Colloidal Structure and Physical Properties of Gel Networks Containing Anionic Surfactant and Fatty Alcohol Mixture

Abstract

We investigated the mechanical properties, thermal behavior, physical state, and colloidal structure of a model gel network formulated with various ratios of sodium dodecyl sulfate polyacrylamide (SDS) and cetyl/stearyl fatty alcohol (FA) mixture in constant amounts of water (89%). The metastable gel, formed by slowly cooling stirred samples from temperatures above the chain melting temperature (Tm) of the long chain FA, has a lamellar structure with a periodic inter bilayer spacing of approximately 30 nm. The bilayers remain homogeneous with SDS being immobilized in the FA matrix upon chain freezing. The chain length mismatch leads to an increased structural disorder among the alkyl chains upon SDS incorporation among the FA. As a result, the elastic modulus decreased with increasing SDS content. Conclusions were based on a large number of experiments involving differential scanning calorimetry, rheology, ¹H NMR spectroscopy, and small angle x-ray scattering. Results from this work have uncovered the physical nature of these networks and gave insight into the role of anionic surfactants on the assembly, physical state, and mechanical properties of gel networks.

Keywords:

• Bilayer
• cetyl/stearyl fatty alcohol
• DSC
• gel network
• NMR
• rheology
• SDS
• structure
• x-ray

Acknowledgments

The authors would like to thank Dr. Gabriel Rata for technical assistance with NMR experiment.

T. S. Awad is currently affiliated with Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, USA