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Representative abstracts
Most recent:
Qingbing
Wang, Jung O. Park, M. Srinivasarao, Satyendra Kumar, “Control of Polymer
Structures in Phase-Separated Liquid Crystal-Polymer
Composite Systems”, Japanese J.
Applied Polymer, 44
(5A), In print (paper # 04R10091) (2005). PDF
Matthew
Burke, Jung O. Park, Mohan Srinivasarao, and Saad Khan, “A
Novel Enzymatic Technique
for Limiting Drug Mobility in a Hydrogel Matrix”, Journal of Controlled Release,
ASAP articles ( 7th April 2005).
Jian Zhou,
David M. Collard, Jung O. Park, and Mohan Srinivasarao, “Control
of Anchoring of Nematic
Fluids at Polymer Surfaces Created by In-situ Photopolymerization”, J. Phys. Chem. B, ASAP
articles (7th April 2005).
Viscoelastic
and mechanical behavior of recombinant protein elastomers Nagapudi K,
Brinkman WT, Thomas BS, Park JO, Srinivasarao M, Wright E,
Conticello VP, Chaikof EL BIOMATERIALS 26 (23): 4695-4706 AUG 2005
Recombinant
DNA synthesis was employed to produce elastin-mimetic protein triblock
copolymers containing chemically distinct midblocks. These materials
displayed a broad range of mechanical and viscoelastic responses ranging
from plastic to elastic when examined as hydrated gels and films. These
properties could be related in a predictable fashion to polymer block size
and structure. While these materials could be easily processed into films
and gels, electrospinning proved a feasible strategy for creating protein
fibers. All told, the range of properties exhibited by this new class of
protein triblock copolymer in combination with their easy processability
suggests potential utility in a variety of soft prosthetic and tissue
engineering applications.
Templated
ceramic microstructures by using the breath-figure method Englert BC, Scholz
S, Leech PL, Srinivasarao M, Bunz UHF CHEMISTRY-A EUROPEAN JOURNAL
11 (3): 995-1000 JAN 21 2005
We
describe the synthesis of two
cyclobutadiene(cyclopentadienyl)cobalt-containing poly(p-phenylene
ethynylene)s (PPEs) and their use as precursors for stable ceramic surface
coatings. Organometallic PPEs were shaped into hexagonally ordered
assemblies by using the breath-figure method. Such breath figures can be
washed away with an appropriate solvent. Upon pyrolysis at 500degreesC
under either nitrogen or air, the bubble arrays persist as ceramics and are
insoluble in organic solvents or water. ne formed pyrolyzed bubble arrays
were analyzed by optical and scanning electron microscopy, as well as
energy dispersive X-ray microanalysis (EDX). The composition of the ceramic
materials is discussed based on EDX and IR data.
Physical characterisation of microporous and
nanoporous polymer films by atomic force microscopy, scanning electron
microscopy and high speed video microphotography Barrow MS,
Jones RL, Park JO, Srinivasarao M, Williams PR, Wright CJ
SPECTROSCOPY-AN INTERNATIONAL JOURNAL 18 (4): 577-585 2004 PDF
We
report studies of ordered microporous and nanoporous polymer films formed
by the evaporation of polymer solutions following exposure to a humid
atmosphere. High speed microphotographic (HSMP) studies of the formation
process showed that near the surface of the polymer solution, vapour
condensation produced near mono-disperse water droplets which form a
close-packed monolayer (or 'breath figure'). Following the evaporation of
the solvent, characterisation of the solid by Atomic Force Microscopy and
Scanning Electron Microscopy revealed that the surface of the polymer film
is characterised by extensive regions of hexagonally close-packed
microscopic pores, whose spatial arrangement replicates that of the initial
droplet monolayer. Characterisation of sections of the film by Atomic Force
Microscopy established that the surficial pores represent open sections of
sub-surficial spheroidal cavities formed by encapsulation of the water
droplets within the polymer solution. An interesting feature of the results
is the occurrence of nano-scale pores at the film surface and at (and
within) the walls of the sub-surficial microscopic pores. This is the first
physical evidence report of such features in porous polymer films produced
by a process involving breath-figures. Their dimensions suggest that more
detailed structural investigations will require alternative techniques to
conventional, optical methods.
