Polymers, gels responsive

Researchers are facing difficulties in improving the properties and response rates of chemomechanical andelectrochemomechanical systems based on polymer gels or proteins that are intended to be used as actuators in robotics. Lack of mechanical toughness and long-term durability are other problems to be solved. A basic improvement in the low efficiency... 

Polymer gels In response to pH changes in their enviromnent, materials derived from poly(acrylonitrile) will swell or shrink in a slow analogy to muscle action, thought to have robotic applications. 

R Kishi, O Hirasa, H Ichijo. Fast responsive poly(N-isopropylacrylamide) hydrogels prepared by gamma-ray irradiation. Polym Gels Networks 5 145-151, 1997. 

The model of electric field-controlled artificial muscles has been described in 1972 [5], Fragala et al. fabricated an electrically activated artificial muscle system which uses a weakly acidic contractile polymer gel sensitive to pH changes. The pH changes are produced through electrodialysis of a solution. The response of the muscle as a function of pH, solution concentration, compartment size, certain cations, and gel fabrication has been studied. The relative change in length was about 10%, and the tensile force was 1 g/0.0025 cm2 under an applied electric field of 1.8 V and 10 mA/cm2. It took 10 min for the gel to shrink. 

Non-silica-based RP-HPLC stationary phases have also been developed and their separation capacity has been compared with those of silica-based ones. The porous structure of crosslinked polymer gels may be responsible for the markedly different selectivity and retention characteristics. Up till now, the mode of separation on polymer stationary phases is not entirely understood at the molecular level. It has been established that the size-exclusion effect may influence the retention of analyses on polymer gels. 

Reports of building up two-dimensional polymers have been published by several research groups [9-12]. Additional reports [13-15] and a review [16] have appeared on stimuli-responsive polymer gels and their application to chemomechanical systems. The preparation and application of new monosized polymer particles have been reviewed [17]. 

The PNIPAM containing benzo[18]crown-6, described in Sect. 4, which underwent the chemical-induced phase transition in aqueous solution can be applied for constructing chemicals-responsive polymer gels. When the PNIPAM is crosslinked to form a gel network, the conformation change accompanied by the phase transition is expected to result in the volume phase transition. 

These considerations sparked our investigation into the possibility of producing responsive polymer gels from cellulose ether polymers. Cellulose ethers are alkyl-substituted cellulose derivatives which are on the FDA s GRAS list for use in food and pharmaceutical formulations. Since most cellulose ethers display lower critical solution temperatures (LCST), as gels they should be temperature... 

Palasis M (expected, 1993) Permeability of responsive polymer gels. Thesis, University of Cincinnati, Cincinnati OH... 

Mechano-chemical or chemo-mechanical systems which exert mechanical energies in response to chemical changes have long attracted interest among scientists, medical researchers and engineers. Katchalsky and his coworkers [74-76] were pioneers in the development of such systems using polymer gels, and their work has been expanded further by various researchers (see Ref. 49). 

Phase transition in gels in response to biochemical reactions [27,28]. Polymer gels were synthesized in which an enzyme (urease) or a biologically active protein (lectin) was immobilized. The volume phase transitions were observed in such gels when biochemical reactions took place. Such mechano-biochemical gels will be used in devices such as, sensors, selective absorbers, and biochemically controlled drug release. 

In order to demonstrate a general scheme for understanding the volume phase transition of polymer gels in response to environmental stimuli, some results of the recent investigations by the author s group and their analysis on the basis of the mean held theory have been presented here. Several conclusions and general principles are summarized as follows ... 

---