Polymer particles gelation properties

In the early days of the commercial development of PVC, emulsion polymers were preferred for general purpose applications. This was because these materials exist in the form of the fine primary particles of diameter of the order of 0.1-1.0 p,m, which in the case of some commercial grades aggregate into hollow secondary particles or cenospheres with diameters of 30-100 p,m. These emulsion polymer particles have a high surface/volume ratio and fluxing and gelation with plasticisers is rapid. The use of such polymers was, however, restricted because of the presence of large quantities of soaps and other additives necessary to emulsion polymerisation which adversely affect clarity and electrical insulation properties. 

Microfluidic generation of polymer particles starts from the emulsiflcation of liquid monomers, oligomers, or polymers. This step is followed by polymerization, cross-linking, or physical gelation of the molecules compartmentalized in droplets. Dimensions of polymer microbeads are predetermined by the dimensions of precursor droplets, which are in turn controlled by the geometry and dimensions of microchannels in MF droplet generator, the mechanism of droplet formation, the macroscopic properties of the droplet and continuous phases, and the relative volumetric flow rates of the continuous and droplet phases. 

Microgels can be produced by the mixing and emulsification of two different polymer solutions that can react to form cross-linked microgel particles that are monodisperse and have predictable swelling properties [8]. An example of this is the use of aldehyde and hydrazide-functionaUzed carbohydrates where heating or UV irradiation can be used for gelation. 

Micro- and nanoparticles of alginate are effortlessly achieved by gelation with calcium ions. This property enables creation of a pre-gel consisting of miniature aggregates of gel particles, which can be tracked by the addition of an aqueous polycationic solution to make a polyelectrolyte complex coating. Poly-L-lysine (PLL) is a cationic natural polymer that has been used with alginates to formulate nanoparticles. 

This chapter studies the local and global structures of polymer networks. For the local structure, we focus on the internal structure of cross-Unk junctions, and study how they affect the sol-gel transition. For the global structure, we focus on the topological connectivity of the network, such as cycle ranks, elastically effective chains, etc., and study how they affect the elastic properties of the networks. We then move to the self-similarity of the structures near the gel point, and derive some important scaling laws on the basis of percolation theory. Finally, we refer to the percolation in continuum media, focusing on the coexistence of gelation and phase separation in spherical coUoid particles interacting with the adhesive square well potential. 

For dry polymer extrusion, where easy pol3mier gelation is Important, powders with a high packing density and good flow properties are required. This requirement is met in practice by using a latex which has a particle diameter in the range 0.02-0.2pm. 

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