Development and characterization of thin polymer films relevant to fiber processing

Dilute solutions of cellulose, polypropylene, polyethylene, nylon and polyester were spun cast onto gold and silica wafers to generate thin films of these polymers, which are commonly used in the manufacture of synthetic fibers. The thin films were used as substrates in the quartz crystal microbalance and nano-indentation techniques to monitor adsorption and friction behaviors after treatment with a polymer solution (as a mimic of a textile finish). The spin coating conditions were optimized in terms of the resulting film morphology, thickness and surface energy. Atomic force microscopy, X-ray photoelectron spectrometry, ellipsometry and contact angle were used to probe the physical and surface properties of the resulting films. Overall, we developed thin films that are helpful to inquire, at the molecular level, phenomena relevant to fiber and textile processing including swelling, degradation, and adsorption of polymers and surfactants.     

Deposition of functional cellulose films on titanium alloy surfaces

Titanium alloy (TiAl6V4) surfaces were treated with ultraviolet (UV) radiation to remove organic “contamination” molecules which remained on the surfaces after conventional cleaning processes. The UV-technique simultaneously revealed reactive surface hydroxyl groups at the metal surface which were monitored by the reaction with perfluorooctanoylchloride and application of Fourier-Transform infrared reflection-absorption spectroscopy and contact angle measurements, respectively. Two different cellulose polymers each made soluble in methanol by functionalized hydroxylalkyl-spacer groups and their mixtures were deposited on UV-treated TiAl6V4 surfaces. Atomic force microscopy measurements could reveal polymer films which covered the metal surfaces completely without defects. Differences were indicated in the surface structure, especially between the pure cellulose phosphate films and cinnamate containing cellulose films.     

The effect of the isopoly tungstate anion on the composition and conductivity of polypyrrole composite films

The polypyrrole composite films were prepared by the electropolymerization of pyrrole from the aqueous solution containing isopoly tungstate (poly-W) and the chloride anion (Cl⁻) at various ratios. The film formation was traced by electrochemical quartz crystal microbalance, and the tungsten concentrations in the films were measured by the inductively coupled plasma spectroscopy. The electric conductivities of the films were measured by the four-point probe method. In the ratio of poly-W concentration to Cl⁻ concentration, ((poly-W)/Cl⁻)), higher than 1.26 × 10⁻² in the solution the concentration of tungsten in the films showed a constant value at 51 wt.% and the chloride anion was not included in the film. The conductivities of these films showed the constant value about 40 S cm⁻¹. In the ratio lower than (poly-W)/(Cl⁻) = 1.26 × 10⁻², the conductivity decreased with the decrease of poly-W concentration and the composite films consisted of two layers; the inner layer initially formed contained larger amount of tungsten than that of the outer layer.     

Electrophoretic deposition of CdSe nanocrystal films onto dielectric polymer thin films

The electrophoretic deposition of cadmium selenide (CdSe) nanocrystal films from a stable hexane suspension onto a dielectric polymer film is reported. The electrodes were prepared by spin casting a ~ 30 nm thick smooth, defect-free, polystyrene film on silicon substrates. Scanning electron microscopy and atomic force microscopy showed that the CdSe films deposited atop polystyrene possessed morphology comparable to CdSe films deposited on the bare silicon electrodes. Factors affecting deposition, such as nanocrystal charging in suspension and wetting of electrode surfaces, are reviewed. This approach to preparing nanocrystal films onto homogeneous dielectric layers will facilitate the fabrication of novel polymer-nanocrystal composites.     

Initiated chemical vapor deposition of polymer films on nonplanar substrates

Thin polymer films are deposited on nonplanar geometries via initiated chemical vapor deposition (iCVD). Films in microtrenches exhibit step coverage of 0.85 for the highest aspect ratio trench studied here. An analytical model shows that the sticking probability of the initiating radical is a function of monomer surface concentration and takes values between 1.1 × 10^− 2 and 5.0 × 10^− 2 for the conditions studied here. These results indicate that iCVD proceeds via reaction of a vapor phase initiating radical with a surface adsorbed monomer. The high degree of conformality allows iCVD to be used to create patterns with features less than 10 µm by physically masking the substrate.     

