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PubMed2000

A Nonlinear Rupture Theory of Thin Liquid Films with Soluble Surfactant.

The effects of soluble surfactant on the dynamic rupture of thin liquid films are investigated. A nonlinear coupling evolution equation is used to simulate the motion of thin liquid films on free surfaces. A generalized Frumkin model is adopted to simulate the adsorption/desorption kinetics of the soluble surfactant between the surface and the bulk phases. Numerical simulation results show that the liquid film system with soluble surfactant is more unstable than that with insoluble surfactant. Moreover, a generalized Frumkin model is substituted for the Langmuir model to predict the instability of liquid film with soluble surfactant. A numerical calculation using the generalized Frumkin model shows that the surfactant solubility increases as the values of parameters of absorption/desorption rate constant (J), activation energy desorption (nu(d)), and bulk diffusion constant (D(1)) increase, which consequently causes the film system to become unstable. The surfactant solubility decreases as the rate of equilibrium (lambda) and interaction among molecules (K) are increased, which therefore stabilizes the film system. On the other hand, an increase of relative surface concentration (the index of a power law), beta(n), will initially result in a decrease of corresponding shear drag force as beta and n increase from 0 to 0.3 and 0.85, respectively. This will enhance the Marangoni effect. However, a further increase of beta and n to greater than 0.3 and 0.85, respectively, will conversely result in an increase of the corresponding shear drag force. This will weaken the Marangoni effect and thus result in a reduction of interfacial stability. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

Effect of Corona Discharge Treatment on the Dyeability of Low-Density Polyethylene Film.

The effect of corona discharge on low-density polyethylene (LDPE) film was studied in terms of surface functionality and surface energetics of the film surfaces, improving the dyeability. The introduction of a polar group (O=C-O, C=O, and C-O) to a corona-treated LDPE film with acrylic acid could be confirmed by ESCA. The Owens-Wendt and Wu models using geometric means were studied to analyze the surface free energy of corona-treated film. It was found that the corona-treated LDPE film did lead to an increase in surface free energy, mainly due to the increase of its specific (or polar) component as the corona discharge power increased. Also, the K/S values were increased as the concentrations of dye increased. From the acid-base interaction point of view, it was found that the graft polymerization of acrylic acid onto the corona-treated LDPE film plays an important role in growing the acidic character which is one of the specific components of surface free energy, resulting in improving the dyeability with basic dyeing agent. A direct linear relationship is shown between the O(1s)/C(1s) ratio and the resulting K/S value or the specific component for this work. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Electrochemistry and Electrocatalysis with Myoglobin in Biomembrane-Like DHP-PDDA Polyelectrolyte-Surfactant Complex Films.

The polyelectrolyte-surfactant complex DHP-PDDA was prepared by reacting the anionic surfactant dihexadecylphosphate (DHP) with polycationic poly(diallyldimethylammonium) (PDDA). Thin films made from DHP-PDDA on solid substrates demonstrated an ordered multibilayer structure by XRD and DSC. Incorporated myoglobin (Mb) in DHP-PDDA films on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible cyclic voltammetric peaks for the Mb Fe(III)/Fe(II) couple at about -0.3 V vs SCE in pH 7.0 buffers. Electron transfer between Mb and PG electrodes was greatly facilitated in the film microenvironment. The positions of the Soret absorption band suggest that Mb maintains its secondary structure similar to its native state in DHP-PDDA films in the medium pH range. Mb could act as an enzyme-like catalyst in DHP-PDDA films as demonstrated by catalytic reduction of trichloroacetic acid, nitrite, and oxygen with a decrease in the electrode potentials required. Mb-DHP-PDDA films may thus have potential application as biosensors. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Thin-Film Morphologies of Random Copolymers as Functions of Thermal History.

Series polymers of butyl methacrylate with various contents of 3-(trimethoxysilyl)propyl methacrylate (MSMA) that introduces crosslinking networks among the macromolecules upon hydrolysis and self-condensation have been synthesized by free radical polymerization, and the influence of crosslinking density on the film properties has been examined. The polymer solutions were spin-cast over a layer of polystyrene brush to yield homogeneous polymer films. When the films of about 30 nm thick were exposed to moisture and then heated at 60 degrees C for hydrolysis and self-condensation of MSMA groups, the initially flat surfaces became slightly coarser but without apparent dewetting. Further annealing at 140 degrees C resulted in dewetting of the thin films, whose morphologies in thermodynamic equilibrium were related to the chemical compositions of the polymers. The polymers having higher contents of MSMA exhibited significantly reduced dewetting at the high temperature, due to the higher density of crosslinking networks that restricted the molecular mobility. In contrast to the thin films of about 30 nm thick, thicker films (about 100 nm) showed only a slight dewetting, even non-dewetting at the elevated temperature. Copyright 2001 Academic Press.

