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PubMed2003

Foam and wetting films: electrostatic and steric stabilization.

Foam films and wetting films on quartz, obtained from aqueous solutions of two different surfactants [cetyltrimethylammonium bromide (CTAB) and PEO-PPO-PEO triblock copolymer (F108)] with NaCl as a background electrolyte, are considered as convenient models to compare the properties of symmetric (free thin liquid films) and asymmetric (thin liquid films on solid substrate) films with the same air/solution interface. Microinterferometric methodology of assessment of foam and wetting films is used to allow precise determination of the film thickness. In the case of CTAB films, experimental data for the potential phi(0) of the diffuse electric layer at the solution/air interface and the potential phi(1) at the solution/quartz interface are used to analyze the stability of the films studied. A conclusion drawn is that electrostatic interaction forces stabilize both kinds of films studied. It is shown that with increasing CTAB concentration a charge reversal occurs at both the solution/air and solution/quartz interfaces that determines the stability/instability of the foam and wetting films. Concentration ranges where both types of films produce stable (equilibrium) films are found. There are also concentration ranges where the films either rupture or are metastable (quasi-equilibrium). The CTAB concentration ranges, which provide formation of unstable (rupturing and metastable) and stable films, are different for symmetric (foam) and asymmetric (wetting) thin liquid films. It is only at high CTAB concentrations (>2 x 10(-4) mol dm(-3)) that both cases render formation of stable equilibrium films. In the case of F108 films, the comparison of foam films and wetting films on quartz indicates film stability that is either electrostatic or steric in origin. On the basis of the effect of electrolyte concentration on film thickness, the transition from electrostatic to steric stabilization is demonstrated for both kinds of films. The critical electrolyte concentration at which this transition occurs is determined. Foam films are found to be always stable (equilibrium). Formation of either unstable (rupturing and metastable) or stable (equilibrium) wetting films on quartz is established depending on the solution composition. The effects are similar for both hydrophilic and hydrophobic quartz surfaces. The results obtained show certain similarity between foam and wetting films. In both cases, electrostatic forces below the critical electrolyte concentration, and above it steric forces govern film stability. Some specific properties of the wetting films are induced by the asymmetric boundary conditions as distinct from symmetric foam films.

Journal Article↗
PubMedDate not supplied

Effect of Fuji pressure sensitive film on actual contact characteristics of artificial tibiofemoral joint.

OBJECTIVE: To investigate the effect of inserting a Fuji pressure sensitive film into an artificial tibiofemoral joint on the actual contact mechanics. DESIGN: The experimental measurement and finite element analysis were used.Background. Although Fuji pressure sensitive film was widespread used for measuring the contact characteristics of artificial joint, how this measurement approaches actual contact characteristics has not yet been studied extensively. METHOD: Two three-dimensional finite element models of an artificial tibiofemoral joint were constructed. The with-film-model was used to mimic the experimental setup and was verified by comparing the contact area and pressure on the simulated film calculated from finite element analysis to the measured one from the Fuji film (ultra-super low and medium grades) in the experimental test. Then the with-film-model was modified to the without-film-model in which the simulated film was removed. The contact characteristics on the film calculated from the with-film-model were represented to the measured one and the contact characteristics on the tibial component calculated from the without-film-model were represented to the actual one. The measured and actual contact characteristics were studied to investigate the effects of Fuji film on the actual contact characteristics in the tibiofemoral joint of knee prosthesis. RESULTS: The contact characteristics calculated from with-film-model was reasonable agreement with measured one by Fuji film in the experimental test. The maximum difference is 13% in maximum contact pressure under a load of 3000 N. The maximum difference of contact area and pressure between the model simulating actual contact circumstance and the model with inserting a Fuji film between contacting surface are 2.4% and 14% respectively. CONCLUSION: This study revealed that contact area and pressure of the tibiofemoral joint of knee prosthesis measured by Fuji pressure sensitive film could be simulated by finite element analysis. The measurement of contact area in the artificial joint by using ultra-super low grade Fuji film is overestimated its actual contact area by 1.2-2.4%, but the measurement of contact pressure by using medium grade Fuji film is underestimated its actual contact pressure by 8-14%. RELEVANCE: This study revealed that the ultra-super low grade Fuji film is a reliable sensor to measure the contact area and the medium grade film would underestimate its actual contact pressure in the artificial tibiofemoral joint. This finding can provide a better understanding of the reliability of Fuji film to measure the contact characteristics of artificial joint in the experimental test.

