particles in a sample, according to an exemplary embodiment of the invention.

[0130] Complementary to FIG. 7 and FIG. 8, for the operation of the combination device, also a display unit 180 and a provision for sample dispersion and for discharging sample waste is advantageously. For the sample preparation and disposal, optionally a sample dispersion unit 900 and a sample waste unit 902 can be embedded in the device 100.

[0131] FIG. 10 shows a device 100 for determining a zeta potential and an electric charge state, respectively, of particles of a sample 130, according to an exemplary embodiment of the invention.

[0132] The device 100 according to FIG. 10 differs from the device according to FIG. 7 substantially in that an electric field generation unit 116 for generating an electric field in the sample 130 is provided, and in that the determination unit 106 is exclusively adapted for determining the zeta potential of the particles in the sample 130 by means of differential dynamic microscopy (DDM). In contrast, the determination unit 106 is not necessarily adapted for evaluating the detector data which are captured by the electromagnetic radiation detector by means of dynamic image analysis. For the remaining components, reference is made to the miscellaneous description in the context of this patent application.

[0133] The device 100 according to FIG. 10 comprises an electromagnetic radiation source 102 for generating electromagnetic primary radiation 108. The device 100 further includes the electric field generation unit 116 for generating an electric field in the sample 130. An electromagnetic radiation detector 104 serves for detecting electromagnetic secondary radiation 110 which is generated by an interaction of the electromagnetic primary radiation 108 with the sample in the electric field. The determination unit 106 is configured for determining the zeta potential based on the detected electromagnetic secondary radiation 110. More precisely, the determination unit 106 is adapted for determining the zeta potential from temporal changes between detector images which are generated from the electromagnetic secondary radiation 110 at different detection points in time, i.e. by means of differential dynamic microscopy.

[0134] FIG. 11 shows a schematic principle arrangement which is corresponding to FIG. 10, of a device 100 for determining a zeta-potential of the particles, according to an exemplary embodiment of the invention, with a field generation unit 116. With respect to the additional components, reference is made to the above description of FIG. 9.

[0135] Complementary, it should be noted that comprising does not exclude any other elements or steps and a or an does not exclude a multiplicity. It should further be noted that features or steps which are described with reference to one of the above embodiments can be also used in combination with features or steps of other above described embodiments. Reference signs in the claims are not construed as limitation.