Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Interlayer Distance Dependence of Thickness Fluctuations in a Swollen Lamellar Phase

Published

Author(s)

Michihiro Nagao, Sukhum Chawang, Takumi Hawa

Abstract

Thickness fluctuations in a swollen lamellar structure, composed of a non-ionic surfactant, water and oil has been characterized by means of small-angle neutron scattering (SANS) and neutron spin echo (NSE) experiments, and coarse-grained molecular dynamics (CGMD) simulation. The static and dynamic structures of the membranes are measured as a function of the interlayer distance (membrane thickness), dm. The oil to surfactant volume ratio is changed at a constant surfactant volume fraction, so that dm is changed while maintaining the inter-lamellar repeat distance constant in the experiments. Two relaxation modes are observed from the NSE data, which are the bending motion and the thickness fluctuations. The bending rigidity of the membranes is a function of the membrane thickness. At low dm the membranes become rigid due to the enhancement of the thickness fluctuations, while at large dm the membranes tend to be flexible because of the decrease in the synchronization between the two interface layers. The thickness fluctuations are measured by NSE as an excess dynamics from the bending motion around the length scales of the membrane thickness, and a similar excess dynamics is observed in the CGMD simulation. Moreover, a method to estimate the thickness fluctuation amplitude in the experiment is proposed, and the validity of the method is clarified by the simulation. An excellent agreement between the experiments and the simulations shows that the amplitude linearly increases with dm. The present result shows the importance of the intra-membrane dynamics to determine the elastic properties of membranes, and the feasibility of the measurement of thickness fluctuations in surfactant membranes using NSE experiments and MD simulations.
Citation
Soft Matter
Volume
7

Keywords

surfactant, thickness fluctuations, dynamics, membrane, lamellar

Citation

Nagao, M. , Chawang, S. and Hawa, T. (2011), Interlayer Distance Dependence of Thickness Fluctuations in a Swollen Lamellar Phase, Soft Matter, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=908318 (Accessed July 15, 2024)

Issues

If you have any questions about this publication or are having problems accessing it, please contact reflib@nist.gov.

Created July 1, 2011, Updated February 19, 2017