FisMat2017 - Submission - View

Abstract's title: Towards a realistic description of computer-generated nano- and microgels: assembly protocol, form factors, density profiles and swelling curves of single soft particles
Submitting author: Lorenzo Rovigatti
Affiliation: CNR-ISC
Affiliation Address: Piazzale Aldo Moro 2 - 00185
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Nicoletta Gnan (CNR-ISC), Emanuela Zaccarelli (CNR-ISC)

Soft colloids are becoming more and more popular in the physics community. Typically, soft particles have an internal polymeric architecture, which allows them to reach very dense regimes, with large interpenetration of the polymer chains. A very interesting class of such soft building blocks comprises soft particles with tunable swelling properties and an extremely broad range of applications, the so-called microgels [1].
Despite the huge experimental interest in microgels, theoretical efforts devoted to understand microgel behaviour have thus far barely scratched the surface of the problem. Most of these have been based on simple models, such as the Hertzian model for elastic spheres [2], which completely neglect the internal polymeric nature of the particles. However, the polymeric degrees of freedom are relevant in high-density states, and thus must be taken into account for a correct description of the behaviour of the dense phases that are required by many applications. Recently, more fine-grained computational studies have investigated nanogels generated with a regular mesh, generally based on the diamond lattice [3].
In this contribution we go one step further and generate microgels out of disordered gel networks obtained by the self-assembly of tetravalent (crosslinkers) and bivalent (monomer beads) patchy particles under spherical confinement. We employ a patchy model that allows for a very fast annealing of the system which, at the end of the assembly stage, is nearly fully bonded. The resulting network topology is used to generate the initial microgel configuration, which is subsequently simulated with a bead-spring model. We investigate the structure (in reciprocal and real space) and the swelling curves of microgels of different size and crosslink concentration, and assess their dependence on the extent of the spherical confinement used during the assembly stage. To highlight the validity of the assembly procedure we design a nanogel with the same crosslinkers concentration of experimental PNIPAM nanogels, finding that the in-silico particle well reproduces the swelling behaviour of the experimental ones. The devised protocol will allow us to not only investigate the dependence of the microgel properties on the underlining microscopic interactions, but also to compute the effective interactions acting between multiple soft particles.

[1] P. J. Yunker et al., Rep. Prog. Phys. 77, 056601 (2014)
[2] Z. Zhang et al., Nature 459, 230 (2009)
[3] H. Kobayashi and R. G. Winkler, Polymers 6, 1602 (2014)