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

Abstract

We investigate the effect of the incorporation of a neutral water-soluble nonadsorbing polymer polyvinylpyrrolidone (PVP) on the bilayer bending moduli \ensuremath{\kappa} and $\overline{\ensuremath{\kappa}}$ of the lamellar phase ${L}_{\ensuremath{\alpha}}$ composed of cetylpiridiniumchloride ${(\mathrm{CPCL})/\mathrm{h}\mathrm{e}\mathrm{x}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{l}/\mathrm{H}}_{2}\mathrm{O}.$ The mean bending modulus \ensuremath{\kappa} is obtained from the measurement of quadrupolar splittings of perdeuterated hexanol by deuterium solid state NMR. It is found that \ensuremath{\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 $\overline{\ensuremath{\kappa}}.$ 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 $\overline{\ensuremath{\kappa}},$ in contradiction with theoretical predictions.