Bending moduli of a nonadsorbing-polymer-containing lyotropic lamellar phase: An experimental study

We investigate the effect of the incorporation of a neutral water-soluble nonadsorbing polymer polyvinylpyrrolidone (PVP) on the bilayer bending moduli kappa and <(kappa)over bar> of the lamellar phase L-alpha composed of cetylpiridinium-chloride (CPCL)/hexanol/H2O. The mean bending modulus kappa is obtained from the measurement of quadrupolar splittings of perdeuterated hexanol by deuterium solid state NMR. It is found that kappa is insensitive to the amount of polymer in the lamellar phase, in agreement with the theoretical predictions. Observations with the polarizing microscope of topological defects in the lamellar phase allow a qualitative study of the Gaussian bending modulus <(kappa)over bar>. Addition of a small amount of polymer in the lamellar phase induces a large proliferation of focal conic domains of second species (positive Gaussian curvature). Cryo-TEM confirms that the polymer drastically modify the texture of the lamellar phase. These results indicate clearly that the presence of the nonadsorbing polymer strongly decreases <(kappa)over bar>, in contradiction with theoretical predictions.