Film thickness studies for the chemically synthesized conducting polyaniline

The chemical oxidation of aniline with ammonium persulphate (APS) in aqueous acidic medium to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. PANI films can also grow onto glass supports immersed in the reaction mixture during the polymerization. The optical absorption for these films was measured. Multilayer deposition of polymer films onto the gold electrode of QCM and onto the glass supports from consecutive repetitive treatments by the reaction mixture containing aniline and APS, were studied. The induction period, the yield and the growth rate of the polymer films during the multilayer deposition were discussed. A relation between the thickness of the films determined, from QCM technique and the optical absorption of the films was established. The electrical conductivity of the PANI films was also measured.     

Electroless deposition of poly(2-alkoxyaniline)s

The in situ deposition of poly(2-alkoxyaniline)s onto oxide surfaces is reported. It is demonstrated that the identity of the substrate can have a pronounced effect on the polymerization rate of these substituted polyanilines. Poly(2-alkoxyaniline)s deposit efficiently onto indium-doped tin oxide (ITO), but deposition onto quartz proceeds slowly. The critical stage in the deposition process is shown to be polymerization of the adsorbed oligomeric species. When this polymerization process is catalyzed by the surface, polymer growth is enhanced, and we find that conducting substrates mediate this apparent catalytic process. We demonstrate selective deposition by growing poly(2-alkoxyaniline) adlayers onto patterned ITO/quartz substrates.     

Antiseptic Nanocapsule Formation via Controlling Polymer Deposition onto Water-in-Oil Miniemulsion Droplets

The stable nanodroplet was prepared by inverse miniemulsion with an aqueous antiseptic solution dispersed in an organic medium of solvent/nonsolvent mixture containing an oil-soluble surfactant and the polymer for shell formation. The change in gradient of the solvent/nonsolvent mixture, obtained by heating at 50 °C, led to the precipitation of the polymer in the organic phase and deposition onto the large interphase of the aqueous miniemulsion droplets. The monodisperse polymer nanocapsule, with the size range of 80–240 nm, dispersed in cyclohexane phase was achieved as a function of surfactant concentration. By variation of polymer content, molecular weight and type, an encapsulation efficiency of 20–100% was obtained as detected by proton-nuclear magnetic resonance spectroscopy measurement. The nanocapsule could be easily transferred into water as continuous phase resulting in aqueous dispersion with nanocapsule containing the antiseptic agent as an aqueous core. The encapsulated amount of the antiseptic agent was evaluated to indicate the durability of the nanocapsule's wall. Additionally, the different types of polymer having glass transition temperature ranging from −60 to 100°C have been successfully used. Currently, the research work on the incorporation of nanocapsules onto natural rubber (NR) latex in order to prepare NR latex glove containing the antiseptic agent nanocapsules is carried out. By using the simple and versatile layer-by-layer (LbL) technique based mainly on an electrostatic interaction between oppositely charged species, the deposition of nanocapsules onto NR latex film has successfully been fulfilled.     

Structural,optical and electric properties of nanocrystalline MgSe thin films deposited by chemical route using triethanolamine as a complexing agent

Semiconducting nanocrystalline thin films of magnesium selenide have been prepared using economic chemical bath deposition technique onto glass substrates at room temperature. The deposition bath consists of magnesium chloride, triethanolamine, hydrazine hydrate and selenium dioxide. The quantity of triethanolamine in the deposition bath was varied to study its effect on growth process as well as on physical properties of MgSe. The deposited films were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy techniques. The effect of complexing agent (TEA) on optical and electrical properties is reported. It was found that as the triethanolamine in deposition bath increases, optical band-gap and electrical resistivity decreases. The thermo-emf measurement shows p-type nature of MgSe.     

