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Research Interests:
Carbon
Nanotube/Polymer Composites
With
collaboration and financial support of NASA-Johnson Space Center
(Houston, Texas), Dr. Caneba’s group has recently embarked on
research involving polymer composites with single-wall carbon
nanotubes (SWCNTs). Continuous fibers of SWCNTs have been shown
to be 100 times stronger than steel and 17 times stronger than
Kevlar™ per weight. They also possess similar thermal and electrical
conductivities compared some metals, while their density is
just over 2 g/cm3. Even though they currently cost about $800
per gram, they are suitable in space applications and they exhibit
dramatically enhanced properties at relatively low loadings
(about 0.5 wt % in a polymer composite). The key is to be able
to attain its percolated structure by proper dispersion of SWCNT
bundles.
Current
efforts in this area involve the formulation of SWCNT/high performance
polymer composites as components of fuel cells in space missions.
Also, efforts are underway to develop SWCNT-based lightweight
dosimeters for the international space station (ISS). Finally,
research is ongoing for the development of lightweight radiation
shields and thermal films.
With
funding from the National Science Foundation through the Nanoscale
Science and Engineering – Nanoscale Undergraduate Education
(NSE-NUE) Program, education of undergraduate students regarding
SWCNT/polymer composites as well as societal aspects of various
nanotechnology systems are currently ongoing.
Precipitation
Polymerization
The
focus of this effort is the free-radical retrograde-precipitation
polymerization (FRRPP) process that Dr. Caneba discovered in
the late 1980s. Here, polymerization occurs above the lower
critical solution temperature (LCST). The local heating that
occurs in exothermic chain polymerization reactions places FRRPP
systems closer to the spinodal curve, wherein diffusional mass
fluxes have been found to vanish. Apparently, even the more
mobile monomer and solvent molecules cannot diffuse from high-concentration
to low-concentration regions that are adjacent to the reactive
sites. Also, an apparent reduction of heat transfer rate from
the reactive sites has been found to occur in the system. The
underlying reason for the heat-trapping phenomenon is still
in question, but it might be rooted from the observed nanometer-scale
features of the reactive sites.
Other
apparent results of the FRRPP process are efficient trapping
of polymer radicals, relatively narrow molecular weight distributions,
stable molecular weight and polydispersity index, reduced conversion
rate, and persistence of nanometer-scale polymer-rich domains.
Materials from and variants of the FRRPP process are the basis
of the following industry, federal, and state-funded applied
oriented projects.
Block Copolymer Emulsions
Styrene-
and methyl methacrylate-based block copolymer emulsions in water
have been efficiently produced from the FRRPP process. Typical
products are specialty adhesives, low VOC paints and coatings,
and even intermediate latices with relatively stable polymer
radicals. These intermediate polymer (polystyrene or poly(methyl
methacrylate)) radical emulsions can be used to generate various
block copolymers by addition of another monomer mixture.
Controlled Statistical Free-Radical Copolymerization
In
conventional statistical free-radical copolymerization, monomer
reactivity ratios and addition protocol dictate monomer distribution
in the resulting polymer chains. In a selectively precipitating
medium that also involves radical trapping and molecular weight
control, a more effective monomer distribution control in the
product copolymer has been obtained. An example product is a
sharply tapered vinyl acetate/acrylic acid block copolymer that
was produced in a single-stage operation; this indicates a segmental
self-assembly mechanism. Also, vinyl acetate/acrylic acid copolymers
were produced with equal acrylic acid spacing in a group of
vinyl acetate segments (roughly one acrylic acid segment per
10 vinyl acetate segments). These materials have been proposed
to have the following unique applications: coupling agent for
plastics-natural fiber composites, surfactants for oil recovery,
soil remediation, water-based degreasers, biodegradable plastic
materials and foams, froth flotation for iron and copper processing,
wood preservation, longterm water-dispersible adhesives, water-based
coating primers, silicone-organic coatings, and water-based
pesticide formulations.
