A STIMULI-RESPONSIVE COMPOSITE MATERIAL, RESPECTIVE PRODUCTION PROCESS AND APPLICATION AS A SENSITIVE FILM

Abstract

The present invention describes composite materials presenting an optical, electrical or optoelectronic response to stimuli, respective production method and application as sensitive films for the detection or quantification of a variety of analytes and analyte patterns, including but not limited to volatile organic compounds (VOC), vapors and gases, biomolecules, microorganisms, viruses, cells, and particles, as well as differences of temperature, pressure and electromagnetic fields. The composite material contains a mixture of (i) at least one liquid crystal; (ii) at least one ionic liquid or molecules with surfactant properties; (iii) polymer(s), preferably with natural or synthetic origin; (iv) appropriate solvent(s); optionally (v) a stabilizing element, such as sorbitol; and (vi) an electrolyte, which can be dispensed when the sensitive film is used to obtain an exclusively optical response or when the ionic liquid(s) or surfactant(s) are also conducting materials.

Claims

1. A composite material comprising: at least one liquid crystal comprising at least one mesogen at least one ionic liquid comprising at least one organic salt having a composition X.sup.+ and Y.sup., wherein X.sup.+ represents a cation of the salt and Y.sup. represents an anion of the salt or molecules with surfactant properties; at least one polymer or optically inactive molecule with self-assembling properties or a mixture thereof; and at least one solvent.

2. The composite material according to claim 1, wherein the solvent is at least one polar, apolar, protic, aprotic, ionically charged or uncharged solvent.

3. The composite material according to claim 1, further comprising at least one stabilizing agent.

4. The composite material according to claim 1, further comprising at least one electrolyte.

5. The composite material according to claim 1, further comprising at least one biomolecule recognizing agent.

6. The composite material according to claim 1, further comprising carbon nanotubes, gold nanoparticles and/or magnetic nanoparticles.

7. The composite material according to claim 1, further comprising active ingredients.

8. Method of production of sensitive film of the composite material described in claim 1, comprising the following steps: formulating a composite material comprising at least one liquid crystal, at least one ionic liquid, at least one polymer or molecule with auto-assembling properties and at least one solvent; modeling the formulated composite material in a layer format to form a thin transparent film through the spreading of the formulated composite material over a non-treated rigid or flexible surface, optically transparent, which cannot exhibit any own anisotropy, through applying spreading techniques.

9. The method according to claim 8, wherein the composite material is prepared through magnetic stirring, manual shaking, vortexing or applying ultrasound.

10. The method according to claim 8, wherein the rigid or flexible surface comprises at least one structure selected from the group consisting of mesh, channel, plurality of collumns, a matrix of test area, or a combination thereof.

11. (canceled)

12. (canceled)

13. (canceled)

14. The composite material according to claim 1, wherein the at least one liquid crystal is present in an amount of 1-90% wt, the at least one ionic liquid is present in an amount of 1-90% wt, the at least one polymer or optically inactive molecule is present in an amount of 0.1-90% wt and the at least one solvent is present in an amount of 1-90% wt.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0063] For an easier understanding of the technique, figures are attached. They represent embodiments but, however, are not intended to limit the subject of this application.

[0064] FIG. 1 illustrates a schematic representation of the structure of the composite material comprising the following elements:

[0065] 1polymer chains;

[0066] 2ionic liquid;

[0067] 3aligned liquid crystals.

[0068] FIG. 2 illustrates a schematic representation of a measuring device (4) of volatile compounds using the optical or optoelectrical sensors, monitored by an electric signal, being the transduction unit of the optical and optoelectronic device comprised by: hybrid sensors (transparent substrate with or without interdigitated electrodes) (5), photodetectors (6), photoemitters (7) polarizing films (8) and printed circuit board (9).