Layered molybdenum oxide thin films electrodeposited from sodium citrate electrolyte solution

Molybdenum oxide thin films were prepared electrochemically onto the selenium predeposited tin oxide-coated glass substrates using 0.22 M sodium citrate (C₆H₅Na₃O₇) solution (pH 8.3) and sodium molybdate as a precursor. Cyclic voltammetry was used to determine the deposition potential effects on molybdenum compound speciation, while quantitative thin film composition was obtained from X-ray photoelectron spectroscopy depth profiles. Thin molybdenum film growth and composition was potential dependant. Predominant molybdenum species was Mo(IV) at all deposition potentials and deposition times. Optical properties of the molybdenum oxide thin films were determined using UV–VIS spectroscopy. The absorption edge varied between 560 and 650 nm, whereas optical band gap values—between 1.79 and 2.19 eV—well within the limits for solar light-induced chemical reactions.     

Fast and slow deposition of silver nanorods on planar surfaces: application to metal-enhanced fluorescence

Two methods have been considered for the deposition of silver nanorods onto conventional glass substrates. In the first method, silver nanorods were deposited onto 3-(aminopropyl)triethoxysilane-coated glass substrates simply by immersing the substrates into the silver nanorod solution. In the second method, spherical silver seeds that were chemically attached to the surface were subsequently converted and grown into silver nanorods in the presence of a cationic surfactant and silver ions. The size of the silver nanorods was controlled by sequential immersion of silver seed-coated glass substrates into a growth solution and by the duration of immersion, ranging from tens of nanometers to a few micrometers. Atomic force microscopy and optical density measurements were used to characterize the silver nanorods deposited onto the surface of the glass substrates. The application of these new surfaces is for metal-enhanced fluorescence (MEF), whereby the close proximity of silver nanostructures can alter the radiative decay rate of fluorophores, producing enhanced signal intensities and an increased fluorophore photostability. In this paper, it is indeed shown that irregularly shaped silver nanorod-coated surfaces are much better MEF surfaces as compared to traditional silver island or colloid films. Subsequently, these new silver nanorod preparation procedures are likely to find a common place in MEF, as they are a quicker and much cheaper alternative as compared to surfaces fabricated by traditional nanolithographic techniques.     

Collagen containing microcapsules: smart containers for disease controlled therapy

The protein collagen is the major component of connective tissue and it is involved in many biological functions. Its degradation is at the basis of different pathological processes. The up-regulated expression of matrix metalloproteinases and the down-regulated expression of their inhibitors are the causes for such degradation. The aim of this work was to evaluate the possibility to fabricate collagen based containers for drug encapsulation and release by cellular demand by the action of matrix metalloproteinases. In present work collagen type I based microcapsules were fabricated by means of the layer-by-layer assembly of oppositely charged collagen and poly (stirene sulfonate) onto colloidal particles, followed by removal of the cores to obtain hollow microcapsules. The process of shell growth on planar supports was monitored by quartz crystal microbalance. X-ray reflectivity measurements were carried out at the solid/water interface to study the interaction of matrix metalloproteinase 1 with LbL films of collagen. The morphology of hollow capsules was characterized by scanning electron microscopy, and compared to that of capsules exposed to the matrix metalloproteinase 1. Finally the matrix metalloproteinase 1 mediated permeability of capsules variation was studied by Confocal Laser Scanning Microscopy. The results demonstrated the possibility to fabricate a drug delivery system where the release of the drug is dependent on the biochemistry of the pathological state.     

Spatially controlled cell adhesion via micropatterned surface modification of poly(dimethylsiloxane)

Spatial control of cell growth on surfaces can be achieved by the selective deposition of molecules that influence cell adhesion. The fabrication of such substrates often relies upon photolithography and requires complex surface chemistry to anchor adhesive and inhibitory molecules. The production of simple, cost-effective substrates for cell patterning would benefit numerous areas of bioanalytical research including tissue engineering and biosensor development. Poly(dimethylsiloxane) (PDMS) is routinely used as a biomedical implant material and as a substrate for microfluidic device fabrication; however, the low surface energy and hydrophobic nature of PDMS inhibits its bioactivity. We present a method for the surface modification of PDMS to promote localized cell adhesion and proliferation. Thin metal films are deposited onto PDMS through a physical mask in the presence of a gaseous plasma. This treatment generates topographical and chemical modifications of the polymer surface. Removal of the deposited metal exposes roughened PDMS regions enriched with hydrophilic oxygen-containing species. The morphology and chemical composition of the patterned substrates were assessed by optical and atomic force microscopies as well as X-ray photoelectron spectroscopy. We observed a direct correlation between the surface modification of PDMS and the micropatterned adhesion of fibroblast cells. This simple protocol generates inexpensive, single-component substrates capable of directing cell attachment and growth.     

