Dr. von Meerwall
Self-diffusion of polymer melts and blends:
Prof. von Meerwall and his students currently are studying the self-diffusion of viscous polymer liquids (alkanes and polyethylene; polybutadiene), pure and in binary blends. This work is done in collaboration with Prof. Mattice and recently also with Prof. Wang (both Polymer Science) and some of their students. The point is to understand exactly how the temperature, molecular weight, and concentration affect the diffusion coefficients, which are measured with the nuclear magnetic resonance (NMR) method. The results are compared in detail with theoretical models and with numerical simulations of self-diffusion in these systems. Recent extensions of this work concentrate on cyclic polymers and on binary blends of highly entangled linear polymers.
Recycling of various industrial rubbers:
Prof. von Meerwall and his group are also interested in the recycling of various industrial rubbers (styrene-butadiene; natural rubber; silicone rubber) to help give them a second life. He collaborates with Prof. Isayev (Polymer Engineering) and some of his students to investigate at the molecular level how powerful ultrasound causes rubbery materials to disintegrate. NMR relaxation and diffusion measurements reveal the molecular motions of various components of the polymer network after it is broken up. The idea is to prepare for industrial implementation of the ultrasound method and to maximize its effectiveness. The project is now evolving to include industrially important rubbers containing solid filler particles.
Development and characterization of biocompatible polymer
materials:
Prof. von Meerwall and members of his group are collaborating with Prof. Kennedy (Polymer Science) and with Profs. Cheung and Lopina (Chemical Engineering) and their students to develop and characterize biocompatible polymer membranes and bicontinuous composites . These are suitable for implants into the body, and will either enclose bioactive substances subject to attack by the immune system, e. g., in the treatment of diabetes, or else directly deliver drugs at carefully controlled rates. NMR diffusion measurements indicate the permeability of various membranes or composites to molecules of widely different sizes and shapes.
In addition, Prof. von Meerwall's group collaborates widely with polymer scientists whose studies call for measurements of molecular motions and diffusion in rubbery polymers, networks, and colloids. The laboratory frequently hosts graduate students and colleagues from other departments at Akron, and from other universities and laboratories.
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Dr.
Ramsier and the Surface Physics Group.
Dr. Mallik:
Certain polymers, and other smaller molecules, chemisorb
on metal oxides via acid-base reactions to form covalent bridges or resonant
bonds. It is important to understand the surface physics and chemistry
of such systems from a fundamental standpoint, but also because they
have important technological applications in aircraft construction, adhesion,
corrosion, lubrication, and catalysis. We have used Multiple Reflection
Absorption Infrared Spectroscopy (MRAIRS) and Inelastic Electron Tunneling
Spectroscopy (IETS) to record spectra of quasi-monolayer films of molecules
as large as polymers adsorbed on metal oxides to reveal information on
the molecules’ adsorbed geometrical configurations. Interpretation of the
adsorption mechanisms for these systems depends on the ability to detect
carbonyl, phosphoryl, phosphonyl, sulphonyl and other vibrational modes
of surface-adsorbed species. Our results for carbonyl containing molecules
show that in addition to stoichiometric and steric differences between
the various adsorbates, the sample fabrication processes involved also
affect the intensity of the associated spectral lines. Comparison of MRAIRS
and IETS spectra in the past has largely ignored these constraints limiting
the effectiveness of these techniques. Our work suggests that these two
techniques, when used in tandem, can provide valuable information for a
wider range of systems of adsorbates.
