In this study, axisymmetric drop shape analysis-profile (ADSA-P) and atomic force microscopy (AFM) were employed to study the surface features of polypropylene (PP) and hydrosilylated polypropylene (SPP). Static and dynamic contact angles were measured using ADSA-P. Water permeability was calculated from the results of static contact angle measurements. To our knowledge, this is the first attempt to obtain permeability using ADSA-P. The water permeability and wettability of PP are greater than those of SPP. Surface free energy was calculated by the equation of state theory and other methods, and the influence of surface roughness on surface free energy was taken into consideration and incorporated into the calculation. Topographic images of the sample surfaces were obtained using AFM. Compared to PP, the SPP surface shows larger but smoother peaks. Calculated results show that SPP has a lower surface free energy than PP. The surfaces of both PP and SPP can be modeled as a homogeneous but rough surface.
The surface tension and adsorption kinetics of aqueous solutions of slightly volatile, organic amphiphiles are influenced by both liquid-and vapor-phase surfactant concentrations. Here we derive a new kinetic transfer equation, based on the classic Langmuir analysis, which can account for adsorption and desorption from both sides of the vapor/liquid interface during surface equilibration. The new transfer equation was tested against dynamic surface tension data from two normal alcohols (1-butanol and 1-hexanol) in aqueous solutions. The experimental data was collected at conditions where the dynamic surface tension is controlled by a combination liquid-and vapor-phase surfactant adsorption. The validity of the transfer equation was assessed based on its ability to model the experimental data accurately and generate suitable values for the kinetic rate constants. The theoretical predictions from the transfer equation fit well with the experimental data for both systems. However, variability was observed in the least-squares estimates of the rate constants. The variability is attributed to the limitations of empirical models that utilize adjustable fitting parameters to optimize the model predictions and the wide range of surfactant concentrations studied. Specific concentration regions were identified where the variability in the rate constants was minimal and, thus, where the model is most appropriate. The new transfer equation can be applied to volatile surfactant systems where the dynamic surface tension is influenced by surfactant adsorption and desorption from both sides of the vapor/liquid interface.
Self-consistent-field theory is used to reproduce the behavior of polymer surface tension with molecularweight for both lower and higher molecular-weight polymers. The change in behavior of the surface tension between these two regimes is shown to be due to the almost total exclusion of polymer from the nonpolymer bulk phase. The predicted two regime surface tension behavior with molecular-weight and the exclusion explanation are shown to be valid for a range of different polymer compressibilities. In this paper, we show that many approximations made in previous works [3][4][5][6] are unnecessary as the polymer surface tension can be calculated using full numerical selfconsistent-field theory (SCFT) with no approximations be yond the mean field. SCFT is an appropriate method to use to study polymer surface tension because although SCFT is a coarse-grained theory, it is microscopic in the sense that it includes all polymer configurational degrees of freedom, un like phenomenological density gradient theory, for example, [7][8][9]. Jones and Richards [10] point out that presently poly mer surface tension MW dependence is "explained" in terms of a mix of phenomenological density gradient theory for higher MW and an empirical formula for lower MW. This is a wholly unsatisfactory situation. We will show that SCFT spontaneously reproduces the expected experimental two re gime behavior of polymer surface tension, and allows us to explain why there is a change of behavior between low and high MW polymer surface tensions. Since an understanding of MW dependence of surface tension is an important ingre dient for the advancement of many industrial processes, these SCFT results represent an important step beyond pre vious theories.The SCFT formalism for polymer surface tension has been described by us in a previous presentation [11] where it was successfully used to predict qualitative surface tension trends as a function of temperature and pressure for a single polymer MW. There we used a parameter a = 0.1; a is the ratio of the volume of a solvent molecule to the volume of a polymer molecule. It is inversely proportional to the polymer MW. In the present work, we lower the value of a (increase the polymer MW) to investigate the behavior of surface ten sion as a function of MW. The free energy for a compressible polymer-solvent system iswhere ' s (r), ' p (r), and ' h (r) are the local volume fractions of solvent, polymer, and "holes," respectively, and w s (r), w p (r), and w h (r) are conjugate chemical potential fields. The function i(r) is a pressure field that enforces a constant total density, including the holes. Compressible systems with in homogeneous total densities are thus modeled in this incom pressible formalism through the presence or absence of va cancies (holes). This is a method introduced by Hong and Noolandi that reduces to the Sanchez-Lacombe equation of state in the limit of a homogeneous system [12]. Other equa tions of state can also be chosen within the SCFT formalism [13]. Q s and Q p are the part...
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