Microgels characterisation

The first theory of gel formation of crosslinked polymers, elaborated by Carothers and Flory, considered the gel formation point as formation of an infinite network of chemical nodes [19]. Since this theory does not always agree with experimental data then the gel formation period concept was proposed. According to the indicated concept two gel formation points exist. The first corresponds to an appearance moment in a reactive medium of crosslinked clusters (microgels), characterised by non-fusibility... 

Therefore, the results stated above have again confirmed that the distribution of D values is the main reason for the variation in the structure of microgels, characterised by its fractal dimension D. The change in D with increased reaction duration is well described quantitatively within the frameworks of the cluster-cluster aggregation mechanism. The fractal space in which the curing reaction proceeds is formed by the structure of the largest cluster in the system [66]. 

Let us note in conclusion the strong dependence of on the structure of the microgels, characterised by the fractal dimension D (Figure 3.48). As follows from Figure 3.48, a sharp decay in is observed for D growth at D < 2 and the values on the asymptotic branch are attained at D > 2. As it is known [92], within the frameworks of irreversible aggregation models the following relationship is true ... 

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... 

This chapter considers the reasons for a variation of microgel structure characterised by its fractal dimension, D, formed in the cure of epoxy resin systems. Quantitatively, change of D during the increase of reaction time is well described within the framework of mechanism of aggregation cluster - cluster. The fractal space, in which the reaction curing proceeds, is formed by a structure of the greatest cluster in system. 

Karg, M. and T. Hellweg (2009). New smart poly (NIPAM) microgels and nanoparticle microgel hybrids properties and advances in characterisation. Current Opinion in Colloid < Interface Science 14(6) 438-450. 

Biffis, A. Graham, N.B. Siedlaczek, G. Stalberg, S. Wulff, G. The synthesis, characterisation and molecular recognition properties of imprinted microgels. Macromol. Chem. Phys. 2001, 202, 163 171. 

Macromolecular Symposia Vol.150, Feb.2000, p.229-34 SYNTHESIS AND CHARACTERISATION OF POLYMETHYL METHACRYLATE MICROLATEXES AND MICROGELS Mura-Kuentz A Riess G... 

Microgels used as rheology control agents in high-solids automotive coatings were characterised. The mechanism... 

Nuclear magnetic resonance (NMR) spectroscopic analysis is another useful technique for the characterisation of microgel particles. The technique provides information regarding the internal environment [60,61] and thermoresponsive transition behaviour of a microgel [62]. 

Application of fractal analysis and irreversible aggregation models for the description of crosslinked polymer curing processes allows it to be elucidated that macromolecular coil (microgel) structure, characterised by its fractal dimension, plays a larger role than purely chemical aspects. Such an approach allows a quantitative description of both curing process kinetics and its final results to be received. 

Therefore, the results stated above have demonstrated that both scaling Equation 3.8 and fractal Relationship 3.1 (or 3.7) describe to an equal extent curing reaction kinetics of haloid-containing epoxy polymer 2DPP+HCE/DDM at different curing temperatures. By virtue of this circumstance there exists an interconnection between the parameters included in the indicated equations. The fractal Relationship 3.7 introduces in consideration of the the kinetics problem the structure of the reaction products (in the given case the structure of microgels and condensed state after the gel formation point), characterised by its fractal dimension D that makes this concept physically more informative [46]. 

If we suppose that time tf corresponds to the percolation threshold of spherical microgels, closely filling reactive space, then x = 0.19 and /= 0.79. Such a value of /"actually corresponds to close packing of spheres of approximately equal diameter [65]. From this it follows that the first gel formation point is characterised by the stopping of growth of the microgels, closely filling the reactive space at their contact. 

It was shown above that curing of epoxy polymers can proceed in both Euclidean (three-dimensional) and fractal spaces. In the last case on conversion degree-reaction duration, continuous change occurs in the part of the kinetic curve a( ) almost up to the gel formation point in the structure of microgels, which is characterised by its fractal dimension D and, more precisely, monotonous increase in D occurs. At such D variation a curve a( ) has qualitative distinctions from a similar curve for curing of epoxy polymers in Euclidean space, namely practically linear growth of a as a function is observed in the indicated part up to the gel formation point (a < 0.8). The authors of paper [66] studied the reasons and mechanism of the structure of microgels, which indicated variation on the system EPS-4/DDM example. 

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