Swelling pressure, 5.26

The parameters which characterize the thermodynamic equilibrium of the gel, viz. the swelling degree, swelling pressure, as well as other characteristics of the gel like the elastic modulus, can be substantially changed due to changes in external conditions, i.e., temperature, composition of the solution, pressure and some other factors. The changes in the state of the gel which are visually observed as volume changes can be both continuous and discontinuous [96], In principle, the latter is a transition between the phases of different concentration of the network polymer one of which corresponds to the swollen gel and the other to the collapsed one. 

Direct mechanical methods can be used to determine the swelling pressure of hydrogels, e.g., by means of devices in the form of a cylindrical chamber equipped with a piston in which the gel contacts the solution through a porous membrane. This technique allows measuring very low pressure (of the order of 0.1-10 kPa) and makes it possible to analyze the SAH with swelling up to 700 ml g-1 [102, 103]. Among others, the method of osmotic deswelling is to be mentioned [104]. 

When considering the effect of the external compression on the SAH swelling their response to mechanical forces is of primary interest. Such forces arise, for instance, when the gel swells in the cavity constraining its volume. In this case the gel swelling pressure (n) expanding the network is counteracted by an external pressure (p)... 

The swelling pressure of polyelectrolyte gels is usually considered as a sum of the network (jtnct) and ionic contributions (nion) [4, 99, 101, 113, 114]. The former describes the uncharged gel while taking into account the interaction between the polymer segments and the solvent as well as the network elasticity [4] ... 

The swelling pressure or osmotic deswelling data can be, therefore, described as the functions of n(w) by either of the theories [115]. This description can be then applied to determining the network parameters (see, for example, Ref. [22]). On the other hand, the swelling pressure which is directly connected with the chemical potential of water in the gel ... 

The effect of the network density on the polyelectrolyte hydrogel elasticity can be understood taking into account the fact that the elastic modulus is closely connected with the swelling pressure (see, for example, Refs. [20, 115]) ... 

Typical SAH are weakly charged flexible networks. A simple theory was proposed to describe these networks, in which the ionic swelling pressure includes only an ideal (Donnan) contribution [4,101], In this approximation, the swelling equilibrium is described by a system of equations including Eq. (3.1) and the... 

The effect of the pressure on the activities of the ions is disregarded here. It is readily shown to be of negligible importance, even for swelling pressures up to many atmospheres. 

However, there are a significant number of cases, sometimes estimated as 19% of fractures, where repair does not occur in a reasonable amount of time. The problems are associated primarily with severe injury, infection, arthritis, or biochemical abnormalities. A very common cause, known as the compartment syndrome, is related to severe swelling pressure on the blood vessels that limits blood access to the muscles. In many of these cases, electrical stimulation has been shown to be effective in accelerating repair. 

The stability of shales is governed by a complicated relationship between transport processes in shales (e.g., hydraulic flow, osmosis, diffusion of ions, pressure) and chemical changes (e.g., ion exchange, alteration of water content, swelling pressure). 

Further stability models based on surface area, equilibrium water-content-pressure relationships, and electric double-layer theory can successfully characterize borehole stability problems [1842]. The application of surface area, swelling pressure, and water requirements of solids can be integrated into swelling models and mud process control approaches to improve the design of water-based mud in active or older shales. 

Fig. 4 Insert Representative macroscopic image of an APNP hydrogel scaffold seeded with human adipose-derived stem cells following 7 days of culture in a 12-well plate. Graph Osmotic swelling pressure profile of APNP hydrogel scaffolds (green-squares) compared to human NP (orange-triangles and red-diamonds) values found in the literature [28]...

We have also shown that these scaffolds generate an osmotic swelling pressure profile (Fig. 4) that mirrors that of a 25-year-old human and that they are conducive to repopulation with human ADSC [28, 113]. 

Urban JP, McMullin JF (1988) Swelling pressure of the lumbar intervertebral discs influence of age, spinal level, composition, and degeneration. Spine 13(2) 179-187... 

For given external vapor pressure and total gas pressure, the liquid pressure (or swelling pressure) in the membrane is obtained from Equations (6.6) and (6.13) ... 

TABLE 2 Effect of Particle Size and Compression Pressure on Swelling Pressure and Disintegration Time ... 

Disintegranf Compression Pressure, (MPa) PartieleSize (pm) Swelling Pressure (kPa) Disintegration Time (s)... 

The imbition of a dried gelatine by the addition of water is accompanied by a heat evolution and the exertion of a swelling pressure. Eodewald Zeit. Phys. Chem. xxiv. 206, 1897) obtained the following values for the heat of wetting ... 

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