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Sol–Gel Processing
Published in M. N. Rahaman, Ceramic Processing and Sintering, 2017
The condensation reactions that cause gelation continue long after the gel point, leading to strengthening, stiffening, and shrinkage of the network. These changes have a significant effect on the subsequent drying and sintering processes. If the gel is aged in the original pore liquid, small clusters continue to diffuse and attach to the main network. As these new links form, the network becomes stiffer and stronger. Many gels exhibit the phenomenon of syneresis, shown in Fig 5.15, where the gel network shrinks and expels the liquid from the pores (35). Shrinkage most likely results from condensation between neighboring groups on the surface of the solid network, as illustrated in Fig. 5.16.
Hydrophilicity and the Structure of Hydrophilic Systems
Published in Richard J. LaPorte, Hydrophilic Polymer Coatings for Medical Devices, 2017
When a stress is applied to a polymeric system, the molecules will be oriented in the direction of the applied stress to minimize its effects. The stress may be induced mechanically or by the introduction of solvent that drives polymer chains apart. Cross-linking may occur when the molecules are in a stressed condition, and after cross-linking is complete, the system will attempt to return to its original configuration [75]. The observed effect is the contraction of the gel upon standing, resulting in separation of the gel and liquid phases, and is referred to as syneresis. Syneresis results when the amount of solvent in the gel surpasses the swelling capacity of the network. This condition is exacerbated when the actual cross-linking density exceeds the critical cross-linking density for gelation.
Gelation studies of high molecular weight polymeric nanoparticles for application in fractured oil reservoirs with harsh conditions
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Mohsen Seid Mohammadi, Eghbal Sahraei, Behrouz Bayati
The result of bottle test demonstrated that by decrease in CCR, lower gelation time obtained for NSPs gel. This can be due to the increase of the number of cross-linking bonds between copolymer molecules. However, further decrease in CCR led to some instability in gel structure called syneresis effect. The gelant with CCR5 collapsed after 48 h during gelation reaction (Figure 9). This is related to the phase stability, which refers to the ability of a gel network to resist syneresis. Generally, syneresis is a phenomenon in which the reaction between the cross-linker and polymer is strong enough to expel water causing a shrinking of the polymer gel volume and collapse of the gel network (Moradi-Araghi 2000).