Electrically sensitive polymers

From their theory derivations, they concluded that for a cationic gel exposed to an electric field, if the gel comes in contact with the anode, that particular side will undergo shrinking. However, if the gel is sufficiently separated from the anode, die side of the gel near the anode will first swell and then shrink (Doi et al. 1992). As for die cathode side, shrinking of the gel occurs regardless of contact. 

Due to their sensitivity to electric stimulus, polyelectrolyte hydrogels have been investigated for their potential applications for electrically controlled drug delivery systems, electro-chemical actuators and sensors, as well as muscular actuators (Kaewpirom and Boonsang 2006). The set up for electrostimulation of 

9 Schematic of a hydrogel within a bath solution under applied electric field as can be seen, bending occurs in the hydrogel when subjected to an electric field (adapted from Li etal. 2007). 

70 Representation of pH-dependent ionization of poly(acrylic acid) and poly(/V,/V -diethylaminoethyl methacrylate) polyelectrolytes (adapted from Qiuand Park 2001). 

a poloxamer, resulted in a pH-sensitive as well as a thermosensitive hydrogel. Determan et al. (2007) loaded this hydrogel with lysozyme and observed its release kineties in vitro. They found that pH of the release media influenced the release rate of the lysozyme from the hydrogel, specifically in that an increase in pH resulted in a decrease in release rate (Determan et al. 2007). 

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IC Kwon, YH Bae, T Okano, SW Kim. Drug release from electric current sensitive polymers. J Controlled Release 17 149-156, 1991. 

The reference ISFET can be modified by chemically reacting the SiOH groups with trimethoxysilanes [7]. An alternative method involves deposition of a hydrophobic polymer on the surface, for example by thermal deposition of parylene [85]. These layers tend to be chemically bound to the SiOH surface, leading to enhanced stability and long lifetimes. Also the layers are very thin, which is essential because of decreased electrical sensitivity as the insulator thickness increases [9]. For ion-blocking layers, a stable attachment has been realized by plasma deposition [86,87]. 

Peridi- or tetrachalcogen-bridged polyacenes have been claimed in the patent Uterature for the preparation of electrical conducting materials <88EUP285564, 93EUP521826>. They have also been claimed as copolymers for the preparation of radiation sensitive polymers <90EUP362143>. 

High-resolution solid-state NMR spectroscopy provides useful information about the structures and dynamics of electrically-conducting polymers in the solid state, which sometimes cannot be determined by X-ray diffraction. NMR chemical shifts are very sensitive to the structure in the solid state and the separable resonance lines lead to an exact structural analysis. 

Electrochemical methods applied to deposit calcium phosphate coatings require an electrical conductor as a substrate as well as post-depositional heat treatment (Abe, Kokubo and Yamamuro, 1990). Hence, they are not well suited to coat non-conducting ceramics and heat sensitive polymers. 

Most polymers have high electrical resistivity, are inexpensive in comparison to other known insulating materials are heat resistant and sufficiently durable. Owing to their sensitivity to oxidation and solvents, they are frequentiy blended to generate better electrical insulating alloys. In the past two decades, there has been serious elfort to modify the electrical properties of polymers and their blends. The electrically conductive polymers can be broadly categorized as (i) electrostatic dissipating polymeric compositions, and (ii) electrically conductive polymer blends. Utracki has reviewed evolution of these materials [Utracki, 1998]. 

In some cases it may be necessary to include humidity control as well. This is invariably a more technically demanding requirement, which in turn carries a significant cost penalty. For this reason many laboratories in the polymer industry are not humidity controlled unless the laboratory is either regularly required to perform tests that are sensitive to moisture content, e.g., electrical tests, or is testing moisture-sensitive polymers, such as nylon. Where a temperature and humidity controlled room is to be provided, it is useful to have the controlled room situated within another room and with the minimum of windows and doors. 

The pseudocapacitance can also be provided by other pseudocapacitive materials such as some metal oxides and electrically conductive polymers (ECPs) that have much higher theoretical capacitance than carbon-based materials. These materials have been reviewed in detail elsewhere [89,90]. Although many materials have been reported to exhibit pseudocapacitive behavior, they are very sensitive to the type and pH of the electrolytes and few of them are suitable for application in strong acid electrolytes. As previously mentioned in Section 1.3.2, RUO2 is one of the most extensively studied pseudocapacitive materials in H2SO4 electrolytes. 

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