Aggregation of hydrophobically modified chitosan in solution and at the air-water interface

Abstract

Oleoyl-chitosans (O-chitosans), with three degrees of substitution (DS), were synthesized by reacting chitosan with oleoyl chloride. The chemical structures of these polymers were characterized by 1H NMR and FTIR. The results suggested the formation of an amide linkage between amino groups of chitosan and carboxyl groups of oleic acid. These O-chitosans exhibited poor solubility in aqueous acidic solution. The solubility of O-chitosans decreased as the DS values increased. The transmittance of O-chitosans (2 g/L) with DS 5%, 11%, 27% in 1% (v/v) HCl solution were 69.5%, 62.7%, 48.6%, respectively. These O-chitosans were not soluble at neutral or alkali pH. Formation of self-aggregation was observed using pyrene as a fluorescent probe in the O-chitosans aqueous solution. The increase of DS of O-chitosans resulted in significant decrease of critical aggregation concentration (CAC). The CAC of the O-chitosans with DS 5%, 11%, 27% were 79.43, 31.6, 10 mg/L, respectively. The surface tension of solution could be reduced slightly by all of the O-chitosans. The surface tension of O-chitosans solution decreased with the increase of DS values. © 2006 Wiley Periodicals, Inc.