Research Interests
Solid state polymerization; X-ray crystallography of
polymers; electrical properties of polymers; ultra-thin
polymer films.
Overview of Research
Langmuir Blodgett (LB) and self-assembled multilayers have
been invesigated using Synchrotron radiation on a Huber
goncometer. Besides confirming the layer Bragg spacings,
Fresnel reflection has given us insight into the uniformity
of the layers. Inplane studies of the packing in polymer
multilayers are continuing. They indicate a nonuniform
inplane structure. We have demonstrated that Phthalocyanine
(Pc) oligomers of the type (C6H3)3SiOSiPcOSiPcOH form good
monolayers and Langmuir Blodgett multilayers films and can
be utilized as gas sensors. We have determined the crystal
structures of the solution crystallized oligomer and that of
LB multilayers. The structures are different. The 25%
density difference between the structures allows for easy
diffusion of gases into the multilayers. Conventional X-ray
diffraction techniques, as well as electron diffraction,
coupled with synchrotron X-ray data, are being utilized to
complete our understanding of this system. Polyaniline and
its oligomers have been prepared as monolayers and LB films
of these materials are being investigated as sensors. Liquid
crystalline films have been prepared for nonlinear optics
and pyroelectrics. These materials are excellent wave guides
in addition to yielding device quality, well-behaved second
harmonic polymers. We have elucidated the way the
pyroelectric coefficient can be optimized, combining
infrared and X-ray structural studies with pyroelectric
measurements. The nature of the pyroelectric response is
being investigated. Other amphiphiles are being
investigated. LB films of polyimides have been prepared
using the precursor method of Kakamoto. They are excellent
alignment layers for twisted nematic liquid crystal
displays. The morphology of these layers has been
investigated spectroscopically and by use of electron
diffraction. Working twisted nematic cells have been
prepared. LB films of polyphenylene have been prepared using
a precursor method. They are excellent alignment layers for
twisted nematic liquid crystal displays. The morphology of
these layers has been investigated spectroscopically and by
use of electron diffraction. Working twisted nematic cells
have been prepared. We are attempting to pattern dope these
alignment layers to replace the indium, tin oxide conducting
layers. We are exploring these materials as LED's. We have
prepared stress/strain sensors from bifunctional
polydiacetylenes containing liquid crystalline spacer
groups. The thermochromism and mechanochromism of these
materials are being investigated. Mechanical properties are
being determined. Diacetylene monomers containing amine
and/or acid terminated end groups have been interculated in
a number of clays. A number of these interculated monomers
have been polymerized forming organo-ceramic nanocomposites.
These systems have been investigated by x-ray and electron
diffraction techniques. Since many polydiacetylenes
graphitize when decomposed the possibility exists that
graphite-ceramic nanocomposites can be prepared. Our study
of phase transitions in poly(butylene terephthalate) and its
copolymers have been completed. They indicate that phase
separation occurs between the components of block
copolymers. Wide angle x-ray scattering patterns of these
segmented poly(ether ester) fibers prepared with
poly(tetramethylene glycol) blocks in poly(butylene
terephthalate) were studied by x-ray diffraction under
tensile stress. As the copolymers were made richer in
polyether the a to b stress induced transition was
inhibited.
Current Activity
Langmuir-Blodgett films of lithium salts of
10,12-nonacosadiynoic acid monomer (Li/16-8 DA) and polymer
(Li/16-8 PDA) were characterized by scanning force
microscopy (SFM) or AFM) to study their surface molecular
structure. Based on analysis of these images, a
two-dimensional oblique unit mesh is assigned for Li/16-8 DA
monomer LB film with unit mesh parameter c = 0.549 ± 0.040
nm and b = 0.541 ± 0.060 nm with an angle of 113º. A
hexagonal unit mesh is assigned for Li/16-8 PDA with unit
mesh parameter c = 0.497 ± 0.052 nm and b = 0.497 ± 0.060
nm. We then report the comparison of two-dimensional, fast
Fourier transform (FFT) of SFM images to the electron
diffraction images. From the viewpoint of a
three-dimensional structure projected onto a plane, centered
rectangular nets can be assigned for both Li/16-8 DA and
Li/16-8 PDA. The monomer unit cell parameters are c = 0.460
± 0.040 nm and b = 1.020 ± 0.060 nm. The polymer cell
parameters are c = 0.485 ± 0.080 nm and b = 0.820 ± 0.010
nm. The correlation between the two very different methods
of surface structure determination is excellent. However,
care must be taken in assigning the unit net
(two-dimensional representation) and the projected unit cell
(three-dimensional) vectors. We have prepared polyaniline
and its oligomers as monolayers and are studying LB
multilayer films of these materials as sensors. Not only do
common solvents reduce conductivity but recovery times as
solvent is removed depends on volatility and/or specific
interactions. We are using electronic, infrared and optical
methods as sensing methods. We intend to use polyaniline and
its oligomers confined by macrocycles (rotaxanes) as
sensors. We have already prepared LB films in two cases. We
have prepared stress/strain sensors from bifunctional
polydiacetylenes containing liquid crystalline spacer
groups. The thermochromism and mechanochromism of these
materials are being investigated. Mechanical properties are
being determined. We have found that one of these liquid
crystalline diacetylenes, when supplied as a cladding on an
optical fiber and then polymerized, acts as a hydrostatic
pressure sensor from 0 to three atmospheres. This occurs
because when light is transmitted through the fiber the
evanescent wave is affected by small changes in cladding
refractive index. This effect has also been used with
polymer dispersed liquid crystal cladding material to sense
electric fields, which change the effective refractive index
of this cladding.
Selected Publications
“Use of Aniline as a Chemical Sensor,” S. Sahasithiwat, T.
Ribar, J.L. Koenig and J.B. Lando, Polym. for Advanced
Tech., 2002.
Awards
Elected President of the Edison Polymer Innovation
Corporation (EPIC), Fall 2000 International Education Award,
Society of Plastics Engineers, May 1999
|