Encapsulation of ionic liquids within polymer shells via vapor phase deposition

We demonstrate the use of vapor phase deposition to completely encapsulate ionic liquid (IL) droplets within robust polymer shells. The IL droplets were first rolled into liquid marbles using poly(tetrafluoroethylene) (PTFE) particles because the marble structure facilitates polymerization onto the entire surface area of the IL. Polymer shells composed of 1H,1H,2H,2H-perfluorodecyl acrylate cross-linked with ethylene glycol diacrylate (P(PFDA-co-EGDA)) were found to be stronger than the respective homopolymers. Fourier transform infrared spectroscopy showed that the PTFE particles become incorporated into the polymer shells. The integration of the particles increased the rigidity of the polymer shells and enabled the pure IL to be recovered or replaced with other fluids. Our encapsulation technique can be used to form polymer shells onto dozens of droplets at once and can be extended to encapsulate any low vapor pressure liquid that is stable under vacuum conditions.     

Preparation of pickering-emulsion-based capsules with shells composed of titanium dioxide nanoparticles and polyelectrolyte layers

A procedure has been proposed for the preparation of capsules with shells composed of titanium dioxide nanoparticles and polymers via the formation of Pickering emulsions (colloidosomes) followed by layer-by-layer deposition of polyelectrolytes. The feasibility of stabilizing oil droplets of emulsions by spontaneous adsorption of partly hydrophobized nanoparticles of anatase-form titanium dioxide at the oil/water interface has been studied. Conditions have been determined for the formation of stable colloidosomes and the subsequent layer-by-layer deposition of oppositely charged polyelectrolytes onto their surfaces. It has been shown that hydrophobic dyes may be encapsulated using the procedure developed for the preparation of the capsules. The photocatalytic activity of TiO₂ particles occurring in the shell has been demonstrated by the example of degradation of Nile red which is incorporated in the oil core of a capsule.     

Polymeric nanocapsules containing an antiseptic agent obtained by controlled nanoprecipitation onto water-in-oil miniemulsion droplets

The modified nanoprecipitation of polymers onto stable nanodroplets has been successfully applied to prepare well-defined nanocapsules whose core is composing of an antiseptic agent, i.e., chlorhexidine digluconate aqueous solution. The stable nanodroplets were obtained by inverse miniemulsions with an aqueous antiseptic solution dispersed in an organic medium of solvent/nonsolvent mixture containing an oil-soluble surfactant and the polymer for the shell formation. The change of gradient of the solvent/nonsolvent mixture of dichloromethane/cyclohexane, obtained by heating at 50 degrees C, led to the precipitation of the polymer in the organic continuous phase and deposition onto the large interface of the aqueous miniemulsion droplets. The monodisperse polymer nanocapsules with the size range of 240-80 nm were achieved as a function of the amount of surfactant. Using various polymer contents, molecular weights and types, an encapsulation efficiency of 20-100% was obtained as detected by proton-nuclear magnetic resonance spectroscopy ((1)H NMR) measurements. The nanocapsules could be easily transferred into water as continuous phase resulting in aqueous dispersions with nanocapsules containing an aqueous core with the antiseptic agent. The encapsulated amount of the antiseptic agent was evaluated to indicate the durability of the nanocapsule's wall. In addition, the use of different types of polymers having glass transition temperatures (T(g)) ranging from 10 to 100 degrees C in this process has been also successful.     