[0069] FIG. 3 illustrates the pneumatic system, composed of computer-controlled solenoid valves, constructed with the purpose of transporting volatiles from the sample to the sensors for analysis. It is comprised by the following parts:

[0070] 10Sample compartment;

[0071] 11Solenoid valves;

[0072] 12Air pump;

[0073] 13Air;

[0074] 14Sensors compartment;

[0075] 15Flow meter;

[0076] 16Admittance Meter with A/D converter;

[0077] 17Computer;

[0078] 18Output of the measuring device (4).

[0079] FIG. 4 shows conductance measurements as a function of the light intensity passing through the sensitive film composed by gelatin, dextran and [BMIM][DCA], during its exposure to different solvents:

[0080] Toluene (19), methanol (20), hexane (21), ethanol (22), acetone (23), chloroform (24).

[0081] FIG. 5 illustrates the conductance due to changes in the anisotropic properties of three optical sensors with different compositions: 25) gelatin, dextran and [BMIM][CVD]; 26) gelatin, sorbitol and [BMIM] [DCA]; 27) gelatin, dextran and [ALOCIM][Cl]. In the figure, 10 cycles of exposure/recovery are shown, while these sensors are exposed to ethyl acetate vapors for 6 sec, followed by pure air for 54 s.

[0082] FIG. 6 illustrates a plot of the principal components analysis (PCA) of the response of an opto-electric noseformed by three optical sensors: (25) gelatin, dextran and [BMIM] [DCA]; (26) gelatin, sorbitol and [BMIM] [DCA]; (27) gelatin, dextran and [ALOCIM] [Cl] in the presence of eleven different solvents: ethyl acetate (28), ethanol (29), dichloromethane (30), dioxane (31), diethyl ether (32), heptane (33), hexane (34), methanol (35), carbon tetrachloride (36), toluene (37), xylene (38).

[0083] FIG. 7 illustrates the electrical and optical response obtained by the hybrid sensor (containing 5CB, [BMIM] [Cl] and dextran) when exposed to acetone.

[0084] FIG. 8 illustrates the conductance obtained over time in the monitoring of tilapia fish quality using an optical gas sensor based on gelatin, 5CB and [BMIM][DCA], as an alternative and/or complementary microbiological bench test, conventionally performed to ensure food quality control of perishable products.

[0085] FIG. 9 illustrates the relative response of the optical sensor, consisting of gelatin, 5CB and [BMIM] [DCA], during a 12 h Tilapia fish monitoring.

[0086] FIG. 10 illustrates the electrical and optical responses of the hybrid sensor, whose composition includes 5CB and [BMIM] [FeCl.sub.4] in a gelatin polymer, simultaneously measured over time upon successive exposure to samples of petrol containing different amounts of ethanol.

[0087] FIG. 11 illustrates the admittance over time obtained from the electrical component of the sensor, as the hybrid sensor (employing 5CB and [BMIM] [FeCl.sub.4] in a gelatin matrix) was exposed to petrol samples with different ethanol contents (% v/v):

[0088] 3820% ethanol;

[0089] 3940% ethanol;

[0090] 4060% ethanol;

[0091] 4180% ethanol;

[0092] 42100% ethanol.

[0093] FIG. 12 illustrates the conductance over time obtained by the optical component of the hybrid sensor (employing 5CB and [BMIM] [FeCl.sub.4] in a gelatin matrix) when it was exposed to samples of petrol with different ethanol contents (% v/volume), respectively:

[0094] 3820% ethanol;

[0095] 3940% ethanol;

[0096] 4060% ethanol;

[0097] 4180% ethanol;

[0098] 42100% ethanol.

[0099] FIG. 13 illustrates the three dimensional graphical representation of the electrical and optical hybrid sensor responses (employing 5CB and [BMIM] [FeCl4] in a gelatin matrix) vs. ethanol content:

[0100] 3820% ethanol;

[0101] 3940% ethanol;

[0102] 4060% ethanol;

[0103] 4180% ethanol;

[0104] 42100% ethanol.

DESCRIPTION OF THE EMBODIMENTS

[0105] The invention will now be described using different embodiments of the same invention, which should not limit the scope of protection of this application.

