The development of the dynamic glass transition in
poly(n-alkyl methacrylate)s is
investigated with broad-band dielectric spectroscopy in the frequency
range from 10-4 to 109 Hz.
The
experimental data were analyzed by adjustment with one or a sum of two
Havriliak Negami functions.
Upon decreasing the temperature, the high-temperature relaxation
(a) changes into the local β relaxation
(Johari Goldstein mode), and the cooperative α relaxation sets in
close to this aβ transition. For poly(n-butyl methacrylate) a separate onset (zero intensity) of
the α process and a parallel course of both
traces in the Arrhenius diagram were observed. The activation
energy of the β process does not change
in spite of the parallel development of the α process. On the
other hand, for poly(ethyl methacrylate) the
α onset is close to a bend in the local process, i.e., the activation
energy of the latter changes after the α
onset. In both materials the intensity of the α process linearly
increases with falling temperatures but
with different intensity. Several scenarios for the
αβ-splitting region are suggested.
Samples with different amounts of
poly(vinyl acetate) adsorbed
on silica particles were prepared in order to study their interfacial
interactions and dynamics. The interface of adsorbed polymers to a
substrate plays an important role in many applications such as polymer
nanocomposites, thin films, and coatings. Characterization of such
interfaces is thus of high importance since they were found to differ
from bulk properties. Thermogravimetric analysis (TGA) is applied
to analyze the amounts of polymer adsorbed on silica particles. Broadband
dielectric spectroscopy (BDS) is employed in a broad frequency (10–1–106 Hz) and temperature range (178–423
K) in order to probe the polymer/silica interface. Two relaxation
processes can be identified for the composites: one corresponding
to the bulklike polymer and a second one related to polymer chains
close to the silica surface. For the latter the dynamic glass transition
is shifted to higher temperature due to reduced mobility. This effect
is investigated in dependence on the polymer content. Further investigations
are done to obtain information about bound and free carbonyl fractions
of poly(vinyl acetate) using Fourier transform infrared spectroscopy
(FTIR) measurements.
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