Swelling hydrogels

Type of Hydrogel Swelling (w), mlmr1 Elastic modulus (G), kPa Refs. 

The swelling pattern considered above allows us to understand the peculiarities of the behavior of SAH and the effects encountered during their application. The kinetic aspects of swelling seem to be as important as the thermodynamics of this process. Therefore, we shall touch upon some problems concerning the kinetics of hydrogel swelling and deswelling. 

Table 10. Characteristics of hydrogel swelling and efficiency as a soil additive1 [139]...

The previous analysis of SAH behavior in the soil clearly shows that their application for improving the water-holding capacity is not universal. Hydrogel swelling in a porous, partially salinized medium is affected by numerous factors, most often negative, and therefore a rational application of SAH demands an accurate consideration of these factors. It is evident that certain principles for adjustment of hydrogels to physical and chemical soil parameters, as well as appropriate laboratory tests and calculation algorithm systems should be worked out. 

A hydrogel is formed by a water-soluble polymer that has been lightly crosslinked. Hydrogels swell as they absorb water but they do not dissolve. The volume expansion is limited by the degree of crosslinking. The minimum number of crosslinks needed to form a three-dimensional matrix is approximately 1.5 crosslinks per chain, and this yields the maximum expansion possible without separation of the chains into a true solution. Thus, a hydrogel may be more than 95% water and, in that sense, has much in common with living soft tissues. 

UV irradiation either of the aqueous solutions of polymers mixtures in the presence of photoinitiators and curing agents, or of the PVA hydrogels swelled with acrylic acid ... 

Mack AC, Jinshu M, McShane MJ. Transduction of pH and glucose-sensitive hydrogel swelling through fluorescence resonance energy transfer. IEEE Sensors 2005,2,912-915. 

The several processes occur simultaneously during the hydrogel swelling in the solution with the additive concentration cj ... 

Table 4 Values of the initial slope v of the hydrogel swelling curves and corresponding calculated values of the OH concentration...

The hydrodynamic transistors shown in Table 2 can be classified in two types distinguished by the function of the gel actuator. The actuator of type B acts as servo drive actuating the valve seat. The actuator of type B is directly placed within the flow channel. Therefore, the stimulant, which is typically a component of the process medium, directly controls the sensor-actuator element. The hydrogel swells or shrinks by absorption or release of the process medium and regulates the channel cross-section. Figure 1 shows two examples of such hydrodynamic transistors. 

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