|
Background
Adam is from Fayetteville,
Arkansas. He received his B.S. in Chemical
Engineering from the University of Arkansas at
Fayetteville in May 2005. As an undergraduate, he
performed research under the direction of Dr. Edgar
Clausen on compound extraction and quantification
from Mimosa and fermentation of grape pomace. He
also attended two NSF-REU programs working on
"Fabrication of Nylon-6 and PET Nanocomposites" with
Dr. Thanasis Papathanasiou at the University of
South Carolina and on "Catalytic Oxidation of
Alkenes" with Dr. Kerry Dooley at Louisiana State
University. He is currently pursuing a Ph.D. in
Chemical Engineering under the direction of Dr.
Peppas at the University of Texas at Austin.
Research Summary
Over the
past 30 years, a distinct strength of our polymer
engineering research has been the development of
novel nanomaterials, platforms for microfabricated
devices, microchips, sound replication systems, drug
delivery systems, biomedical devices and therapeutic
systems.
In this
effort, we have been in the forefront of
bionanotechnology and nanomaterials analysis. We
have utilized the basics of transport phenomena,
kinetics, thermodynamics and control theory to
design novel feedback control devices and to begin
to optimize their behavior of nanomaterials in
contact with various fluids, even the body.
Adjustment and optimization of functional components
of these devices has been based on simple or
sophisticated models analyzing the changed in such
materials. Such changes are the result of penetrant
(liquid) transport through these polymers. When this
polymer is crosslinked, the process will lead only
to expansion. If it is uncrosslinked, polymer
dissolution will be achieved.
In
addition to experience in device design, operation
and control of such systems, we have a well-defined
ability to link these systems to cellular and
physiological responses.
To
examine the behavior of such systems both in the
macroscopic and molecular level, it is important to
study the penetrant diffusion process in polymers.
In such transport, the macromolecular chains
rearrange toward new conformations where the rate of
relaxation depends on the penetrant concentration.
The relative rates of penetrant diffusion and
macromolecular chain relaxation determine the nature
of the transport process and lead to a variety of
penetrant transport phenomena such as Fickian, Case
II, Super Case II and anomalous (non-Fickian).
Particular aspects of non-Fickian transport have
been described by numerous models based on Fick's
law, linear irreversible thermodynamics (LIT), and
rational thermodynamics.
Fickian
diffusion models are useful in their relatively easy
solution by analytical or numerical methods. The
adjustable material properties are generally
determined by fitting the experimental data to the
model. Non-Fickian transport process has been often
described by the models considering a convective
term in the penetrant flux; changes in the polymer
morphology resulting in a variable penetrant
diffusion coefficient; and non-Fickian propagation
of a swelling front.
Linear
irreversible thermodynamics suggests that the fluxes
can be expressed in terms of linear combinations of
chemical potential, temperature gradients and stress
distributions the equilibrium state. Some models
applying LIT theory have predicted anomalous
transport albeit with limited agreement with
experiments. Since LIT is valid for only small
perturbations away from equilibrium states, it may
not be appropriate to describe mixtures which
experience continuous macromolecular relaxation or
glassy materials which possess non-equilibrium
character.
The
primary goal of my thesis will be a detailed
analysis of the phenomenon of penetrant (or solvent)
transport through swellable (but not soluble)
polymers or through fully soluble polymers.
The main
vision of your PhD thesis are to give a final answer
to the questions that are posed by the glassy and
semicrystalline/glassy nature of most polymers used
in microelectronic, nanotechnological and biological
applications.
Swellable
but not soluble systems: In these systems we l
examine the effect of various parameters on the
phenomenon. Recall that when a penetrant enters a
thin polymer film, there are several observed
‘fronts”: transition or swelling front
(rubbery/glassy) and external front. Therefore,
investigate:
•
Penetrant uptake as a function of time;
•
Anisotropy of sample by studying expansion in all
directions;
• Front
position as a function of time;
•
Possible cracks or crazes using polarized
microscopy:
• Major
structural changes using computer assisted X-ray
tomography
Specific
parameters to be studied include:
• Degree
of crosslinking
•
Linearity of chains between crosslinks
• Degree
of Crystallinity
•
Hydrophilicity vs Hydrophobicity
•
“Goodness” of penetrant
Swellable
amd soluble systems: In these systems we will
examine the effect of various parameters on the
phenomena of swelling and dissolution. Recall that
when a penetrant enters a thin polymer film, two
distinct ‘fronts” are observed: transition or
swelling front (rubbery/glassy) and erosion front.
The latter front is associated with a major
disentanglement. Therefore, investigate:
•
Penetrant uptake as a function of time;
•
Anisotropy of sample by studying expansion in all
directions;
• Sample
dissolution as a function of time;
• Front
positions as a function of time;
•
Possible cracks or crazes using polarized
microscopy:
• Major
structural changes using computer assisted X-ray
tomography
Specific
parameters to be studied include:
• Polymer
MW and MWD
•
Linearity vs branching
• Effect
of entanglements
• Degree
of Crystallinity
•
Hydrophilicity vs Hydrophobicity
•
“Goodness” of penetrant
Publications
A.K. Ekenseair, L. Duan, D.J. Carrier, D.I.
Bransby, and E.C. Clausen. "Extraction of Hyperoside
and Quercitrin from Mimosa (Albizia julibrissin)
Foilage." Applied Biochemistry and Biotechnology.
(in press).
|
