BENDING MODULI AND SPONTANEOUS CURVATURE .1. BILAYERS AND MONOLAYERS OF PURE AND MIXED NONIONIC SURFACTANTS

The mean and Gaussian bending elasticity moduli of monolayers and bilayers of nonionic surfactants are computed from the solution properties of the surfactant, without adjustable parameters. To that end, the grand potential OMEGA (the grand canonical characteristic function) is calculated as a function of the surface curvature-using a modification of the self-consistent field lattice model of Scheutjens and Fleer. The interfaces are formed by self-assembling of the surfactants. It is found that with increasing tail length of the surfactant, the bending modulus kc of a bilayer rises linearly, whereas the Gaussian bending modulus k(c)BAR shows a maximum. The addition of short linear alcohols considerably decreases k(c) and k(c)BAR, whereas the presence of long chain alcohols can increase the rigidity of the bilayer. The spontaneous curvature of a monolayer at an oil-water interface strongly depends on the concentration of the surfactant.