[0106] Formulation of the Composite MaterialGeneral Procedure

[0107] The formulation of the composite material may be performed under agitation or sonication and may require temperature control. The order of addition of the components of the composite material as well as the ratios between the different components of the mixture may be controlled to obtain the desired formulation. The mass ratio of each component, defined by weight % component/total mass of the mixture may range being 1 to 90% of liquid crystal, 1 and 90% for the ionic liquid, 0.1 to 90% for the polymer or molecule with self-assembling properties and 1 to 90% of solvent.

[0108] Preparation of the Sensitive FilmGeneral Procedure.

[0109] Once the mixture is considered ready, a pre-determined portion was pipetted immediately and deposited on a clean, dust-free microscope slide (without any additional pretreatment). A clean smooth glass rod was used to obtain a thin film on the glass slide. The film was allowed to cool to room temperature and then examined under polarized light microscopy. The films may also be prepared through the use of mechanical or automatic propulsion techniquespin coating, which consists of depositing a known volume of polymer solution on the substrate secured to a turntable, which is programmed to rotate at a controlled speed, for a certain time and at controlled temperature, or by any other process which enables the formation of sensitive films using the composite material. It is also possible to shape the composite material to other geometries and different formats.

[0110] Depending on the composition, the formulation after deposition on the surface, can give a transparent, permeable, flexible or semi-rigid film, as illustrated in FIG. 1. When observed through crossed polarizers under an optical polarizing microscope, the uniformly distributed liquid crystal micelles are visible and show a radial configuration.

[0111] Hereinafter, this process is described in greater detail and specifically with reference to examples. However, the examples should not limit the present technology.

Example 1Preparation of Polymer Matrix

[0112] The reaction for forming the composite material takes place under stirring and controlled temperature of between 25 and 40 C. In one embodiment, the ionic liquid, or a mixture of ionic liquids (50 l) is added to a container containing a magnetic stir bar, and stirred for 15 minutes. A liquid crystal sample or a mixture thereof (10 l) is added to the vessel and stirring is continued for another 10 minutes. The suitable polymer, or a mixture, (50 mg) is then added. After 10 more minutes of stirring, distilled water (50 l) is pipetted to the mixture and the entire formulation is stirred and observed until an opaque viscous mass, which can take between 10 to 20 minutes depending on the constituents of the mixture.

Example 2Preparation of the Polymeric Matrix with Stabilizer

[0113] Where optionally add additional components to structural and organizational improvement of composite material such as sorbitol, mannose, sucrose, and other mono-, oligo- or polysaccharides, used alone or in admixture, a sample following procedure is as follows: It is used a container, preferably of glass, for example for up to 5 ml, containing a small magnetic bar to permit good agitation of the components. The ionic liquid, or a mixture of ionic liquids (50 l) is added to the flask and stirred for 15 min. A liquid crystal sample or a mixture thereof (10 l) is added to the vessel and stirring is continued for another 10 min. The suitable polymer (or a mixture) (25 mg) is added along with the structural improvement agent such as sorbitol (25 mg). After another 10 min of stirring, distilled water (50 l) is pipetted to the mixture and the entire formulation is stirred and observed until an opaque viscous mass, which can take between 10 to 20 minutes depending on the constituents of the mixture.

Example 3Application of the Sensitive Film

[0114] Micelles containing liquid crystal molecules are firmly encapsulated in the polymer network of the film, but nevertheless remain sensitive to external stimuli such as chemical vapor of a solvent, or any other analyte. Upon contact with an analyte, the orderly arrangement of the liquid crystal micelles are disrupted leading to isotropy, which can be observed through an optical microscope system using polarized light. This change is seen as a complete disappearance of the micelles and is recorded in real time. The removal of vapor causes 5CB to reorganize into micelles that have the same initial configuration, size and distribution within the same field of view. This process can be repeated several times without detrimental change to the micelles or the entire film.

[0115] The time required for the liquid crystal to re-align to the initial observed configuration is directly correlated with the identity of the solvent. The optical change provides a qualitative measure of the external stimulus.

