The formation of specific phase-separated morphologies is central to achieving high performance polyurethanes. Polyurethanes are composed of various structural elements possessing a mixture of different functional groups, molecular weights, and sequence lengths. The chemistry, the phase behavior, and the kinetics of phase evolution will influence the type of phase-separated morphology formed. In fact, the phase behavior also depends upon the chemical structure and the molecular weight distribution of the components. Despite the importance of chemical structure, it is still not understood quantitatively. In addition, little is known about how the developing structure organizes into different phase-separated morphologies. The work herein addresses these issues. The molecular weight distributions, end groups, and linkages of polyurethane structural elements were quantitatively determined. The structural elements included polyether and polyester macrodiols, polyurethane prepolymers, and polyurea hard segments. Under homogeneous conditions, the molecular weight distribution formed obeys a Schultz-Flory distribution; although when toluene diisocyanates are used as the diisocyanate the effect of change in reactivity narrows the distribution. Under heterogeneous conditions, the phase separation of water causes a change in the local stoichiometry and narrows the distribution further. In the presence of typical polyurethane side reactions, the distribution is broadened. The formation of allophanate linkages was most prevalent in PPG prepolymers prepared at reaction temperatures of 145°C. Infrared spectroscopy was used to study the crystallization behavior of semicrystalline polyurethanes and the reaction and morphological evolution of polyurethane foams. Hydrogen bonding between urethane groups was shown to influence all aspects of the crystallization behavior, including the initial state, nucleation and growth rates, and the final morphology. Hydrogen bonding proves to be less crucial in the onset of phase separation in polyurethane foams. The most crucial parameter was shown to be hard segment anisotropy. Foams prepared from diisocyanates yielding highly anisotropic hard segments phase separate at lower reaction conversion, with a faster rate, and to a higher degree of phase separation and perfection.

The initial part of this dissertation describes the preparation of the first reported poly(p-xylylene) polymer/polymer composites. Poly(p-xylylene) (PPXN) and its derivatives, known collectively as parylenes, are solvent resistant and blends or composites cannot be easily made by conventional methods. Supercritical carbon dioxide was used as both a plasticizer and solvent to infuse and polymerize a variety of vinyl monomers inside the parylene films. Infrared spectroscopy, wide angle X-ray diffraction, and thermal gravimetric analysis were used to characterize the composites. Multilayer coatings of PPXN and other polymer films were prepared and selectively modified with metal nanoparticles. The second part details the modification of atomic force microscope (AFM) probes using a variety of monochlorosilanes to improve the chemical sensitivity of AFM. X-ray photoelectron spectroscopy revealed that the silane reaction was successful. Adhesion force measurements between the modified probes and similarly modified silicon wafers were performed, but showed only a slight variance between the different tip chemistries. Surfaces with patterned chemistry were prepared and examined with the modified probes using tapping mode AFM. The contrast in the phase images was dependent on the tip chemistry. The ability to confine and direct the motion of liquid droplets on a surface using only gravity and differences in surface chemistry is discussed in the first chapter of Part III. A hydrophobic alkylsilane surface with low contact angle hysteresis was patterned with lines of a more hydrophobic fluoroalkyl silane. Liquid droplets moved easily on the low hysteresis matrix, but pinned at the more hydrophobic lines. A variety of patterns were used to demonstrate that a decrease in the hysteresis reduces the force needed to induce drop motion and also lowers the barriers that are needed to confine the droplets. Condensation on a variety of ultrahydrophobic surfaces was examined in the second chapter of Part III. Optical microscopy showed that water condensed between the hydrophobic surface features before being expelled to the top. The condensed liquid pinned the contact line of a macroscopic droplet and dynamic contact angle measurements revealed an increase in hysteresis which corresponded to a decrease in liquid mobility.