Microgels particles

Saunders B R and Vincent B 1999 Microgel particles as model colloids theory, properties and applications Adv. Colloid Interface Sol. 80 1 -25... 

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

Xanthan has several undesirable properties. It ordinarily forms microgel particles that can plug permeability(137), it is expensive relative to other natural polysaccharide gel agents, and it resists degradation by ordinary gel breaker additives. These features have kept xanthan applications in fracturing gels to a minimum. Some literature(138) on xanthan has appeared. 

Preparation and Characterisation of Novel pH Responsive Microgel Particles. Matt Hearn, Department of Chemistry, University of Bristol, http //www.chm.bris.ac.uk/vincent/matt.html... 

The size distribution of the PVCL microgel particles synthesised by a batch emulsion polymerisation was monomodal and reasonably narrow [177], regardless of the choice of the emulgator, SDS (El, E2) or macromonomer (E3, E4). The size distributions remain monomodal upon subsequent grafting. A typical size distribution of a PVCL microgel (El) at 20 °C is presented in Fig. 17, as well as the effect of grafting, as a second step, on the hydrodynamic size (El-g). 

Thermosensitive microgel particles (Rh = 300-500 nm) were synthesised by electron beam irradiation of dilute aqueous PVME solutions [330]. It was noted that when the irradiation of the PVME solution (4.0g I, ) was... 

By using lipophilic initiators, such as 2,2 -azobis(isobutyronitrile) (AIBN), in the micro-ECP, diffusion of monomers is too slow compared with the reaction rate. Therefore, copolymerization is confined to the incoherent, lipophilic phase [112,113] and very small microgel particles with a rather uniform size result. 

In non-crosslinking ECP, monomers are supplied to the growing polymer species by diffusion of monomer from droplets. In crosslinking ECP, however, the gel effect increases the copolymerization rate in the droplets as well as in the growing microgel particles. As the diffusion rate of lipophilic monomers in the aqueous phase is lower than the copolymerization rate, monomer droplets may... 

Because the copolymerization of the components of micelles is very rapid, the microgel particles scarcely grow by intermicellar diffusion of the comonomers or by diffusion from the microemulsion droplets. This has been confirmed by the microgel composition [112] which remains constant over the whole reaction time (Fig. 25), even when using different ratios of EUP/comonomer [113,116]. 

A possible reason for the inaccessibility of a part of the acid groups could be the crosslink density which depends on the composition of the microgels. However, because the number of titratable acid groups does not depend on the composition and, therefore, on the crosslink density of the microgels, it must be concluded that electrostatic forces prevent ions from entering the microgel particles. 

On repeated freeze-drying of microgels with EUP-components an irreversible formation of an insoluble aggregate was observed [ 135]. It was supposed that this aggregation is due to radical reactions between adjacent microgel particles. The radicals are possibly formed by a mechanical rupture of chains due to stresses within the particles caused by freezing. 

Microfluidic devices, 26 959 effect of scale on, 26 960t fabrication of, 26 963-966 Microfluidics, 26 959-980 applications of, 26 966-975 basic features of, 26 959-966 future directions for, 26 976-977 history of, 26 959 industrial impact of, 26 976 Microfluidic structures fabrication of, 26 963-966 MicroFluidic Systems, 26 976 Micro-gas chromatography (micro-GC), 6 434 37 Microgel particles... 

Fig. 1.5 Connectivity of microgel particles within macroporous resin beads showing formation of small pores, A, from a network of...

It appears that networks formed from dimethacrylates are not uniformly crosslinked, as was often assumed in pioneering studies (9 10). Instead they have some resemblance to the "porridge" microstructure first attributed by Houwink to Bakellte ( ) and subsequently adopted to account for mlcrostructural observations on other networks prepared by stepwise polymerization reactions ( ) As far as is known, microgel particles have not been observed in networks formed by chain polymerization reactions. However, it seems necessary to invoke their formation in order to account for turbidimetric observations ( ), the onset of gelation, and gel partition Q9). In the present work a case has been made for invoking something like a "porridge" microstructure in order to account for some mechanical properties. 

Entrapping of bioactive ingredients by polymer matrix in gel or microgel particles heat-induced or cold-induced aggregation and gelation of globular proteins (microcapsules of 5-5000 pm)... 

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