Method of fabricating patterned cellulose nanocrystal composite nanofibers and nano thin films and their applications
11572450 · 2023-02-07
Assignee
Inventors
Cpc classification
D01D5/003
TEXTILES; PAPER
D01F2/00
TEXTILES; PAPER
International classification
Abstract
The present invention provides a method for fabricating patterned cellulose nanocrystal (CNC) composite nanofibers and thin films for optical and electromagnetic sensor and actuator application, comprising the following steps of: selecting materials for fabricating patterned cellulose nanocrystal (CNC) composite nanofibers; and fabricating patterned CNCs composite nanofibers by incorporating secondary phases either during electrospinning or post-processing, wherein the secondary phases may include dielectrics, electrically or magnetically activated nanoparticles or polymers and biological cells mechanically reinforced by CNCs.
Claims
1. A method for fabricating a cellulose nanocrystal (CNC) nanofiber display device, comprising the steps of: fabricating a plurality of CNC nanofibers, each of the CNC nanofibers having a CNC core and an outer concentric CNC layer; fabricating a polymeric substrate, the polymeric substrate having a grid patterned surface with a first plurality of trenches in a first direction and a second plurality of trenches in a second direction orthogonal to the first direction, the first plurality of trenches intersecting with the second plurality of trenches; and disposing a first plurality of the CNC nanofibers in the first plurality of trenches, and a second plurality of the CNC nanofibers in the second plurality of trenches; wherein each of the first plurality of the CNC nanofibers is disposed in one of the first plurality of trenches, and each of the second plurality of the CNC nanofibers is disposed in one of the second plurality of trenches and crosses over above the first plurality of the CNC nanofibers.
2. The method according to claim 1, wherein the grid patterned surface of the polymeric substrate is patterned by using E-beam lithography.
3. The method according to claim 1, wherein the CNC core comprises an electrode material and the outer concentric layer comprises an active material.
4. The method according to claim 3, wherein the active material is an electroluminescent material.
5. The method according to claim 1, wherein the CNC core and the outer concentric CNC layer are spatially separated conductive polymers, and electroluminescent colloidal nanocrystal quantum dots are injected into the conductive polymers.
6. The method according to claim 5, wherein the CNC nanofibers are fabricated by using a coaxial electrospinning process and the electroluminescent colloidal nanocrystal quantum dots are injected during the coaxial electrospinning process.
7. The method according to claim 5, wherein the electroluminescent colloidal nanocrystal quantum dots comprise CdS or CdSe nanocrystals.
8. The method according to claim 1, wherein the CNC nanofibers are fabricated by using a diameter variable extrusion system.
9. The method according to claim 1, wherein the CNC nanofibers are fabricated by using a coaxial syringe electrospinning system.
10. The method according to claim 1, wherein the CNC nanofibers are fabricated by using a parallel multi syringe electrospinning system.
11. A method for fabricating a cellulose nanocrystal (CNC) nanofiber display device, comprising the steps of: fabricating an alignment layer, the alignment layer being formed with a tooth-shape structure having a plurality of V-shaped grooves; fabricating a plurality of CNC nanofibers on top of the alignment layer with each of the CNC nanofibers being disposed in one of the V-shaped grooves, each of the CNC nanofibers having a CNC core and an outer concentric CNC layer; and a top electrode disposed on top of the plurality of CNC nanofibers.
12. The method according to claim 11, wherein the tooth-shape structure of the alignment layer is fabricated by the steps of: spin-coating a photoresist layer on a silicon wafer; patterning the photoresist layer using E-beam lithography; performing silicon anisotropic etching of the silicon wafer using KOH to form a silicon mold with a tooth-shape pattern; mixing a polydimethylsiloxane (PDMS) solution and pouring the PDMS solution onto the silicon mold to form a PDMS mold with the tooth-shape pattern; and pressing the PDMS mold on a polymer layer to form the tooth-shape structure.
13. The method according to claim 11, wherein the CNC core comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and the outer concentric CNC layer comprises an active layer.
14. The method according to claim 11, wherein the step of fabricating the plurality of CNC nanofibers is performed by using a diameter variable extrusion system.