Journal Article↗
PubMed2002

Fast transient fluorescence technique (FTRF) for studying vapor-induced latex film formation.

A fast transient fluorescence (FTRF) technique was used to study latex film formation induced by organic solvent vapor. Seven different films with the same latex content were prepared separately from poly(methyl methacrylate) (PMMA) particles and exposed to vapor of various chloroform-heptane mixtures in seven different experiments. Latex films were prepared from pyrene (Py)-labeled latex particles and fluorescence lifetimes of Py were monitored during vapor-induced film formation. It was observed that pyrene lifetimes decreased as vapor exposure time increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in pyrene lifetimes. A Prager-Tirrel model was employed to obtain back-and-forth frequencies, nu, of the reptating PMMA chains during latex film formation induced by solvent vapor. nu values were found to be correlated with chloroform content in vapor mixture. It was observed that polymer interdiffusion obeyed a t(1/2) law during film formation. The results of optical transmission experiments were found to support these findings.

Journal Article↗
PubMed2002

Effect of foam films on gas diffusion.

We report an experimental investigation of the permeability to gas of systems of one or several soap films freely standing in a straight tube, using either reactive gas (NH(3)) or inert gas (argon). The series of soap films appears to be the simplest paradigm of successive lamellae arrangements encountered in foams confined in a porous medium. To conduct the experiments, we devised two novel methods for the determination of gas diffusion fluxes: one based on reactive changes of pH by NH(3) and the other on mass spectrometry. The permeability of a single film, stabilized by sodium dodecyl sulfate solution, was found to be 3.50+/-0.04 10(-2) cm/s for argon and 3.18+/-0.07 10(-4) cm/s for NH(3). The permeability value for the inert gas is in good agreement with data obtained by the diminishing-bubble method. When the number of films increases, the permeability decreases considerably as a result of cumulative film resistance effects. We also developed a simple phenomenological model based upon a combination of gas kinetic and energy barrier concepts to interpret our data. This model takes into account gas solubility and the effects of salinity, which have seemingly been ignored in previous models. The predicted film permeability decreases sharply with increase surfactant concentration, indicating the occurrence of higher adsorption and increasingly compact surfactant layers.

Journal Article↗
PubMed2002

Layer-by-layer self-assembled ultrathin multilayer films of lanthanide polyoxometalates and poly(allylamine hydrochloride) and their photoluminescent properties.

Ultrathin multilayer films of two lanthanide polyoxometalates (LPOMs), K(17)[Eu(P(2)W(17)O(61))(2)] (EPW) and K(13)[Eu(SiW(11)O(39))(2)] (ESW), and poly(allylamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. UV-vis spectroscopy and ellipsometry respectively show that the absorbance values at characteristic wavelengths and the thicknesses of the multilayer films increase linearly with the number of LPOM/PAH bilayers, suggesting that the deposition process is linear and highly reproducible from layer to layer. Average thicknesses of ca. 3.4 and 2.4 nm were determined for the EPW/PAH and ESW/PAH bilayers by ellipsometry, respectively. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide the surface morphology of the LPOM/PAH films, indicating that the film surface is relatively uniform and smooth. The photoluminescent properties of these films have also been investigated by fluorescence spectroscopy. The LPOM/PAH multilayer film has a good thermal stability as shown by UV-vis, X-ray photoelectron, and fluorescence spectra.

Journal Article↗
PubMed2002

Site percolation model for latex film formation in soft polymer matrix.

The UV-visible (UVV) technique was used to monitor latex film formation in a soft polymer matrix. Various film samples were prepared by increasing the amount of poly(methyl methacrylate) (PMMA) particles in a poly(isobutylene) (PIB) matrix. These samples were then annealed above the glass transition temperature to promote latex film formation. Transmitted photon intensities, Itr, were measured for each film. It is observed that Itr decrease as the latex content is increased, which was explained by the increase in scattered light intensity, Isc. The drastic increase in Isc above a certain latex content is attributed to the site percolation of latex particles in the PIB matrix. The percolation threshold and the critical exponent were measured and found to be 0.3 and 0.4, respectively. The increase in Itr by annealing of film samples above Tg was explained with the void closure process below 0.8 occupation probability. When the film is occupied completely with the latex particles, interdiffusion of polymer chains was observed. Viscous flow and chain diffusion activation energies were determined and found to be 8 and 51 kcal/mol, respectively.

