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Summary of Research Projects (Supports in 2004
Fiscal Year)
| Subjects |
Molecular Aggregates Produced by Radiation Pressure
of a Focused Laser Beam: Structural Analysis using Micro spectroscopy combined
with Laser Trapping Technique |
| Representative researcher |
Graduate School of Science,Hokkaido University
Yasuyuki TSUBOI |
| We developed a confocal Raman microspectroscopy
system combined with a laser trapping technique and applied it to aqueous
solutions (H2O and D2O) of poly(N-isopropylacrylamide) (PIPA)
and poly(vinyl methyl lether)(PVME), which are well-known as representative
thermo-responsive
polymers, i.e., phase transition/separation between coiled and globular
states. By introducing a near-infrared (1064 nm) laser beam into a microscope,
PNIPA and microparticles were produced at the focused spot of the laser
beam, both in H2O and D2O. By using the present system, we succeeded in
obtaining the Raman spectra of PIPA in the coiled and globular states over
a wide wavenumber region (800-3500 cm-1) for the first time. For the D2O
solutions (in which the photothermal effect is negligible and hence the
microparticles should be produced purely by the effect of radiation pressure),
some significant differences were observed in the Raman spectra for the
coiled state, in the globular state, and for laser induced microparticles.
By analyzing these spectra in detail, we revealed that the structure of
the laser-induced microparticles was analogous to that in the globular
state. We also discuss the fundamental mechanism underlying the transformation
of the higher order structure of a polymer by radiation pressure. For PVME,
the similar behavior, i.e., the photo-induced phase transition was also
confirmed. Moreover, influence of the radiation pressure was examined for
volume phase transition of PIPA gel. By the integration of above results,
we demonstrated radiation pressure of a focused laser beam can induce structural
changes of thermo-responsive polymer systems. |
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