Temperature-sensitive hydrogels based on poly(vinyl methyl ether) (PVME) with ferroelectric or ferromagnetic properties were synthesized by high-energy irradiation. Barium titanate and poly(vinylidene fluoride) (PVDF) were used as ferroelectric filler and Ni as ferromagnetic filler. The filled PVME hydrogels were synthesized by electron beam or ␥-ray irradiation (of a suspension with 5-50 wt % of filler (with respect to polymer mass) in a 20 wt % aqueous PVME solution). Filling of the gel reduces the absolute swelling degree at low temperatures, but do not influence the phase-transition temperature of the gel. The particle distribution of the fillers inside the gel was visualized by field emission scanning electron microscopy. The fillers were incorporated in the PVME network and fixed because of their size (inorganic particles), as well as by chemical bonds (PVDF). The ferroelectric or ferromagnetic properties of the filled gels were proved. Measurements in a corresponding alternating field provide the hysteresis loop, for both the ferromagnetic and ferroelectric gel.
Temperature‐sensitive hydrogel beads were prepared by radiation crosslinking of poly(vinyl methyl ether) PVME spheres wrapped in Ca‐alginate. The obtained gel beads have diameters in the sub‐millimeter or millimeter range (depending on the PVME concentration). They were characterized by sol‐gel analysis, swelling measurements, and differential scanning calorimetry.The gel content g increases with increasing radiation dose D. The swelling degree Qv decreases with increasing PVME concentration cp and increasing D. In comparison to PVME bulkgels the phase‐transition temperature of the synthesized PVME gel beads is a little decreased.
Water swellable polymer networks, better known as hydrogels, are widely used in various applications, for example as superabsorbers, in flow control or drug release. Some of these hydrogels are showing responses to changes in external conditions, like pH, temperature or electric fields. Of special interest are hydrogels based on temperature sensitive polymers, which is caused by their LCST-(lower critical solution temperature) behavior. Above a certain temperature phase transition occurs-accompanied with a transformation of the hydrogel from the swollen to the deswollen state.
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