Journal Article↗
PubMed2002

Disjoining pressure isotherms of water-in-bitumen emulsion films.

In the oil sands industry, undesirable water-in-oil emulsions are often formed during the bitumen recovery process where water is used to liberate bitumen from sand grains. Nearly all of the water is removed except for a small percentage (approximately 1 to 2%), which remains in the solvent-diluted bitumen as micrometer-sized droplets. Knowledge of the colloidal forces that stabilized these water droplets would help to increase our understanding of how these emulsions are stabilized. In this study, the thin liquid film-pressure balance technique has been used to measure isotherms of disjoining pressure in water/toluene-diluted bitumen/water films at five different toluene-bitumen mass ratios. Even though a broad range of mass ratios was studied, only two isotherms are obtained, indicating a possible change in the molecular orientation of surfactant molecules at the bitumen/water interfaces. At low toluene-bitumen mass ratios, the film stability appears to be due to a strong, short-range steric repulsion created by a surfactant bilayer. Similar isotherms were obtained for water/toluene-diluted asphaltene/water films, indicating that the surface active material at the interface probably originated from the asphaltene fraction of the bitumen. However, unlike the bitumen films, films of toluene-diluted asphaltenes often formed very rigid interfaces similar to the "protective skin" described by other researcher.

Journal Article↗
PubMed2002

Assembly of electroactive layer-by-layer films of myoglobin and ionomer poly(ester sulfonic acid).

Layer-by-layer films were assembled on solid substrates by alternate adsorption of negatively charged ionomer poly(ester sulfonic acid) or Eastman AQ55 from its aqueous dispersion and positively charged myoglobin (Mb) from its solution at pH 4.5. The film assembly process was monitored by cyclic voltammetry (CV), UV-vis spectroscopy, and quartz crystal microbalance (QCM). [AQ/Mb](n) films grown on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible CV peaks at about -0.20 V vs Ag/AgCl in pH 5.5 buffers, characteristic of the Mb heme Fe(III)/Fe(II) redox couple. Although the amount of Mb adsorbed in each bilayer was essentially the same, the fraction of electroactive Mb decreased dramatically with an increase of bilayer number (n). Soret absorption bands of [AQ/Mb](n) films on glass slides suggest that Mb in the films retains its native state in the medium pH range. Trichloroacetic acid, oxygen, and hydrogen peroxide were electrochemically catalyzed by [AQ/Mb](6) films with significant lowering of reduction overpotential.

Adsorption↗
PubMed1998

Prevention of retrosternal adhesion formation in a rabbit model using bioresorbable films of polyethylene glycol and polylactic acid.

The purpose of this study was to test the efficacy of three bioresorbable films of polyethylene glycol (EO) and polylactic acid (LA) (EO/LA = 1.5, 2.5, and 3.0) in the prevention of adhesion formation between the epicardium and the sternum (retrosternal adhesions) in a rabbit model. Retrosternal adhesions were generated by sternotomy, pericardiotomy, and abrasion of the anterior epicardium. The adhesion barrier was placed between the epicardium and the sternum and sutured to the edge of the pericardium. Epicardial adhesions were evaluated 14-20 days later by assessing the area of the epicardium covered by adhesions. In the control rabbits, tenacious adhesions were observed between sternum and the central portion of epicardium (portion exposed through the pericardiotomy) which were difficult to dissect. When a bioresorbable film was placed over the pericardium, adhesion formation at the central strip of the epicardium (area between the sternum and the epicardium exposed through the pericardium) could be reduced or prevented. At this site, the areas of adhesion formation were 0% (EO/LA = 1.5), 8.4 +/- 2.8% (EO/LA = 2.5), and 5.6 +/- 4.7% (EO/LA = 3.0) of the central strip, significantly less than that observed in the control group, 78.0 +/- 5.8% (P < 0.01). At the anterior left and right and posterior apex of the heart (sites where the film was not placed), there were no differences between control and treatment groups. The films were completely resorbed at the time of necropsy in group EO/LA = 2.5 and 3.0. Small pieces of film were observed in group EO/LA = 1.5. In conclusion, the bioresorbable films [EO/LA = 1.5 (REPEL-CV), 2.5, or 3.0] were efficacious in the reduction of retrosternal adhesions to the epicardium.

Animals↗
PubMed1977

Structural and spectroscopic characteristics of bacteriorhodopsin in air-water interface films.

