Characterization of dynamics and internal structure of a mixed-surfactant wormlike micellar system using NMR and rheometry

Barhoum, Suliman Abdallah and Castillo, Rolando and Yethiraj, Anand (2012) Characterization of dynamics and internal structure of a mixed-surfactant wormlike micellar system using NMR and rheometry. Soft Matter, 8. pp. 6950-6957. ISSN 1744-6848

[img] [English] PDF - Published Version
Available under License Creative Commons Attribution Non-commercial.

Download (565Kb)

Abstract

We use complementary experiments—proton NMR diffusometry and relaxometry, deuterium NMR lineshapes, and rheometry—to construct a comprehensive picture of the microscopic structure of a mixed-surfactant wormlike micellar system composed of a zwitterionic surfactant and an anionic surfactant in brine. In this system, at some surfactant concentrations, the time for micellar breaking and recombination sb is not small compared with the micellar reptation time sR, weakening the condition to obtain a stress relaxation function with just one relaxation time at long times. FromNMRrelaxometry, we determine the overlap concentration. Deuterium NMR spectral lineshapes indicate the presence of a wide angular distribution in the orientational order. NMR diffusometry and rheology probe different timescales and yield complementary information indicating polymer-like behaviour at the corresponding lengthscales. Via NMR, surfactant diffusion coefficients are seen to decrease with increasing diffusion time, consistent with restricted diffusion within a reptating micelle. At the same time, comparison of measurements with protonated and deuterated surfactants strongly suggests that the measured short and long time diffusion coefficients correspond to intra-micellar and micellar diffusion, respectively. Fitting the diffusion results to a simple model, the average end-to-end micellar distance is estimated to be in the 1 mm range and only weakly dependent on concentration. The water diffusion measurements, on the other hand, imply a high degree of water structuring at the micellar surface. We also find that the wormlike micelles obeyed simple polymer-like scaling behaviors, with a crossover from Zimm-like (diffusion) to Rouse-like (rheology) exponents.

Item Type: Article
URI: http://research.library.mun.ca/id/eprint/8053
Item ID: 8053
Department(s): Science, Faculty of > Physics and Physical Oceanography
Date: 25 May 2012
Date Type: Publication
Related URLs:

Actions (login required)

View Item View Item

Downloads

Downloads per month over the past year

View more statistics