The miscibility of poly( d, l-lactide-co-glycolide) with amphiphilic molecules and the interaction of their mixtures with DNA at air/water interface

Abstract

The miscibility of poly( d, l-lactide-co-glycolide) (PLG) with three amphiphilic molecules and the interaction of the PLG/surfactant mixtures with DNA at air/water interface are investigated by π-A isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) techniques. The π-A isotherms of the PLG mixtures with cationic C 12AzoC 6PyBr, and C 12AzoC 6N(CH 3) 3Br, are quite different from the π-A isotherm of pure PLG on water subphase. In contrast to the case, the π-A isotherm of PLG mixed with nonionic C 12AzoC 6OPy is almost identical to the pure PLG except some increasing of molecular area. Similar phenomena are observed on DNA subphase. The in situ BAM and ex situ AFM observations demonstrate that the dispersion of PLG at air/water interface becomes good when it mixes with the two cationic surfactants, whereas quite poor due to the phase separation when it mixes with the nonionic amphiphilic molecule. Based on these results we conclude that the cationic surfactants can affect the conformation change of PLG at air/water interface and figure a well miscibility with polymer whereas the nonionic amphiphilic molecule presents poor miscibility. In addition, the even mixing of the PLG and the cationic surfactants is favorable for the adsorption to DNA more effectively.