Shrink-swell phenomena

To understand how to control the level in the water drum for the boiler, one must first understand the shrink-swell phenomena of this process unit. If the demand for steam... 

There are several notable phenomena in the phase transition of gels in mixed solvents. One of them is the reentrant phase transition phenomenon. This is the phenomenon in which a successive change, swelling-shrinking-swelling, occurs as a function of solvent composition. Although... 

An important difference between Protein-Pak columns and other size exclusion columns is the silica backbone of the Protein-Pak columns. Because the silica structure is unaffected by the solvent, these columns do not swell or shrink as a function of the solvent. This is a general advantage compared to other size exclusion columns. However, silica-based columns can only be used up to pH 8, which limits their applicability. Also, surface silanols are accessible for interaction with the analytes, but this phenomenon has been minimized by proper derivatization techniques. Generally, a small amount of salt in the mobile phase eliminates interaction with silanols. 

It was observed, that a gel swollen to equilibrium in the liquid solvent shrinks as soon as it is transferred to the vapour phase of the same solvent. This phenomenon is known as the paradox of Schroeder (Freundlich 1932). For a theory of swelling with solvents in various phases, see (Borchard Steinbrecht 1991). 

The swelling effect results from additional embedding of water molecules into these thin layers. With the increase of the water content, the thickness of the water film increases. If the water is not pure, ion concentration results in a decrease of the film, which may be described by the electric double layer theory. As a consequence of this process, porosity and permeability will change. Swell-ing/shrinking is therefore a strong hydraulic-mechanic-chemical (HMC) coupling phenomenon. 

Mechanical instabilities of polymer systems usually arise in shrinking or swelling gels. A classic example is the formation of patterns on the surface of ionized acrylamide gels that swell due to an osmotically driven inflow of water (20-22). This inflow leads to mechanical stress within the gel and shear bending of the solvent-exposed gel layer. Despite the complex reactivity of the PA-MBO system, this type of mechanical instability seems to persist in our experiments and provides a possible explanation for the sudden, often front-like transition to honeycomb patterns. In this process, the reduction of mechanical stress is affected by the spatially periodic concentration patterns. Consequently, one can interpret the outward displacement of particles during the third phase of motion as a truly chemo-mechanical phenomenon. 

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