Raman spectroscopy of dip-coated and spin-coated sol–gel TiO2 thin films on different types of glass substrate

The photoinduced self-cleaning and super-hydrophilic properties of titania (TiO₂) coated glasses are considered to be utilized in many applications. The photocatalytic activity of titania is inherent to the glass composition and to the deposition method. Particularly sodium ions diffused to the titania film from the substrate have tremendous impact on its crystallinity. The deposition method influences surface, structure, and the density of the film. This study aims to provide new findings regarding the mechanism of crystallization of sol?Cgel synthesized titania and its thin films deposited by means of two different methods (dip-coating and spin-coating) onto the glass substrate with a high content of sodium ions (soda-lime glass) and without sodium ions (quartz glass). The main attention is devoted to Raman spectroscopy and Raman point-to-point mapping of the films. The content and the chemical state of the sodium ions were judged using the XPS. It is shown that the dip-coating method led to dense compact material. In this case the crystallization is localized in randomly distributed centers of nucleation. Contrary the spin-coated samples embodied a web-like pattern of cracks, from which the crystallization proceeds throughout the film. Additionally SEM, AFM, XRD, GDS, UV?CVIS methods were performed to support the results.     

Deposition of Oil Drops on a Glass Substrate in Relation to the Process of Washing

The attachment of emulsion drops to glass substrates is investigated in relation to the redeposition of oil drops in the process of washing. It turns out that the drops of a surfactant-stabilized oil-in-water emulsion cannot be attached to an immersed glass plate simply by the buoyancy force. However, the same drops can be deposited on the plate when the latter is pulled out of the emulsion, i.e., when the drops are pressed against the substrate by a receding meniscus. We measured the amount of the oily deposit as a function of the pH, ionic strength, and composition of an amphoteric-anionic surfactant mixture. The enhanced oil deposition at low pH correlates with the domain in which the emulsion drops and the solid substrate bear opposite electric charges. This was established by zeta-potential measurements with oil drops and glass particles. The anionic surfactant brings negative surface charge to the oil droplets and suppresses the oil deposition on the negatively charged glass. With the increase of the fraction of the amphoteric surfactant in the mixture, the zeta-potential is converted from negative to positive, and the oil deposition grows almost linearly with the potential. In general, the deposition of oil drops by a receding meniscus is governed by an interplay of electrostatic and hydrodynamic factors. Copyright 2000 Academic Press.     

Indirect micromanipulation of single molecules in water-in-oil emulsion

Based on real-time observation and micromanipulation, analytical methods for single DNA molecules have been under development for some time. Precise manipulation, however, is still difficult because single molecules are too small for conventional techniques. We have developed a chemical reaction system that uses water droplets in oil as containers of materials. The water droplets can be manipulated by optical force. The manipulation of the water droplets permits the fusion of two selected droplets. This process corresponds to mixing of different samples. We designate this system as "w/o (water-in-oil emulsion) microreactor system", and each droplet can be thought of as a "microreactor". In this system, single molecules can be manipulated readily, as a molecule can be contained in a microm-sized microreactor. The microreactor utilizes extremely small quantities of samples, therefore, reactions are rapid, as diffusion times in the microreactor are very short. The manipulation technique of the microreactors based on optical force has been applied to induce fusion between microreactors loaded with DNA and YOYO, a fluorescent dye that binds to DNA. This fusion induced a rapid binding of YOYO.     

Elaboration of fluorescent and highly magnetic submicronic polymer particles via a stepwise heterocoagulation process

Using the stepwise heterocoagulation concept, fluorescent and highly magnetic submicronic core-shell polymer particles were prepared. For this purpose a negatively charged oil-in-water magnetic emulsion was first modified by adsorbing the poly(ethyleneimine) (PEI). Secondly, low glass transition temperature (T _g=10°C) anionic film-forming nanoparticles were adsorbed onto the cationic magnetic droplets. Finally the encapsulation was induced by heating the heterocoagulates above the T _g of the film-forming nanoparticles. To produce labeled magnetic particles, fluorescent nanoparticles and film-forming nanoparticles were simultaneously adsorbed. PEI adsorption was investigated. Also investigated was the influence of the amount of film-forming nanoparticles and fluorescent nanoparticles on the encapsulation efficiency.     