[0116] Vapors of pure substances solvents such as acetone, n-hexane, chloroform, toluene, methanol, ethanol were placed in contact with sensitive films deposited on glass, using water as control. The apparatus consisted of an airtight container of solvent, namely one beaker covered with a rubber septum, containing the test solvent. The septum was pierced with a needle affixed to a plastic syringe. The needle falls below the level of the solvent. The tip was used to drill an exit point through the septum. A thin silicon hose was affixed to the top of the tip and served as the vapor inlet. The input led to a purpose-built glass chamber capable of housing the sensitive film. The sensitive film was placed face down on a raised platform to allow the vapor from the inlet to come into contact with the sensitive film. After each test, any residual vapor was expelled with a purging syringe connected to a venting conduit of atmospheric air. The purging syringe was also used to re-introduce the ambient air into the chamber.

Example 4Application of Sensitive Film

[0117] Sensitive films containing encapsulated liquid crystals were exposed to selected volatile organic compounds vapors. The device consists of a light source and a light detector, a sensitive film deposited on a glass slide forming a sensor and two crossed polarizing films, between which the sensitive film is positioned, arranged, for example, as shown in FIG. 2. The light detector converts the light intensity which is perceived in a proportional electrical signal. An analog to digital converter makes 20 readings per second, and transmits the data to a computer. The computer controls a pneumatic system, as shown in FIG. 3, which feeds the sensor with a stream of dry air which can be pure, called recovery time, or be saturated with a particular volatile organic compound (VOC), called exposure period. During the recovery period, valve V3 is open while V1 and V2 are closed so that the air from the air pump flows directly to the sensor chamber and passes through a flow meter before leaving the system. To expose the sensors to the volatiles from the sample, V3 is closed and V1 and V2 are open, allowing air to reach the sample chamber dragging with it the saturated air with volatiles of the sample to the sensor chamber. The sensors are connected to an acquisition board that sends a digital signal to the computer.

[0118] In the tests, the sensor has been exposed to air saturated with VOCs for 5 s followed by 55 s of recovery with pure air vent. Exposure/recovery cycles were repeated 10 times for each tested sample. With crossed polarizers, micelles of 5CB are visible and therefore, part of the light (base value) is able to pass through the sensory film and reaches the photodetector. The photodetector converts the light signal into a measurable output signal, in this example, the conductance. In contact with VOCs, the order of liquid crystals within the micelles is disrupted, thereby preventing light from passing through to the photodetector element. Removal of the VOC allows the liquid crystals to re-organize back into the familiar micelle pattern exhibited before the exposure, hence the light detection levels returns to the base value. The power disruption/reorganization of liquid crystals and respective sensitive films as well as the kinetics of the phenomenon depends on the nature of the analyte, which in this case are the volatile solvent molecules interacting with the sensor, as shown in FIG. 4.

[0119] Three films made up of different compositions, were exposed to several solvents: ethyl acetate, ethanol, dichloromethane, dioxane, diethyl ether, heptane, hexane, methanol, carbon tetrachloride, toluene and xylene. After repeated cycles of exposure and recovery, the conductances, which are proportional to the light intensities reaching the three different sensors, were plotted against time for each solvent. As an example, the response obtained for ethyl acetate is shown in FIG. 5. The sensors were exposed to the headspace of the solvents for 6 s followed by a recovery period for 54 s, in which atmospheric air was used to remove the volatiles from the sensors, restoring them back to their original state. The samples were pre-heated for 10 min and thermostated to 36 C. Twelve consecutive exposures were performed with a gas flow of 1.7 L/min. In FIG. 5, the observed decrease in conductance is due to the decrease in light intensity that can pass through the two crossed polarizers when the disorder in the arrangement of liquid crystals on the sensor (caused by volatile solvent) restricts the capacity of these molecular structures to rotate the axis of plane of polarized light. Thus, the change in conductance is intimately related to the interaction between the volatile compound from the solvent and the liquid crystal micelles organized through the intermediary of ionic liquid(s). Depending on the solvent and the composition of the sensitive film of the optic sensor, the micelles disruption/reorganization kinetics changes, which allows to obtain a different response pattern for each volatile analyte, thereby defining their fingerprint.