A suspension of purple membrane fragments in a solution of soya phosphatidyl-choline in hexane is spread at an air-water interface. Surface pressure and surface potential measurements indicate that the membrane fragments and lipids organize at the interface as an insoluble film. Electron microscopy of shadow-cast replicas of the film reveal that in the bacteriorhodopsin to soya PC weight ratio range of 2:1 to 10:1, these films consist of nonoverlapping membrane fragments which occupy approximately 35% of the surface area and are separated by a lipid monolayer. Furthermore, the membrane fragments are oriented with their intracellular surface towards the aqueous subphase. Nearly all the bacteriorhodopsin molecules at the interface are spectroscopically intact and exhibit visible spectral characteristics identical to those in aqueous suspensions of purple membrane and in intact bacteria. In addition, bacteriorhodopsin in air-dried interface films show spectral changes upon dark-adaptation and upon flash illumination similar to those observed in aqueous suspensions of purple membrane, but with slower kinetics. The kinetics of the spectral changes in interface films can be made nearly the same as in aqueous suspension by immersing the films in water.

Air↗
PubMedDate not supplied

Clinical significance of discrepancies in roentgenographic film interpretation in an acute walk-in area.

To determine the clinical significance of discrepancies in roentgenographic film interpretation, housestaff's interpretations of 248 outpatient x-rays obtained in a walk-in/emergency room area were compared with the interpretations by radiologists. There was complete agreement for 134/248 (54%) films. Discrepancies for 114 films were classified as potentially significant (n = 28, 25%) or insignificant (n = 86, 75%). Most significant discrepancies (26 of 28) were related to the indication for the film. Most insignificant discrepancies (75 of 86) were unrelated to the film's indication. No discrepancies resulted in serious adverse patient outcomes, although one resulted in delayed treatment of a fractured humerus, one resulted in delay of antibiotic treatment, and three resulted in antibiotic use that may have been unnecessary. In two cases, the initial treatment plan was changed based on the final radiologist's report. These results indicate that while discrepancies in film interpretation are frequent, their clinical impact may be small.

Emergency Service, Hospital↗
PubMed1984

Interfacial properties of hydrophilic surfaces of phospholipid films as determined by the method of contact angles. Comparison with cell surfaces.

Hydrophilic films of phospholipids were deposited onto plastic substrates (surface-treated for cell cultures) and shown to adhere sufficiently for measuring their interfacial properties by the method of contact angles. Both by absolute magnitude and by their dependence on temperature, the interfacial properties of these phospholipid films were indistinguishable from those determined for black lipid bilayer membranes with a different method by other authors. According to both their vesicular micromorphology and water permeability, the surface films can be interpreted to consist essentially of multibilayer vesicles with the hydrophilic groups facing outward. Treatment of these films with cell-culture medium containing calf serum results in changes of interfacial properties that are very similar to those effected on virus-transformed 3T3 cells (earlier work). These interfacial effects may be attributed essentially to serum proteins (such as albumin) adsorbing to phospholipid or cellular surfaces. The interfacial properties of nontransformed 3T3 cells are much less affected by serum treatment (earlier work), which correlates closely with their higher serum requirement for proliferation. Comparison of these results with those on the interfacial effects of serum on phospholipid films suggests that at least part of the proliferation-stimulating effect of serum is mediated by changes of interfacial properties of cell membranes upon adsorption of serum proteins such as albumin. Treatment of phospholipid films with concanavalin A, an inhibitor of cell proliferation, does not result in effects on their interfacial properties correlating with those on cellular membranes. This confirms previous suggestions that the latter depends on specific binding of concanavalin A to specific carbohydrates on the cell membrane.

Concanavalin A↗
PubMed2004

Ferrocene-containing polyelectrolyte multilayer film-covered electrodes: electrocatalytic determination of ascorbic acid and use of inner blocking layers to improve the upper detection limit of the electrodes.

A multilayer film composed of ferrocene(Fc)-appended poly(allylamine hydrochloride) (Fc-PAH) and poly(potassium vinylsulfate) (PVS) has been prepared on the surface of a gold(Au) electrode by using a layer-by-layer self-assembly technique. Fc-containing polyelectrolyte multilayer (PEM) film-modified electrodes can electrochemically catalyze the oxidation of ascorbic acid successfully. For a 2 (Fc-PAH/PVS) bilayer-covered electrode the catalytic current increased linearly with increasing concentration of ascorbic acid over the concentration range 6 micromol L(-1)-3 mmol L(-1). To extend the dynamic range for ascorbic acid, the surface of the Au electrode was first covered with a (PAH/PVS)(2) film on which an additional (Fc-PAH/PVS)(5) film was coated. This strategy successfully extended the dynamic range of the electrode up to 25 mmol L(-1) ascorbic acid, because the (PAH/PVS)(2) layer blocked access of ascorbic acid to the electrode surface. The upper detection limit of the (PAH/PVS)(2) (Fc-PAH/PVS)(5) film-modified electrode is much higher than those of Fc-based ascorbic acid sensors reported so far. Electron transfer is diffusion-controlled within the (PAH/PVS)(2)(Fc-PAH/PVS)(5) film.