Effect of dopant on the physical properties of polymer films for microphotonics

This paper presents experimental results concerning the influence of the additives on the physical properties of polymer films. Metal oxides/inorganic salts were used as additives in vinyl-polymers solutions. The physical properties of the metal doped polymer films can be significantly modified by the composition of the doping elements and the curing conditions of the polymer. Morphologic, electronic, magnetic and optic properties of the doped polymers were analysed by AFM, SEM, Mössbauer spectroscopy and optical measurements. The film composition and the deposition processes were optimized to allow a better control of the optical parameters (refractive index, transmission), to reduce the processing temperatures and to improve the chemical sensitivity of the films for sensor applications. These compounds can be easily spin coated onto a variety of directly patterned semiconductor substrates.     

Formation of CdS thin films in a chemical bath environment under the action of an external magnetic field

External magnetic fields were applied during thin film preparation of CdS on glass substrates by the chemical bath deposition technique (CBD). Some physical properties of the polycrystalline films, like layer thickness, grain size and optical quality depend in a characteristic manner on the strength and orientation of the external field during the growth process. The characterization of the samples includes atomic force microscopy (AFM), optical absorption, and dark conductivity measurements. The data interpretation follows a line based on the specific interaction of cadmium and sulfur ions with acting magnetic fields within the chemical bath This article was submitted by the authors in English.     

Vacuum coating of plastic optics

Vacuum technologies for the deposition of optical interference coatings on polymer substrates, based on long-term experience in glass coating, have been under development for about 20 years. A growing market for precision optical elements and consumer optics moulded from thermoplastic polymers requires antireflective properties and hard coatings. Owing to the manifold chemical and physical properties of optical polymers, special efforts are essential for each type of plastic to find polymer-capable coating conditions. The main focus of this article is on evaluating the state of the art in vacuum-coating processes applied to plastics today, and on discussing specific coating techniques and evaluation procedures. A better understanding of the complex interactions between low-pressure plasmas and the various polymer materials will be a key factor in making durable plastic optics for future applications; achieving this will be a challenge to surface scientists.     

Microcapsules with a pH responsive polymer: Influence of the encapsulated oil on the capsule morphology

Microcapsules were prepared by microsieve membrane cross flow emulsification of Eudragit FS 30D/dichloromethane/edible oil mixtures in water, and subsequent phase separation induced by extraction of the dichloromethane through an aqueous phase. For long-chain triglycerides and jojoba oil, core-shell particles were obtained with the oil as core, surrounded by a shell of Eudragit. Medium chain triglyceride (MCT oil) was encapsulated as relatively small droplets in the Eudragit matrix. The morphology of the formed capsules was investigated with optical and SEM microscopy. Extraction of the oil from the core-shell capsules with hexane resulted in hollow Eudragit capsules with porous shells. It was shown that the differences are related to the compatibility of the oils with the shell-forming Eudragit. An oil with poor compatibility yields microcapsules with a dense Eudragit shell on a single oil droplet as the core; oils having better compatibility yield porous Eudragit spheres with several oil droplets trapped inside.     

Oil coating on hydrophilic surfaces from emulsions and under shear flow

We study the formation of silicone oil coating on negatively charged hydrophilic surfaces via emulsion deposition. Cationic surfactants usually adsorb and form bilayers onto negative surfaces. As a result, direct emulsions stabilized with cationic surfactants are paradoxically poorly efficient at coating negative substrates. We show in this work an alternative and new method, still based on electrostatic attractions, to coat negative substrates. Our method consists of using emulsions stabilized with nonionic surfactants and of adding to the oil cationic additives that are non-water-soluble and of high molecular weight to minimize their solubilization in the micelles formed by the neutral surfactant. The positively charged droplets stick efficiently onto the substrates. They form monolayer and uniform coatings. We study the kinetics and the density of the resulting coating using a flow cell experiment. This technique allows us to finely analyze the influence of several physicochemical parameters.