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Novel hydrogels that shrink in response to light irradiation and temperature change have been developed. Since any technical application of polymer gels critically depends on the response rate, therefore porous hydrogels have been prepared in order to accelerate the response reaction. Poly( N -isopropylacrylamide) gels were functionalized with photo-responsive spirobenzopyran and solvent/nonsolvent mixtures were used as swelling agent to introduce network heterogeneities during the gelation process. Both photo- and thermo-responsive properties of gels have been investigated and compared. The time dependence of bending deformation due to the asymmetric light irradiation as well as kinetics of shrinking has been measured. It was found that the fastest photo- and thermo-responsive shrinking was observed for loosely crosslinked porous hydrogels. Furthermore, it was confirmed that the highly cross-linked cylindrical gel rod with macroporous structure showed rapid bending deformation due to the asymmetric light irradiation.

The present paper describes the preparation and characterization of novel biodegradable nanoparticles based on self-assembly of poly-gamma-glutamic acid (γ-PGA) and chitosan (CH). The nanosystems were stable in aqueous media at low pH conditions. Solubility of the systems was determined by turbidity measurements. Sur- face charge and mobility were measured electrophoretically. The particle size and the size distribution of the polyelec- trolyte complexes were identified by dynamic light scattering and transmission electron microscopy (TEM). It was found that the size and size distribution of the nanosystems depends on the concentrations of γ-PGA and CH solutions and their ratio as well as on the pH of the mixture and the order of addition. The diameter of individual particles was in the range of 20-285 nm measured by TEM, and the average hydrodynamic diam- eters were between 150 and 330 nm. These biodegradable, self-assembling stable nanocomplexes might be useful for several biomedical applications.

A novel polymer gel exhibiting simultaneous temperature and magnetic field sensitivity has been prepared and studied. Poly(N-isopropylacrylamide) (PNIPA) and magnetic nanoparticles (magnetite, Fe 3 O 4 ) loaded PNIPA gel beads with mm size and monolith gels with cm size were prepared. The dependence of swelling degree on the temperature has been studied. The effects of cross-linking density and the presence of magnetic nanoparticles on the equilibrium swelling degree as well as on the collapse transition have been investigated. Swelling kinetic measurements were also made. By comparing the equilibrium swelling properties of PNIPA and magnetite loaded PNIPA gels it was found that the built in magnetic nanoparticles do not modify the temperature sensitivity of these gels. Within the experimental accuracy the temperature of the collapse transition was not sensitive to the presence of magnetic particles. We have compared the swelling behaviour of mm size gel beads to the cm size monolith gels in order to study the influence of surface skin layer on the swelling equilibrium. It was established that the extent of surface skin formation was decreased by the presence of magnetic particles.

Novel composite-gel membranes capable of regulating permeability in response to external temperature change are being explored. These membranes containing ordered nanochannels can act as “on−off” switches or “permeability valves”. The channels are designed to contain an ordered array of core−shell type magnetic polystyrene latex particles that can change their size in response to external stimuli. Expansion and contraction of the thin shell of magnetic latex particles affect the permeation pattern from the membrane “on” state to “off” state.

Several attempts have been made recently in order to develop smart windows, which can moderate light and heat intensities. Thermotropic gels have met with growing interest because of their advanced properties. Based upon phase transitions of polymer gels, a novel thermally adjustable window, which includes a gel layer, has been developed in our laboratory. The so-called gel-glass becomes opaque when the temperature exceeds a certain value and goes back to its original transparent state when it is cooled below the critical value again. Intelligent gel-glasses made of these materials can moderate the amount of sunlight and radiated heat. The optical properties of the gel layer are also modified by the Joule heat of audio frequency AC current. Two types of gel-glasses have been developed and investigated. Phase transition temperature of a poly(N-isopropylacrylamide) based gel was adjusted by copolymerization and by changing of the solvent composition. The cloud point of a poly(methyl vinyl ether) - water system in a PVA gel was varied by modifying the composition of the swelling agent. In the case of electrically adjustable thermotropic windows, optical properties, energy consumption and temperature changes during the switching process were studied.

