Fabrication Of Functional Nanostructures Using Polyelectrolyte Nanocomposites And Reduced Graphene Oxide Assemblies

A wide variety of nanomaterials ranging from polymer assemblies to organic and inorganic nanostructures (particles, wires, rods etc) have been actively pursued in recent years for various applications. The synthesis route of these nanomaterials had been driven through two fundamental approaches - \u27Top down\u27 and \u27Bottom up\u27. The key aspect of their application remained in the ability to make the nanomaterials suitable for targeted location by manipulating their structure and functionalizing with active target groups. Functional nanomaterials like polyelectrolyte based multilayered thin films, nanofibres and graphene based composite materials are highlighted in the current research. Multilayer thin films were fabricated by conventional dip coating and newly developed spray coating techniques. Spray coating technique has an advantage of being applied for large scale production as compared to the dip coating technique. Conformal hydrophobic/hydrophilic and superhydrophobic/hydrophilic thermal switchable surfaces were fabricated with multilayer films of poly(allylaminehydrochloride) (PAH) and silica nanoparticles by the dip coating technique, followed by the functionalization with thermosensitive polymer-poly(N-isopropylacrylamide)(PNIPAAM) and perfluorosilane. The thermally switchable superhydrophobic/ hydrophilic polymer patch was integrated in a microfluidic channel to act as a stop valve. At 70 degree centigrade, the valve was superhydrophobic and stopped the water flow (close status) while at room temperature, the patch became hydrophilic, and allowed the flow (open status). Spray-coated multilayered film of poly(allylaminehydrochloride) (PAH) and silica nanoparticles was fabricated on polycarbonate substrate as an anti-reflection (AR) coating. The adhesion between the substrate and the coating was enhanced by treating the polycarbonate surface with aminopropyltrimethoxylsilane (APTS) and sol-gel. The coating was finally made abrasion-resistant with a further sol-gel treatment on top of AR coating, which formed a hard thin scratch-resistant film on the coating. The resultant AR coating could reduce the reflection from 5 to 0.3% on plastic. Besides multilayered films, the fabrication of polyelectrolyte based electrospun nanofibers was also explored. Ultrathin nanofibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylaminehydrochloride) (PAH) were fabricated using the electrospinning technique and methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. The fiber was also loaded with a real life anti-depressant drug (2,3-tertbutyl-4-methoxyphenol) and fiber surface was made superhydrophobic. The drug loaded superhydrophobic nanofiber mat was immersed under water, phosphate buffer saline and surfactant solutions in three separated experiments. The rate of release of durg was monitored from the fiber surface as a result of wetting with different solutions. Time dependent wetting of the superhydrophobic surface and consequently the release of drug was studied with different concentrations of surfactant solutions. The results provided important information about the underwater superhydrophobicity and retention time of drug in the nanofibers. The nanostructured polymers like nanowires, nanoribbons and nanorods had several other applications too, based on their structure. Different self-assembled structures of semiconducting polymers showed improved properties based on their architectures. Poly(3-hexylthiophene) (P3HT) supramolecular structures were fabricated on P3HT-dispersed reduced graphene oxide (RGO) nanosheets. P3HT was used to disperse RGO in hot anisole/N, N-dimethylformamide solvents, and the polymer formed nanowires on RGO surfaces through a RGO induced crystallization process. The Raman spectroscopy confirmed the interaction between P3HT and RGO, which allowed the manipulation of the composite\u27s electrical properties. Such a bottom-up approach provided interesting information about graphene-based composites and inspired to study the interaction between RGO and the molecular semiconductor-tetrasulphonate salt of copper phthalocyanine (TSCuPc) for nanometer-scale electronics. The reduction of graphene oxide in presence of TSCuPc produced a highly stabilized aqueous composite ink with monodispersed graphene sheets. To demonstrate the potential application of the donor (TSCuPc)\u27acceptor (graphene) composite, the RGO/TSCuPc suspension was successfully incorporated in a thin film device and the optoelectronic property was measured. The conductivity (dark current) of the composite film decreased compared to that of pure graphene due to the donor molecule incorporation, but the photoconductivity and photoresponsivity increased to an appreciable extent. The property of the composite film overall improved with thermal annealing and optimum loading of TSCuPc molecules

Method of Forming Composite Materials including Conjugated Materials attached to Carbon Nanotubes or Graphenes (CIP)

A method of forming composite materials includes dispersing a conjugated material, a solvent for the conjugated material, and a plurality of carbon nanotubes (CNTs) or graphene including structures having an outer surface to form a dispersion. The solvent is evaporated from the dispersion to yield a CNT or graphene composite including a plurality of crystalline supramolecular structures having the conjugated material non-covalently secured to the outer surface of the CNT or the graphene including structure. The supramolecular structures have an average length which extends outward in a length direction from the outer surface of the CNT or graphene including structure, where the average length is greater than an average width of the supramolecular structures

