(6at) Surfactants and Polyelectrolytes as Building Blocks for Soft Materials

Lapitsky, Y., University of Toronto
Shoichet, M. S., University of Toronto
Kaler, E., Stony Brook University

Many commercial products and academic research projects use ?smart? materials that respond to external stimuli such as changes in pH, ionic strength, or temperature, and mechanical or electromagnetic perturbations. Surfactants and polyelectrolytes both provide acutely sensitive building blocks for these materials. Consequently, they are used together in a broad range of applications, which include household products (e.g., foods, personal care products, cleaning solutions, paints, and cosmetics), pharmaceutical formulations, oil recovery, and templates for the synthesis of novel materials. However, many frontiers of their physicochemical properties and applications remain unexplored. To this end, we have investigated the interactions, properties, and applications of surfactant-polyelectrolyte gels and solutions on both the molecular and macroscopic levels. This poster summarizes our work on the formation, characterization, and applications of surfactant-polyelectrolyte gels.

I. Formation, Structure, and Stability of Surfactant-Polyelectrolyte Gels

Interactions between oppositely charged surfactants and polyelectrolytes in aqueous solutions can lead to associative phase separation, where the concentrated phase is a viscous liquid, gel, or precipitate. We have exploited this phenomenon to form gel particles (ranging from microns to millimeters in diameter), fibers, and coatings from mixtures of cationic polysaccharides with oppositely charged surfactants via phase inversion. Their stability is governed by the equilibrium phase behavior of the surfactant-polyelectrolyte mixture, and can be enhanced by either varying the molecular structures of their constituents or through covalent crosslinking of the polymer chains. Conversely, the internal morphologies of these materials (which are either solid or hollow) are dictated by their gelation kinetics and vary with the gel dimensions and the solution compositions used in their preparation. This work illustrates that phase separation in surfactant-polyelectrolyte mixtures can be exploited to form soft materials with controlled phase stabilities and morphologies on a variety of lengthscales.

II. Applications of Surfactant-Polyelectrolyte Gels

We have tested the performance of these structures in the encapsulation and release of hydrophobic compounds and preparation of novel biomaterials. Aromatic oil (cymene) was encapsulated inside surfactant-polyelectrolyte gel particles and released into both aqueous and organic receiving mediums. The release rate is governed by the effective diffusivity and solubility of the oil in the aqueous gel matrix, and can vary from a few hours to a few days, depending on the receiving solution. Likewise, we have developed cell-adhesive and cytocompatible gel fibers with controlled degradation rates from mixtures of fatty acid salts (sodium caprate, laurate, and myristate) and a water-soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan chloride (HTCC). The dissolution times of these fibers depend on surfactant hydrophobicity, are modulated through the selection of the fatty acid molecule, and range from minutes (for HTCC-caprate), to hours (for HTCC-laurate), to days (for HTCC-myristate). These studies suggest that surfactant-polyelectrolyte gels can serve as controlled release agents and offer an attractive alternative to conventional hydrolytic and enzymatic mechanisms for controlling the degradation rates of biomaterials.