Aqueous block copolymer-surfactant mixtures-Surface tension, DLS and viscosity measurements and their utility in solubilization of hydrophobic drug and its controlled release

The effects of sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium bromide (DTAB) and poly-oxyethylene (10) isooctyl phenyl ether (TX-100) as additives on the association characteristics of an amphiphilic tri-block copolymer P105 (E(37)P(56)E(37)) were monitored by surface tension, dynamic light scattering and viscosity measurements at 303.15 and 313.15 K in water as well as in 200 mM sodium chloride aqueous solutions. The successive addition of surfactants resulted not only in the increase of critical micelle concentration (CMC) of the copolymer and also in CMC/C(20) values indicating that the adsorption tendency of the copolymer-surfactant complexes at water/air interface is more than the association in the bulk. The experimental CMC data of binary mixtures were analyzed using regular solution theory to calculate the interaction parameter. The mixtures exhibited synergistic interaction behavior. The apparent hydrodynamic radius of copolymer micelles decreased drastically by the addition of surfactants and this destabilization effect has been attributed to the shift of copolymer micelle <-> unimer equilibrium in favor of latter. Dexamethasone, a drug poorly soluble in aqueous media was solubilized into individual copolymer or copolymer-surfactants solutions followed by their loading onto agar agar hydrogels for its immobilization and dispersion. The drug release profiles were established and drug diffusion coefficients were calculated. (C) 2011 Elsevier B.V. All rights reserved.