“…Theoretical calculations based on Förster kinetics were applied to analyze the diffusion of polymer segments, assuming time-dependent Gaussian distributions of chromophores in the direction normal to the layer plane. The details of the computer simulation have been described previously. , Fitting of the theoretical curve to the time-dependent energy-transfer efficiency allowed us to evaluate the diffusion constant D for the LB films. Obtained values of D were plotted in Figure .…”
Section: Resultsmentioning
confidence: 99%
“…Thus, it is necessary to know the mechanism of the structural relaxation of the LB films. We have studied the layered structure of poly(vinyl octanal acetal) (PVO) LB films and its thermal relaxation behavior through the interlayer energy transfer. − The energy-transfer method is a powerful one to observe the structures in a molecular dimension. Previously, the effect of side chain length 13 and that of molecular weight 14 on the structural relaxation have been reported.…”
Poly(vinyl octanal acetal) (PVO) was prepared from poly(vinyl alcohol) (PVA) in which the
main chain had three different tacticities and the stereoregularity was characterized by 1H NMR
spectroscopy. a-PVO prepared from atactic-PVA and s-PVO from syndiotactic-PVA had similar fractions
of cis- and trans-acetals in the main chain, but i-PVO from isotactic-PVA had different ones. Ultrathin
films of these polymers were prepared by the Langmuir−Blodgett (LB) technique, and the thermal
relaxation of their multilayer structure was investigated by the energy-transfer method. When the LB
films were composed of polymers which had a main chain with a similar stereostructure, the polymers
were intermingled with each other by the thermal treatment and the onset of the diffusion of polymer
segments was affected by the glass-transition temperature of the bulk. In contrast, the polymers with
different stereostructures in each layer were not mixed with each other, but phase-separated, presumably
forming droplets in the ultrathin films. It is concluded that the relaxation behavior of polymer LB films
strongly reflects the stereoregularity of the sample polymers.
“…Theoretical calculations based on Förster kinetics were applied to analyze the diffusion of polymer segments, assuming time-dependent Gaussian distributions of chromophores in the direction normal to the layer plane. The details of the computer simulation have been described previously. , Fitting of the theoretical curve to the time-dependent energy-transfer efficiency allowed us to evaluate the diffusion constant D for the LB films. Obtained values of D were plotted in Figure .…”
Section: Resultsmentioning
confidence: 99%
“…Thus, it is necessary to know the mechanism of the structural relaxation of the LB films. We have studied the layered structure of poly(vinyl octanal acetal) (PVO) LB films and its thermal relaxation behavior through the interlayer energy transfer. − The energy-transfer method is a powerful one to observe the structures in a molecular dimension. Previously, the effect of side chain length 13 and that of molecular weight 14 on the structural relaxation have been reported.…”
Poly(vinyl octanal acetal) (PVO) was prepared from poly(vinyl alcohol) (PVA) in which the
main chain had three different tacticities and the stereoregularity was characterized by 1H NMR
spectroscopy. a-PVO prepared from atactic-PVA and s-PVO from syndiotactic-PVA had similar fractions
of cis- and trans-acetals in the main chain, but i-PVO from isotactic-PVA had different ones. Ultrathin
films of these polymers were prepared by the Langmuir−Blodgett (LB) technique, and the thermal
relaxation of their multilayer structure was investigated by the energy-transfer method. When the LB
films were composed of polymers which had a main chain with a similar stereostructure, the polymers
were intermingled with each other by the thermal treatment and the onset of the diffusion of polymer
segments was affected by the glass-transition temperature of the bulk. In contrast, the polymers with
different stereostructures in each layer were not mixed with each other, but phase-separated, presumably
forming droplets in the ultrathin films. It is concluded that the relaxation behavior of polymer LB films
strongly reflects the stereoregularity of the sample polymers.
“…Apparently, the change of I A /I D by the thermal treatment was small, revealing the excellent thermal stability of the layered structure for the PG LB films. The stability was much higher than that for the LB films of low molecular weight fatty acids or other polymers with a flexible main chain. , 8 (a) Effect of heating/cooling on the I A /I D for the C- n LB films up to 100 °C. Filled symbols indicate the values on the heating process, and open ones indicate the cooling process.…”
Ultrathin films of α-helical polyglutamate with long flexible side chains (PG) were fabricated
by the LB technique, and their nanostructure was investigated by the energy transfer method. The rodlike
main chain of PG was labeled by incorporating either energy donor (naphthalene, Np) or acceptor
(anthracene, An) molecules via short side chains. The fluorescence spectra of Np−An multilayers with
the same number of spacing layers gave different energy transfer efficiencies, depending on the mode of
depositions. This phenomenon was interpreted as being caused by the noncentered structure of the polymer
backbone, which was probed by both X-ray reflectometry and fluorescence spectroscopy. The Y-type
deposition induced a bilayer structure in which the stiff main chains of each monolayer were located
close to the center of the bilayer. The layered structures showed excellent thermal stability up to around
120 °C. By thermal treatment higher than 120 °C, the layered structure relaxed to a stable state in
which the α-helical backbones in each layer became intermingled.
“…Theoretical calculation was performed to examine the disordering process of the layered structure quantitatively. The diffusion constant, D , of the polymer chain in the direction of the film thickness was obtained by a method described in detail elsewhere. , The diffusion in the LB film results in a distribution of chromophores in the direction normal to the film plane. We assumed a Gaussian function for the chromophore distribution, which is characterized by the distribution center x 0 and the variance σ 2 : where c ( x ) is the concentration of chromophores at a displacement x and c 0 is related to the total number of chromophores placed in the system.…”
Section: Methodsmentioning
confidence: 99%
“…To examine thermal stability of polymer LB films, small-angle X-ray scattering , is used to probe the periodic layered structure, and polarized infrared spectroscopy , and optical second-harmonic generation (SHG) method to probe the orientational stability of polymer side chains. We employed the energy-transfer technique to study the structural relaxation of the polymer LB films in nanometer dimensions. − It is powerful to observe the microscopic change in the ultrathin films because of high sensitivity. Particularly, in amorphous polymer LB films, which do not show clear peaks of X-ray reflection due to their low contrast of electron density, the energy-transfer method is effective for structural analysis.…”
Thermal relaxation of ultrathin polymer films prepared by the Langmuir−Blodgett (LB)
technique was studied by a comparison with a three-dimesional bulk system. Poly(vinyl alkanal acetal)s
(PVAA) with different side chain lengths were synthesized and the thermal stability of their LB films
was investigated by the energy-transfer phenomenon between fluorescence probes labeled to the polymer
chains. The multilayer structure was irreversibly disordered and mixed by the thermal treatment. A
close relationship was found between the glass-transition temperature (T
g) of the polymer bulk and the
temperature at which the layered structure of LB films started to disorder. Theoretical calculations
based on Förster kinetics were applied to measure the diffusivity of polymer segments, which was successfully evaluated by assuming time-dependent Gaussian distributions of chromophores in the direction
normal to the layer plane. The apparent activation energy ΔE
a of the diffusion constant for the LB films,
however, was much smaller than that for polymer bulk obtained by the viscoelastic measurement. It
was concluded that the relaxation process of the ultrathin polymer films occurs by conformational changes
from the two-dimensional nonequilibrium state given by the LB deposition. The confined form could be
released by the local motion of the polymer segments under the heating to temperatures higher than T
g.
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