Time Dependence Of Surface Tension Research Articles

Influence of Gas Sorption on Surface Tension of Liquid Crystalline Substances:—Influence of CO2 on Time-dependence of Surface Tension

As one part of the experimental studies on the influence of gas sorption on the surface tension of liquid crystalline substances (LCs), this paper reports on the CO2 sorption in low molecular LC MBBA (4-methoxybenzylidene-4′-n-butylaniline) and thus caused the time-dependence of surface tension. The experiments have been performed in the CO2 atmosphere over the temperature range which covered the phase transitions of MBBA, and at pressures up to 15 bar. Separately, the surface tension measurements and the gas sorption measurements have been carried out under the same experimental conditions, by using a computer-aided measuring setup based on the pendant drop method and a high pressure electromicrobalance, respectively. The paper provides experimental evidences for our previous suggestion, that the unusual time-dependence of surface tension of the freshly formed LC surfaces may be mainly attributed to the gas sorption processes, by comparing the results from above different measurements. The paper also reports the phase transition behaviors of MBBA as a function of the sorbed gas concentration, and the reversibility of the CO2 sorption.

Polymer−Surfactant Interaction As Revealed by the Time Dependence of Surface Tension. The EHEC/SDS/Water System

Adsorption properties at an air/water interface and interaction between a nonionic polymer ethyl(hydroxyethyl) cellulose (EHEC) and sodium dodecyl sulfate (SDS) were studied by pendant drop tensiometry, enhanced by video-image digitization and computerized data handling. Three studies were performed over the concentration range 0−19 mM SDS with fixed concentrations of EHEC: 0.2% w/w, 12 ppm, and 2 ppm. Particular emphasis was placed on the investigation of the dynamics of surface tension in the presence and absence of SDS. This study demonstrates that the onset of complex (cluster) formation can be identified by surface-tension measurements even when a very hydrophobic polymer such as EHEC is part of the complex. Considerable synergism in surface activity is observed in the EHEC−SDS mixtures. Below the critical aggregation concentration (cac), the degree of surface-tension reduction was found to depend on the bulk concentration of surfactant molecules, as well as the number of polymer segments in actual contact with the surface at the time of measurement. At and above cac an extraordinary acceleration of polymer adsorption was observed following the addition of SDS. Considerable evidence regarding the presence of a polymer/surfactant complex at the air/water interface is discussed in the paper. The dynamics of surface tension, at and above cac, are explained in terms of the observations that charged clusters are bound along the polymer chain and cause an appreciable change of the polymer conformation. In agreement with the results, polyelectrolytic properties of the EHEC/DS- complex cause the complex to become firmly adsorbed to the air/water interface. The adsorption kinetics strongly suggested a progressive ordering of the polymer/surfactant aggregates within the monolayer, based on observations of the surface film after aging (17 h). The findings can be of practical use in applications where quick wetting and absorption are required, e.g., in injected, spread, or inhaled drug formulations.

Dynamic Surface Tension of Aqueous Polymer Solutions, I: Ethyl(hydroxyethyl)cellulose (BERMOCOLL cst-103)

The dynamic surface tension of aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) was measured using the pendant-drop method and digital-image analysis. The EHEC concentrations studied ranged from 3.2·10−5to 0.28% w/w. The time dependence of surface tension was analyzed using a diffusion-kinetics-controlled theory where the adsorption kinetics depended on the fraction of the total surface coverage. For EHEC concentrations ≤10−3% w/w, the isotherms showing surface tension vs log time follow a sigmoidal pattern. Three consecutive kinetic regions exist: the induction region, the surface-coverage region, and the mesophase region. The process of the adsorption of polymer segments is described in terms of relaxation times and the critical points of time, at the onset and at the end of the region of surface coverage. An extremely slow surface equilibration in the mesophase region indicates a progressive ordering of the polymer segments within the surface layer.

Surface active properties at the air–water interface of β-casein and its fragments derived by plasmin proteolysis

Summaryβ-Casein, was enzymically modified by incubation with plasmin to yield γ-caseins and proteose peptones. Whole γ-, γ1-, γ2/γ3-caseins and whole proteose peptone (pp) were isolated from the hydrolysate mixture. The time dependence of surface tension at the air-water interface of solutions of β-casein and its plasmin derived fragments, at concentrations of 10−1 to 10−4% (w/v) protein, pH 7.0, was determined, at 25 °C, using a drop volume apparatus. The ranking of the proteins with respect to rate of reduction of surface tension, during the first rate determining step, at 10-2% (w/v) protein, was γ2/γ3 ≫ pp > whole γ- > γ1- > β-casein. The ranking of the proteins with respect to surface pressures attained after 40 min (π40) was concentration dependent. γ2/γ3-Caseins were found to be very surface active, decreasing surface tension rapidly and giving a high π40. γ1 Casein decreased surface activity somewhat faster than β-casein, but generally reached a lower π40. Whole γ-casein reflected the properties of both γ1 and γ2/γ3-caseins. Proteose peptone was found to decrease surface tension rapidly during the initial rate determining step; it gave a relatively high π40 at a bulk phase concentration of 10−3% (w/v) protein, but, it was the least surface active protein at 10−1 and 10−2% (w/v) protein.

Some limitations in the interpretation of the time dependence of surface tension measured by the maximum bubble pressure method

Some limitations in the interpretation of the time dependence of surface tension measured by the maximum bubble pressure method

The surface tension of poly(acrylic acid) in sodium chloride solutions

Surface tension of polyacrylic acid (PAA) in sodium chloride solutions was measured at various ionic strengths. Surface activity of PAA solutions increases and shows a large time dependence with increasing salt concentration. Surface activity and time dependence of surface tension is explained by the changing flexibility of PAA chains.

Strain Gauge Electromicrobalance for Surface Tension Measurement

Abstract Two types of apparatus using an unbonded strain gauge of a cantilever type for the measurement of surface tension were constructed. One is a sensitive electromicrobalance equipped with an extended arm attached to the cantilever of the strain gauge. The apparatus proved suitable as a surface balance in a completely closed system. By this apparatus, the measurement of surface tension ranging from 0 to 74 dyn/cm is possible with the accuracy of ±0.10 dyn/cm. The other type was constructed by connecting the sensing lever of strain gauge to the arm of a torsion balance with a strip of phosphor bronze. This device together with a counterbalance on the opposite side of the arm also proved to be useful as a tensiometer. Accuracy of this apparatus was a little better than that of the extended arm type balance, although a larger space is required. Both apparatus are inexpensive, easy to construct and simple to operate, and are suitable for the self-recording of time dependence of surface tension or weight change in general with sufficient accuracy. Equations proposed for the time dependence of surface tension of surfactant solution were checked by using the strain gauge tensiometer of the extended arm type.

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. IV. Direct Measurement of Adsorption of Tritiated Nonionic Surfactant

Abstract The radio- and surface-chemically pure nonionic surfactant, C10H21(CHT)2O(C2H4O)6H, was synthesized, and surface tension and adsorbed amount of its aqueous solution were measured directly at the air-solution interface at 30°C. Surface tension was measured by the drop-volume and Wilhelmy plate methods, while adsorbed amount was measured by the radiotracer method. The adsorption isotherm showed saturation values of 2.73×10−10 mol/cm2 above the concentration of about 1/5 of the critical micelle concentration. The observed amount of adsorption was in good agreement with the values calculated from surface tension data measured by the Wilhelmy plate method by applying the Gibbs adsorption isotherm for a single solute system. The time dependence of surface tension of surfactant solution was further discussed, and the inherent time dependence was shown for pure surfactant solution.