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T h e rm o - and p H
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sensitive hydrogels composite.
There are many
polymeric hydrogels that can dramatically change its properties with a slight
oscillation parameters of the environment (temperature, pH, ionic strength, etc.).
Usually fixed size volume change of the hydrogel polymer is expressed by the
degree of swelling in water. Based on this property of many polymeric hydrogels
applications: the controlled release of substances sorbed hydrogel by changing
external conditions; the use of hydrogels as sensors in technical devices
responsive to changes in temperature, pH or other parameters.; creating bio- ..
sensors, etc. The spread obtained hydrogels based on carboxyl-containing
polymers, collapsing at low pH due to the dehydration of the hydrogel when the
polymer transition from the ionized salt form of a weakly dissociated acid
condition, and hydrogel polymers and IPA copolymers are sensitive to
temperature changes. This feature IPA polymers due to the fact that they contain
as hydrophilic (amide) and hydrophobic (isopropyl) groups. As the temperature
increases above 32-34 °C, the phase change due to the transition from the
conformation of macromolecules PIP highly swollen with water coil in
dehydrated collapsed globular structure. There are works which discloses
polymeric hydrogels increased sensitivity due to the introduction therein of
inorganic components. In [125] are composite hydrogels PIP-silica. The
composition prepared by the sol - gel method, mixing alkaline (pH 12), 10
%
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high-molecular solution was PIP (M = 15. 8 x 105) with different amounts of
tetramethoxysilane. Hydrolysis of tetramethoxysilane and subsequent
condensation of the silanol groups formed during hydrogel PIP weight ratio:
SiO
2
= 60:40 to 50:50. The authors of [125] is believed that the resulting
composite structure has a semi-IPN, wherein PIP linear molecules embedded in
the inorganic net. In addition, the hydrogel formation is enhanced by the
physical mesh emergence of hydrogen bonds between the polymer and the
silanol groups of the silica. The question of the formation of the floor - the UPU
is not quite clear, as strongly alkaline environment is not conducive to the
formation of fine silica structure. Nevertheless nanoscale SiO
2
particles disturb
homogeneous polymer morphology and increase the temperature sensitivity of
the composite hydrogel. A study of identical samples of hydrogels in the form of
1 mm thick discs showed that conventional hydrogels with increasing
temperature up to 60 °C, collapsing reach equilibrium degree of swelling for
more than 600min, while the balance comes composite hydrogels for 1-15 min.
The difference in degree of swelling at 20 and 60 °C for conventional hydrogels
was 11. The PIP 85, and filled with silica hydrogels have this value is 26.20
(27.0 at 20 °C and 0.80 at 60 °C).
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