Electric field-responsive fibers

HGURE 5.4.5 (a) Schematic representation of electric field-responsive movement of PVA fiber swollen with DMSO. 

Systems that develop contractile forces are very intriguing as analogues of physiological muscles. The idea for gel muscles was based upon the work of Katchalsky and Kuhn. They have prepared polyelectrolyte films or fibers which become elongated or contracted in response to a change in pH of the surrounding solution, and have estimated the induced force and response time. The contraction of gel fibers is also achieved by electric fields. Use of electric fields has the merit that the signals are easily controlled. 

Sukigara [115] studied the effect of electrospirming parameters (electric field, tip-to-collector distance and concentration) on the morphology and fiber diameter of regenerated silk from Bombyx mori using response surface methodology and concluded that the silk concentration was the most important parameter in producing uniform cylindrical fibers less than 100 run in diameter. 

In this section, physical stimuli-responsive fibers will be introduced, which are composed of polymers responsive to temperature, light/UV, or electric/magnetic field, which enable on/off switching and reversible property changes of nanofibers. 

Lithium niobate [niobium + -ate[ (1966) n. LiNb03. A crystaUine material whose physical properties change in response to pressure or the presence of an electric field and which is used in fiber optics and as a synthetic gemstone. 

As a host crystal a p-terphenyl crystal, with a few micrometers in diameter, has been used, which has been doped with a low concentration (10 ) of ter-rylene molecules. The tip of the optical fiber has been cooled to 1.4 K in order to avoid broadening of the fluorescence line via collective phenomena such as interaction with the phonons of the host crystal. The observed linewidth in fact is the natural linewidth (a few tens of MHz Fig. 9.9). The spectral response of fhese individual molecules can now be used for a local analysis of the surface, albeif with relatively low resolution (180 nm) (Fig. 9.10). Further experimental tricks such as electrical field induced Stark shifts can be applied to determine at least the position of the investigated molecules to within a few 10 nm. 

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