15. The method according to claim 11, wherein the step of fabricating the plurality of CNC nanofibers is performed by using a coaxial syringe electrospinning system.
16. The method according to claim 11, wherein the step of fabricating the plurality of CNC nanofibers is performed by using a parallel multi syringe electrospinning system.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
(35) The present disclosure may be embodied in various forms, and the details of the preferred embodiments of the present disclosure will be described in the subsequent contents with reference to the accompanying drawings. The drawings (not to scale) show and depict only the preferred embodiments of the present disclosure, and will not be considered as limitations to the scope of the present disclosure. Modifications of the present disclosure should be considered within the spirit of the present disclosure.
(36)
(37) As shown in
(38) Step 102 is to perform fabricating the patterned cellulose nanocrystal composite nanofibers and thin films by incorporating secondary phases either during electrospinning or post-processing, wherein the secondary phases may include dielectrics, electrically or magnetically activated nanoparticles or polymers and biological cells mechanically reinforced by CNCs.
(39) In the step 101, the material selection will depend on the application for optical and/or electromagnetic sensor and/or actuator application. After the step 102, a new CNC composite NF having unique and tunable mechanical and/or optical properties is produced.
(40) According to the present invention, different embodiments of the method for fabricating patterned cellulose nanocrystal (CNC) composite nanofibers and thin films can be implemented to produce CNC composite fiber, and/or thread, and/or textile, and/or foam for optical, sensor and actuator applications by using a diameter variable extrusion system, and/or a multi-coaxial electrospinning system, and/or parallel multi-syringe electrospinning system through variable external electric and magnetic field combining with electrically or magnetically active CNC composite.
(41) For the CNC composite thread, in the step 102, the thread fabrication uses modified electrospinning process (repulsive force in fiber creating natural twisting swirling motion).
(42) For the CNC composite thin film, in the step 102, the thin film fabrication uses spin coating with diluted CNC solution.
(43) For the CNC composite foam, in the step 102, the foam fabrication uses chemical process and supercritical temperature process.
(44) Meanwhile for the CNC composite foam, in the step 102, as for applications of Cellulose in THz gas detection, a preparation of thin film Cellulose nanoporous foam is disclosed.
(45) Ionic liquid is an alternative solvent for cellulose which is non-volatile and less dangerous comparing with organic solvent, like NMMO and sulfuric acid. Mehmet Isik et al. summarized the recent advances in the development of cellulosic material which is using ionic liquid to directly react with the cellulose. This process for creating the cellulose foam is modified from the process flow developed by Deng. One significant variation of the process is that the concentration of cellulose ionic solution is slightly higher to 5 to 10 wt %. And we put on a step of spincoating to get a liquid thin film, which later turn into a cellulose nanoporous solid foam on the target substrate with a desired thickness.
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(47) As shown in
(48) Next, in the spin-coating on the substrate process, the solution was spin-coated onto a polytetrafluoroethylene (PTFE) film with glass template: Spin speed: 500 rpm for lOsec and 5200 rpm for 30 sec.
(49) Finally, in the solvent exchange and rapid-freeze drying process, the substrate is coagulated in the water to obtain a transparent gel followed by being washed with deionized water. After solvent exchange, the substrate placed in a petri dish is then quickly immersed in liquid nitrogen for 0.5 h, which turns the cellulose hydrogel into ice. The function of liquid nitrogen can shrink down the size of the ice crystal to nanoscale through quick freezing. After that, the ice film is put into a freeze drier to remove this ice crystal. The freeze dryer can create a low pressure (100 mtorr) and low temperature (−30°) environment so that the ice can sublimate to gas.
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(51) According to the SEM results in the
(52) Meanwhile for the CNC composite foam, in the step 102, as for applications of Cellulose in THz gas detection, an application of cellulose nano-foam in THz technology is disclosed.
