Effect of Charge on the Mechanical Properties of Surfactant Bilayers
Robert David Bradbury, Michihiro Nagao
The viscoelastic properties of surfactant bilayers have been measured over a range of surface charge densities, for a system with a low ionic strength, using small-angle neutron scattering and neutron spin echo (NSE) spectroscopy. An increase in the surface charge density leads to greater structural ordering and a stiffening of the membrane, which are consistent with classical theory of charge effects on membranes. The membrane viscosity was also found to increase with charge density, which we can quantify by application of a recent theoretical prediction [Bingham et al,., Europhys. Lett., 111, 18004 (2015).] to the present NSE results on the relaxation rate of the membrane thickness fluctuations. This increase in membrane viscosity can be postulated as being the stronger interaction among the charged headgroups, promoting greater intra-membrane friction. Furthermore, the amplitude of the thickness fluctuations is observed to remain almost constant with variation in surface charge density which indicates almost constant values for the bilayer compressibility modulus. The present result verifies experimentally that the time scale and amplitude of membrane thickness fluctuations are controlled by different viscoelastic properties of the membrane. This work demonstrates that charge stabilization of lamellar bilayers is not merely affected by intermembrane interactions and structural ordering but the intramembrane dynamics also have a significant contribution.
and Nagao, M.
Effect of Charge on the Mechanical Properties of Surfactant Bilayers, Soft Matter, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=920319
(Accessed December 8, 2023)