Surface coatings on glassy materials:
Common silica glass, SiO2, is one of the most widely
used materials in the world. Various types of glass, either pure silica
or those with metal or other inorganic ions incorporated in their amorphous
structure, have had many uses over the centuries. Currently, silica glasses
are used primarily for the production of various optical elements such
as lenses, mirrors, plates, and diffraction gratings and printed circuit
boards. Those doped with metal and/or inorganic ions are used in a diverse
range of applications. These include, amongst many other things, the manufacture
of optical filters, storage vessels, and fiber optics, the production of
steel, and in the nuclear power industry for radiation screening. In many
instances surface coatings are applied to the glasses for protection against
erosion, or for optical filtering. We have fabricated ultra-thin (~ 1-2
nm) sputtered amorphous films of SiO2 and GeO2, characterized their topography
and that of the underlying substrates using Scanning Tunneling Microscopy
(STM) and Atomic Force Microscopy (AFM), and recorded their vibrational
spectra with and without various adsorbates of commercial significance
such as silane coupling agents. Our results reveal the nature of the bonding
mechanism at the glass/coating interface, which cannot be obtained easily
by other means. Currently we are studying different types of glasses.
Surface states of amorphous materials:
Over approximately the last two decades much work has
been done to investigate the optical end electronic properties of various
semiconducting materials as candidates for pholtovoltaic applications (in
particular solar cells); they represent a renewable energy source, which
has few detrimental effects on the environment. Currently, about 95% of
commercially available photovoltaic cells are made from crystalline silicon
wafers, similar to those in the computer chip industry. The remainder
is primarily amorphous thin-film semiconductor materials such as rare-earth
doped silicate and fluoride glasses, the so-called III-V materials (e.g.,
GaAs) and most recently the promising II-VI class of materials (e.g., CdTe,
and CdSe). Semiconducting materials such as these are much cheaper to produce
but, at present, their efficiency (at best approximately 7%) is vastly
inferior to crystalline materials (as high as 18%). The efficiency is lower
mainly because charge carriers or other impurities are absorbed at defect
sites such as dangling bonds and unwanted impurities thus reducing the
magnitude of the photocurrent.
Commercially viable manufacture of thin-film amorphous
photovoltaic devices relies primarily on Chemical Vapor Deposition (CVD),
Molecular Beam Epitaxy (MBE), and sputtering; the goal is to increase device
efficiency by minimizing the number of defects created during the fabrication
process. In order to do this, the various types of defects and their sources
must be identified. Several workers have used Photoluminescence Spectroscopy
(PLS), Raman Spectroscopy, Infrared Spectroscopy (IR) and other related
techniques to study thin films of photovoltaic materials. These spectroscopies
can record the energies and intensities of phonons, excitons and vibrational
modes of the films. Many studies have been done to characterize the electronic
and optical properties of amorphous hydrogenated silicon (a-Si:H), polycrystalline
silicon, and their oxides. The chemical structure and composition has also
been studied by a variety of spectroscopic techniques including Fourier
Transform Infrared Spectroscopy (FTIR) infrared ellipsometry, neutron scattering,
X-ray Photoelectron Spectroscopy (XPS), and Auger Electron Spectroscopy
(AES). Our work focuses on our experience in the fabrication of ultra-thin
(~ 1-2 nm) sputtered amorphous films of Si, Ge, and their oxides with and
without various adsorbates. We have published their vibrational spectra
using IETS and are now working on III-V and II-VI materials where we plan
to identify adsorption mechanisms for surface coatings.
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Dr. Henriksen... biological applications of AFM...
A major area of research in surface science is thin film
growth and characterization. Of
particular interest is the onset of epitaxial growth
and critical island size for metal films. Four vacuum chambers are available
for film growth. Presently growth characterization is limited to scanning
probe microscopy (one ambient STM/AFM and one UHV STM), reverse-view electron
diffraction, and measurements of electronic properties such as Hall voltages
and magnetoresistance. Related to the thin film work is the study of mechanisms
by which molecular compounds adsorb on the surface of highly reflective
metal films. Chemical compounds of particular interest are those related
to adhesion or lubrication. Techniques used for these studies are inelastic
electron tunneling spectroscopy (IETS), infrared (IR) spectroscopy, and
programmed thermal desorption (PTD) spectroscopy.
Dr. Griffin: Physics education and computer
assisted instruction.
