Confinement effects induced by a solubilized polymer on the micellar nematic-lamellar transition

Abstract

We studied the effect of polyethylene-oxide (PEO, molecular weight from ${10}^{5}$ to 4\ifmmode\times\else\texttimes\fi{}${10}^{6}$) dissolved in the micellar nematic (N) and lamellar (L) phases of the surfactant system cesium perfluoro-octanoate (CsPFO) water by microscopy and calorimetry. Replacement of water by PEO suppresses the lamellar phase above a critical concentration (${\mathit{w}}_{\mathit{c}}$) which depends on the molecular weight of the polymer by a power law. In a limited range below ${\mathit{w}}_{\mathit{c}}$ a reentrant nematic is observed. The N-L transitions become less sharp with increasing concentration. The observed effects are due to the disruption of the lamellar order by the polymer.