Research
I have been working on different experimental aspects of liquid crystals,
a soft condensed matter.
Tutorials on liquid crystals can be found in
http://www.lci.kent.edu/lcimages.html
http://www.tu-berlin.de/~insi/ag_heppke/clark/lcintro.htm
http://abalone.cwru.edu/
http://fy.chalmers.se/lc/engelska/tutorial/contents.html
http://www.phys.hawaii.edu/~ppc/lctut.html
One of the main topics I am currently involved in is
Photo-induced Phase Transitions
Some of my papers in this field are
Investigations of the opto-dielectric effect on a nematic liquid crystal
doped with a photo-active azo mesogen
J. APPL. PHYS. 87, 2084 (2000) [
Abstract
]
Effect of photocontrolled nanophase segregation in a re-entrant nematic liquid
crystal
ADV.MATER. 13, 40 (2000)
[Abstract
]
Effect of light on the polarization of a banana-shaped achiral compound doped
with a photoactive azobenzene material
J. APPL. PHYS. 90, 48 (2001)
[Abstract
]
Effect of pressure on the photoinduced nematic-isotropic phase transition
PHYS. REV.E., (in press)
[Abstract
]
Photoinduced nematic-isotropic phase transition: A case for the random-field
Ising model
PHYS. REV.E., 64, 041702 (2001)
Photoinduced effects in the vicinity of the smectic-C_alpha- smectic-A transition
PHYS. REV.E., 65, 031718 (2002) [
Abstract
]
Some microphotographs
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Abstracts of papers
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Investigations of the opto-dielectric effect on a nematic liquid crystal
doped with a photo-active azo mesogen
Geetha G.Nair, S.Krishna Prasad and C.V.Yelamaggad
Centre for Liquid Crystal Research, Jalahalli, Bangalore 560 013, INDIA
J. APPL. PHYS. 87, 2084 (2000).
We report the detailed temperature variation of the dielectric constant across
the nematic-isotropic transition in both the normal and UV-irradiated states
of a commercially available room temperature nematic mixture (E7 from E-Merck)
doped with a small quantity (4.5 mol%) of a liquid crystalline azo compound.
The photo-irradiation was done using a very low power (0.1mW/cm2) UV source.
Data of time-resolved measurements of the dielectric constant through both
the UV-activated "trans-cis" transformation and the thermal back relaxation
process are also presented and compared with time-dependent absorbance data.
Even for this low concentration of the photo-active material, UV irradiation
of as small a magnitude as 0.1 mW/ cm2 is observed to lower the nematic-isotropic
transition temperature by 15oC.
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Effects of photo-controlled nanophase segregation in a reentrant nematic
liquid crystal
S.Krishna Prasad and Geetha G.Nair
Centre for Liquid Crystal Research, Jalahalli, Bangalore 560 013, INDIA
Adv. Mater., 13, 40 (2001)
Liquid crystals composed of photoactive groups, such as azobenzene, are promising
materials for optical switching and image storage applications. On exposure
to light LC
materials commonly undergo an order-to-disorder transition. Here, an unusual
disorder-to-
order transition is presented and a photo-controlled nanophase segregation
mechanism is invoked to explain it.
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Effect of light on the polarization of a banana-shaped achiral compound doped
with a photoactive azobenzene material
Geetha G.Nair, S.Krishna Prasad, Uma S.Hiremath and C.V.Yelamaggad
Centre for Liquid Crystal Research, Jalahalli, Bangalore 560 013, INDIA
J. Appl. Phys. (in press)
We report photo-induced effects on a liquid crystal comprising of bent-core
molecules, doped with a photoactive azobenzene compound and exhibiting the
recently discovered “banana” B2 mesophase. The photoisomerization of the
azobenzene molecules, brought about by the UV-radiation, hardly changes the
B2-isotropic transition temperatures, but has a significant influence on
the spontaneous polarization (Ps) as well as the switching time in the B2
phase. The efficiency of this opto-polarization effect has been observed
to be strongly dependent on the temperature at which the irradiation is carried
out. A possible mechanism responsible for the observed phenomenon has been
suggested.
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Effect of Pressure on the Photoinduced Nematic-Isotropic Phase Transition
S.Krishna Prasad, D.S.Shankar Rao and P.Jeyagopal*
Centre for Liquid Crystal Research, Jalahalli, Bangalore 560 013, INDIA
* Permanent address: LCD Division, Bharat Electronics, Bangalore 560 013,
INDIA
We report the results of the first high pressure studies on photoinduced
nematic-isotropic phase transition. It is observed that pressure has a significant
influence on the shift in the transition temperature caused by the UV radiation.
We propose a possible mechanism to explain the observed results.
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Photoinduced effects in the vicinity of the smectic-C_alpha- smectic-A transition
S. Krishna Prasad*, K.L.Sandhya* and Y.S.Negi+}
*Centre for Liquid Crystal Research, Jalahalli, Bangalore 560 013, INDIA
+Centre for Materials for Electronics Technology, Panchwati, Off Pashan
Road, Pune 411 008, INDIA
We report the first results of photoinduced effects near the smectic-C_alpha-
smectic-A transition in a binary liquid crystalline material. Dielectric
dispersion measurements show that the softening of the tilt fluctuation mode
in the vicinity of the transition gets enhanced in the presence of the UV
light.