Albert Joseph Post

Solubility limits and phase diagrams for fatty acids in anionic (SLES) and zwitterionic (CAPB) micellar surfactant solutions

The limiting solubility of fatty acids in micellar solutions of the anionic surfactant sodium laurylethersulfate (SLES) and the zwitterionic surfactant cocamidopropyl betaine (CAPB) is experimentally determined. Saturated straight-chain fatty acids with n=10, 12, 14, 16, and 18 carbon atoms were investigated at working temperatures of 25, 30, 35, and 40°C. The rise of the fatty acid molar fraction in the micelles is accompanied by an increase in the equilibrium concentration of acid monomers in the aqueous phase. Theoretically, the solubility limit is explained with the precipitation of fatty acid crystallites when the monomer concentration reaches the solubility limit of the acid in pure water. In agreement with theory, the experiment shows that the solubility limit is proportional to the surfactant concentration. For ideal mixtures, the plot of the log of solubility limit vs. the chainlength, n, must be a straight line, which is fulfilled for n=14, 16, and 18. For the fatty acids of shorter chains, n=10 and 12, a deviation from linearity is observed, which is interpreted as non-ideal mixing due to a mismatch between the chainlengths of the surfactant and acid. The data analysis yields the solubilization energy and the interaction parameter for the fatty acid molecules in surfactant micelles. By using the determined parameter values, phase diagrams of the investigated mixed solutions are constructed. The four inter-domain boundary lines intersect in a quadruple point, whose coordinates have been determined. The results can be applied for the interpretation and prediction of the solubility, and phase behavior of medium- and long-chain fatty acids and other amphiphiles that are solubilizable in micellar surfactant solutions, as well as for determining the critical micellization concentration (CMC) of the respective mixed solution.

Hard particles in narrow pores. Transfer-matrix solution and the periodic narrow box

We derive an exact transfer‐matrix solution for an infinite system of hard particles confined in a manner that precludes non‐nearest‐neighbor interactions. The solution takes the form of a functional eigenvalue equation which may be solved numerically for the thermodynamic and structural properties of the confined fluid. Barker [Aust. J. Phys. 15, 127 (1962)] originally derived this solution by a different route, and we apply it in a number of new ways. We present the first calculations based on this solution for systems of hard disks between parallel lines, and for hard spheres in a cylindrical pore. Through comparison with Monte Carlo simulations, we examine the range of validity of the solution when applied to systems in which non‐nearest‐neighbor interactions may occur. We find that the transfer‐matrix approach provides acceptable results for pore widths up to two particle diameters, and that the approximation becomes quite poor as the pore is widened further, particularly at high density. This soluti...

Solute partitioning between a micropore and a bulk solution: A linear density functional approach

Abstract The effect of solute concentration on the partitioning of solute species between regular geometric pores and a bulk phase is investigated with a linear density functional theory. The theory requires specification of the pore geometry and the direct correlation function c ( r ) of the bulk fluid. We consider the simple hard-sphere solute, and employ the analytic Percus—Yevick c ( r ) for the hard-sphere fluid in these calculations. Density distributions and partition coefficients are reported for the hard-sphere solute in slit-shaped and cylindrical pores.

Statistical thermodynamics of a fluid adsorbed onto a spherical surface. II. Scaled particle theory

Scaled particle theory is applied to the prediction of the thermodynamic properties of a system of identical hard spheres adsorbed onto another sphere of different diameter. The finite nature of the system requires modification of the usual boundary conditions on the contact correlation function. The calculated activities of the adsorbate are in good agreement with Monte Carlo simulation results and with exact values for systems of few particles.

Soap Bar Performance Evaluation Methods

Abstract: This chapter surveys the assessment procedures that are practiced in soap bar factories or in development laboratories around the world to ensure that manufacturing standards are met and, ultimately, that consumers will be satisfied with the cleansing bars they purchase. In principle, the appraisal methods include analytical chemistry tests to evaluate raw materials and finished product, methods of materials science to assess product structure, and straightforward tests of the consumer-observable attributes like lather, wet-bar feel, and wear rate, either in the laboratory or by consumer panel assessment. The main focus in this chapter concerns the finished product, although characterization (rheology) of partially manufactured soap is also considered.