isosbestic point found for series of spectra recorded as a function of any factor
(temperature, pressure, pH, time, etc.) proves that under the given factor, the system
transits from one state to another and it should be also useful to study conformational changes in organic compounds. If the bands related to isosbestic point are
separated and do not overlap with other bands, it can be easily found by an analysis
of differential spectra as a signal amplitude at the isosbestic point that they are equal
to 0 and located between two extremes, which should be proportional to the part of
molecules at the given state. However, in the case of polymer systems, overlapping
of many lines often occurs. Therefore, the deconvolution process is the only way to
analyse the integral intensities of bands related to various states. In the case of
PVME gels, it was shown [162] that the ratio of symmetric and asymmetric
stretching vibrations of CH 2 groups located in the polymer main chain may be used
to monitor conformational changes during VPT and to estimate the activation
energy of a VPT process. The spectra were recorded as a function of the temperature. The natural logarithm of the ratio of integral intensities of symmetric and
asymmetric stretching vibrations of CH 2 groups as a function of inverse temperature according to Arrhenius-type equation was shown in Fig. 8.11b. In the range of
temperatures related to VPT, the relationship was found linear and the slope corresponding to activation energy was estimated at ca. 88 kJ/mol. A similar value
(80 kJ/mol) was found for the PNIPAM coil-to-globule transition [169].
As it was shown in this section, the vibrational spectroscopy can be very useful
to study various issues related to thermo-responsive polymers, such as a degree of
polymer hydration and its changes induced by the temperature, the water structure,
polymer chain conformations related to the coil-to-globule transition or VPT, etc.
However, a lot of information on polymer systems that can be extracted from IR
and Raman spectra is usually averaged over billions of molecules. To overcome
this, computer simulations seem to be most useful as they give access to specific
local molecular states.
8.5 Computer Simulations of Thermo-Responsive
Polymer–Water Systems
A short overview of computational methods applicable to study ‘smart’ polymer–
water systems is presented in this section. In spite of water importance in aqueous
SRPS, computational studies performed for pure water are not included in the
discussion as a separate and very broad topic. A wide variety of different methods
applied for liquid water modelling makes them impossible to be presented here
even briefly. However, for readers interested in this matter some references can be
recommended [170, 171].
Modelling and simulation have constituted an important part of the research
process in material sciences for a few decades. This field plays an important role in
predicting and explaining experimentally observed phenomena. Newly developed
8 Vibrational Spectroscopy in Analysis of Stimuli-Responsive …
245
(temperature, pressure, pH, time, etc.) proves that under the given factor, the system
transits from one state to another and it should be also useful to study conformational changes in organic compounds. If the bands related to isosbestic point are
separated and do not overlap with other bands, it can be easily found by an analysis
of differential spectra as a signal amplitude at the isosbestic point that they are equal
to 0 and located between two extremes, which should be proportional to the part of
molecules at the given state. However, in the case of polymer systems, overlapping
of many lines often occurs. Therefore, the deconvolution process is the only way to
analyse the integral intensities of bands related to various states. In the case of
PVME gels, it was shown [162] that the ratio of symmetric and asymmetric
stretching vibrations of CH 2 groups located in the polymer main chain may be used
to monitor conformational changes during VPT and to estimate the activation
energy of a VPT process. The spectra were recorded as a function of the temperature. The natural logarithm of the ratio of integral intensities of symmetric and
asymmetric stretching vibrations of CH 2 groups as a function of inverse temperature according to Arrhenius-type equation was shown in Fig. 8.11b. In the range of
temperatures related to VPT, the relationship was found linear and the slope corresponding to activation energy was estimated at ca. 88 kJ/mol. A similar value
(80 kJ/mol) was found for the PNIPAM coil-to-globule transition [169].
As it was shown in this section, the vibrational spectroscopy can be very useful
to study various issues related to thermo-responsive polymers, such as a degree of
polymer hydration and its changes induced by the temperature, the water structure,
polymer chain conformations related to the coil-to-globule transition or VPT, etc.
However, a lot of information on polymer systems that can be extracted from IR
and Raman spectra is usually averaged over billions of molecules. To overcome
this, computer simulations seem to be most useful as they give access to specific
local molecular states.
8.5 Computer Simulations of Thermo-Responsive
Polymer–Water Systems
A short overview of computational methods applicable to study ‘smart’ polymer–
water systems is presented in this section. In spite of water importance in aqueous
SRPS, computational studies performed for pure water are not included in the
discussion as a separate and very broad topic. A wide variety of different methods
applied for liquid water modelling makes them impossible to be presented here
even briefly. However, for readers interested in this matter some references can be
recommended [170, 171].
Modelling and simulation have constituted an important part of the research
process in material sciences for a few decades. This field plays an important role in
predicting and explaining experimentally observed phenomena. Newly developed
8 Vibrational Spectroscopy in Analysis of Stimuli-Responsive …
245