Radiation-Initiated FRRPP
If
the reaction rate in FRRPP systems is under control, then it
means that polymer-rich domain growth will also be under good
control if domain interaction is minimized. If the reaction
is carried out in a quiescent fluid, then one should expect
the formation of nanometer-scale particles. Indeed, morphological
and X-ray scattering experimental results confirm this hypothesis.
Nanometer-scale particles produced by this method could be used
in bioseparations and drug delivery systems.
If
polymerization is induced by radiation with nanometer-sized
wavelengths, it is possible to control the dimensional features
of the polymer product within the radiation zones.
It
is evident that this approach (bottom-up method) is different
from established lithographic methods (top-down approaches);
which involve casting a polymer film, irradiating the film,
and then dissolving away irradiated or unirradiated regions.
The FRRPP-based bottom-up method produces nanometer-scale polymer
structures from the monomer in situ, using low-wavelength low-divergence
directed radiation (such as that of the synchrotron X-ray source
at Argonne National Laboratory) for free-radical initiation.
Current results are microlithographic patterns of pure thermoreversibe
hydrogels that can be used in microfluidic and tissue engineering
systems.
Enhanced Oil Recovery
At
a time of uncertainty in foreign crude oil supplies, decreasing
domestic oil production, and projected increases in demand for
petroleum products, there is a need for new technologies to
efficiently recover more of the oil-originally-in-place (OOIP)
from existing oilfields in an environmentally responsible fashion.
Around 300 billion barrels of oil is recoverable in the United
States using enhanced recovery methods.
Newly-discovered
vinyl acetate-acrylic copolymers from the FRRPP process are
being investigated as surfactant/thickener for secondary and
tertiary oil recovery operations. In secondary operations, recoveries
of up to 90% of oil from water-wet formations were obtained
with a sharp breakthrough and copolymer consumption of 1 lb
per barrel of oil produced. As a foaming surfactant, the copolymer
was found to outperform commercially available anionic and nonionic
surfactants per lb of usage. These performance results are accompanied
by the competitive cost of the copolymer compared to lower priced
oil recovery surfactants in the market.
Recent
Publications
Y.
Dar and G.T. Caneba, “Transport Phenomena Aspects of the Free-Radical
Retrograde-Precipitation Polymerization (FRRPP) Process”, Chemical
Engineering Communications, 189, 571 (2002).
R. Saxena, L. Shi, and G.T. Caneba, “Studies of Spinodal Decomposition
in a Ternary Polymer-Solvent-Nonsolvent System”, Polymer Engineering
and Science, 42, 1019 (2002).
G.T. Caneba, Y. Zhao, and Y. Dar, “Amphiphilic Styrene-Acrylic
Acid Copolymers from Free-Radical Retrograde-Precipitation Polymerization
(FRRPP)”, ACS Polymer Preprints, 43(2) 156 (2002).
G.T. Caneba and Y.L. Dar, “Free-Radical Retrograde
Precipitation Copolymers and Process for making the Same”, submitted
to U.S. Patent and Trademark Office, January, 2002, Publication
2003/0153708..
G.T. Caneba, and J.E. Axland, “Vinyl Acetate-Acrylic
Acid-based Copolymers for Enhanced Oil Recovery”, The Journal
of Minerals and Materials Characterization and Engineering,
1(2), 97 (2002).
G.T. Caneba and L. Shi, “Lower Critical Solution
Temperature of Polymer-Small Molecule Systems: A Review”, in:
Phase Separation in Polymer Solutions and Blends, P.K. Chan
(Ed.), Research Signpost, ISBN #81-7736-097-3, Chap. 4, pp.
63-104 (2002).
V.R. Tirumala, G.T. Caneba, N. Moldovan, ,D.
Mancini, and H._H. Wang, “Self-Organization in Synchrotron X-Ray
Induced Controlled Polymerization”, Proceedings of the A.I.Ch.E.
Annual Meeting, Indianapolis, IN, November 3-8, 2002.
