Available at: http://digitalcommons.calpoly.edu/theses/1411
Date of Award
MS in Polymers and Coatings
Chemistry & Biochemistry
Dr. Shanju Zhang
Water soluble conjugated polyelectrolytes (CPEs), which fall under the category of conductive polymers, possess numerous advantages over other conductive materials for the fabrication of electronic devices. Namely, the processing of water soluble conjugated polyelectrolytes into thin film electronic devices is much less costly as compared to the processing of inorganic materials. Moreover, the handling of conjugated polyelectrolytes can be performed in a much more environmentally friendly manner than in the processing of other conjugated polymers because conjugated polyelectrolytes are water soluble, whereas other polymers will only dissolve in toxic organic solvents. The processing of electronic devices containing inorganic constituents such as copper indium gallium selenide (CIGS), is much more expensive and poses much greater environmental risks because toxic metals may be released into landfills or waterways upon cell disposal.75 Because conjugated polyelectrolytes enjoy an assortment of advantages over other materials for the manufacturing of thin film electronic devices, there is globally vested interest in the researching of their properties. Despite the fact that CPEs can serve as efficient electron transport mediums, devices such as organic solar cells cannot realize their highest efficiencies unless the morphology of CPEs is precisely controlled. Charged surfactants can electrostatically and ionically interact with CPEs, and when introduced in specific concentrations, molar ratios, and temperature ranges, will aid in a ‘coil to rod’ transition of the CPE, wherein polymer chains undergo intramolecular transitions to obtain rigid-rod morphologies. The kinetics and thermodynamics of the ‘coil to rod’ transition are heavily dependent upon the type(s) of charged surfactant complexed with the CPE (i.e. on the surfactant architecture). By performing UV/Vis Spectroscopy and Fluorometry on dilute polymer/surfactant solutions, Polarized Optical Microscopy (POM) and Small Angle X-Ray Scattering (SAXS) on high concentration polymer/surfactant solutions, and Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) on solid-state polymer/surfactant samples, the role of various surfactant architectures on the kinetics and thermodynamics of the ‘coil to rod’ transition was studied. The liquid crystalline physical properties and the extent of solid state crystallinity were also investigated. Through an analysis of the data obtained from these various techniques, it was found that the ‘coil to rod’ transition is progressively favored when the alkyl chain length of a single tailed surfactant is sequentially increased, and that as the concentration of double-tailed surfactant increases, the ‘coil to rod’ transition is negated.