Mechanical syneresis

Mechanical sugarcane harvesting, 23 446 Mechanical syneresis, 22 56 Mechanical testing, of acrylic fibers,... 

The spontaneous shrinking of a colloidal dispersion due to the release and exudation of some liquid frequently occurs in gels and foams but also occurs in flocculated suspensions. Mechanical syneresis refers to enhancing syneresis by the application of mechanical forces. Micro-syneresis is a special case of syneresis in which the polymer molecules cluster together while retaining some of the original bulk gel structure. This process creates regions of free liquid within the gel network. 

Mechanical Syneresis Any process in which syneresis is enhanced by mechanical means. See also Syneresis. 

Aging. When a gel is maintained in its pore Hquid, the stmcture and properties continue to change long after the gel point. This process is called aging. Four aging mechanisms can occur, singly or simultaneously polycondensation, syneresis, coarsening, and phase transformation (9,21). 

Gels with a low dynamic WeiBenberg number that means with large elastic and increasing viscous shares are soft and show better spreadability. They are more stable against mechanical treatment and have less syneresis. 

A second consideration concerned with propellant storage and which applies specifically to slurried propellants is its mechanical stability. The suspended particles must remain in stable suspension in the gelled liquid for long times, and the mixture must not exude liquid (syneresis). To... 

Condensation of TEOS could be controlled by the reaction rate and/or the diffusion of water, while copolymerization could be controlled solely by the diffusion rate of PDMS. Proposed structural models of ormosils based on the reaction mechanisms before gelation are shown in Figure 14. The TEOS/PDMS ratio of the ormosils was 1/0.082. Immediately after mixing, the self-condensation of TEOS(I) was predominant over copolymerization between PDMS and TEOS. As the reaction time increased, copolymerization between PDMS and TEOS(II) was promoted. At this time, the PDMS chains were broken into shorter chains and/or cyclic D4C tetramers. As copolymerization and condensation reactions of TEOS proceeded, the solution gelled (III). After gelation, syneresis (IV) occurred and nonbridging PDMS chains and cyclic D4C tetramers were released from the gel. 

Strazhesko, Strelko, Vysotsky, and co-workers (49-51) investigated the polymerization of monosilicic acid. Polysilicic acid is more acidic than monosilicic acid, and the dissociation constant of the acidic centers on the surface of polysilicic acid is 2 to 3 orders of magnitude greater than that of the monomer (49-51). Strazhesko, Vysotsky, and co-workers (52-55) showed that the isoelectric point represents not only the minimal rate of the gel formation process but also its syneresis. As a result, mechanically strong silica gels were obtained that had a maximum specific surface area. 

The path that leads to an understanding of the fundamental process of contraction ends at the syneresis effect given by unoriented actomyosin in gel. Neither the study of the individual purified proteins of the myofibril, nor the brilliant investigations on the fine structure of the fibril, has led to any well-founded theory as to the nature and mechanism of the structural changes which take place in the contractile particles. 

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