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PubMed1995

Electrochemical and microstructural study of oxide films formed electrochemically at microcrystalline Al-Fe-V-Si alloys.

A recent advance in metallurgical technology has been the application of rapid solidification techniques to Al alloy production. FVS0812 is the designation given to a microcrystalline Al-based alloy consisting of 8 wt% Fe, 1 wt% V and 2 wt% Si. It is a two-phase alloy, consisting of ca. 27 vol percent of approximately spherical Fe-V-Si-rich dispersoids in an essentially pure Al matrix. The high strength, low density properties of this advanced material, and other related alloys, have not yet been realized, however, due, in part, to the inability of the alloy to form a thick, adherent, abrasion-resistant outer surface oxide film, a feature readily achieved at conventional Al alloys by normal anodizing methods. The present research has involved an electro-chemical study of oxide film growth at the 812 alloy, with the specific goals being to seek an understanding of the origin of the oxide film growth problem and ultimately to propose alternative approaches to the formation of a thick, stable oxide film at this material. The techniques used in this research have included electrochemical methodologies such as cyclic voltammetry and electrochemical impedance spectroscopy. Crucial information has been obtained through transmission electron microscopy (TEM) of ultramicrotomed specimens. Experiments were carried out initially in neutral borate solutions to characterize the compact barrier oxide film formed in this environment and expected to be present beneath the porous oxide film formed in the normal sulfuric acid anodizing medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Alloys↗
PubMed2006

Bioadhesive monolayer film for the in vitro transdermal delivery of sumatriptan.

The work presented here aims to develop a bioadhesive monolayer film containing sumatriptan as adjuvant for the treatment of headache pain in a severe migraine attack. Permeation experiments were performed from the films prepared and from the respective solution, to evaluate the relevant permeation parameters. The effect of the penetration enhancers Transcutol, 2-pyrrolidone, and polyethylene glycol 600 was evaluated. The results obtained show that Transcutol and 2-pyrrolidone decreased sumatriptan permeation from solution, whereas a modest increase was produced by polyethylene glycol 600. The enhancers produced the same effects when they were included in the film. Compared to solution, the film showed a higher sumatriptan flux in the early times of the experiment. When the film was applied in occlusive conditions the profiles were much higher, indicating the importance of patch drying. Concerning skin retention, the bioadhesive film produced a reduction of the amount of sumatriptan remaining in the skin, but this can be advantageous in the control of drug input, since it reduces the reservoir effect in the skin and allows for an immediate interruption of drug input when the patch is removed.

Administration, Cutaneous↗
PubMed1975

Drug-biomolecule interactions: interaction of gentamicin with lipid monomolecular films.

The interaction of gentamicin with monomolecular films of a series of biologically important lipids spread on an aqueous buffered subphase was studied. The surface pressure, pi, of these films was determined by the Wilhelmy plate method as a function of surface area, A, and pi-A curves were constructed. Changes in the pi-A characteristics in the presence of gentamicin were used as a measure of antibiotic-film interaction. No interaction was observed between gentamicin and films of cholesterol, egg lecithin, dipalmitoyl lecithin, phosphatidyl ethanolamine, stearyl alcohol, and bovine ceramides at all pH values studied. Stearic acid films showed no interaction with gentamicin at pH 5. At pH 7 and 8, a small increase in pressure (approximately 3 dynes/cm) was noted. A dramatic increase in surface pressure was observed in the presence of stearyl aldehyde films ranging from approximately 9 dynes/cm at pH 7,2 to 23 dynes/cm at pH 8.4. This effect was attributed to a Schiff-base reaction between the nonprotonated primary amino groups on the gentamicin molecule and the stearyl aldehyde. Further evidence was reported by the fact that the addition of glucose (which has been reported to participate in Schiff-base formation with amines) to the subphase inhibited the stearyl aldehyde-gentamicin interaction. Sucrose did not show a corresponding effect. The addition of sodium bisulfite, which reacts with aldehydes to form alpha-hydroxysulfonic acid, also inhibited the gentamicin-stearyl aldehyde interaction. It is postulated that Schiff-base formation is a step in the in vivo transport of gentamicin across the membrane of sensitive organisms.

Chemical Phenomena↗
PubMed1975

Effect of surface roughness and coating solvent on film adhesion to tablets.

The adhesion of a polymer film to selected tablet substrates was studied. The effect of tablet surface roughness and film-coating solvent on the adhesion of the film to the tablet was determined. A film-coating solvent having a solubility parameter close to that of the polymer was found to produce a stronger adhesional bond than a solvent having a lower surface tension. An increase in tablet surface roughness also increased film adhesion to the tablet. The adhesion was measured as the force required to peel a section of film from the tablet with a stress-strain analyzer.

