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

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 H-1 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 C-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 C-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. (c) 2006 Wiley Periodicals, Inc.