Some Research Projects of the Ade Research Group
Polymer Morphology and Dynamics in Confined Geometries
Polymers are rather large molecules. For example, a “random coil” polymer such as polystyrene, can consist of more than 100,000 atoms, and its radius of gyration, a measure of its size, can be tens of nanometers. If these large molecules are confined to geometries that are smaller than a few times the molecule’s size, properties such as the viscosity are influenced by the presences of the confining interfaces. In addition, the interfacial energy has a significant effect on the morphology of the polymer, particularly if several polymer species are present.
One of the simplest confined geometries is a polymer thin film on a substrate, where the substrate surface provides a rigid and the transition to air a flexible interface. We use quantitative mapping based on NEXAFS spectroscopy to study a variety of effects in these constraint systems. We are in particular interested in determining the influence of polymer and surface composition as well as block-copolymers and small solid additives on the morphology formed and the dynamics of phase separation. (more details)
Compatiblization of Polymers with Clays
Clays might be able to compatibilize immiscible polymers after suitable treatment. We are collaborating with the Garcia Center (NSF MRSEC) in characterizing blends that have been modified through the addition of clays. Initial studies show that certain clays arrest the phase separation in PS/PMMA thin films. However, we still need to accertain if this is simply due to kinetics, or if indeed compatibilization has occured.
Polyurethanes
Scanning transmission X-ray microscopy (STXM) and Atomic Force Microscopy have been used to study the morphology and chemical composition of macrophase segregated block copolymers in plaque formulations based on water-blown flexible polyurethane foams. Although there has been a large body of indirect evidence indicating that the observed macrophase segregated features in water rich polyurethane foams are due principally to urea components, NEXAFS microscopy provides the first direct, spatially resolved spectroscopic proof to support this hypothesis. Our results are consistent with a segregation model where ureas segments segregate, forming enriched phases with the majority of the polyether-polyol and urethane groups at the chain ends of the urea hard segments. Chemical mapping of the urea, urethane and polyether distribution about the urea-rich segregated phases shows a distinct fuzziness of the spherical aggregate in the butylene oxide-based foams and a partial network of hard urea phase components in the ethylene oxide/propylene oxide samples.
NEXAFS Spectroscopy of Polymers
In order to use NEXAFS microscopy to its fullest, it is important to understand details of the infomation content of NEXAFS spectra and to have an accurate data base. We thus developed careful procedures, such as in-situ energy calibration and measurements of higher order spectral contamination in order to achieve the best spectral fidelity.
Development of a STXM Dedicated to Natural and Sythetic Polymer Research
The growing need for NEXAFS microscopy applicationsnecessitates an increase in access for all users and additional X-ray microscopy capacity. We are thus developing a microscope at a dedicated and optimized bending magnet beamline (BL5.3) at the Advanced Light Source. We anticipate a spatial resolution of better than 40 nm and an intensity in the zone plate focus above 500,000 kHz. (more details). (fist results)
More projects/results: Orientation in Kevlar fibers; "Defective" Liquid Crystalline Polyester; Macrophase-Separated Random Block Copolymer/Homopolymer Blend; Morphology of PET/LDPE/Kraton Ternary Polymer Blend; Poly(ethylene terephthalate)/Vectra Blends;
Last updated November 10, 2000 by Harald Ade; harald_ade@ncsu.edu