[0120] Relative response (Ra) values, defined by Equation 1, where G1 is the minimum and G2 is the maximum conductance, were calculated using data from the optical and opto-electrical sensors.

[00001]$\begin{array}{cc}\mathrm{Ra}=\frac{G_2-G_1}{G_1}& \mathrm{Equation}.Math..Math.1\end{array}$

[0121] Thus, as a proof of concept in tests with solvents, a set of Ra values was used as input for Principal Component Analysis (PCA), performed by the commercial software, Statgraphics XV. A two-dimensional plot of the first two principal components (PCs) is represented in FIG. 6, where a clear separation of the 11 solvents is observed.

[0122] The ability to distinguish and identify solvents not only proves the concept of the opto-electric nose, but also shows its efficiency using only three optical sensors.

[0123] Hybrid sensors were also used in which an area of the sensitive film was deposited on interdigitated electrodes. Thus it was possible to simultaneously acquire optical and electrical responses from a single sensor, as exemplified in FIG. 7, as proof of concept for the opto-electronic system.

Example 5Application of a Sensitive Film

[0124] In order to monitor the quality of fresh fish, using a gas sensor, a system was built consisting of two closed compartments, separated by a door controlled by computer. This system allowed to alternate periods of exposure (to the volatiles from the fish sample and recovery, in fresh air, of the sensor, monitoring the emission of volatile compounds over extended periods of time. In the upper compartment an optical sensor formed by biopolymer (gelatin), liquid crystal (5CB) and ionic liquid ([BMIM] [Cl]) was introduced, and in the lower compartment fresh fish (Tilapia) was placed for sensory analysis, using a sensor gas. Under the same conditions, eight pieces of Tilapia, weighing 25 g each, were placed in a vessel for periodic microbiological analysis. Both testsgas sensor and bench microbiological testingaimed to assess the quality of the fish over time as tools for food safety analysis. The gas sensor is able to quantify volatile compounds emitted during the fish deterioration process while the microbiological tests count the colony forming units (CFUs), being this last test a validation of the first.

[0125] The relative response of the sensor was calculated as the ratio of the difference between the maximum and minimum conductance and maximum conductance. FIGS. 8 and 9 are graphical representations of the conductance and relative response, respectively, obtained over time. The plot shows an abrupt increase in the relative response of the sensor at about 7 h after start of the test, reaching a peak at 10 h. From 10 h onwards, the sensor gradually loses its responsiveness until it reaches a saturation phase. Around 6 h after the beginning of the test, a slight decrease is observed in the sensor response, which is consistent with the results of microbiological count assay performed simultaneously. The above assay was accompanied by conventional microbiological bench testing methods used to evaluate the quality of fish. The microbiological tests were carried out simultaneously, at every 2 h throughout the assay. Tilapia fish samples were subjected to enumeration of mesophilic bacteria, following the method of APHA, 2001. In this analysis, 25 g samples in 25 mL of peptone water were subjected to serial dilutions (1:10) until the fifth dilution, and subsequently inoculated into duplicate plates in standard agar culture medium for counting. The plates were incubated in inverted position at 37 C. for 48 h. The results of the total count of mesophilic bacteria show that, similarly to what was detected by the gas sensor, there was a decrease in bacterial count at 6 h of the assay and a significant increase at 8 h. This fact suggests that two bacterial strains may be present competing for the substrate, being the first strain better adapted to the environment and dominating in the first stage of the assay. From the 6 h on, a second strain develops and kills the first strain, this way initiating an exponential growth from that moment. At 8 h a count of 510.sup.6/g was obtained for mesophilic bacteria.

[0126] The information obtained by microbiological analysis is strictly coherent with the data obtained by the sensor during the test, where the increased sensor response can be associated with an increase in bacterial population in the fish. It is noteworthy that a single optical sensor was efficient in monitoring perishable products, giving information on the quality of the fish. This sensor can potentially be used to monitor perishable products such as fish, which are exposed in supermarkets, open street markets, fish shops etc., informing suppliers and customers on the quality of the sold products.

