Interfacial effects on moisture absorption in thin polymer films

Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced. The enhanced swelling in the thin films is due to the attractive nature of the hydrophilic substrate, leading to an accumulation of water at the silicon/polymer interface and subsequently a gradient in concentration from the enhancement at the interface to the bulk concentration. As films become thinner, this interfacial excess dominates the swelling response of the film. This accumulation was confirmed experimentally using neutron reflectivity. The water rich layer extends 25 +/- 10 A into the film with a maximum water concentration of approximately 30 vol %. The excess layer was found to be polymer independent despite the order of magnitude difference in the water solubility in the bulk of the film. To test if the source of the thickness dependent behavior was the enhanced swelling at the interface, a simple, zero adjustable parameter model consisting of a fixed water rich layer at the interface and bulk swelling through the remainder of the film was developed and found to reasonably correspond to the measured thickness dependent swelling.     

Film autoradiography used for hot particle identification

Summary Two types of films were tested and compared for the purposes of film autoradiography. Commercial black and white photographic film proved to have the highest sensitivity and the best resolution. The film was calibrated by specially prepared sources that contained alpha- and beta-emitting isotopes in the form of particles. Application examples for hot particle identification using the developed film autoradiographic technique are given.     

Dip and wait: a facile route to nanostructured porphyrin films for QCM functionalization

A facile and straightforward way to deposit nanostructured porphyrin films onto quartz surfaces is presented. The particular peripheral functionalization on the macrocycle is exploited to drive the formation of aggregates in solution, which then spontaneously deposit as ordered solid layers. Film deposition is then achieved by simple dipping the quartz slide into a solution containing porphyrin aggregates and waiting the formation of the related thin films. QCMs covered with different metalloporphyrin derivatives have been exposed to some model VOCs, showing in general good performances especially in all the cases where film morphology is fundamental for sensing interactions.     

毛细管电泳免疫化学发光高灵敏检测人血清中肿瘤标志物甲胎蛋白

本文首次报道了人血清免疫反应后直接进样并利用毛细管电泳分离化学发光灵敏检测AFP的新方法, 检测结果与医院使用的全自动微粒子化学发光仪检测结果吻合.     

Determination of the specific radioactivity of amino acids by a combination of thin-layer chromatography and quantitative autoradiography

A new method for the analysis of the specific activity of amino acids is described. The analysis is carried out by thin-layer chromatography of the dansylated amino acids, computerized fluorescence evaluation and activity measurement by quantitative autoradiography. Quantitative evaluation of the autoradiographs is achieved by careful calibration of the X-ray film blackening. As shown for 14C-labelled phenylalanine and tyrosine, the method allows the simultaneous determination of the specific activity of 22 amino acids. About 10(-13) mol of an amino acid with a specific activity of less than 5 GBq/mmol can be detected and measured by this method.     

Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles

In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising the surface scattering effect; thus, the contrast ratio is much enhanced. The symmetric and asymmetric LCR films produced multidirectional scattering that enhances the reflectance at lower viewing angles, which has importance in future display applications. In particular, the prism LCR film has been found to be more influential on the reflectance of D-PDLC films due to multidirectional scattering of light by non-symmetric arrays. The improvement in contrast ratio has been confirmed by the enhancement of optical properties for reflective D-PDLC displays at lower viewing angles below 30°.     

A SIMPLE METHOD FOR THE INCORPORATION OF LOW MOLECULAR WEIGHT DYES IN ULTRATHIN FILMS

A simple method for the fabrication of ultrathin films containing low molecular weight dye material is introduced(post-adsorption technique). The chromophore used is 4-nitro-4'-decyloxy azobenzene quaternary ammonium salt (azo-10Q).In classical layer-by-layer (LBL) procedures, where the substrate is dipped alternately into the chromophore solution and thecomplementary polyelectrolyte, the chromophore tends to desorb from the film during subsequent immersion in thepolyanion solution, and there is little or no indication of multilayer growth. The extent of desorption depends somewhat onthe selection of polyelectrolyte, the ionic strength and the pH of solution. An alternative approach is to first prepareconventional LBL films from a pair of oppositely charged polyelectrolytes, and then to soak this film into the chromophoresolution, where adsorption by penetration into the LBL film may take place. In preliminary results, a linear dependence ofUV absorbance on layer number of LBL film thus prepared was found, demonstrating the apparent effectiveness of the post-adsorption technique for the preparation of azo-10Q-containing ultrathin films.     

