Microgels mechanical properties

Improvement in the processing and vulcanized qualities of a range of systems have been reported over the past decades. Modification of natural rubber, due to work in the British Rubber Producers Research Association, yields some of the most striking applications of microgel. A detailed study at the MV Lomonosov Institute of Fine Chemical Technology, in Moscow, on the effect of microgels on mechanical properties of cis-polyisoprene and butadiene-styrene rubbers extensively illustrates the properties of blends from latex combination of microgel and conventional or linear systems.(31)... 

Thus, in order to interpret the above correlations between mechanical properties and cocrosslinkers, the function of glycol bis(allyl phthalate)s as cocrosslinkers on the polymerization process of DAP beyond the gel-point conversion should be considered in connection with the microgel and, moreover, macrogel formation. Here it should be recalled that PEGBAP showed a rather drastic effect ... 

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. 

Evans, 1. D. and Lips, A. 1993. Influence of soluble polymers on the elasticity of concentrated dispersions of deformable food microgel particles, in Food Colloids and Polymers Stability and Mechanical Properties, eds. E. Dickinson and P. Walstra, The Royal Society of Chemistry, Cambridge, England. 

Nonaqueous dispersion polymer microgels have also found application as the main film former for certain types of exterior architectural coating where they give long term maintenance of mechanical properties leading to improved exterior durability on wooden substrates [3.94a]. 

The efect of crosslinking on the dynamic mechanical properties of polymers has been studied for many years. But one should note a clear distinction in the case of film formation from disposions of crosslinked latex particles. Each particle is a microgel. The crosslinks are confined to the particle itself without any additional ctosslinking across the particle boundaries [68]. Of course in some systems, like those formed from butadiene-containing latexes or from other latexes containing reactive functional groups, cross-boundary crosslinking can occur subsequent to film formation. 

Kumachev A, Tumarkin E, Walker GC, Kumacheva E (2013) Characterization of the mechanical properties of microgels acting as cellular microenvironments. Soft Matter 9 2959-2965... 

Chau M, Abolhasani M, Li Y et al (2014) Microlluidic generation of composite biopolymer microgels with tunable compositions and mechanical properties. Biomacromolecules 15 2419-2425... 

Schmidt, S., Zeiser, M., Hellweg, T., Duschl, C., Eery, A., Hwald, M., et al. (2010). Adhesion and mechanical properties of PNIPAM microgel films and their potential use as switchable cell culture substrates. Advanced Functional Materials, 20, 3235-3243. 

Figure 8.10 Microfluidic generation of micro-gel-based cellular microenvironments with varying internal compositions, (a) Co-emulsification of two cell suspensions to achieve control over the ratio of co-encapsulated "red" and green" cells by varying the volumetric flow rates of the suspensions, Qr and gc. respectively, (b) Control of the mechanical properties of cell-laden microgels achieved by varying agarose concentration in the micro-...

Mechanical properties of microgels from indentation measurements made using AFM cantilevers with sharp tips 382... 

Recently, Raz et al synthesized microgels with a double interpenetrating polymer network (IPN) stmcture containing Ca CTOSS-linked alginate and poly(N-isopropylactylamide) (PNIPAm) to use as the model cell. Hie mechanical properties were tuned by variation of the relative quantities of polymers and cross-linking component comprising the miaogel. 

The mechanical properties of the microgels are expressed in terms of their Young s moduli and characteristic relaxation times. The results of AFM compression experiments are shown in Figure 2. 

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