Acacia↗
PubMed2004

Sustained release of BSA from a novel drug delivery matrix -- bullfrog skin collagen film.

A novel drug delivery system, bullfrog skin collagen film, was employed to release bovine serum albumin (BSA). The biophysical properties of bullfrog skin collagen film used were evaluated by thermal denaturation temperature and percentage water loss. The film obtained exhibited good stability and can be taken as a good candidate for drug delivery matrix. Compared with conventional collagen from molecular weight and amino acid composition, bullfrog skin collagen showed significant differences. For safety considerations, bullfrog skin collagen has great advantages. The release kinetics of BSA from bullfrog skin collagen film was measured in vitro. The results indicated bullfrog skin collagen film could be used for sustained release of BSA. Thus, bullfrog skin collagen film can be taken as a novel drug delivery system.

Amino Acids↗
PubMed2006

Suppression of cell and platelet adhesion to star-shaped 8-armed poly(ethylene glycol)-poly(L-lactide) block copolymer films.

To explore the potential of a star-shaped 8-armed poly(ethylene glycol)35K-block-poly(L-lactide)37K (8-armed PEG35K-b-PLLA37K: M(n) of PEG = 35 000, M(n) of PLLA = 37 000) film as a novel bioabsorbable adhesion-prevention membrane, the water structure, surface contact angle, protein adsorption, and cell and platelet anti-adhesion properties of such a hydrated film are investigated. Based on the results, it is found that the 8-armed PEG35K-b-PLLA37K film exhibits a biologically inert surface, which is the result of a large number of PEG chains and a free water layer on the film surface. This leads to a reduction in protein absorption and cell and platelet adhesion onto the film surface. This implies that the star-shaped 8-armed PEG35K-b-PLLA37K film can be utilized as a novel bioabsorbable adhesion-prevention membrane.

Absorption↗
PubMed2006

The effects of kaolin particle film on Plutella xylostella behaviour and development.

Studies were conducted to evaluate the effect of a kaolin-based particle film against the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The effect of the particle film on development, survival and host plant selection was tested on calabrese seedlings, Brassica oleracea italica Plenck cv. Fiesta F(1), under controlled environmental conditions in the laboratory. Survival to adulthood was significantly reduced and development time increased on kaolin-treated compared with water-treated host plants. The hatch rate of neonate P. xylostella larvae from eggs laid on an artificial substrate was unaffected by the particle film applied after oviposition. Experiments showed that, when given the choice, significantly fewer larvae first made contact with the kaolin-treated compared with the water-treated plant material and that after 24 h there were still significantly fewer larvae present on kaolin-treated leaves. Adult females, however, deposited more eggs on host plants coated with the kaolin particle film. As part of this series of experiments the water control treatment was compared with plant material which had been sprayed with kaolin on the upper surface only and on both leaf surfaces. In general, any observed treatment effect was enhanced with an increase in the particle film coverage. The results warrant the extension of investigations of kaolin-based particle films to field-based P. xylostella management strategies.

Animals↗
PubMed2005

Bulk and compound-specific isotopic characterisation of illicit heroin and cling film.

Comparative analysis involves various but complementary methods and can be used for forensic intelligence purposes to group seizures of heroin into batches. Much forensic analysis now combines expertise in the traditional area of drugs investigation with a detailed understanding of supply, packaging, distribution, and drugs intelligence. It was the intention of this research to determine whether illicit heroin seizures and packaging material can be grouped according to isotopic compositions, and to explore factors that affect the isotopic compositions. In order to achieve these aims, 14 samples of seized heroin, thirteen provided by Avon and Somerset Constabulary (UK), were analysed by elemental analysis/isotope ratio mass spectrometry (EA/IRMS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) for carbon and hydrogen isotopes. These tests elucidated that a combination of the delta13C, delta15N, delta18O and delta2H results from EA/IRMS is able to distinguish between most samples of bulk heroin. We speculate that the delta13C values of the alkaloids, obtained by GC/C/IRMS, give indications of different geographical or temporal origins of some of the heroin samples. GC/C/IRMS of the cutting agent, caffeine, provides a means to link dilution events. Fifteen retail cling film samples and seven cling film samples from heroin seizures were analysed by EA/IRMS. A multivariate comparison of the carbon, hydrogen and oxygen isotope ratios was able to distinguish between most of the samples. This technique enabled the cling films from the heroin to be grouped according to seizure. Three solvents were tested on two samples of cling film of known composition. Methanol and chloroform were both found to extract material from PVC and from non-PVC cling films. Water-treated PVC was indistinguishable from the untreated PVC and thus water was found to be the most suitable solvent when washing cling film prior to IRMS analysis.

Forensic Sciences↗
PubMed2000

Rapid SLT gene detection on polyethylene-coacrylic acid film without molecular labels or surface-fouling agents.