Example 6Application of the Sensitive Film

[0127] In view of concerns about automotive gas emissions and increasing efforts towards the use of renewable fuels, the automotive industry has created flex-fuel vehicles, available in several countries, such as Brazil. Flex-fuel vehicles accept ethanol-gasoline blends in any proportion, varying from pure ethanol to pure gasoline. It is crutial to measure the composition of the fuel in the vehicle's tank and convey it to the engine because the ideal air:fuel ratio that enters the combustion chamber depends on the composition of the fuel and is essential for the proper operation of the engine. Currently, manufacturers use oxygen sensors, called lambda sensors, positioned in the exhaust manifold to measure combustion quality and regulate the air:fuel proportion, regardless of the real composition of the fuel that is being burnt. Blending ethanol with gasoline in Brazil is allowed up to a maximum of 25% of ethanol. Control of this content is necessary in view of the occurrence of several cases of tampering, in which up to 50% ethanol content was found in market fuels.

[0128] In order to quantify ethanol in gasoline, the opto-electric (hybrid) sensors now described were exposed to fuel samples containing different concentrations of ethanol ranging from 0% (pure gasoline) to 100% (pure ethanol). The hybrid sensor comprises of a sensitive film composed of a mixture of liquid crystal and ionic liquid encapsulated in a biopolymer matrix of gelatin which was deposited by spin coating over gold interdigitated electrodes on a transparent glass substrate. The ionic liquid used in this sensor is [BMIM] [FeCl.sub.4] and the liquid crystal is 5CB. The volatiles were led from the sample chamber to the sensor by means of a volatile delivery system as depicted in FIG. 3. The sample was heated for 10 min and thermostatted at 35 C. and, then the sensor was exposed for 5 s to the headspace of the sample followed by 55 s exposure to fresh dry air, at a flow rate of 1.7 L/min. Admittance and conductance readings (20 readings per second) were performed simultaneously and are shown in FIG. 10. Each component of the hybrid sensor produces a different response according to the content of ethanol in the corresponding fuel sample. The electric response, illustrated in FIG. 11 shows that the admittance increases when the sensor is exposed to the volatiles and that this increase is inversely proportional to the level of ethanol in the fuel. In the optical response, as illustrated in FIG. 12, the exposure to volatiles resulted in a decrease of conductance, whose variation is also inversely proportional to the level of ethanol in the mixture. The observed reduction in optical response variation in the presence of ethanol is in accordance with the previous trials where several organic solvents were tested. Ethanol was the solvent that had lower effect on liquid crystal micelles, this way leading to a lower variation on the obstruction of light path and resulting in a lower conductance variation. Admittance and conductance variation were estimated from the height of the respective signal peaks. The results were fitted to a multiple linear regression model, to describe the relation between the content of ethanol and the two variables, conductance and admittance, as illustrated in FIG. 13. The equation of the fitted model is:

Ethanol content=211630,0466744*conductance-92,5484*Log(admittance)

[0129] Since the P-value is lower than 0.05, there is a statistically significant relation between the variables within a 95% level of confidence. The R-squared value indicates that the model explains 94.2% of the variability of ethanol content.

[0130] A single sensitive film is enough to quantify the content of ethanol in a gasoline sample since both the optical and the electrical components respond proportionally to the amount of ethanol in the sample, in an independent manner. However, since gasoline is a complex mixture susceptible to fluctuations in the composition, a double-variable model with two independent variables resulting from distinct transduction principles was employed. The combination of the two types of response in the same sensor and in a same model aims to lower the influence of that variable on the model. The opto-electric (hybrid) sensor shows, through this application, its usefulness and practicality in the quantification of ethanol content in gasoline, which can be detected immediately when filling the vehicle's fuel tank or in petrol stations.

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[0152] The current forms of embodiment are not, in any way, restricted to the embodiments described in this document and a person with average knowledge in the area could forecast many possibilities for modification of the embodiments described in this document, without deviating from the general scope of the invention, as defined in the claims.