(53) The optical gas sensor can offer advanced capabilities such as wireless sensing and high selectivity which are indispensable for monitoring hazardous air pollutions. The fingerprint of various dangerous gases, such as carbon monoxide and methane can be identified through various terahertz detection schemes such as absorption-induced transparency, absorption spectrum, time transient etc. However, to overcome the low sensitivities of current direct spectral measurement methods, we propose a meta surface resonating sensor, in which the concentration of a gas can be detected based on the resonant frequency shift. To further increase the sensitivity, the implantation of cellulose foam nanostructure can enhance adsorption of the gas. Thus, the detection can be determined from the transmission of the THz ray. The configuration of the device is shown in
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(56) The optical gas sensor can offer advanced capabilities such as wireless sensing and high selectivity which are indispensable for monitoring hazardous air pollutions. The fingerprint of various dangerous gases, such as carbon monoxide and methane can be identified through various terahertz detection schemes such as absorption-induced transparency, absorption spectrum, time transient etc. However, to overcome the low sensitivities of current direct spectral measurement methods, we propose a meta surface resonating sensor, in which the concentration of a gas can be detected based on the resonant frequency shift. To further increase the sensitivity, the implantation of cellulose foam nanostructure can enhance adsorption of the gas. Thus, the detection can be determined from the transmission of the THz ray. The configuration of the device is shown in the
α.sub.eff=α.sub.gasR+(α.sub.cellulose1−R),
where R, α.sub.gas, α.sub.cellulose and α.sub.eff are the filling ratio of pores and the absorption coefficients of gas, cellulose, and the effective media, respectively. Owing to the ultrahigh porous of the cellulose, the filling ratio is high up to 98%, which can reduce the THz attenuation by the cellulose media. In adittion, LLL model can be used to derive and calculate the resonate shift of THz:
∛√{square root over (ε.sub.eff)}=∛√{square root over (ε.sub.gas)}R+∛√{square root over (ε.sub.cellulose)}(1−R),
where ε.sub.eff, ε.sub.gas and ε.sub.cellulose are the dielectric permittivity of effective media, air and cellulose, respectively. Based on the simulation result, the resonate peak has a frequency shift (˜0.02 THz) in the device with 50 ppm acetone vapor.
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(60) For unique application in optical, electromagnetic sensor and actuator application, in the step 102 for nanofibers or micro fibers biosensor, Nanofiber E. coli or Multi-Virus sensor uses evanescent sensor and Bragg grating using the diameter variable extrusion system, the multi-coaxial electrospinning system.
(61) For optical application, in the step 102 for nanofiber display system, the parallel multi-syringe electrospinning system and also additional MEMS fabrication process are used to fabricate crisscross layered of electroluminescent CNC nanofibers.
(62) For electromagnetic sensor application, in the step 102, the diameter variable extrusion system with post processing is used to fabricate the CNC composite fiber humidity sensor.
(63) For the thin film IC, optical devices, electromagnetic sensors and actuators application, in the step 102, spin coating processes are used.
(64) For the CNC composite yarn and textile, in the step 102, a modified electrospinning process is used.
(65) For the CNC composite yarn and textile, a modified electrospinning, electrostatic repulsion induced fiber twist, water spout like spinner and sorter and weaving device fabrication is used.
(66) For the yarn, in the step 102, the yarn is made by electrospinning process.
(67) For the CNC composite foam, in the step 102, the foam fabrication process combined with typical clean room process for fabricating meta-material is used to fabricate the CNC composite foam gas absorbing foam combined with the meta-material to improve THz gas detection for electromagnetic sensor.
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(69) As shown in
(70) Step 202 is to perform fabricating the patterned cellulose nanocrystal composite nanofibers and thin films for optical fiber by incorporating secondary phases either during electrospinning or post-processing, wherein the secondary phases may include dielectrics, electrically or magnetically activated nanoparticles or polymers mechanically reinforced by CNCs.
