A BODY COMPRISING A PARTICLE STRUCTURE AND METHOD FOR MAKING THE SAME

Abstract

The invention relates to a method for forming a body comprising a particle structure fixated in a matrix material, comprising: Providing an amount of particles, Providing a viscous matrix material to include said particles, Forming a particle structure of at least a portion of said amount of particles, Fixating said viscous matrix so as to fixate said particle structure in the matrix material; characterized by at least a portion of said amount of particles being paramagnetic or ferromagnetic and the formation of the particle structure includes the steps of: First, the particles are provided in a mixture with the viscous matrix material, Second, the viscous mixture is subject to the magnetic field created by a Halbach array so as to form the particle assemblies, Third, the viscous mixture with the particle assemblies is subject to electric field so as to move and/or rotate the particle assemblies in the viscous matrix material. The invention also relates to a body obtained by said method, and to the use of said method in various applications.

Claims

1. A method for forming a particle structure fixated in a matrix material, the particle structure including at least an amount of particles within the matrix material, at least a portion of said amount of particles being at least one of paramagnetic and ferromagnetic, the method comprising: subjecting the matrix material to a magnetic field created by a Halbach array so as to form particle assemblies; subjecting the matrix material to an electric field so as to at least one of move and rotate the particle assemblies in the matrix material; and securing said particle structure in the matrix material

2. The method according to claim 1, wherein the amount of particles are subjected to the magnetic field by moving the amount of particles through at least part of the magnetic field generated by the Halbach array.

3. The method according to any one of the previous claims, wherein the Halbach array is provided by at least one of a refrigerator magnet, a magnetic stripe, a magnetic paper, a magnetic tape and a Halbach magnetic cylinder.

4. The method according to any one of the previous claims, wherein said particle structure includes at least one pathway of particles extending through the matrix material.

5. The method according to claim 4, wherein the at least one pathway is a conductive pathway.

6. The method according to any one of the previous claims, wherein the amount of particles have a concentration in the matrix material being less than a percolation threshold.

7. The method according to any one of the previous claims, wherein the amount of particles have a concentration in the viscous matrix material in the a range from 0.1 to 10 vol %.

8. The method according to any one of the previous claims, wherein the amount of particles include particles comprising at least one of carbon, metal and metal alloys.

9. The method according to claim 8, wherein the amount of particles are selected from a group consisting of silver-iron particles, silver-nickel particles, graphite-nickel particles, nickel particles, carbon nanoparticles and mixtures thereof.

10. The method according to any one of the previous claims, wherein a size of the amount of particles is in a range from 0.5 micrometers to 150 micrometers.

11. The method according to any one of the previous claims, wherein the electric field is at least one of an AC field and a DC field.

12. The method according to any one of the previous claims, wherein the matrix material comprises a polymer.

13. The method according to any one of the previous claims, further comprising a body, the body comprising the particle structure fixated in the matrix material, wherein said body is obtainable by any one of the previous claims.

14. The method of claim 13, wherein the body is used for at least one of creating printed electronics, RF shielding, transistors, strain sensors, force sensors, membrane switches, anisotropic conductive films, conductive tapes, and three dimensional geometries of conductive pathways.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] The invention will now be further described with reference to exemplary embodiments, with reference the enclosed drawings, wherein:

[0088] FIG. 1 is a schematic illustration of an embodiment of a Halbach arrangement.

[0089] FIG. 2 shows a flux diagram of a Halbach array.

[0090] FIG. 3a is a photograph showing particles in a viscous matrix after having been subjected to an electric field followed by curing.

[0091] FIG. 3b is a photograph showing particles in a viscous matrix.

[0092] FIG. 3c is a photograph showing particles in a viscous matrix after having been subjected to a magnetic field created by a Halbach array followed by curing.

[0093] FIG. 3d is a photograph showing particles in a viscous matrix after having been subjected to a magnetic field followed by an electric field and curing.

[0094] It should be noted that the drawings have not been drawn to scale and that the dimensions of certain features have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0095] As mentioned in the above, a magnetic field created by a Halbach arrangement may advantageously be used with the method described herein.

[0096] An embodiment of a Halbach array is illustrated in FIG. 1. Several pieces of magnets are put together. The arrows show the orientation of each piece's magnetic field. The Halbach array of FIG. 1 would give a strong field underneath the array, while the field above would cancel.

[0097] FIG. 2 shows the flux diagram of a Halbach array. The flux lines are augmented on the top side and virtually cancelled on bottom side. Thus, the overall effect is a one-sided flux

[0098] FIG. 3a illustrates silver-iron particles in an amount of 1.5 vol. % dispersed in a viscous matrix material after having been subjected to an electric field and curing. The matrix material was made of polyurethane. It can be seen that a network of particles is formed. The resulting body of particles in a matrix material was found to be electrically conductive.

