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drying because the water peaks (or peaks due to interactions of water
with other molecules) can be accurately monitored in the wet state of
the fi lm, something which is not straightforward with infrared tech-
niques. Thus, confocal Raman spectroscopy has been applied to measure
the distribution (depth profi ling) of water-soluble (initiator moieties
such as sulfates) and surface-active species (surfactants) in acrylic latex
systems [84,85] and to analyze phase separation and surfactant stratifi -
cation in styrene/butyl acrylate copolymer and latex blend fi lms [86] .
More recently, an excellent work on drying and fi lm formation of
latexes in both vertical and horizontal directions has been presented
by Ludwig et al. [87] using an inverse micro- Raman spectroscopy by
combining an inverse microscope with a confocal Raman spectrometer.
The equipment allows scanning a fi lm of 150
μ
m in 30 seconds at slices
of 5
m and the same scans can be performed horizontally starting from
the edge to the center at every 3 mm. In the same way, oxidation of
waterborne alkyd resins [88] during fi lm formation was followed by
tracking the oxidation reaction of the double bonds and the subsequent
reactions of the radicals formed. It was observed for model compounds
(methyl oleate, ethyl linoleate, and methyl linoleate) that oxidation
proceeded fi rst converting the
cis
C
μ
C and then to con-
jugated double bonds, and upon reaching a maximum level, the double
bonds tend to disappear by addition of radicals to these double bonds.
The confocal Raman spectroscopy has shown to be a complementary
tool to ATR-FTIR and atomic force microscopy in understanding
drying and fi lm formation processes.
=
C to
trans
C
=
5.5 FUTURE CHALLENGES AND TRENDS
5.5.1 Challenges of the Implementation of Raman
Spectroscopy in Industrial Polymerization Reactors
As it has been shown throughout the chapter, Raman spectroscopy is
a robust, noninvasive, and accurate sensor to monitor emulsion polym-
erization processes and polymer latex characteristics. However, most
of the applications shown earlier are related to monitoring and control
of laboratory reactors. It is nevertheless desirable to implement this
technique in large-scale industrial polymerization plants. There are
already several emulsion polymer-producing companies that use Raman
probes in polymerization reactors. The implementation of Raman spec-
troscopy in harsh environments, such as those of emulsion polymer
plants, has been possible because of the possibility of applying fi ber-
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