(71) In the step 201, the material selection will depend on the application for optical fiber application. After the step 202, as shown in
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(73) The presence of two or more different passive materials within the optical fiber 11 can induce different physical or chemical responses within the same optical fiber 11, raising the possibility of multilayer threads as possible smart devices. Spatially incorporating passive materials will result in localized responses in nano and micro scale, which leads to distributive sensing. The advantage the method of the present invention possesses over a conventional mix-spun material is that the location of adjacent materials can be controlled by the threads, and with the usage of different materials (and air), the threads can also be made porous, which is an essential property in biological applications, such as scaffolds and drug delivery, or in display applications by embedding active materials (such as liquid crystal (LC)) for color and electroluminescent material (such as CdSe/CdS nanocrystals) for light emission. The eventual outcome of the present invention is the creation of a new, patentable product line of green CNC optical fiber sensors at the nano and micron scale that allow active controlled and monitoring of materials at a cellular level.
(74) Optical NF Design
(75) Prior to fabricating CNC nano optical fiber 11, it is necessary to check the optical design based on the measured optical properties. For photonic applications, single-mode waveguide is mostly preferred to avoid multimode interference. Single-mode condition for a freestanding photonic waveguide nanowire is determined by
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where D is the nanowire diameter and ni and nz are refractive indices of the nanowire and the surrounding material, respectively. The λ.sub.1, λ.sub.2, and λ.sub.3, are wavelengths, respectively. The diameter of a typical nanowire should be close to or smaller than the wavelength of the light. For an 800 nm diameter fiber, the cutoff wavelength for a single mode operation has to be above 1182 nm when operating in air.
(77) The field distribution and wave propagation is obtained using CST numerical software.
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(81) As shown in
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(83) Low-loss connection to the existing optical fiber 11 and fiber optics components is made possible by incorporating a tapered waveguide coupling structure. The NF is stretched from a larger core CNC fiber that maintains the typical fiber size at their input and output, allowing ready splicing to standard fibers and fiber optics components. The observed coupling loss is low (<0.3 dB) and the mode field is maintained.
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(85) As shown in
(86) Step 302 is to perform fabricating the patterned cellulose nanocrystal composite nanofibers and thin films by incorporating secondary phases either during electrospinning or post-processing, wherein the secondary phases may include dielectrics, electrically or magnetically activated nanoparticles or polymers and biological cells mechanically reinforced by CNCs.
(87) In the step 301, the material selection will depend on the fabricated patterned cellulose nanocrystal (CNC) composite nanofibers and thin films. After the step 302, the patterned cellulose nanocrystal composite nanofibers and/or thin films are produced.
(88) Composite Fabrication
(89) The plasticized CNC composite thin films being the patterned cellulose nanocrystal composite nanofibers and thin films were made by systematically varying the weight ratios of fiber, matrix and glycerol to optimize the film's mechanical strength. The different matrices such as PVA, PLA and PCL/nylon-6 will be used beside glycerol and methanol. PLA and PCL are bio-based polymers and provide an opportunity for a “bio-bio” biodegradable composites. Thermoplastic Polycaprolactam or nylon 6 is synthesized by anionic ring opening polymerization of caprolactam is another good option due to its low pressure and temperature operation. Ring opening polymerization of lactams to generate polyamides has been studied extensively. Caprolactam is by far the most studied lactam. The Nylon 6 prepared from caprolactam compares well with that prepared by the conventional hydrolytic polymerization. Due to fast reaction kinetics and absence of by-products, Nylon 6 produced by anionic ring opening polymerization is a compelling choice for industrial application. Due to high strength, high stiffness, and hydrophilicity, Nylon 6 should be good for a matrix with CNCs. Anionic ring opening polymerization of caprolactam is known to take only minutes and can be done at 140° C. with no byproducts. The rate of monomer conversion to caprolactam is fast and the molecular weights attained are considerably higher than for hydrolytic Nylon 6. The Nylon 6 absorbs 9.7% moisture. Therefore, the ring opening polymerization of caprolactam will be of much interest because ring opening polymer with CNC and natural fiber is an unexplored work. The monomer is also a liquid, thus by direct polymerization, CNC composites NF can be formed without high pressures or temperature.
(90) In the step 301, after a set of matrix and solvent are selected with an optimal weight ratio, the CNC mixture will be prepared. In the step 302, the prepared mixture will then be electrospun into composite NFs. The optimum casting weight percent of fiber (CNC) and matrix (obtained from the previous studies and preliminary results) will be used for electrospinning. The different formulations and solvents will be used, along with varying weight % of PVA, and H.sub.2O dilution. Furthermore, to improve bonding performance and dispersion of CNC in the active composite NF, maleic anhydride and oligomers will be added to the solution.
