Advanced scanning probe techniques for the study of polymer surfaces.

摘要

Important contributions to our understanding of polymer surfaces rely very heavily on the development of new techniques for the study of those surfaces. The unifying aspect of the research described in this dissertation is the exploitation of advances in polymer surface characterization for purposes of elucidating surface behavior and properties. The results have implications for an interesting diversity of polymer science applications ranging from the design of superior latex films, to detection of trace components on surfaces, to the engineering of blend surface properties by varying chain molecular architecture.;To design superior latex films it is important to connect mesoscale morphological features as well as adhesion properties of dried latex films to their macroscopic properties observable by eye. Using conventional scanning probe microscopy (SPM) probes, but exploiting in particular highly resolved adhesion mapping, dried latex films containing various fluorosurfactants, polymers, and cross-linking agents were studied. It was found that a complex that forms between the fluorosurfactant and a zinc cross-linking agent leads to mesoscale lateral phase separation. The presence of these lateral inhomogeneities correlates well with the poor performance on the macroscopic level.;While conventional SPM techniques can analyze surface properties of samples, there is still a need for a non-invasive, robust imaging technology capable of simultaneously collecting topographic and chemical information with nanoscale resolution. This has been realized with tip enhanced Raman spectroscopy (TERS). Metallized probes are a key enabling component for this technique, which has the potential for high sensitivity detection and surface chemical imaging with very high (nm) resolution. However, the robustness of the metallized probes has been a hindrance to the application and commercialization of the technique. An ultrathin protective coating of aluminum oxide for the metallized probe was developed to extend the storage life of these probes to three months in a dessicator and to double the scanning life under harsh scanning conditions. These robust protected probes were then used to investigate the mechanism of “blinking” of the Raman signal. Results are consistent with the contention that thermal diffusion of molecules is the major mechanism behind blinking. Using the extreme enhancement from protected probes, individual species in an isotopically labeled polymer blend were detected for the first time using molecules that were not Raman resonant.;TERS has limited potential for use with samples engineered to contain two species that have the same chemistry but differ in chain architecture, such as a blend of linear and cyclic polystyrenes. To quantify the surface composition of such a blend, a new mass spectrometry technique was developed. This technique, which we term surface layer matrix assisted laser desorption/ ionization time-of-flight mass spectrometry (SL-MALDI-TOF MS), has the ability to unambiguously identify species in the top molecular layer of a film with the same repeat chemistry as long as each species has a unique mass to charge ratio (m/z).