The commercially available copolymer of 10 mol% acrylic acid and polyethylene is easily formed into a nonfluorescing, non-polynucleotide-adsorbing film. The film has surface carboxylate functions whose concentration can be increased by heating to 80 degrees C in 30% NaOH. The carboxylate groups will react at pH approximately 7 with commercially available, oligo-DNA, 2-8 ng/microl, that has been synthesized with a C(12)-alkylamino tail on the 5'-end. The reaction is mediated with water-soluble carbodiimide reagent and is assumed to result in a primary amide bond between the polymer film and the modified oligo-DNA. The tethered oligo-DNA retains its hybridization activity, and its surface concentration is sufficient to permit qualitative, labelless detection of hybridized target by fluorescence after brief staining with ethidium bromide. The film is used to detect Shiga-like toxin gene II (SLT-II) from Escherichia coli O157:H7 after asymmetric, capillary, PCR amplification, and a 4-h hybridization. Captured target may be removed from the film using distilled water, after which the film can be used again without noticeable loss of activity. The method provides relatively rapid detection of PCR amplimers without having to use molecular labels, or surface-fouling agents.

Acrylates↗
PubMed1996

Photophysical Studies in AOT Films Deposited on Fused Silica Slides

Thin surfactant films were made by dip-coating a fused-silica slide in reverse micelles of bis(2-ethylhexyl) sulfosuccinate sodium salt [AOT] in cyclohexane. The fluorescence quenching analysis of charge transfer between Ru(bpy)$^{2+}_3$ and MV2+, of resonance energy transfer between pyrene and coumarin-153, and of pyrene excimer formation has revealed that the original micellar structure is to a large extent transferred into the structure of the film. The film consists of a hydrophilic and a hydrophobic subphase. Nondried films contain entrapped cyclohexane which allows diffusion of the hydrophobic probes in the film and a rather random distribution of them. Drying leads to solvent evaporation and hydrophobic probe aggregation. The kinetics of the hydrophilic probes reflect the structure of the hydrophilic domain which is not affected by drying procedure. The above films are transparent matrices and make excellent hosts for photophysical studies.

Journal Article↗
PubMed1999

Dewetting of Thin Block Copolymer Films.

The dewetting of thin films of low molecular weight diblock and triblock copolymers of poly(oxyethylene)/poly(oxybutylene) on silicon has been studied using video microscopy and X-ray reflectivity. Dewetted films were observed to comprise polygonal domains of polymer droplets, with a domain size of several millimeters. The dewetted films were studied using X-ray reflectivity, which showed that a film of polymer <50 Å thick remains on the substrate at the same time as the macroscopic droplets. This suggests that autophobic dewetting occurred in this system; i.e., a microscopically thin film was in equilibrium with macroscopic droplets. The growth velocity of holes in the polymer film was found to be constant at a fixed temperature in the stage of hole growth that could be studied using optical microscopy. The velocity was found to be an exponential function of temperature. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Dewetting of a Heated Surface by an Evaporating Liquid Film under Conjoining/Disjoining Pressures.

In the present work we consider a model for the evolution of a thin nonpolar liquid film on a coated solid surface under the action of attractive and repulsive molecular forces governed by a 3-4 power-law potential, rather than the Lennard-Jones 3-9 potential employed for an ideal plane interface (molecularly clean and smooth). The model is used for both volatile and nonvolatile isothermal liquid films. It is shown that in the nonvolatile case the evolution results in the emergence of static steady states consisting of liquid ridges separated by very thin films. A supercritical bifurcation from the trivial state is shown to be possible in the presence of repulsive forces, while in the presence of only attractive forces the bifurcation is subcritical. In the evaporative case the long-time evolution of the film is shown to lead to its flattening and then to its apparent vanishing. Several scenarios for the film disappearance are found. A relationship between the rate of expansion of the dry spot and the apparent contact angle is examined. The effect of thermocapillarity on the film evolution is also considered. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Properties of Langmuir Surface and Interfacial Films Built up by Asphaltenes and Resins: Influence of Chemical Demulsifiers.

The influence of chemical additives on asphaltene films on water surface and at oil/water interface is studied by means of the Langmuir technique. It was found that some demulsifiers of high molecular weight alter the asphaltene film on water surface in the same way as the resin fraction, i.e., increasing the compressibility of the film which results in a reduced film rigidity. The films that build up at the oil/water interface in model oil systems, containing naturally occurring surfactants, are studied during compression. In this system chemical additives of high molecular weight totally prevent formation of a rigid film at the interface. Adding resins to the bulk phase together with asphaltenes hamper the adsorption of the heavy fraction. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Isotherms of Capillary Condensation Influenced by Formation of Adsorption Films.