(91) PVA will be added to give the solution enough viscous and elastic to spin out the continuous NF. The mixture of solution containing of 25 ml of CNC (11 wt %) with 15 ml of PVA(7.2%) was spun out as continuous NF. This formulation and further dilution by adding more ethanol will be used to spin out NF. In addition, ethanol will be added to increase the rate of evaporation. For NF with two layers or more, the concentration of CNC (wt %) will be different in each layer. The inner layer will start with the above CNC concentration and the outer layer with slightly lower or higher concentration will be used by adding more ethanol such as mixture of 25 ml of CNC (11 wt %) with 25 ml of ethanol. This will affect the mechanical and optical properties of these NF. In the step 301, after NF with these mixtures are produced, a small percentage of PVA with an increase of 0.5% wt will be added into the solution to produce CNC-PLANF. The feeding system is for two layers or more.
(92) In the step 302, the electrospinning is an easily controlled technique. However, the various phenomena taking place while spinning make it difficult to draw a clear correlation between instrument design, operational conditions, and the characteristics of the produced micro or NFs. Processing parameters such as the voltage and distance between the spinning tip and the collector, the properties (conductivity, viscosity, density, surface tension, etc.) of the spinning solution and its flow rate can drastically affect the outcome of the spinning process. Thusly, these variables (conditions) have effects on the quality of the final composite NF. In addition to optimizing typical conditions/variable used in the electrospinning of the step 302, alignment of the CNCs will be controlled by a set of interdigitated electrodes or magnetic coils that are electrically or magnetically insulated from the CNC solution. The electric and magnetic field will attempt to align the CNCs to control its anisotropy and fiber orientation.
(93) In addition to aligning CNC by electric and magnetic fields, surface modification of the CNC and matrix is performed to improve bonding. Maleic anhydride will be used for surface modification and grafting to improve bond performance and dispersion of CNC for both composite NF. PLA oligomers will also be added to PLA to improve surface attached and dispersion of CNC. Effort will be made on improving bonding performance between CNC and matrix and CNC dispersion.
(94) The validated model will be used to fabricate optimum CNC-filled composites of glycerol, and PLA with/without surface modification.
(95) In addition to the composite studies, layered and spatially patterned composite NFs will be investigated. Special design syringe system will be developed to allow coaxial concentric multilayer or non-coaxial composite NFs to be manufactured using electrospinning.
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(97) As shown in
(98) In the non-coaxial setup, the multiple solution feed system 21 including two syringes and needle 211 allows injection of one or more solutions into another at the tip of the spinneret 212 as shown in
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(100) As shown in
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(102) As shown in
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(105) An alternative to solvent-based electrospinning is melt electrospinning. According to the present disclosure, a modified version of melt electrospinning is provided to accommodate the type of polymer. The technique of the present disclosure differs from the traditional melt electrospinning as a CNC or CNC PLA preform of the concentric layer composite is first created. Then the preform will be reheated to their glass transition temperatures (˜220° C.) and stretched into thin strain using typical fiber draw process (
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(107) As shown in
(108) Step 402 is to perform fabricating the patterned cellulose nanocrystal composite nanofibers and thin films by incorporating secondary phases either during electrospinning or post-processing, wherein the secondary phases may include dielectrics, electrically or magnetically activated nanoparticles or polymers and biological cells mechanically reinforced by CNCs.
(109) In the step 401, the material selection will depend on the application for optical and/or electromagnetic sensor and/or actuator application. After the step 402, a new CNC composite NF having unique and tunable mechanical and/or optical properties is produced.
(110) According to the present invention, different embodiments of the method for fabricating patterned cellulose nanocrystal (CNC) composite nanofibers and thin films can be implemented to produce CNC composite fiber, and/or thread, and/or textile, and/or foam for optical, sensor and actuator applications by using a diameter variable extrusion system, and/or a multi-coaxial electrospinning system, and/or parallel multi-syringe electrospinning system through variable external electric and magnetic field combining with electrically or magnetically active CNC composite.
