Study On The Diffusion Properties Of Model Drug Molecules In Poly (Vinyl-alcohol) Aqueous Solution

The dissolution and diffusion of the effective components of drugs are important for drug's bioavailability and medicine efficiency. In order to get more information on drug control release, the effect of carrier on the diffusion of some drug model compounds have been studied. Poly (vinyl-alcohol) (PVA) hydrogel was chosen as a drug carrier model. Drug motion in the network of hydrogels is simulated by a motion in PVA aqueous solution. The volumetric and viscous properties of some model drug molecules in PVA aqueous solution have been measured experimentally. The effect of PVA's concentration on the drug diffusion was discussed. This work include following sections.1. Hexanedioic acid was chosen as a hydrophobic model drug molecule. Viscosity and density for the ternary solution of hexanedioic acid dissolves in poly (vinyl alcohol) (PVA) + water at the temperatures from 293.15 to 313.15 K are reported. A liner relation between the viscosity and the concentration of hexanedioic acid is observed, and the viscosity B-coefficient is extracted. The activation free energy for the viscous flow of the solution is found from the slope of the linear equation by using the Eyring-Feakins equation. By investigating the concentration effect, we have found that with the increase of PVA concentration, the activation free energy of viscous flow first decreases, and then increases. This implies that PVA promotes the diffusion of hexanedioic acid at lower concentration, but demotes the diffusion of hexanedioic acid at higher concentration.2. Viscosity, density and electric conductance for the solution of sodium salicylate dissolves in poly (vinyl alcohol) aqueous solution at the temperatures 293.15 to 313.15 K are reported. The Jones-Dole equation was used to correlate the viscosity and the concentration of sodium salicylate. Conductivity data was used to obtain the molar conductance at infinite dilution, through them, the contribution of ion interaction to viscosity is considered. The viscous B-coefficient, which account for the solute solvent interaction, is extracted from experimental data. By using Eyring's transition state treatment, the activation free energy of the viscous flow is evaluated. By analyzing the effect of PVA's concentration on activation parameters, the diffusivity of sodium salicylate in aqueous PVA solution can be observed. The result indicates that PVA demotes the diffusion and dissolution of sodium salicylate in water.3. The viscosities and densities of ternary solution of sodium nicotinic acid + PVA + water were measured. And the system's activation parameters of viscous flow were evaluated. Nicotinic acid is lipophilic solute. It diffuses in water with a positive activation free energyΔμm3≠, but the value is very small. If PVA is added, the solute molar activation enthalpyΔHm3≠and molar activation entropyΔSm3≠will increase sharply. It indicates that PVA can make the diffusion of nicotinic acid easier in aqueous solution.