Electrophoretic separation of nucleic acids: evaluation by video and photographic densitometry

The separation of DNA by gel electrophoresis provides a rapid method for determining size distributions of DNA in solution. Densitometric scanning of photographs of gels has been the standard method of analysis of agarose gels. However, analysis of photographs is complicated by the non-linear response of photographic film. Charged-coupled device video cameras have become popular for quantitative densitometry and we have used a charge-coupled device camera to image agarose gels to quantitate DNA damage. We compare video and photographic densitometry for quantitation of ultraviolet radiation (UV)-induced DNA damage and find that the two methods give equivalent results.     

Electrochemical modulation of electrogenerated chemiluminescence of CdS nano-composite

An in-situ induction precipitation approach via electrochemical reduction has been successfully used to prepare CdS-Polyamidoamine (CdS–PAMAM) nano-composite membranes on electrode surfaces, and that the resulting film showed 55-fold enhanced red electrogenerated chemiluminescence compared with that of CdS nano-film without PAMAM and the stability of the ECL can be modulated by electrochemical methods for the first time. It would open a way in preparation of stable and strong ECL nano-composite films for analytical application.     

Interfacial electrical properties of DNA-modified diamond thin films: intrinsic response and hybridization-induced field effects

We have investigated the frequency-dependent interfacial electrical properties of nanocrystalline diamond films that were covalently linked to DNA oligonucleotides and how these properties are changed upon exposure to complementary and noncomplementary DNA oligonucleotides. Frequency-dependent electrical measurements at the open-circuit potential show significant changes in impedance at frequencies of >10(4) Hz when DNA-modified diamond films are exposed to complementary DNA, with only minimal changes when exposed to noncomplementary DNA molecules. Measurements as a function of potential show that at 10(5) Hz, the impedance is dominated by the space-charge region of the diamond film. DNA molecules hybridizing at the interface induce a field effect in the diamond space-charge layer, altering the impedance of the diamond film. By identifying a range of impedances where the impedance is dominated by the diamond space-charge layer, we show that it possible to directly observe DNA hybridization, in real time and without additional labels, via simple measurement of the interfacial impedance.     

Bacterial cellulose films with controlled microstructure–mechanical property relationships

Bacterial cellulose (BC) films with different porosities have been developed in order to obtain improved mechanical properties. After 13 days of incubation of Gluconobacter xylinum bacteria in static culture, BC pellicles have been set. BC films have been compression molded after water dispersion of BC pellicles and filtration by applying different pressures (10, 50, and 100 MPa) to obtain films with different porosities. Tensile behavior has been analyzed in order to discuss the microstructure–property relationships. Compression pressure has been found as an important parameter to control the final mechanical properties of BC films where slightly enhanced tensile strength and deformation at break are obtained increasing mold compression pressure, while modulus also increases following a nearly linear dependence upon film porosity. This behavior is related to the higher densification by increasing mold compression pressure that reduces the interfibrillar space, thus increasing the possibility of interfibrillar bonding zones. Network theories have been applied to relate film elastic properties with individual nanofiber properties.     

The Influence of Peroxide on Bubble Stability and Rheological Properties of Biobased Poly(lactic acid)/Natural Rubber Blown Films

This study investigated the effects of natural rubber(NR)and an organic peroxide on the rheological properties,mechanical properties,morphology,and bubble stability during film blowing of poly(lactic acid)(PLA).The NR and peroxide contents were varied from 0 wt%to 25 wt%and 0 wt%to 0.5 wt%,respectively.The results confirmed that the presence of well-dispersed NR could significantly improve the toughness,elongation at break,and processability of PLA films,where the optimal amount of NR was 15 wt%.For the reactive blending with peroxide,a suitable peroxide content for good film toughness and clarity was 0.03 wt%,while the higher content of 0.1 wt%could provide slightly higher processability.These contents are considered much lower than that in the PLA system(without NR),which required up to 0.5 wt%peroxide.The rheological studies indicated that the melt strength,the storage modulus(G’)and complex viscosity(η*)at low frequency could be correlated with good film blowing processability of the PLA/NR films at low gel contents.These parameters failed to correlate in the films having high gel contents as the deformation rate experienced by each test was different leading to the different levels of response to the type and amount of gels.     