(111) For unique application in optical, electromagnetic sensor and actuator application, in the step 402 for nanofibers or micro fibers biosensor, Nanofiber E. coli or Multi-Virus sensor uses evanescent sensor and Bragg grating using the diameter variable extrusion system, the multi-coaxial electrospinning system.
(112) For optical application, in the step 402 for nanofiber display system, the parallel multi-syringe electrospinning system and also additional MEMS fabrication process are used to fabricate crisscross layered of electroluminescent CNC nanofibers.
(113) For electromagnetic sensor application, in the step 402, the diameter variable extrusion system with post processing is used to fabricate the CNC composite fiber humidity sensor.
(114) For the thin film IC, optical devices, electromagnetic sensors and actuators application, in the step 402, spin coating processes are used.
(115) For the CNC composite foam, in the step 402, the foam fabrication process combined with typical clean room process for fabricating meta-material is used to fabricate the CNC composite foam gas absorbing foam combined with the meta-material to improve THz gas detection for electromagnetic sensor.
(116) Sensor and Actuator Development
(117) Although the present disclosure has been described with reference to the preferred embodiments, it will be understood that the disclosure is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the disclosure as defined in the appended claims.
(118) Here are some examples of sensor application using spatially pattern NFs.
(119) Nanofiber E. coli or Multi-Virus sensor
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(121) For the first composite sensor, an antigen is simply coated such as Escherichia coli (E. coli) to the CNC-based composite NFs (during electrospinning process). E. coli antibodies will coat the outer surface of the CNC composite NF using the dip coating coaxial electrospinning technique. Antigen of E. coli will be coated to the CNC NF. During the coating process, CNC NF will be immersed vertically into Antigen of E. coli at a constant speed. The CNC NF is left in the solution for a set period, allowing a thin layer of E. coli antigen to deposit itself on the CNC NF. The fiber is then withdrawn at a constant speed to ensure uniformity of the coating layers, verified via SEM.
(122) Using this method (and a new system), a simple multiband evanescent wave NF E. coli sensor is created based on the refractive index change due to bacteria binding to the antibodies (as shown in
P=P(0)exp(−a) (2)
where P and P(0) are, respectively, the power transmitted through the fiber 6 with [P] and without [P(0)] an absorbing medium over the entire fiber length L. a=r.sub.f αm C L is the evanescent wave absorbance, C is the concentration of the absorbing medium, r.sub.f is the effective fraction of the total guided power in the sensing region and m is the bulk absorption coefficient of the absorbing species. As shown in the equation, evanescent absorbance is directly proportional to the species concentration and the effective fraction of the total guided power in the sensing region of the fiber. By using a concentric electrospinning system to periodically taper the fiber 6 along the axial direction (as shown in
(123)
λ.sub.B=2n.sub.eff Λ (3)
where n.sub.eff is the effective index of the propagating mode and Λ is the grating pitch. The detection will be based on the Bragg wavelength shift due to the effective index change induced by adsorption of E. coli virus on the antibody coating on the Bragg grating sensor (as shown in
(124) The amount of contamination in the sample or E. coli will be evaluated by calculating the change of the output signal from a stable baseline to the peak value recorded. Baseline values will be calculated by averaging the sensor signal over large amount of samples, where baseline noise is represented by standard deviation. Absolute change is calculated as the difference between the peak values recorded and the stable baseline value.
(125) In this study, optical biosensor will be developed to detect bacterial/Escherichia coli (E. coli ) in media (solution, e.g. water). Optical biosensors are particularly attractive for detection of bacteria. These sensors are able to detect minute changes in the refractive index or thickness, which occurs when cells bind to receptors immobilized on the transducer surface. They correlate changes in concentration, mass or number of molecules to direct change in characteristics of light.
(126) The target application will be on food-related E. coli infections as well as contaminated ground water due to composted manure or human or animal wastes. Other antigens can be and will be added and further develop the cellulose sensor into more complex multi-parameter sensors.
