Computational investigation of microgels: synthesis and effect of the microstructure on the deswelling behavior

Abstract

We present computer simulations of a realistic model of microgels. Unlike the regular network frameworks usually assumed in the simulation literature, we model and simulate a realistic and efficient synthesis route, mimicking cross-linking of functionalized chains inside a cavity. This model is inspired, e.g., by microfluidic fabrication of microgels from macromolecular precursors and is different from standard polymerization routes. The assembly of the chains is mediated by a low fraction of interchain crosslinks. The microgels are polydisperse in size and shape but globally spherical objects. In order to deeply understand the microgel structure and eventually improve the synthesis protocol we characterize their conformational properties and deswelling kinetics, and compare them with the results found for microgels obtained via underlying regular (diamond-like) structures. For the same molecular weight, monomer concentration and effective degree of cross-linking, the specific microstructure of the microgel has no significant effect on the locus of the volume phase transition (VPT). However, it strongly affects the deswelling kinetics, as revealed by a consistent analysis of the domain growth during the microgel collapse. Though both the disordered and the regular networks exhibit a similar early growth of the domains, an acceleration is observed in the regular network at the late stage of the collapse. Similar trends are found for the dynamic correlations coupled to the domain growth. As a consequence, the fast late processes for the domain growth and the dynamic correlations in the regular network are compensated, and the dynamic correlations follow a power-law dependence on the growing length scale that is independent of the microgel microstructure.

Coarsening Kinetics of Complex Macromolecular Architectures in Bad Solvent

“…The exponents are x 0.6 for all the microgels, irrespective of the microstructural degree of disorder. The exponents obtained here for f = 0.02 are slightly smaller than those found in our previous work [23] (x ∼ 0.7) for a much higher degree of crosslinking (f = 0.1). We believe that the slightly higher value of the exponent for f = 0.1 is just an artifact originating from the proximity of the cross-links in such a system.…”

“…On the other hand in the diamond-like microgels no loops are present and all the cross-links are elastically active. Therefore, for a fair comparison with the disordered ones, the diamond-like microgels were constructed with the same fraction of cross-links (nodes) as the average number of intermolecular bonds in the disordered microgels, tuning the number of nodes so that the total mass of both kinds of microgels was essentially the same [23]. Thus, we simulated a diamond-like microgel of N = 21615 beads containing 78 nodes.…”

The influence of an applied magnetic field on the self-assembly of magnetic nanogels

“…The importance of micro-and nanogels stimulated the application of many different approaches, experimental and theoretical, to study their structural, mechanical, and rheological properties [48][49][50][51][52][53][54][55][56][57][58][59][60]. In particular, computer simulations on these systems have experienced an important development in very recent years with the adoption of a more realistic representation of the polymer network, moving away from the lattice or regular structures used in former models [57,61,62]. In this context, two years ago we presented the first coarse-grained simulation model of magnetic nanogels with a non regular internal structure [63].…”

Deformability and solvent penetration in soft nanoparticles at liquid-liquid interfaces

“…loops) is formed. 34 The use of excluded volume interactions between the nanogel's monomers is also essential in modelling realistic nanogels. Whereas in the case of regular diamond networks the use of DPD interactions for both the liquid and the monomers 30,31,33 might still be sufficient to model their spatial distribution, such interactions are clearly inadequate for the monomers in the disordered networks.…”

“…Several efforts to provide realistic models have been reported very recently. [34][35][36][37][38] See, e.g., the recent reviews 26,39 for more details about the progress on modelling gel-like colloidal particles.…”