Morphology and surface properties of blends of Eudragit RS with different poly(ethylene glycol)s.

The purpose of this study was to investigate the morphology and surface properties of blends of Eudragit RS, a hydrophobic polymer mainly used for film coating, and poly(ethylene glycol)s (PEG), amphiphilic polymers used as softeners for films. Blends of Eudragit RS and PEGs were prepared as films using the casting technique from methylene chloride. The morphology of those films was evaluated by scanning electron microscopy before and after treatment with water. Sessile drop technique was used to measure solid/liquid contact angles in order to calculate surface free-energy parameters and to investigate phase separation using the Cassie-Baxter approach. Films containing 20, 40, 50, and 60% PEG 3400 and PEG 6000 appeared morphologically unchanged after treatment with water; no phase separation was noticed. Films containing PEG 14,000 after treatment with water showed the presence of a solid emulsion in the range 40, 50, and 60% PEG; a multiple solid emulsion was shown for films containing 60% PEG 20,000. The presence of two-phase systems was shown using contact angle measurements and results were in agreement with microscopic analysis. Calculated surface free-energy parameters indicated that PEG 3400 and 20,000 in a critical concentration of 10% can modify surface parameters of Eudragit RS: for PEG 6000 and 14,000 this critical concentration was found to be between 10 and 20%. The surface polarity of PEG 3400, 6000, and 14,000 was found to be drastically reduced upon addition of 5% Eudragit RS; spontaneous surface layering of Eudragit RS could be reasonably hypothesized for PEG 3400. This study revealed that surface parameters of a polymer can be modified in the presence of a relatively small amount of a second material.

Investigation of surface properties of some polymers by a thermodynamic and mechanical approach: possibility of predicting mucoadhesion and biocompatibility.

Mucoadhesive properties of several polymers, such as sodium alginate, hydroxypropylmethyl cellulose, scleroglucan, xanthan gum, polyacrylic acid (Carbopol), and poly co-(methyl vinyl ether-maleic anhydride) (Gantrez), have been investigated by comparing a thermodynamical and a mechanical approach. Surface properties of polymers in the dry state have been studied by contact angle measurements and thermodynamical parameters derived by using different equations. This tensile adhesive strength of polymers in hydration conditions was measured by a modified DuNoy tensiometer. Comparison of the two different approaches has allowed us to conclude that thermodynamical consideration on surface energy can be used to evaluate mucoadhesive properties of materials. Data obtained with the two methods yielded a good linear correlation. Calculation of surface free energy of the considered materials also allowed a prediction of the water-polymer interface free energy: biocompatibility, defined according to the minimal interfacial free energy concept, could consequently be evaluated.

Micellar effects on the basic hydrolysis of indomethacin and related compounds.

The kinetics of hydrolysis of indomethacin and related compounds was studied in an alkaline medium at 25 degrees C in the presence of anionic (sodium dodecyl sulfate) and cationic (hexadecyltrimethylammonium bromide) surfactants. The rate-surfactant profiles for rate inhibition in the presence of sodium dodecyl sulfate and rate enhancement in the presence of hexadecyltrimethylammonium bromide were analyzed in terms of the current theory of micellar effects.

Kinetic study of the hydrolysis of 1-(4-nitrophenyl)-3-methyltriazene in aqueous solution and in the presence of surfactants.

The hydrolysis of 1-(4-nitrophenyl)-3-methyltriazene in aqueous solution has been studied over a pH range of 3-14. The effect of the anionic and cationic surfactants (sodium lauryl sulfate and hexadecyltrimethylammonium bromide) on the rate of hydrolysis was investigated. The quaternary ammonium bromide causes a rate decrease at all pH values studied, while sodium lauryl sulfate enhances the acid-catalyzed hydrolysis and decreases the observed rate constants in the pH-independent region. The results are discussed in terms of the current theory of micellar effects.