Isotherms of capillary condensation are often used to determine the vapor sorption capacity of porous adsorbents as well as the pore size distribution by radii. In this paper, for calculating the volume of capillary condensate and of adsorption films in a porous body, an approach based on the theory of surface forces is used. Adsorption isotherms and disjoining pressure isotherms of wetting films are presented here in an exponential form discussed earlier. The calculations were made for straight cylindrical capillaries of different radii and slit pores of different width. The mechanisms of capillary condensation differ in cylindrical and slit pores. In cylindrical pores capillary condensation occurs due to capillary instability of curved wetting films on a capillary surface, when film thickness grows. In the case of slit pores, coalescence of wetting films formed on opposite slit surfaces proceeds under the action of attractive dispersion forces. Partial volumes of liquid in the state of both capillary condensate and adsorbed films are calculated dependent on the relative vapor pressure in a surrounding media. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Electroactive Films of Alternately Layered Polycations and Iron-Sulfur Protein Putidaredoxin on Gold.

Layered, electrochemically active films of bacterial iron-sulfur protein putidaredoxin (Pdx) and poly(dimethyldiallyammonium) (PDDA) polycations were constructed on gold electrodes coated with mercaptopropane sulfonate (MPS) and on quartz slides. Second-derivative UV-vis spectra suggested similar structures of Pdx in films and solutions at pH 7. Direct electrochemistry was achieved between Pdx and gold electrodes in these films, with significantly better electrochemical reversibility than in cast Nafion-lipid-Pdx films. A formal potential dispersion model gave a good fit to square wave voltammograms by regression analysis and was used to estimate an average apparent rate constant of 4.5 s(-1). Reduced Pdx in the polyion films did not react with its natural redox partner cytochrome P450(cam) because of unfavorable thermodynamics in the film environment. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Removal of Solid Organic Films from Rotating Disks Using Emulsion Cleaners.

Measurements have been made of the rate of removal of a solid organic film (phenanthrene) from the surface of a rotating disk using emulsions containing water, the nonionic surfactant Tween 20, and d-limonene as the organic phase. The results show that phenanthrene removal initially occurs by the uptake of phenanthrene into the emulsion drops as small aggregates. Simultaneously, the organic phase penetrates into the phenanthrene film, diminishing the adhesive force between the film and the substrate. After sufficient time, the phenanthrene film detaches from the rotating disk surface as a solid. This detachment mechanism accounts for the vast majority of the phenanthrene removal ( approximately 90%). Initial solubilization rates were analyzed using two solubilization models. Both models assume that phenanthrene removal occurs via a mass transfer limited removal of phenanthrene-laden emulsion drops from the phenanthrene film surface into the bulk solution. One model treats the emulsion as homogeneous while the other accounts for the finite size of the emulsion droplets. The latter model was also used to relate the flux of organic phase impacting the phenanthrene film to the detachment times. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Film Mass Transfer Coefficient Expressions for Electroosmotic Flows.

Expressions are developed and presented that could be used to determine the film mass transfer coefficient of a solute in electroosmotic flows. In contrast to pressure-driven flows at low Reynolds numbers where the film mass transfer coefficient is independent of the linear characteristic dimension of the channel for flow, in electroosmotically driven flows at low Reynolds numbers the film mass transfer coefficient is shown to be a function of the ratio R/lambda, where R is the channel radius and lambda is the Debye length. This result implies that for electroosmotically driven flows in a packed bed or porous monolith with channels for flow having similar geometry but different sizes, the film mass transfer coefficient would vary with the size of the interstitial channels for bulk flow while in pressure-driven flows the film mass transfer coefficient would be the same for all interstitial channels. From the expressions presented in this work, one can show that for the same volumetric flow rate the film mass transfer coefficient of electroosmotically driven flows is proportional to that for pressure-driven flows. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

Effect of gamma Irradiation on Latex Film Dissolution.

Latex films have been prepared by annealing pyrene (Py)-labeled poly(methyl methacrylate)-polyisobutylene particles at the glass transition temperature (100 degrees C). These films were then irradiated by gamma rays from (60)Co in a gamma cell at room temperature at various dose rates (rad/h). Before dissolution the films were annealed at 200 degrees C for a 30 min time interval to complete the film formation process. Steady-state fluorescence techniques were used to monitor the dissolution of irradiated latex films. Dissolution of films in a chloroform-heptane (80%-20%) mixture was monitored in real time by the Py fluorescence intensity change. Relaxation constants, k(0), and dissolution coefficients, D(d), of polymer chains were measured. Two different regimes of D(d) values were observed during dissolution, which are related to two different molecular weight distributions caused by scission and branching of polymer chains when they were irradiated and annealed. Copyright 2001 Academic Press.

Journal Article↗