Preparation and properties of epichlorohydrin-cross-linked chitosan/hydroxyethyl cellulose based CuO nanocomposite films

This study introduces an effective route to fabricate chitosan (CS)-based film. The films were prepared through cross-linking reaction between CS and hydroxyethyl cellulose (HEC) using epichlorohydrin (ECH) as the cross-linker and simultaneously in-situ loading with CuO nanoparticles. FT-IR and loading efficiency results indicated the occurrence of inter- and intra-molecular cross-linking reaction between CS and HEC. XRD and EDS analyses showed that the CuO nanoparticles were evenly deposited onto CS film matrixes. SEM characterization showed that the films were of compact, dense and uniform cross morphologies, as well as obvious voids. The films also exhibited desired swelling ratio and water vapor permeability. The enhanced tensile strength was obtained with a maximum value of 77.02?±?3.26 MPa, while the stretch-ability slightly decreased. The thermal stability of the films decreased after cross-linking with HEC. The antibacterial ability of the films was generally improved with the increase of HEC and ECH contents.

Graphical abstract

Preparation and properties of epichlorohydrin-cross-linked chitosan/hydroxyethyl cellulose based CuO nanocomposite films

     

Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements

The ionization degree, charge density, and conformation of weak polyelectrolytes can be adjusted through adjusting the pH and ionic strength stimuli. Such polymers thus offer a range of reversible interactions, including electrostatic complexation, H-bonding, and hydrophobic interactions, which position weak polyelectrolytes as key nano-units for the design of dynamic systems with precise structures, compositions, and responses to stimuli. The purpose of this review article is to discuss recent examples of nanoarchitectonic systems and applications that use weak polyelectrolytes as smart components. Surface platforms (electrodeposited films, brushes), multilayers (coatings and capsules), processed polyelectrolyte complexes (gels and membranes), and pharmaceutical vectors from both synthetic or natural-type weak polyelectrolytes are discussed. Finally, the increasing significance of block copolymers with weak polyion blocks is discussed with respect to the design of nanovectors by micellization and film/membrane nanopatterning via phase separation.     

Additive route to lithographically defined nanoporous silica, polymer, and carbon films

A facile method was investigated for patterning microporous and mesoporous silica, polymer, and carbon films using a combination of lithography and solid-state chemistry. This process exploits the difference in chemical reactivity between the lithographically exposed and unexposed regions to control the reaction of a target precursor from the vapor phase. A block copolymer film loaded with a photoacid generator is utilized as a preformed template, and tetraethylorthosilicate (TEOS) and furfuryl alcohol (FA) are the silica and carbon precursors, respectively. Following UV exposure and reaction with vaporized precursors, thermal decomposition of the polymeric template yields a mesoporous film in the exposed regions. Dense line-space patterns down to 1.5 microm features were resolved with I-line lithography. Sharper features were formed using FA; this behavior is attributed to the requirement for water in the system during TEOS condensation. Moisture in the system appears to lead to enhanced diffusion of the photoacid and a small decrease in the feature resolution. This methodology provides a simple etch-free route to patterning mesoporous films using commercially available materials.     