Design,preparation, and application of ordered porous polymer materials

Ordered porous polymer (OPP) materials have extensively application prospects in the field of separation and purification, biomembrane, solid supports for sensors catalysts, scaffolds for tissue engineering, photonic band gap materials owing to ordered pore arrays, uniform and tunable pore size, high specific surface area, great adsorption capacity, and light weight. The present paper reviewed the preparation techniques of OPP materials like breath figures, hard template, and soft template. Finally, the applications of OPP materials in the field of separation, sensors, and biomedicine are introduced, respectively.     

Measurement technique for thermal conductivity of thin polymer films

We present a modified steady-state heat flow technique, which allows measuring the thermal conductivity of films applied on a substrate. The measurement technique with the here presented setup provides an accuracy (overestimation) of 5-10% for film thickness up to 100 μm. For thicker films a correction factor based on finite-element simulations has to be used or the geometry has to be adapted. The technique is validated with thin glass plates of known thermal conductivity. To demonstrate the application of the technique the thermal conductivity of a thin polymer film of fluorinated acrylate is determined as 0.19 ± 0.02 W/mK.     

Vacuum deposited polymer/metal multilayer films for optical application

Vacuum-deposited polymer/silver/polymer reflectors and tantalum/polymer/aluminum Fabry-Perot interference filters were fabricated in a vacuum web coating operation on polyester substrates with a new, high-speed deposition process. Reflectivities were measured in the wavelength range from 0.3 μm to 0.8 μm. This new vacuum processing technique has been shown to be capable of deposition line speeds in excess of 500 linear m min⁻¹ (D.G. Shaw and M.G. Langlois, Proc. 7th Int. Conf. Vacuum Web Coating, November 1993, p. 268). Central to this technique is a new vacuum deposition process for the high-rate deposition of polymer films. This polymer process involves the flash evaporation of an acrylic monomer onto a moving substrate. The monomer is subsequently cured by an electron beam or ultraviolet light. This high-speed polymer film deposition process has been named the polymer multi-layer process. Also, vacuum-deposited, index-matched, polymer/CaF₂ composites were fabricated from monomer slurries that were subsequently cured with ultraviolet light. This second technique is called the liquid multi-layer process. Each of these polymer processes is compatible with each other and with conventional vacuum deposition processes such as sputtering or evaporation.     

Matrix-assisted pulsed laser deposition of polymer and nanoparticle films

Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was used to deposit films of Poly(9,9-dioctylfluorene) - PFO and Methoxy Ge Triphenylcorrole [Ge(TPC)OCH3]. The PFO was dissolved in different matrices, like chloroform-CHCl3, tetrahydrofuran - THF and toluene with a 0.5 wt % concentration, while Ge(TPC)OCH3 was diluted in THF with a concentration of 0.01 wt %. The frozen targets were irradiated with a KrF excimer laser. The, films presented good emission properties to be exploited in light emitting devices and gas sensors based on luminescence quenching. The working principle of the MAPLE technique was used for the deposition of colloidal nanoparticles and nanorods, too. TiO2 colloidal nanoparticles (diameter: ∼10 nm) and nanorods (diameter: 5 nm; length: 50 nm) were diluted in deionised water (0.02 wt %) and toluene (0.016 wt %) respectively. The deposited nanostructures preserved dimensions and structural properties of the starting particles and the films showed very interesting electrical responses when exposed to oxidizing gases for sensing applications.     

