This research endeavor focuses on
obtaining a fundamental understanding of the effects of high-pressure
Carbon Dioxide on various polymeric materials. Two different experimental
approaches have been pursued. First, polymer swelling in the presence
of high-pressure CO2 has been examined. Kinetic
swelling experiments can be manipulated to provide information about CO2 solubility, diffusion coefficients, and free-volume expansion. Secondly,
the viscosity of polymeric melts with dissolved high-pressure CO2 has been investigated by designing a high-pressure rheometer. The ultimate
objective is to correlate the swelling and rheological behavior of polymer
melts in order to obtain a comprehensive understanding of CO2-induced
plasticization. Physical insights obtained from these studies are critical
for the design and optimization of polymerization schemes and melt processing.
In this regard, we have accomplished the following:
Built an optical set-up to measure in situ the
kinetics and extent of swelling for polymers; related the swelling measurements
to the Sanchez-Lacombe equation of state.
Designed and constructed a new high pressure
slit die rheometer (see schematic below) to measure the viscosity of a
polymer melt with dissolved CO2 over a wide range
of viscosities.
Measured the viscosity of several polymer melts
under high pressure (up to 5000 psi) in the presence of CO2 (see figure below).
Developed a predictive model based on coupling
of free volume and Tg depression in the presence of high pressure CO2 that enabled a priori prediction of viscosity reduction.
Devised a novel magnetically-levitated sphere
rheometer to measure viscosities of polymer solutions with CO2.
b) : Generation of Microcellular
and Nanocellular Polymer Foams using Carbon dioxide
This research endeavor taps into our fundamental
understanding of plasticization of polymer melts using carbon dioxide. The
objectives of this project include investigation of foaming processes to
create micro and nanoporous polymers using carbon dioxide, understanding
the underlying mechanism of the foaming process, studying the effect of
nanofillers and micelle-forming tailored CO2-philic
surfactants on foam nucleation and developing a theoretical model to predict
characteristics of foam structures under various processing conditions.
We have designed and constructed two experimental systems to create these
novel materials in both a continuous extrusion-based process and a batch
process. We have successfully generated foams of many polymers including
poly(methyl methacrylate), polystyrene and polyvinylidene fluoride. We are
currently working on manipulating foam nucleation in thin polymer films
using liquid (as opposed to supercritical) carbon dioxide in the presence
of nanoglass beads or specific surfactants designed to interact with the
polymer-CO2 interface. Our accomplishments include:
Polymer electrolytes are becoming increasingly important because of their potential use in rechargeable solid-state lithium batteries. However, the successful use of these materials requires them to be mechanically strong, yet be processible and have high conductivities. Our novel approach of making composite polymer electrolytes using fumed silica nano-fillers (see figure below) in low molecular weight polyethylene glycol (PEG) (and its derivatives) is capable of simultaneously satisfying all of these criteria. Key to the success of our method are: (i) the unique rheological behavior of fumed silica; i.e. it can form strong network structures that are also processible, and, (ii) the use of low molecular weight PEG which allows for high conductivity.
Designed and constructed a novel extrusion-based
continuous microcellular foaming process.
Developed new foaming paradigm for continuous
generation of microcellular semicrystalline materials.
Extended microcellular foaming process to create
novel nanoporous materials of thin polymer films
Demonstrated advantages of novel CO2-foamed
nanocomposites
Shown CO2 to be an excellent
blowing agent for foaming all the polymers studied. 'Smart' foamed structures
can be generated by manipulating CO2 properties.
Nanofoams of thin PMMA films using supercritical carbon
dioxide
