Structural investigation of water/lecithin/cyclohexnae microemulsions by FT-IR spectroscopy

FT-IR spectra of water/lecithin/deuterated cyclohexane microemulsions as a function of water/lecithin molar ratio R (R = [water]/[lecithin]) at various volume fractions (O) of the micellar phase have been recorded at 25 degrees C. After elimination of the small spectral contributions due to deuterated cyclohexane and normalization, the shape of the C-H stretching band due to lecithin has been found dependent upon R and 0 whereas that of the O-H stretching band has been found dependent only upon R. The change in shape of the C-H band was interpreted in terms of a modification of the lecithin alkyl chain packing order. The analysis of the O-H band provides evidence that the hydroxylic groups of lecithin form strong hydrogen bonds whereas the added water is confined in bulk-like water domains. (C) 1995 Academic Press, Inc.