POLYELECTROLYTE-SURFACTANT SYSTEMS


     The interaction between polyelectrolytes and surfactants has been studied extensively due to various applications of these systems ranging from personal care products, pharmaceuticals to industrial usages. It has been known that the properties such as viscosity, and solubility of polymers can be altered upon interacting with surfactants. The interaction is generally referred to as binding of the surfactant to the polymer and represented as a “binding isotherm”. At the critical surfactant concentration known as the critical aggregation concentration or CAC, the interaction between surfactant micelles and polymer chains starts. CAC is thus an analog of “the critical micellization concentration” or CMC of polymer-free surfactant solution. It has been found that the systems of polyelectrolytes and surfactants of opposite charges generally show strong interactions, whereas the systems of uncharged polymers and ionic surfactants or polyelectrolytes and surfactants of the same charges show relatively weak or no interaction.


      Figure 1 - Illustration of the interaction of the surfactant molecules and micelles with the oppositely charged polyelectrolyte.  (Ref.: Abuin, E. B. and Scaiano, J. C. Journal of American Chemical Society, 1984, 106, 6274.)

     Our current interests focus on the effects of adding an oppositely charged surfactant on the rheological properties of polyelectrolytes. A simple system of poly(acrylic acid), PAA and alkyltrimethylammonium bromide, CnTAB has been chosen. We propose a simple viscosity model to predict the reduction of the viscosity of polymer solution upon adding an oppositely charged surfactant. This model is based on the scaling theory for rheology of unentangled semidilute polyelectrolyte solution. The change of polymer chain length, and ionic strength resulting from surfactant addition are included in this model. All parameters are independently determined by using various instruments including a Contraves viscometer, a sodium-selective electrode and a surfactant-selective electrode. The model gives a quantitative description of solution viscosity with no adjustable parameters. The results from this study might help us understand how electrostatic interactions alter the self-assembly that pervades many important biological problems involving charged polymers such as DNA and proteins.


Figure 2 - The specific viscosity of 0.01M PAA with different degrees of neutralization, a, as a function of added C12TAB compared between experimental data (filled symbols) and the predictions (solid lines).

PUBLICATIONS


  1. A. J. Konop, and R. H. Colby, “Role of Condensed Counterions in the Thermodynamics of Surfactant Micelle Formation with and without Oppositely Charged Polyelectrolytes” Langmuir, 15 (1), 58-65 (1999).

  2. N. Plucktaveesak, L.E. Bromberg and R.H. Colby, “Effects of Surfactants on the Gelation Threshold Temperature in Aqueous Solutions of a Hydrophobically Modified Prolyelectroyte”, in Proceedings of the XIIIth International Congress on Rheology, 3, 307 (2000).

  3. L. E. Bromberg, M. Temchenko, and R. H. Colby, “Interactions among Hydrophobically Modified Polyelectrolytes and Surfactant of the Same Charge”, Langmuir, 16,(6), 2609-2614, 2000.

  4. R. H. Colby, N. Plucktaveesak and L. E. Bromberg, “Critical Incorporation Concentration of Surfactants Added to Micellar Solutions of Hydrophobically Modified Polyelectrolytes of the Same Charge” Langmuir, 17 (10), 2937-2941, 2001.

  5. N. Plucktaveesak, A.J. Konop and R.H. Colby, “Viscosity of Polyelectrolyte Solutions with Oppositely Charged Surfactant”, J. Phys. Chem. B, 107, 8166 (2003).

  6. F. Bordi, C. Cametti and R.H. Colby, “Dielectric Spectroscopy and Conductivity of Polyelectrolyte Solutions”, J. Phys.: Condens. Matt., 16, R1423 (2004).