PART I: A STUDY OF THE ADSORPTION OF POLYMERS ONTO POLYMETHYLMETHACRYLATE. PART II: DETERMINATION OF THE ENERGY CHANGE ASSOCIATED WITH THE DISSOLUTION OF A SOLID
Abstract
Part I. An apparatus consisting of two polymethylmethacrylate plates was used to determine the adhesional force created by placing a drop of a polymer solution between the two plates and measuring the force required to pull the two plates apart. The force obtained experimentally was compared with the theoretical value of the force calculated from an equation based on the Young and LaPlace equation. The agreement between the two values indicated that the force is a function of the contact angle and the surface tension of the liquid if the distance between the two plates is held constant. The equilibrium adsorption and rate of adsorption of polyvinyl alcohol, methylcellulose and hydroxypropyl methylcellulose from aqueous solutions onto polymethylmethacrylate powder were studied. Langmuir type adsorption isotherms were observed in all three cases. The maximum amount of polymer adsobed per gram of polymethylmethacrylate followed the order methylcellulose > polyvinyl alcohol (GREATERTHEQ) hydroxypropyl methylcellulose. The rate of adsorption, however, followed the order polyvinyl alcohol (GREATERTHEQ)(, )hydroxypropyl methylcellulose > methylcellulose. The apparent difference in the order of the extent and rate of adsorption was related to the proposed configuration of the adsorbed polymer molecules on the polymethylmethacrylate surface and the flexibility of the adsorbed molecules. Part II. The dissolution of a solid was considered as a consecutive process consisting of (1) wetting of the solid by the solvent, (2) solvation of the solid at the interface, and (3) transfer of the solvated solid into the bulk of the solution. The energy changes involved in each step were studied for the dissolution of m-acetotoluidide in hexane and in heptane. An energy diagram was constructed according to the proposed mechanism of dissolution. The heats of dissolution determined from the energy diagram agreed well with those obtained experimentally. A rate expression for dissolution was proposed based on the assumption that dissolution is interfacially controlled. A bimolecular interaction between solid and solvent was presumed. The surface area of the solid m-acetotoluidide was calculated from the experimental data and the proposed rate equation and agreed very well with that calculated from molecular structure information. Simulation of solid-liquid dissolution by liquid-liquid dispersion studies showed that an effective interfacial concentration, approximately one-tenth of the saturation solubility, existed at the interface of solid and the solvent. It was apparent from these studies that the dissolution at m-acetotoluidide in hexane and heptane was an interfacially controlled process.
Degree
Ph.D.
Subject Area
Pharmaceuticals
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