Computer-Aided Design↗
PubMed2006

Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions.

In order to understand the mechanisms behind the undesired aging of films based on vital wheat gluten plasticized with glycerol, films cast from water/ethanol solutions were investigated. The effect of pH was studied by casting from solutions at pH 4 and pH 11. The films were aged for 120 days at 50% relative humidity and 23 degrees C, and the tensile properties and oxygen and water vapor permeabilities were measured as a function of aging time. The changes in the protein structure were determined by infrared spectroscopy and size-exclusion and reverse-phase high-performance liquid chromatography, and the film structure was revealed by optical and scanning electron microscopy. The pH 11 film was mechanically more stable with time than the pH 4 film, the latter being initially very ductile but turning brittle toward the end of the aging period. The protein solubility and infrared spectroscopy measurements indicated that the protein structure of the pH 4 film was initially significantly less polymerized/aggregated than that of the pH 11 film. The polymerization of the pH 4 film increased during storage but it did not reach the degree of aggregation of the pH 11 film. Reverse-phase chromatography indicated that the pH 11 films were to some extent deamidated and that this increased with aging. At the same time a large fraction of the aged pH 11 film was unaffected by reducing agents, suggesting that a time-induced isopeptide cross-linking had occurred. This isopeptide formation did not, however, change the overall degree of aggregation and consequently the mechanical properties of the film. During aging, the pH 4 films lost more mass than the pH 11 films mainly due to migration of glycerol but also due to some loss of volatile mass. Scanning electron and optical microscopy showed that the pH 11 film was more uniform in thickness and that the film structure was more homogeneous than that of the pH 4 film. The oxygen permeability was also lower for the pH 11 film. The fact that the pH 4 film experienced a larger and more rapid change in its mechanical properties with time than the pH 11 film, as a consequence of a greater loss of plasticizer, was presumably due to its initial lower degree of protein aggregation/polymerization. Consequently, the cross-link density achieved at pH 4 was too low to effectively retain volatiles and glycerol within the matrix.

Chromatography, High Pressure Liquid↗
PubMed1983

Structure analysis of sputter-coated and ion-beam sputter-coated films: a comparative study.

Gold, platinum and tungsten films were deposited by low energy input (7 mA, 450 V), or high deposition rate (80 mA, 1500 V), diode sputter coating and by ion beam sputter coating. Film structures on Formvar coated grids and on the surface of coated erythrocytes, resin embedded, sectioned, and recorded at high magnification in a TEM were compared using computer-assisted measurements and analysis of film thickness and grain size. The average grain size of the thinnest gold and platinum films was relatively independent of the mode or rate of deposition but as the film thickness increased, significant differences in grain size and film structure were observed. Thick platinum or gold films deposited by low energy input sputter coating contained large grain size and electron transparent cracks; however, more even films with narrower cracks but larger grain size were produced at high deposition rates. Ion beam sputter coated gold had relatively large grain size in 10 nm thick films, but beyond this thickness the grains coalesced to form a continuous film. Platinum films deposited by ion beam sputter coating were even and free of electron transparent cracks and had a very small grain size (1-2 nm), which was relatively independent of the film thickness. Tungsten deposition either by low energy input or ion beam sputter coating resulted in fine grained even films which were free of electron transparent cracks. Such films remained granular in substructure and had a grain size of about 1 nm which was relatively independent of film thickness. Tungsten films produced at high deposition rates were of poorer quality. We conclude that thick diode sputter coated platinum and gold films are best deposited at high deposition rates provided the specimens are not heat sensitive, the improvement in film structure being more significant than the slight increase in grain size. Thick diode or ion beam sputter coated gold films should be suitable for low resolution SEM, and thin discontinuous gold films for medium resolution SEM. Diode sputter coated platinum should be suitable for medium resolution SEM and ion beam sputter coated platinum for medium and some high resolution SEM. 1-5 nm thick tungsten films, deposited by low energy input or ion beam sputter coating should be suitable for high resolution SEM, particularly where contrast is of less importance than resolution.

Animals↗