Stretched polymer gels

The structure of water at the PVA/quartz interface was investigated by SFG spectroscopy. Two broad peaks were observed in the OH-stretching region at 3200 and 3400 cm , due to ice-like and liquid-like water, respectively, in both cases. The relative intensity of the SFG signal due to liquid-like water increased when the PVA gel was pressed against the quartz surface. No such increase of the liquid-like water was observed when the PVA gel was contacted to the hydro-phobic OTS-modified quartz surface where friction was high. These results suggest the important role of water structure for low friction at the polymer gel/solid interfaces. 

Brown AEX, Litvinov RI, Discher DE et al (2009) Multiscale mechanics of fibrin polymer gel stretching with protein unfolding and loss of water. Science 325 741-744... 

Bin, Y., Tanabe, Y., Nakabayashi, C., Kurosu, H., and Matsuo, M. 2001. Morphology and mechanical properties of swollen gels and dry gel films of poly(vinyl alcohol) prepared by crystallization from solutions under simultaneous biaxially stretching. Polymer 42 1183-1200. 

The principle of motility of this gel looper is associated with reversible and cooperative complexion of surfactant molecules on the polymer gel in an electric field that causes shrinkage of the gel. The electric field drives and controls the direction of the equilibrium to give anisotropic complex formation. Thus, with alternative application of the electric field the gel moved forward stretching and bending along the ratchet bar suspended in the surfactant solution. 

Recently, a remarkable apparatus for rapid and reversible gel stretching based on gelatine as the polymer gel has been developed by Kuchel et al. and its usefulness demonstrated by the distinctions of enantiomers using RDCs and other anisotropic parameters. It has been demonstrated by Kummerlowe et al that such an apparatus is not limited to gelatine, but can also be used with covalently cross-linked hydrogels and even with gels... 

Fig. 2. Stages of relaxation in diluted polymer gel a) Undeformed gel b) short times gel (black) and sol (green) polymers are stretched and aligned c) intermediate times sol polymers (in green) relax but gel network (black) is still deformed d) long times polymer in gel network relaxes but retains an equilibrium deformation.

The peak at small distances in the force versus distance curve is related to the onset of cavitation, or the formation of small air pockets between the polymer gel and the probe (c.f. Figure 11b). Once cavitation occurs, the measured force decreases significantly. The air pockets then grow as the polymer gel is stretched further and fibrils are formed. The force increases as the fibrils are stretched and strain harden. Finally, the fibrils detach cleanly from the probe and the measured force returns to a value of zero. The debonding mechanisms are discussed further in Section 4. 

Figure 1 shows a polymer gel made of a urease-containing copolymer made of NIPAAm and acrylic acid as an example of a gel that exhibits the biochemomechanical function. This gel reversibly stretches and contracts in the presence or absence of urea. To actuate behavior, a urea concentration of 1 mM (60mg/ml) was sufficient. Therefore, this function makes it possible to use it as a urea sensor. In fact, Koopmann et al. [21] used this concept and developed a sensor for ionic saccharide detection. Unfortunately, there are no other examples on the study of this new type of sensors. Hence, it must await further research for the evaluation of its practicality. 

Gel spinning, also known as semi-melt spinning, is a method that prepares high-strength and high-elastic module fibre in the gel state. After the extrusion of the polymer solution or plasticised gel from the spinnerets, it is cooled in solvent or water before being stretched into gel fibre by ultra-high... 

---