G.T. Caneba, Y.-L. Chen, and K. Solc, “Computer
Simulation of Spinodal Decomposition in One, Two, and Three
Dimensions”, Proceedings of the A.I.Ch.E. Annual Meeting, Indianapolis,
IN, November 3-8, 2002.
G.T. Caneba, “Foaming Characteristics of Vinyl
Acetate-Acrylic Acid Copolymers”, Proceedings of the A.I.Ch.E.
Annual Meeting, Indianapolis, IN, November 3-8, 2002.
Yi Zhao, Y.L. Dar, M.-L. Kosonen, and G.T.
Caneba, “Influence of Relative Block Sizes of Styrene-Acrylic
Acid Copolymer Coupling Agent to the Tensile Behavior of Polystyrene-Wood
Composites”, Proceedings of the A.I.Ch.E. Annual Meeting, Indianapolis,
IN, November 3-8, 2002.
V. Tirumala, Y. Dar, H.-H. Wang, D. Mancini,
and G.T. Caneba, “Nanopolymer Particles from a Controlled Polymerization
Process”, Advances in Polymer Technology, 22, 126 (2003).
G.T. Caneba, Y. Zhao, and Y. Dar, “Amphiphilic
Styrene-Acrylic Acid Copolymers from the Free-Radical Retrograde-Precipitation
Polymerization (FRRPP) Process”, in press, J. Appl. Polym. Sci.
Y.L. Dar and G.T. Caneba, “Free-Radical Retrograde-Precipitation
Polymerization: Mathematical Modeling of Styrene Polymerization
in Diethyl Ether”, in press, Chem. Eng. Commun.
M.E.P Walinder, D.J. Gardner, M.-L. Kosonen,
and G.T. Caneba, “Surface Energy Characteristics of Maple Wood
Particles coated with Hydrophilic-Hydrophobic Polystyrene-Acrylic
Acid (PSAA) Block Copolymers”, submitted to Holzforschung.
G.T. Caneba, E.R. Fisher, and D. Caspary, “Poly(dimethyl
siloxane) Experiments for the Unit Operations Laboratory”, submitted
to Chemical Engineering Education.
V.R. Tirumala, R. Divan, D.C. Mancini, and
G.T. Caneba, “Lithographically-Assisted Synthesis of High Aspect
Ratio Hydrogel Microstructures”, submitted to Microsystems Technologies
Journal.
V.R. Tirumala, D.C. Mancini, and G.T. Caneba,
“Synthesis of Ultrafast Response Microgels for MEMS Applications”,
submitted to Smart Structures and Materials.
Y.L. Dar, V.R. Tirumala, G.T. Caneba, and D.C.
Mancini, “Novel Sparse-Matrix Representations for Free-Radical
Polymerization Simulations”, submitted to Journal of Macromolecular
Theory and Simulations.
G.T. Caneba and Y.L. Dar, “Free-Radical Retrograde
Precipitation Copolymers and Process for making the Same”, foreign
submission to the Patent Cooperation Treaty, January, 2003,
Publication WO 03/059974.
V.R. Tirumala, G.T. Caneba, D.C. Mancini, and
H.H. Wang, “Spatially Controlled In Situ Synthesis of Polymers”,
submitted to U.S. Patent and Trademark Office, June, 2003.
K.K. Mohanty and G.T. Caneba, “Enhanced Oil
Recovery – A Review”, submitted to Encyclopedia of Chemical
Processing.
G.T. Caneba, Y.L. Dar, and Y. Zhao, “Vinyl
Acetate-Acrylic Acid Copolymers as Coupling Agents for Wood
Flour-Vinyl Composites”, Proceedings of the 7th International
Woodfiber-Plastic Composites Conference, Madison, WI, May 19-20,
2003.
V.R. Tirumala, R. Divan, D. Mancini, and G.T. Caneba, “Lithographically-Assisted
Synthesis of High Aspect-Ratio Hydrogel Microstructures”, this
paper was partly presented at the Fifth International Workshop
on High Aspect Ratio Miscrstructure Technology (HARMST), Monterey,
CA, June 15-17, 2003
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