[0099] FIG. 3b illustrates particles in an amount of 1.5 vol. % dispersed in a viscous matrix material after curing. The matrix material was a UV curable polyurethane from Dymax.

[0100] FIG. 3c illustrates silver-iron particles in an amount of 1.5 vol. % dispersed in a viscous matrix material after having been subjected to a magnetic field created by a Halbach array and curing. The matrix material was made of polyurethane. The photograph shows that assemblies of particles are formed. However, the resulting body of particles in a matrix was not electrically conductive.

[0101] FIG. 3d illustrates silver-iron particles in an amount of 1.5 vol. % dispersed in a viscous matrix material after having been subjected to a magnetic field created by a Halbach array in the form of a refrigerator magnet followed by an electric field and curing. The matrix material was made of polyurethane. The resulting material had a particle structure in the form of a network. The particles being conductive the resulting body was found to be electrically conductive. The electrical conductivity proved to be superior to the body in FIG. 3b in which only an electric field was used.

[0102] Hence, it is concluded that subjecting an amount of particles in a viscous matrix material to a magnetic field created by a Halbach array followed by application of an electric field and curing results in a body of particles in a matrix material with improved connectivity in the form of electrical conductivity compared to application of solely an electric field and curing.

[0103] When low amounts of particles were used the assemblies of particles or the particle structure had the form of conductive pathways aligned with the magnetic field lines. At higher amounts of particles the assemblies of particles or particle structure had the form of one or more networks. Depending on the particles used and the amount of particles the material resulting from the method described herein exhibited no, little or satisfactory electrical conductivity.

[0104] The bodies created using the method described herein may moreover present additional advantages and different properties as compared to those using prior art methods in which only a single field is used or a magnetic field is used repeatedly.

[0105] The invention is further illustrated by the following non-limitative examples.

EXAMPLES

[0106] Silver coated iron particles were used in all samples below.

[0107] Electric field only vs magnetic and electric field

[0108] For preparation of a first sample, the silver coated iron particle was mixed with a viscous matrix material, the polymer Dymax 3094, such that the particles were uniformly dispersed in the matrix. The particle fraction was approximately 3 vol %. The dispersion was then coated on a PET substrate, so that the resulting film had a thickness of 100 m.

[0109] For alignment, an interdigitated finger electrode was used, where every each finger has the opposite electric polarity compared to its neighbour on either side. The sample was placed on top of the electrode so that the PET substrate was between the electrode and the dispersed film. To align the particles, an alternating electric field was applied to the electrode, and the sample was moved back and forth over the electrode perpendicular the fingers for the duration of the both the alignment step and the curing step.

[0110] The field strength used was about 5 kV/cm, and the frequency was 20 kHz sine wave, applied for one minute to align the particles.

[0111] After alignment, the sample was cured using UV-light for 60 seconds. The film was then separated from the PET substrate, and the presence of conductive pathways confirmed by having the film bridge a 1 cm gap between two copper electrodes and measuring the resistance with a multimeter. In this case the measured resistance was about 10 kOhm. Hence, this first sample was prepared using an electrical field only, in accordance with prior art technology.

[0112] For preparation of a second sample, the same particles and particle concentration in the same viscous matrix was used. The particles were first subject to a magnetic field created by a Halbach array in the form of magnetic paper bought from Biltema, Norway. In this case the sample was passed back and forth over the Halbach array for 30 s. The movement of the sample was perpendicular to the striped domains of the Halbach magnet. This caused the particles to form a plurality of particle assemblies extending parallel with the direction of movement. The sample was then cured, separated from the substrate and measured in the same way as for the first sample. The measured resistance was in this case about 1 kOhm.

[0113] For preparation of a third sample, the sample was subjected first to the magnetic field of the Halbach array as described above (second sample), and then to the electric field of the electrode as described for the first sample. After curing and separating from the substrate, the measured resistance was 200 Ohm.

[0114] The examples above were different than those referred to in FIGS. 3a-3c.

[0115] As a control, a fourth sample was made where the sample was not subjected to neither electric nor magnetic field. In this case the resistance was outside the measuring range of the multimeter (>100 MOhm), illustrating that the 3 vol % concentration is below the percolation threshold for this particle.

[0116] Hence, in view of the above, it is understood that the magnetic field is indeed of importance when forming the particle structure of both the second and third sample. The resulting films show lower sheet resistance after having been aligned using a magnetic field created by a Halbach array. Furthermore, comparing FIG. 3b with FIGS. 3c and 3d, it is clear that using a Halbach array to align the particles sometimes also leads to more linear particle structures, as opposed to the more two-dimensional network in FIG. 3b.

[0117] Accordingly, the method as proposed herein may be used to provide bodies having different properties than those prepared in accordance with prior art methods.

[0118] It should be noted that the described features of the various embodiments may be combined with each other. Accordingly, no embodiment is intended to limit any combination of features which are presented in the embodiments, but rather to illustrate examples of embodiments.