Molecular-level
insulation: An approach to controlling interfacial charge transfer Haque SA, Park JS, Srinivasarao
M, Durrant JR ADVANCED MATERIALS 16 (14): 1177-+ JUL 19 2004
A
novel approach to the attachment of molecular dyes to nanocrystalline TiO2
electrodes (see Figure) is reported. Cyclodextrin encapsulation of an
organic dye is shown to result in strong binding to the metal oxide
electrode. The encapsulation furthermore results in a well-defined spatial
separation of the organic dye from the electrode surface, allowing the
photogeneration of a long-lived charge-separated state.
Permanent
bubble arrays from a cross-linked poly(para-phenyleneethynylene): Picoliter
holes without microfabrication Erdogan B, Song LL, Wilson JN, Park JO, Srinivasarao
M, Bunz UHF JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 126 (12):
3678-3679 MAR 31 2004
Facile
microstructuring of organic semiconducting polymers by the breath figure
method: Hexagonally ordered bubble arrays in rigid-rod polymers Song L, Bly RK,
Wilson JN, Bakbak S, Park JO, Srinivasarao M, Bunz UHF ADVANCED
MATERIALS 16 (2): 115 JAN 16 2004
Microstructuring
of conjugated polymers is facile utilizing,the breath figure approach.
Dilute solutions of conjugated polymers in carbon disulfide form highly
ordered 2D hexagonal bubble arrays (see Figure and inside cover). The
arrays are obtained if moist air is blown over the polymer solutions.
Evaporative cooling leads to condensation of water droplets onto the liquid
surface. After the solvent is evaporated, the ordered bubble array is
observed.
Control
of the anchoring behavior of polymer-dispersed liquid crystals: Effect of
branching in the side chains of polyacrylates Zhou J, Collard DM,
Park JO, Srinivasarao M JOURNAL OF THE AMERICAN CHEMICAL SOCIETY,
124 (34): 9980 AUG 28 2002
A
temperature-driven anchoring transition in a polymer/nematic fluid
composite that is far from the bulk nematic-isotropic transition
temperature is reported. A series of poly(methylheptyl acrylates) were
studied to probe the subtle effects of the side chain structure of the polymer
on control of the anchoring. A polymer-dispersed liquid crystal film made
from TL205 and 1-methylheptyl acrylate shows only planar anchoring over the
temperature range studied, while the films made from TL205 and each of the
other methylheptyl acrylates or n-heptyl acrylate show the
homeotropic-to-planar anchoring transition at temperatures between 70 and
78  C.
An interfacial model is proposed in which the different conformation of the
side chains is suggested as the cause for the dramatic difference in the
observed anchoring behavior.
Magnetic
field induced instabilities in nematic solutions of polyhexylisocyanates Srinivasarao M,
Park JO POLYMER 42 (21): 9187 OCT 2001
Magnetic
field induced Freedericksz transition in the twist geometry of an initially
well-aligned nematic solution of a rod-like polymer, polyhexylisocyanate
(PHIC), is studied. For the angle a between the magnetic field and the
unperturbed director no, one finds a homogeneous distortion if this angle
is less than 45 degrees. For angles greater than 45 degrees, the
reorientation is inhomogeneous, and is coupled to secondary flow, giving
rise to spatially periodic structures. The director deformation involves an
out-of-plane tilt at short times, which manifests itself as a phase grating
for transmitted polarized light. It is found that the wavelength of the instability
is independent of the magnetic field strength in the experimental range,
contrary to prior results for nematic solutions of polybenzylglutamate. We
postulate that the insensitivity of the wavelength of the periodic
structure is due to the nonflow-aligning character of PHIC solutions.
