The proposed dissertation research project will examine the behavior of polyelectrolytes in the presence of oppositely charged surfactants. When polyelectrolytes and surfactants of opposite charge are mixed at a stoichiometric charge ratio, they self-assemble into highly ordered complexes. These types of assembly processes have been well documented in the past, but a great deal still remains to be understood. The proposed research will specifically be related to the examination of the thermodynamics associated with polymer/surfactant interactions, the morphological sensitivity to surfactant concentration, and the overall effect of ionic strength on aggregation. We have chosen to study a number of polyanions, of varying hydrophobic character and charge density to determine how they will interact with the cationic surfactant, cetyltrimethylammonium chloride (CTAC). Structural evaluation of complexes will be accomplished using small-angle neutron scattering (SANS) to examine soluble complexes, while insoluble precipitates will be examined through small-angle X-ray scattering (SAXS). Thermodynamic investigations will be carried out through the use of isothermal titration microcalorimetry in conjunction with potentiometry. The enthalpic data is of much greater value when combined with measured changes in surfactant chemical potential during the binding process. The change in chemical potential can be used to calculate the total change in free energy for the surfactant during the binding process. Combining this information with the free enthalpy change will provide the means necessary to describe the full thermodynamic profile of polyelectrolyte/surfactant binding. We will achieve these measurements through the use of a surfactant selective electrode that directly allows for measurement of the free surfactant concentration. Both the thermodynamics of binding and the structural evolution will be greatly influenced by the concentration of small-molecule electrolytes present in the solutions. By varying the ionic strength during these experiments, we would also like to be able to quantify the contribution made by counter-ion release to the binding process. In a similar fashion, the effect of polyelectrolyte charge density will also be examined, to address the effect of localized charge density on the driving force for surfactant binding.

Diblock copolymers are a class of polymers where two dissimilar polymer blocks are joined together at a common end. The dissimilarity of the blocks causes a phase separation to take place, however the connectivity of the blocks keeps the length scale of this phase separation on the order of the radius of gyration of each of the blocks. Throughout this thesis, the synthesis and morphology of diblock copolymers that have a specific, UV cleavable chemical moiety located at the junction point between the two blocks is investigated. The two junction points targeted to this end are the [4π + 4π] photodimer of anthracene and the 2-nitrobenzyl ester. The diblock copolymer containing the [4π + 4π] photodimer of anthracene exhibits thermal as well as UV lability upon heating above ∼130°C, or UV irradiation at 280 nm. Thin films of this polymer on neutrally-interacting substrates were annealed at 80°C under the presence of supercritical carbon dioxide to avoid thermal degradation that would occur if films were annealed above the glass transition temperature of both blocks (>110°C). The transition from microphase-separated to macrophase-separated morphology is thoroughly investigated by AFM upon thermal and UV cleavage to create blends of diblock and homopolymer in situ. In addition, the selective removal of each polymer block after cleavage by washing with selective solvents is demonstrated. The diblock copolymer containing the 2-nirobenzyl ester moiety is also synthesized and its morphology in thin films is investigated. This diblock, upon cleavage, leaves behind more useful functionality than the diblock with the [4π + 4π] photodimer of anthracene as junction point, as well as being thermally stable at temperatures that allows thermal annealing of thin films. The UV cleavage characteristics of this copolymer in solution are investigated by SEC. Also, irradiation of thin films at a wavelength that does not degrade or cross-link either polymer block causes selective junction point cleavage, as expected. The morphology of UV cleaved thin films on neutrally-interacting substrates is investigated by AFM.