Supramolecular Structures Comprising At Least Partially Conjugated Polymers Attached to Carbon Nanotubes and Graphenes

A composition of matter includes at least one carbon nanotube (CNT) or grapheme type structure having an outer surface and a plurality of crystalline polymer supramolecular structures that includes a conjugated polymer that are non-covalently secured to the outer surface of the CNTs or the grapheme type structure. The conjugated polymer can be a conjugated homopolymer or a block copolymer including at least one conjugated block. The supramolecular structures extend outward from the outer surface of the CNTs or grapheme type structures

Position dependent photodetector from large area reduced graphene oxide thin films

We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemically synthesis and interconnecting sheets

An analytical model for the wettability switching characteristic of a nanostructured thermoresponsive surface

The applications of thermoresponsive surfaces require the development of a rigorous mathematical treatment for these surfaces to understand and improve their behavior. We propose an analytical model to describe the transfer characteristics (variation in contact angle versus temperature) of a unique nanostructured thermosensitive surface, consisting of silica nanoparticles and a hydrophilic/hydrophobic thermoresponsive polymer, poly(N-isopropylacrylamide). Three different thermo-sensitive platforms were fabricated and the contact angle change of a water droplet on the surface with varying surface temperature was analytically modeled

A Multifunctional Gold Nanoparticle/Polyelectrolyte Fibrous Nanocomposite Prepared from Electrospinning Process

Gold nanoparticles are introduced to a fibrous nanocomposite material prepared from electrospinning a polyelectrolyte solution of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). The functional groups in the fiber allow convenient thermal crosslinking of the fibers and the binding of tetrachloroaurate ions. Gold nanoparticle-modified nanofibers can be further treated by silver enhancement that increased the electrical conductivity of the nanofibers to 10(-2) S/cm. The FT-IR analysis of the nanocomposite fibers shows that the deposition of gold nanoparticles significantly enhances the IR absorption intensity of the polymer fibers, offering a potential sensing capability through enhanced FT-IR absorption of molecules. Upon laser irradiation, the photothemal effect generated by gold nanoparticles caused deformation, melting, or local decomposition of the nanofibers which allows the patterning of nanofibers. The multifunctional composite nanofibers may find many important potential applications in sensors, optical and electronic devices, tissue engineering and catalysis

Invited Paper: Fabrication Of Antireflection Coatings For Displays

Antireflection and antifogging coatings were fabricated on polycarbonate substrates using the layer-by-layer self-assembly of polyelectrolytes and silica nanoparticles. Antireflective coatings were also built on glass substrates by alternating spraying polyelectrolyte and silica nanoparticle solutions. The transmittance of the sample with both sides coated using the dipping method is above 99 % while the coating built through spraying can reduce the one side reflection from 4% to 1 %. Such technology provides a simple approach to fabricate antireflection coatings on displays. © 2008 SID

Reduced Graphene Oxide/Poly(3 -Hexylthiophene) Supramolecular Composites

Poly(3-hexylthiophene) (P3HT) supramolecular structures are fabricated on P3HT-dispersed reduced graphene oxide (RGO) monolayers and surfactant-free RGO monolayers. P3HT is able to disperse RGO in hot anisole/N,N-dimethylformamide solvents, and forms nanowires on RGO surfaces through a RGO induced crystallization process. The TEM and AFM investigation of the resultant P3HT/RGO composites shows that P3HT nanowires grow from RGO, and connect individual RGO monolayers. Raman spectroscopy confirms the interaction between P3HT and RGO, which allows the manipulation of the RGO electrical properties. Such a bottom-up approach provides interesting graphene-based composites for nanometer-scale electronics. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA,

Fabrication Of Ultrathin Polyelectrolyte Fibers And Their Controlled Release Properties

Ultrathin fibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) were fabricated using the electrospinning technique. Methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The controlled release of drugs from electrospun fibers have potential applications as drug carriers in biomedical science. © 2007 Elsevier B.V. All rights reserved

IMECE2008-68732 1 A NANOSTRUCTURED THERMOSENSITIVE SMART SURFACE WITH INTEGRATED MICROHEATER FOR WETTABILITY CONTROL

ABSTRACT This paper describes the design and fabrication of a switchable thermosensitive polymer with an integrated microheater as a smart surface platform for wettabilty control. The thermoresponsive surface is synthesized on a glass substrate using the polymer poly(N-isopropylacrylamide) (PNIPAAm) which can change its wettability when subjected to change in temperature. PNIPAAm is hydrophilic when the surface temperature is less than the lower critical solution temperature (LCST) range of about 28-33 ºC and is hydrophobic above the LCST range. The PNIPAAm surface is heated by spiral gold microheaters which are fabricated on the lower side of the glass substrate. The contact angle change with change in temperature is tested using a standard goniometer. Time response analysis of the surface is presented. This smart surface can be used as an active or adaptive component for microflow regulation and can be potentially integrated into large scale lab-on-chip (LOC) systems