Single molecule study of Polymer-Surfactant Interactions:Achievements:- Developed Fluorescence Correlation Spectroscopy (FCS) technique to follow the dynamics of polymer/surfactant systems which provided the association behavior of polymer in complex media
- Without tedious covalent labeling of dye molecules, the entire system was studied with the same precision as covalently labeled ones
- Discovered a precise method to determine Critical Micelle Concentration(CMC) of surfactant at a single molecule level
- This method is fast, more accurate and sensitive to detect even pre-micellar concentration as conventional methods fail.
- Correlated single inter-chain aggregates to hydrodynamic size and related this to surfactant concentration which impacts on personal care product formulation
- First to utilize optical single molecule technique to monitor the association of cellulose ethers/surfactant upon gelation
- FCS results coincided with rheological analysis from piezoelectric axial vibrator (PAV)
The association between polymers and surfactants has drawn much attention in the last decades. Water soluble polymer-surfactant systems are important for a variety of industrial applications in the areas of cosmetics, personal-care, food, pharmaceutics, detergents, and mineral processing. In particular complexes formed between non-ionic cellulose ethers and ionic surfactant in aqueous solution were investigated in the past. Among the various non-ionic cellulose ethers, methyl cellulose (MC) is the simplest and most well known. Commercial MC is a heterogeneous polymer consisting of highly substituted hydrophobic zones and less substituted hydrophilic zones resulting in an amphiphilic multiblock copolymer. The amphiphilic nature of the polymer leads to weak inter and intra molecular hydrophobic interactions in aqueous environment. The addition of an anionic surfactant like sodium dodecyl sulfate (SDS) is expected to lead to aggregation in the hydrophobic zones of MC.
Methylcellulose-SDS interactions: At low SDS concentration (region I) we expect some hydrophobic interaction between the hydrophobic regions on the MC chains with barely any influence of the surfactant. In region II complexes are formed between SDS and the hydrophobic regions of MC leading to a significant strengthening of the physical network. Finally, at high enough SDS concentrations (region III) the hydrophobic regions of the MC molecules are saturated by SDS micelles and the physical network breaks down.
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