Three-dimensionally
ordered array of air bubbles in a polymer film Srinivasarao M,
Collings D, Philips A, Patel S SCIENCE 292 (5514): 79 APR 6
2001 PDF
We
report the formation of a three-dimensionally ordered array of air bubbles
of monodisperse pore size in a polymer film through a templating mechanism
based on thermocapillary convection. Dilute solutions of a simple,
coil-like polymer in a volatile solvent are cast on a glass slide in the
presence of moist air flowing across the surface, Evaporative cooling and
the generation of an ordered array of breath figures Leads to the formation
of multilayers of hexagonally packed water droplets that are preserved in
the final, solid polymer film as spherical air bubbles. The dimensions of
these bubbles can be controlled simply by changing the velocity of the
airflow across the surface. When these three-dimensionally ordered
macroporous materials have pore dimensions comparable to the wavelength of
visible Light, they are of interest as photonic band gaps and optical
stop-bands.
Diffusion
of macromolecules in polymer solutions and gels: A laser scanning confocal
microscopy study Burke
MD, Park JO, Srinivasarao M, Khan SA MACROMOLECULES 33 (20):
7500-7507 OCT 3 2000
Laser
scanning confocal microscopy combined with fluorescence recovery after
photobleaching is an effective tool to measure the diffusion coefficients
of macromolecules in cross-linked hydrogels and polymer solutions. In this
study, the effects of enzyme treatment on the diffusion of macromolecules
(FITC-dextran) in guar solutions and titanium-guar hydrogels are examined.
Enzyme treatment with beta-mannanase, a polymer backbone cleaving enzyme, quickly
increases the diffusion coefficient of the probe molecules in both
solutions and hydrogels to that in water. Enzyme treatment of guar
solutions and hydrogels with alpha-galactosidase, a side chain cleaving
enzyme, displays a unique behavior due to changes in the fine structure of
guar. The removal of galactose branches from the mannan backbone of guar
creates additional hyperentanglements ii.e., cross-links), which reduce the
water holding capacity of guar and induce syneresis. If the depth at which the
diffusion coefficient is measured remains constant, a minimum is observed
in the diffusion coefficient asa-galactosidase enzyme treatment time
increases. At the site of measurement, the sample changes from a
homogeneous guar system to a phase-separated polymer-rich hydrogel and
finally to a dilute polymer phase as the polymer-rich hydrogel phase
precipitates below the site of measurement. The diffusion coefficient in
the dilute polymer phase increases to that in water, while the diffusion
coefficient in the hydrogel phase continues to decrease to a value of
approximately 6 x 10(-8) cm(2)/s.
Chirality and polymers Srinivasarao M CURRENT
OPINION IN COLLOID & INTERFACE SCIENCE 4 (2): 147-152 APR 1999 PDF
Optical
activity, since its discovery, has been a fascinating field, from the
seemingly simple issues related to transfer of (chiral) information to its
cosmic connections and the origin of life itself. There has been much
progress made on both fronts which include the discovery of strong infrared
circular polarization from dust scattering to the more down to earth
knowledge of how chiral information is transferred to solutes by chiral
additives, piezoelectricity and opalescent elastic networks. The progress
made in the past few years and their implications for various aspects of
chirality are discussed.
Nano-optics in the biological world: Beetles,
butterflies, birds, and moths Srinivasarao M CHEMICAL
REVIEWS 99 (7): 1935 JUL 1999 PDF
In
a world that is as colorful as ours, it is not surprising to find that
colors produced in nature by a variety of creatures have attracted the
attention of scientific giants such as Newton, Michelson, and Lord
Rayleigh, just to name a few. It is perhaps somewhat surprising to find
that there are still many questions remaining to be answered with regard to
color produced by animals, like butterflies and beetles, and what that
color means to them. This gets us into the realm of color vision and color
perception in the animal world. This review will primarily focus on color
production in nature purely by physical means such as diffraction,
interference, and scattering but will not include those due to dyes,
usually referred to as biochromes or pigments, thereby eliminating color
due to absorption or emission of light.
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