Surface active agents, commonly referred to as surfactants, have a characteristic molecular structure comprised of a hydrophilic head group as well as a hydrophobic tail group. Due to their amphipathic nature, surfactants form thermodynamically stable nanoscale aggregates both in solution and at interfaces. At concentrations above a critical micelle concentration (CMC), surfactants self-assemble in the bulk to form micelles with the head groups forming a hydrophilic shell around a hydrophobic core comprised of the tail groups. In addition to forming micelles, surfactants adsorb at interfaces (solid/liquid and liquid/gas) and decrease the interfacial free energy. The adsorbed surfactant aggregates (admicelles) act as a two dimensional solvent to allow partitioning of organic molecules into hydrophobic regions of the admicelle in a phenomenon termed “adsolubilization.” In the late 1980’s, researchers began to investigate the application of the adsolubilzation of monomers into the admicelle and initiating radical polymerization to produce ultrathin films on a wide array of surfaces. This technique, called admicellar polymerization, offers several advantages over traditional methods used to form polymeric films on surfaces. The process is environmentally friendly as it creates ultrathin films with minimal chemical usage without the need for organic solvents. Additionally, the films formed by admicellar polymerization show strong adherence to porous substrates due to the presence of the surfactant layer acting as a compatiblizer between the hydrophilic substrate and the hydrophobic polymer film and to the entrapment of the formed polymer within the pores of the substrate. Despite the growing number of reports on admicellar polymerization, there remains a dearth of fundamental knowledge regarding the polymerization process in the adsorbed bilayer structure and the properties of the resultant polymeric film. We are interested in the effect the location of the monomer in the admicelle, the solubility of the initiator, and the porosity of the substrate on the properties of the thin film. We are also investigating the use of admicellar polymerization in enhanced oil recovery, drug delivery, and protective surface coatings.
Figure 1. Schematic of the steps in the admicellar polymerization process: (a) Surfactant adsorption and admicelle formation, (b) Monomer adsolubilization, (c) Polymerization, and (d) Surfactant removal.
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