Ascorbic Acid↗
PubMed2006

Selective detection of dopamine in the presence of ascorbic acid by use of glassy-carbon electrodes modified with both polyaniline film and multi-walled carbon nanotubes with incorporated beta-cyclodextrin.

A simple, sensitive, and reliable method based on a combination of multi-walled carbon nanotubes with incorporated beta-cyclodextrin (beta-CD-MWNTs) and a polyaniline (PANI) film-modified glassy-carbon (GC) electrode has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The PANI film had good anti-interference properties and long-term stability, because of the permselective and protective properties of the conducting redox polymer film. The acid-treated MWNTs with carboxylic acid functional groups promoted the electron-transfer reaction of DA and inhibited the voltammetric response of AA. Sensitive detection of DA was further improved by the preconcentration effect of formation of a supramolecular complex between beta-CD and DA. The analytical response of the beta-CD-MWNTs/PANI film to the electrochemical behavior of DA was, therefore, better than that of a MWNTs/PANI film, a PANI film, or a bare glassy-carbon (GC) electrode. Under the conditions chosen a linear calibration plot was obtained in the range 1.0 x 10(-7)-1.0 x 10(-3) mol L(-1) and the detection limit was 1.2 x 10(-8) mol L(-1). Interference from AA was effectively eliminated and the sensitivity, selectivity, stability, and reproducibility of the electrodes was excellent for determination of DA.

Aniline Compounds↗
PubMed2007

Surface plasmon resonance biosensor based on Hg/Ag-Au film.

Mercury or silver was electrodeposited on an Au surface to form an Hg-Au or Ag-Au film. Wavelength-modulation SPR biosensors based on this Hg/Ag-Au film were then used to determine human IgG and rabbit IgG. When direct immunoreactions were performed on the Au sensing surface, the range of concentrations of human IgG and rabbit IgG that could be determined were 2.00-40.00 microg/ml and 2.50-40.00 microg/ml, respectively. When Hg was electrodeposited onto the Au film for 1200 s, the range of concentrations of human IgG and rabbit IgG that could be determined were 0.50-40.00 microg/ml and 0.63-40.00 microg/ml, respectively. When Ag was electrodeposited onto the Au film for 1500 s, the range of concentrations of human IgG and rabbit IgG that could be determined were 0.25-20.00 and 0.42-20.00 microg/ml, respectively. The biosensor based on Ag-Au film was therefore found to be the most sensitive of the three types of biosensor tested, giving limits of determination that were up to eight times lower than those obtained with a biosensor based on Au film alone.

Biosensing Techniques↗
PubMed1998

A comparison between digital fluoroscopic hard copies and 105-mm spot films in evaluating vesicoureteric reflux in children.

OBJECTIVE: To compare fluoroscopic freeze-frame digital images with conventional 105-mm spot films during voiding cystourethrography (VCUG) with regard to diagnostic quality and radiation dose. MATERIALS AND METHODS: VCUG was performed on 57 consecutive children by a commercially available fluoroscopic digital system. Both freeze-frame digital images and conventional 105-mm spot films were obtained during 90 s of fluoroscopy. Skin radiation dose was assessed separately for spot films and for both fluoroscopy and spot films, employing thermoluminescent crystals on the anterior surface of the body. Patients were classified into three age groups: group A younger than 12 months, group B 1-5 years old and group C 5-12 years of age. RESULTS: Digital and conventional images provided diagnostically identical results in 108 out of 114 ureters examined (94.7%). Percentage reductions in skin radiation dose due to the fluoroscopic hard copies compared with the four 105-mm radiographs were 53.8%, 50.5% and 57.1% for groups A, B and C, respectively. CONCLUSION: Substitution of conventional 105-mm spot films during VCUG with digital fluoroscopic hard copies resulted in a substantial reduction in radiation dose. Digital images were as accurate as the conventional films in excluding vesicoureteric reflux (VUR). The two methods correlated well in diagnosing and grading VUR.

Child↗