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Below is a brief summary of some of our current and upcoming projects. You will find that our research is focused in many aspects of Interfacial Science. The descriptions below were generated by Dr. Aston.

Thin Films for Chemical Selectivity
Existing membranes for gas separations are made from relatively thick (> 1 mm) polymer gel materials that preferentially adsorption and dissolve one species in a mixed phase over the others. Due to low throughput and high pressures of gas membrane separation techniques, very large surface area requirements have dictating the use of hollow fibers instead of the more conventional flat film geometry. However, gas permeation experiments are more easily conducted on flat samples, which are also easier to prepare and modify. Furthermore, there is a very weak dependence of film thickness on separation quality compared to a very strong dependence on throughput, or pressure. Thus, a very poorly performing polymer, or other material, may be used as a supporting substrate for a chemically selective thin-film that provides the barrier to unwanted components. In principle, the ideal situation would be to have an extremely porous support with a single, dense monolayer that allows only one gas species to adsorb and diffuse through to the underlying substrate. In practice, the support will have some significant resistance to overall gas transport and the selective thin-film will have to be several layers thick, which will still allow some small fraction of contaminants to perfuse.

The two areas of study listed below have three components: literature search for current technologies and materials compatibility, computational thermodynamics for adsorption, solubility, and interfacial strength, and the making and testing of membranes for gas sorption performance and morphology. A gas sorption apparatus is available for testing flat membrane perfusion and AFM will be used for imaging topography of substrates and films, before and after curing, annealing, treating, and use. Contact angle goniometry will also be used extensively to characterize the surface energies of samples for correlation to interfacial strength and adsorption data. Depending on the success of adhesion AFM research, these may be further correlated with pull-off forces.

I. Polymer Gel Membrane Surface Modification
Several film formation techniques will be used to modify existing gel membranes in use in Dr. Wudnhe Admassu’s lab: dip-coating in solution, vapor deposition, and spin-coating. Polymers, self-assembling monolayers (SAMs), or reactive cross-linking chemicals will all be investigated for feasibility and availability as materials for membrane modification. This will likely be the focus of a graduate student project.

II. Ceramic Supports for Crosslinked Organosilane Thin-Film Membranes
Silane-coupling agents are now commercially available with hundreds of organofunctional varieties. This group of reactive species is widely used for surface modification of hydroxyl-baring ceramic surfaces, like silica, titania, alumina, and mica. Deposition and cross-linking of siloxanes into multilayers is currently being investigated by a number of research groups, but none of them have yet implemented silane chemistry into the field of membrane separation. It may be possible to find nanoporous ceramic substrates to support cross-linked siloxane films for gaseous separations that would be viable and competitive with current gel membranes.


Adhesion AFM (The JKR Theory, Etc.)
This project involves learning the basic, theoretical relationships for thermodynamic work of adhesion being determined from pull-off forces measured between spheres and plates with AFM. The second stage includes experimental measurements of pull-off force and statistical analysis for correlation with existing, and perhaps new, theories. Experiments will encompass everything from operating the AFM to microsphere attachments onto cantilevers to sample and/or microsphere manufacturing. The first specific goal will be to attempt to correlate know interfacial strengths of composition materials to pull-off force. Samples and/or spheres will be chemically modified for various investigations. One useful modification of the existing AFM would be the addition of a heating/cooling sample stage able to test the affects on adhesion of surface water (e.g., humidity) or polymer mobility (e.g., glass transition).


UV-Ozone Cleaner for AFM Applications
All organic samples have a tendency to gum up the AFM tips used to scan them. The usual chemical methods, such as multiple solvent or surfactant cleaning, do not yield reproducibly acceptable levels of decontamination for reusing AFM probes. Most research labs use sophisticated and expensive techniques involving reactive plasma chambers for cleaning purposes. A commercial UV-Ozone tip cleaner is now available from BioForce Laboratory (www.bioforcelab.com) for $2499. Our goal is to design and build an equivalent, and safe!, unit for under $500. Keep in mind that UV radiation and ozone are hazardous to our health!


Nanowire Probes for AFM Imaging
Even though AFM can be a very powerful tool with regard to topographical and physico-chemical-spatial resolution of surfaces, it sorely lacks as a robust and routine application at length scales below about 10 nm with standard, commercially available probes. The usual and widely available tips are on limiting factor at this stage. One complication is high surface energy; another is low aspect ratio. The nominal surface chemistry (Si of SiN) can be easily altered by coating or attaching particles of differing composition, but only nanowires provide the high aspect ratio necessary to reduce imaging artifacts to an acceptable level for molecular resolution. Dr. Dave McIlroy in the UI Physics department has the capability and expertise to make wires, and sometimes springs, of various chemical composition (ceramics) with diameters of the order of tens of nanometers that range over larger orders in length, perhaps 100 nm to 10 mm. We need to development a method for attaching, or perhaps growing, these nanowires to the tips of AFM cantilevers.


Polymer Photonic Crystals
A photonic crystal is made from a periodic dielectric structure in one or more spatial dimensions. Variations in permittivity or magnetic permeability restrict the propagation of electromagnetic waves (e.g., light, radio frequencies, etc.) and can be constructed to produce more complex "wave guides" for trapping and transporting photons, analogous to semiconductor conduits for electrons. The dielectric constants (also, index of refractions) required for photonic bands are typically those for insulators, viz., many ceramics and polymers. Dr. Dave McIlroy in the UI Physics department has a concept for making a new type of polymeric photonic crystal which requires the specialize input of chemical engineers knowledgeable in solution thermodynamics and interfacial phenomena. This project will involve literature research and computations for determining material compatibility. Also, we will be involved in the making and testing of the photonic band-gap materials, although at least one graduate student in physics will have the primary role in these investigations.