Some properties of polyvinyl acetate films cast from methanol,acetone and chloroform as solvent

Polyvinyl acetate was cast into films on a clean mercury surface from its solution in either methanol, acetone or chloroform. Some mechanical properties of the films, exposed at 20 °C and 65% r.h., and 45 and 60 °C in air ovens, were studied. They were found to be highly dependent on the solvent used for film casting and the time of exposure of film at each of the temperatures. The initial modulus, yield stress, tensile strength and work to rupture of the polymer films were greater for those cast from acetone than those cast from chloroform, and for all the films these properties increased with exposure time, with an induction period in some cases. The elongation at break decreased with exposure time from an initial value which was higher for the chloroform-cast than the acetone-cast films. Films cast from methanol were found to be too brittle for testing.The results are interpreted on the basis of interactions between the solvent molecules and those of the polymer. Of the three solvents, chloroform produced polyvinyl acetate films with the most constant mechanical properties over the longest period of exposure which depended on the temperature of exposure, decreasing as the temperature increased. Hence chloroform is recommended for casting films of polyvinyl acetate. Methanol is practically unsuitable while acetone could be used where chloroform is not available.     

Tuning stability of mesoporous silica films under biologically relevant conditions through processing with supercritical CO2

Mesoporous materials have been proposed for use in numerous biological environments such as substrates for cell culture and controlled release for drug delivery. Although mesoporous silica synthesis is facile, recent reports (Dunphy et al. Langmuir 2003, 19, 10403; Bass et al. Chem. Mater. 2007, 19, 4349) have demonstrated instability (dissolution) of pure mesoporous silica films under biologically relevant conditions. In this work, we demonstrate a simple processing handle (pressure) to control the dissolution of mesoporous silica films that are synthesized using preformed template films and supercritical CO 2. Spectroscopic ellipsometry is utilized to quantify changes in both the film thickness and porosity; these properties provide insight into the dissolution mechanism. The pore size increases as the films are exposed to phosphate-buffered saline (PBS) through preferential dissolution at the pore wall in comparison to the film surface; a mechanism reminiscent of bulk erosion of scaffolds for drug delivery. Thin mesoporous silica film lifetimes can be extended from several hours using traditional sol-gel approaches to days by using CO 2 processing for identical film thickness. Osteoblast attachment and viability on these films was found to correlate with their increased stability. This enhanced stability opens new possibilities for the utilization of mesoporous silica for biological applications, including drug delivery and tissue engineering.     

An exactly solvable Ogston model of gel electrophoresis. VI. Towards a theory for macromolecules

In this article, we present a generalized version of our lattice model of low-field gel electrophoresis that allows us to treat the case of macromolecules such as short linear or circular oligomers and semi-flexible rods. We show that free-solution electrophoresis problems can be seen as random walks in the conformational space of the analyte. For sufficiently small molecules, our mathematical approach provides exact mobilities. In a quenched gel-like environment, however, both conformational and positional degrees of freedom must be used, but exact solutions can also be obtained. As an example, we then investigate several two-dimensional model gels, as well as a simple channel system where we see evidence of entropic effects that cannot be captured by the traditional Ogston concept of free volume.     

Two-layer model description of polymer thin film dynamics

Experiments in the past two decades have shown that the glass transition temperature of polymer films can become noticeably different from that of the bulk when the film thickness is decreased below ca. 100 nm. It is broadly believed that these observations are caused by a nanometer interfacial layer with dynamics faster or slower than that of the bulk. In this paper, we examine how this idea may be realized by using a two-layer model assuming a hydrodynamic coupling between the interfacial layer and the remaining, bulk-like layer in the film. Illustrative examples will be given showing how the two-layer model is applied to the viscosity measurements of polystyrene and polymethylmethacrylate films supported by silicon oxide, where divergent thickness dependences are observed.     

Image analysis techniques for automatic evaluation of two-dimensional electrophoresis.

Techniques for automatic analysis of two-dimensional electrophoresis gels by computer-aided image analysis are described. Original gels or photographic films are scanned using a laser scanner and the files are transferred to a microcomputer. The program package first performs a compression and preevaluation of the files. Spot identification and quantification is performed by the chain code algorithm after appropriate zooming and cutting. Labeling facilitates spot identification and quantification in numerical and graphical (pseudocolor) representation on peripheral devices for camera ready output. Interpolation between measured basepoints is performed by cubic spline algorithms which are automatically switched on and off, depending on the need by the program. High speed analysis and graphic representation is achieved using fast Assembler language routines rather than high level languages. One-dimensional gels can be analyzed using the same software. Spot matching between parallel two-dimensional gels has not yet been implemented.