Temperature-sensitive filled poly(N-isopropylacrylamide) (PNIPAAm) gel beads with diameters in the range of millimeters were prepared using the alginate technique. The polymerization and cross-linking reaction of NIPAAm in the presence of inorganic filling particles was performed in spherical networks of Ca-alginate forming interpenetrating networks (IPN). Thermo-sensitive gel beads could be obtained by washing these IPN with EDTA solution. The PNIPAAm gel beads were analyzed by optical methods to observe there swollen diameter in dependence on the temperature. The diameters of the swollen gel beads were in the range of 0.1 - 2 mm. The influence of the monomer to cross-linker ratio (MCR) and the filling materials (ferrofluid, BaTiO 3 , TiO 2 , and Ni,) were studied. The phase transition temperature (T pt ) was only weakly influenced by the MCR and the filling material remaining at around 34 °C.

The effect of cross-link density on the structure of Poly-(N-isopropylacrylamide) microgel particles prepared by emulsion polymerization was investigated by static and dynamic light scattering meas...

In this paper we summarise the effects induced by electric field on the motility and the shape of polymer gels. Then it is followed by a description of a new driving mechanism to induce deformation of a neutral polymer gels in a non-conducting medium. The main idea is to incorporate such finely distributed colloidal particles into a swollen network which responds to electric field. Since the particles cannot leave the gel matrix, all the forces acting on the particles are transmitted directly to the polymer chains resulting in either locomotion or deformation of the gel. Bending of weakly cross-linked poly(dimethyl siloxane) gels containing finely distributed electric field sensitive particles has been studied in silicon oil. Under an external electric field these gels underwent significant and quick bending. A theoretical approach has been developed and compared with the experimental results.

A novel polymer gel characterized by temperature and magnetic field sensitivity has been prepared. By incorporation of magnetite nanoparticles into poly(N-isopropylacrylamide) hydrogels, we are able to target and separate the gel beads by a magnetic field. It was established that the presence of magnetic material does not modify the temperature sensitivity of these gels.

Poly(N-isopropylacrylamide) microgel particles prepared by emulsion polymerisation in the presence of anionic surfactant have been investigated in different media in the swollen and collapsed state by static and dynamic light scattering measurements. The microgel latex was found to be highly monodisperse. The particle scattering function fits well to the theoretical function of a sphere. The hydrodynamic diameter of the particles is significantly higher than the diameter calculated from the measured radius of gyration for a sphere of constant density. The discrepancy was interpreted by a core/shell structure of the microgel particles. If the particles are in the collapsed state the two kinds of diameter coincide with each other, indicating that the microgel particles are compact spheres. In the globular state the gel still has 39% (w/w) water content. The particles bear a small surface charge resulting in a long-range electrostatic interaction between the particles in an aqueous environment. It was observed for the first time that at a sufficiently low ionic strength the aqueous microgel particle system undergoes an ordered/disordered phase transition.

Monodisperse poly(N-isopropylacrylamide) (PNIPA) nanogel latexes with temperature and magnetic field sensitivity were prepared and characterized. The phase transition of the latex was characterized by dynamic light scattering. Electrokinetic measurements revealed that the particles have a negative surface charge, which depends on the pH of the swelling medium. Incorporation of magnetite nanoparticles facilitates the separation of the gel beads and their application in targeted delivery in an external magnetic field. The incorporation of magnetic material does not modify the temperature sensitivity of the PNIPA latex.

The kinetics of swelling of spherical poly(dimethyl siloxane) (PDMS) composite networks in cyclohexane has been studied. The PDMS composite gels contain magnetite and iron particles built in the network either in randomly distributed form or in chain-like structure. The composite gel becomes anisotropic in the terms of both, mechanical and swelling properties. As a consequence the swelling kinetics can be characterized by direction dependent relaxation time. The swelling kinetics of these samples has been compared to that of pure PDMS gels. It was found that Li-Tanaka theory can be applied to describe the swelling kinetics of PDMS network.

Electric-, and magnetic field sensitive polymer gels are soft smart materials whose elastic and thermodynamic properties are strong function of the field strength imposed upon them. Since electric and magnetic fields are convenient stimuli from the point of signal control, therefore it is of great importance to develop and study such gel systems. In the first part of this paper we introduce a new concept to classify responsive polymer gels. Then it is followed by the discussion of a new driving mechanism which was discovered to induce deformation and movement of neutral polymer gels in non-conducting medium. Bending of weakly crosslinked poly(dimethyl siloxane) gels containing finely distributed TiO 2 particles as well as colloidal iron particles has been studied in silicon oil. Under electric field these gels undergo a significant and quick deformation.