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(128) Nanofiber Display System
(129) A more complicated structure such as display system can be constructed using arrays of proposed CNC composite nanofibers and thin films. Electroluminescent colloidal nanocrystal quantum dots such as CdS will be injected into concentric layers of conductive polymer layers during the program controlled coaxial electrospinning process. The coaxial setup will enable a spatially separated two layer composite nanofiber with appropriate active materials such as in
(130) To avoid ambiguity in display point trigger, a time division multiplexing system will be employed to handle the timing of the firing of these criss crossing CNC composite nanofibers and thin films to correctly create the display image.
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(134) More details on how to manufacture the above display system:
(135) Light-emitting electrochemical cells (LECs) are simple and single active layer devices that can be easily prepared from wet process such as spin-coating and inkjet printing. Comparing with OLED process, the thick active layer makes the process higher error tolerance and the air-sensitive charge injection layers are unnecessary which is attractive for industrial processing. The first configuration for light emitting electrochemical cells was developed based on conjugated polymer, ionic species, and a buffer polymer. The presence of ionic species in the active layer of conjugated polymer that contains electrolyte to provide the necessary counter ions for doping. When potential field is applied to the counter electrode, the p-type and n-type doping is respectively initiated on the opposite side of electrode and the charge carriers will move between the regions. The recombination of holes and electrons will emit light from the p-n junction of the electroluminescent polymer. The quantum efficiency of LECs is shown below.
EQE=bφ/2n.sup.2 (4)
where b is the recombination efficiency of electrons and holes, φ is the exciton-to photon efficiency, n is the refractive index of output coupling.
(136) A basic planer light emitting electrochemical cell is a single layer structure, composed of an air-stable metal layer, and a transparent electrode layer for light coupling out and an active light emitting layer. Comparing with OLED, it doesn't require multilayer structure for electrons and holes transportation and complicated fabrication process. However, for coupling the LECs with fabric, the planer structure is not useful for electronic textile.
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(142) The present disclosure is composed with active nanofibers, an SU-8 alignment layer, and a top electrode. As shown in
(143) The SU-8 alignment layer was fabricated on the glass by solvent assisted micro molding. The process of it can be generally separated into three process: creating the V grove shape on si-wafer as a mold; transfer the pattern to PDMS by directly pouring PDMS into the Si mold; use PDMS mold to press the SU8 polymer and get the tooth shape structure.
(144) For creating the two layered nanofiber, electrospinning combined with coaxial needle is the method to create the two layered morphology. When the nanofiber was pulled out of the needle, the alignment will help to arrange the nanofibers in the direction of grating.
(145) The following are two examples of electromagnetic sensors using CNC composite in microfiber and nanofiber yarn configuration.
(146) Humidity sensing fiber
(147) Urinary incontinence is a critical problem in elderly woman and man. It is shown that the problem is usually associated with other disease like Parkinson's disease or dementia. To reduce the risk that patients with physical or intellectual disability suffer from possible ramifications caused by soiled diaper, a new configuration of humidity sensor is provided to apply in the nursing home according to the present disclosure. Many commercial humidity sensors suffer from a complicated fabrication process and are restricted to a planer structure.
(148) CNCs are rod like materials with diameter 3 to 50 nm in diameter and several hundred nanometers long. They are derived from abundant cellulose, through a series chemical process such as acid hydrolysis. Owing to their fascinating optical and electromagnetic properties, they have attracted many researches recently in energy and electronic application. CNC is an affinity to water. The water molecule is easily absorbed by the branch of CNC. It shows that the electrical impedance of cellulose is highly sensitive to water which makes it a good choice for developing a humidity senor.
(149) The present disclosure is to disclose a disposable polymer based humidity sensor in microfiber configuration. The present disclosure is based on a biodegradable Poly(DL-lactide) (PDLLA) fiber dip coated with a thin layer of CNC/ PEDOT:PSS on its surface which can detect water vapor stem from body or surrounding. Owing to its light weight flexible fiber shaped, this biocompatible device can be easily for weaving into fabric. Owing to its current fabrication, a long spool of fiber of controllable diameter can be drawn and sensitivity and range can be tune by varying the mixing weight ratio of the composition. In addition to the application in textile electronics, this device is also suitable for detection of water leak in tight spaces or hard to reach areas.