Preparation and surface properties of mesoporous silica particles modified with poly(N-vinyl-2-pyrrolidone) as a potential adsorbent for bilirubin removal

The surface of silica particles was modified with polyvinyl pyrrolidone (PVP) through sol–gel process. The different experimental techniques, i.e., thermogravimetric analysis (TGA and DTG), nitrogen adsorption, scanning electron microscopy (SEM), laser diffraction analysis (LDA), fourier transform spectroscopy (FTIR) are used to characterize the pure non-functionalized and functionalized silicas containing different amount of PVP. It was shown that PVP-modified silica samples have well developed porous structure; the values of specific surface area for PVP-modified silicas are in the range of 140–264 m² g⁻¹. While the non-functionalized silica shows the low surface area (S_BET = 40 m² g⁻¹). The BJH analysis showed that PVP can be used as an effective agent to increase an average pore size and total pore volume. The results indicate that PVP functionalized silicas show a potential as effective adsorbents for bilirubin removal compared to other available adsorbents.     

Electrospun polylactic acid and cassava starch fiber by conjugated solvent technique

Smoothed fibers of PLA/cassava starch were prepared by single nozzle electrospinning process intended for tissue scaffold application. PLA in dichloromethane (DCM) solution was immiscible with cassava starch in dimethylsulfoxide (DMSO) solution. A conjugated solvent system was introduced to simply prepare a well-mixed solution of both components. In this experiment, methanol was used as a conjugated solvent between PLA/DCM solution and cassava starch/DMSO solution to create well-mixed solution. Conjugated solvent selection was based on values of polarity index, intermediate between values of DCM and DMSO. Smoothed electrospun fiber of PLA/cassava starch was obtained.     

Phase separation and surface morphology of spin-coated films of polyetherimide/polycaprolactone immiscible polymer blends

The surface morphology in thin films of immiscible polyetherimide and polycaprolactone blends was studied using scanning electron and atomic force microscopy. The thin films were obtained by spin-coating from dichloromethane solution. A self-assembled periodic pattern of phase separated domains was observed, which was induced by capillary effects along with the solution radial flow and the unsteady air flow field above the film during the initial stages of spin-coating. A secondary phase separation was observed during the solvent evaporation stage of spin-coating. The differences in surface topographies of the two distinct phases are attributed to different solvent evaporation rates within each phase. In addition, a great variety of domain structures and surface morphologies were observed as a function of polymer blend composition.     

Optical properties of pyrene doped polymer thin films

Thin films of pyrene in polystyrene matrix have been prepared by spin coating technique. The concentration of polystyrene is kept constant to 1 wt.% while that of pyrene dopant varied in the range 2.30×10⁻⁴-2.30×10⁻¹ wt.%. Thickness of the films was found to depend upon concentration of pyrene and varies from 90 to 782 nm. The results of X-ray diffraction analysis reveal the crystalline nature of the films. The optical properties were studied by absorption, excitation and fluorescence spectroscopy. The band gap energy of pyrene in polymer films was calculated from absorption results. A transition from monomer to excimer is observed with thickness variation of the films. The structured part of the spectrum is assigned to the monomer emission while the broad emission band is attributed to well known pyrene excimer-like emission.     

Fabrication,characterization and in vitro drug release behavior of electrospun PLGA/chitosan nanofibrous scaffold

In this study both aligned and randomly oriented poly(d,l-lactide-co-glycolide) (PLGA)/chitosan nanofibrous scaffold have been prepared by electrospinning. The ratio of PLGA to chitosan was adjusted to get smooth nanofiber surface. Morphological characterization using scanning electron microscopy showed that the aligned nanofiber diameter distribution obtained by electrospinning of polymer blend increased with the increase of chitosan content which was similar to that of randomly oriented nanofibers. The release characteristic of model drug fenbufen (FBF) from the FBF-loaded aligned and randomly oriented PLGA and PLGA/chitosan nanofibrous scaffolds was investigated. The drug release rate increased with the increase of chitosan content because the addition of chitosan enhanced the hydrophilicity of the PLGA/chitosan composite scaffold. Moreover, for the aligned PLGA/chitosan nanofibrous scaffold the release rate was lower than that of randomly oriented PLGA/chitosan nanofibrous scaffold, which indicated that the nanofiber arrangement would influence the release behavior. In addition, crosslinking in glutaraldehyde vapor would decrease the burst release of FBF from FBF-loaded PLGA/chitosan nanofibrous scaffold with a PLGA/chitosan ratio less than 9/1, which would be beneficial for drug release.     

