MEMBRANE FLEXIBILITY IN A DILUTE LAMELLAR PHASE - VARIATION WITH TEMPERATURE AND COMPOSITION

The dilute regime of the lamellar phase in the SDS/pentanol/water/dode cane system is investigated by H-2 and Na-23 NMR. From the reduction o f the quadrupole splitting on dilution, we determine-the temperature a nd composition variation in the bilayer bending rigidity kappa. We fin d an essentially temperature independent kappa = (9 +/- 1) x 10(-21) J in the range 0-60 degrees C. The variation in kappa with the bilayer composition displays an increasing rigidity on removing pentanol and w ater from,the bilayer. The composition and temperature variation in ka ppa correlate with the extension of the lamellar phase in the phase di agram The predictions of recent theories for the molecular interaction s contributing to kappa-mainly the hydrocarbon tail conformational ent ropy and the electrostatic interactions in the polar region-can accoun t for the experimental results.