(150) An example of cellulose based composite can be synthesized by physically mixing diluted CNC aqueous solution (5.75%) with PEDOT:PSS (PH1000, Clevios) aqueous solution. Beside these two materials, 99% Isopropyl alcohol (IPA) was used to help mixing the gel-like CNC into PEDOT:PSS. The as mixed suspensions were homogenized by putting into ultrasonic cleaner for lhr. The extruded PDLLA fibers were first cleaned and degassed. Then the fiber was vertically dipped into the mixed suspension and pulled out with a uniform pulling rate. This pulling process is operated in the room temperature (25° C.). Thickness of coated composite can be defined by the relationship derived by Landau and Levich for a Newtonian fluid:
(151)
(152) Ag glue is coated on the surface of the fiber to provide an electrical path of CNC composite and connected to the contact pads.
(153) A CNC Conductive Composite Nanofiber Yarn
(154) Electrospinning is one of the efficient methods to prepare polymer micro or nanofiber. The electrospun nanofibers can be collected and form many configurations of mats by manipulation of the applied electric field, or by changing the ground collector geometry. Traditionally a drum collector spins and collects fibers into a spool. A pair of conductive substrate (counter-electrodes) separating by a gap can be used to collect them uniaxially. For certain applications, like wearable nanotechnology, it is essential to produce twisted yarns instead of parallel fiber columns traditionally found in electro-spinning process. Recently, several groups have successfully produced these yarns. Dalton et al. proposed two ring electrode system with one ring rotating to twist the aligned nanofiber. However, the distance between the two rings limited the production length of the yarn. Ramakrishna et al. resolve this problem by using a dynamic liquid collector to help collect sort and feed the fiber to a mandrel using vortex generated inside a corn shape container placed directly below the spinneret. However, the mechanism is too complicated with too many parameters to control the hydrodynamic motion of water.
(155) In order to solve the problem of collecting nanofiber yarn, a simple solution is presented. The setup is similar to the conventional method for preparing a non-woven mats with two design difference: First, the suspension in this method needs to be conductive and available to form nanofibers. Second, a sharp triangular steel tip is mounted on the top of the metal stage which the vertical distance between the needle to the ground can be adjusted. The triangular tip serves as the ground to attract the nanofibers. Electrostatic force drives the polymer suspension to the electric ground. The overall system setup is shown in
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(157)
(158) Novelty of the mechanism of the present disclosure will be more apparent from the following detailed description. An electrospinning jet generally comprises of three segments, the Taylor cone, the stable segment and the bending segment. The electrically driven solution jet will solidify in the stable region and bending region between needle and collector. Due to the high electric field, the bending segment leads to the formation of disordered nanofiber. In
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(160) As shown in
(161) Moreover, the step S146 of creating a tooth-shape alignment layer further comprise the steps of: creating a V grove shape on a Si wafer as a mold; transferring a pattern to the PDMS by directly pouring the PDMS into the Si mold; pressing polymer by the PDMS mold; and obtaining a tooth-shape structure.
(162) In addition, the suspension is composed of PEDOT:PSS (PH1000, Clevios), Cellulose Nanocrystals (University of Maine) and PVA (First Chemical Manufacture Co.). An example of the composition of the suspension is shown in Table 1. The working parameters are shown in Table 2.
(163) TABLE-US-00001 TABLE 1 Composition of the CNC/PEDOT:PSS/PVA suspension PEDOT:PSS CNC PVA water Weight 0.38% 1.50% 5.56% 92.56% percent
(164) TABLE-US-00002 TABLE 2 Working parameters Feed rate voltage distance needle size working 5 uL/min 10 KV 12 cm 30 gage parameter
(165) In addition,
(166) Further, potential applications include smart clothing (monitoring humidity, temperature, heart rate, provide electric interconnect, lighting, display etc.) and wearable health care sensor-based systems for point of care monitoring and diagnostic.
(167) Although the present disclosure has been described with reference to the preferred embodiments, it will be understood that the disclosure is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the disclosure as defined in the appended claims.