Adsorption of polyethyleneimine (PEI) on hematite. Influence of magnetic field on adsorption of PEI on hematite

A research on influence of magnetic field of various inductions on adsorption of polyethyleneimine (PEI) onto hematite is presented. Properties of the adsorbent surface (Magnetic Force Microscopy images and nitrogen adsorption data) and its behaviour in a water solution (particle size distribution) are also studied. Moreover, new analytical approach is proposed to compare the shape of the isotherms (e.g. presence of plateaus) by calculating a reciprocal derivative.     

Functional polyaniline nanofibre mats for human adipose-derived stem cell proliferation and adhesion

Conductive polymer poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) and polyaniline (PANI) were blended with a biodegradable, biocompatible polymer, poly(l-lactic acid) and were electrospun into nanofibres to investigate their potential application as a scaffold for human adipose-derived stem cells (hASCs). These polymers, in both conductive and non-conductive form, were electrospun with average fibre diameters of less than 400 nm. Novel nanoindentation results obtained on the individual nanofibres revealed that the elastic moduli of the nanofibres are much higher at the surface (4–10 GPa, h_max <75 nm) than in the inner fibre core (2–4 GPa, h_max >75 nm). The composite nanofibres showed great promise as a scaffold for hASCs as they supported the cell adhesion and proliferation. After 1 week of cell culture hASCs were well spread on the substrates with abundant focal adhesions. The electrospun mats provide the cells with comparably stiff, sub-micron sized fibres as anchoring points on a substrate of high porosity. The conductive nature of these composite nanofibres offers exciting opportunities for electrical stimulation of the cells.     

Thermo-responsive copolymer coated MnFe2O4 magnetic nanoparticles for hyperthermia therapy and controlled drug delivery

This study is about multifunctional magnetic nanoparticles surface-modified with bilayer oleic acid, and coated with a thermo-responsive copolymer poly(N-isopropylacrylamide-co-acrylamide) by emulsion polymerization, for controlled drug delivery and magnetic hyperthermia applications. Nanoparticles were loaded with anticancer drug doxorubicin into the copolymer chains at 25 °C. Composite nanoparticles (hydrated) of average diameter 45 nm were of core–shell structure having magnetic core of about 18 nm and shell was composed of organic compounds and water. Magnetic core was superparamagnetic lacking coercive force and remanance due to the pseudo-single domain nanostructure. Lower critical solution temperature (LCST) of the thermo-responsive copolymer was observed to be around 39 °C. Below this temperature, copolymer was hydrophilic, hydrated and swelled. But above LCST, copolymer became hydrophobic, dehydrated and shrank in volume. UV visible spectrophotometer was used to investigate the drug loading and releasing profile at different temperatures as well as under magnetic heating. There was almost absence of drug release at around 37 °C (normal body temperature). Drug was released at temperatures above LCST, which is significant for controlled drug delivery. Magnetic heat-generation was studied by exposing the magnetic fluid to alternating magnetic field of 7.2 kA m⁻¹ having frequency 70 kHz. A simple magnetic capturing system (simulating a blood vessel) was used to analyze the capturing of magnetic nanoparticles under various applied fields for drug targeting purpose.     

Role of template and infiltration technique on resulting morphology of polymer nanostructures

Polymer nanotubes are commonly fabricated using the template-assisted method. In the present study, polystyrene nanotubes were formed through a unique dipping technique that has not previously been reported. Anodized aluminum (AAO) templates were synthesized and infiltrated with polystyrene-tetrahydrofuran solutions. The effects of the template, polymer molecular weight and concentration on the final morphology were examined. The results indicate that stable nanotubes can be formed in homemade and commercial templates with polymer concentrations as low as 0.5 wt%. Nanotubes also resulted from a range of molecular weights indicating that the infiltration technique may be the primary factor enabling the formation of hollow structures.