A new look at effective interactions between microgel particles

Bergman, Maxime J.; Gnan, Nicoletta; Obiols‐Rabasa, Marc; Meijer, Janne‐Mieke; Rovigatti, Lorenzo; Zaccarelli, Emanuela; Schurtenberger, Peter

doi:10.1038/s41467-018-07332-5

Cited by 118 publications

(134 citation statements)

References 58 publications

(115 reference statements)

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“…For example, the phase behavior of soft colloidal particles has been studied in Monte Carlo simulations using soft sphere potentials [1][2][3][4]; these simulations find a freezing point at higher densities than in hard spheres, consistent with experiments [5,6]. Furthermore, the Hertzian potential has been used to model the compressibility of soft microgel particles [7][8][9], and interactions analogous to that of polymer brushes have also been proposed to model the contact interaction between the fuzzy outskirts of swollen microgels [10][11][12].…”

Section: Introductionmentioning

confidence: 87%

Spontaneous deswelling of microgels controlled by counterion clouds

2019

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Concentrated pNIPAM microgel suspensions at a fixed temperature below the deswelling transition of pNIPAM exhibit spontaneous particle deswelling. The microgels deswell before they are in direct contact and, in polydisperse suspensions, this deswelling is most pronounced for the largest microgel particles; as a consequence, the polydispersity of the suspension is reduced. Recently, we presented a model for this spontaneous deswelling that is based on the presence of counterions originating from charged groups on the surface of the pNIPAM microgels [A. Scotti et al., Proc. Natl. Acad. Sci. USA 113, 5576 (2016)]. Here, we present numerical Poisson-Boltzmann calculations of the electrostatic potential and osmotic pressure inside and outside a pNIPAM microgel that could trigger the observed deswelling at high particle concentrations.

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Section: Introductionmentioning

confidence: 87%

Spontaneous deswelling of microgels controlled by counterion clouds

2019

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“…Altogether these features paved the way for using microgels as model systems to elucidate fundamental problems in condensed matter physics. Among others, examples are the nucleation of squeezable particles [9], frustration in colloidal crystals [11], soft depletion and effective interactions [10], glass [12] and jamming transitions [13], as well as the rheological behavior of such jammed states [14].…”

Section: Introductionmentioning

confidence: 99%

Atomic scale investigation of the volume phase transition in concentrated PNIPAM microgels

Zanatta

Tavagnacco

Buratti

et al. 2020

The Journal of Chemical Physics

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Combining elastic incoherent neutron scattering and differential scanning calorimetry, we investigate the occurrence of the volume phase transition (VPT) in very concentrated PNIPAM microgel suspensions, from a polymer weight fraction of 30 wt% up to dry conditions. Although samples are arrested at the macroscopic scale, atomic degrees of freedom are equilibrated and can be probed in a reproducible way. A clear signature of the VPT is present as a sharp drop of the mean square displacement of PNIPAM hydrogen atoms obtained by neutron scattering. As a function of concentration, the VPT gets smoother as dry conditions are approached whereas the VPT temperature shows a minimum at about 43 wt%. This behavior is qualitatively confirmed by calorimetry measurements. Molecular dynamics simulations are employed to complement experimental results and gain further insights into the nature of the VPT, confirming that it involves the formation of an attractive gel state between the microgels. Overall, these results provide evidence that the VPT in PNIPAM-based systems can be detected at different time-and length-scales as well as in overcrowded conditions.

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“…25,26 In the last case, the interaction between two polymers can be described via soft, effective potentials, which are realized by, for example, micelles, star polymers, dendrimers or microgel particles. [27][28][29][30] In this paper, we propose two new approaches to MD-MPCD simulations of macromolecular systems suspended in a solvent. Both methods build on the use of the average (radial) distribution of monomers ρ mon (r) around the center-ofmass of the macromolecule, which embodies its global conformation.…”

Section: Introductionmentioning

confidence: 99%

Multi-particle collision dynamics for a coarse-grained model of soft colloids

Ruiz-Franco

Jaramillo-Cano

Camargo

et al. 2019

The Journal of Chemical Physics

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The growing interest in the dynamical properties of colloidal suspensions, both in equilibrium and under an external drive such as shear or pressure flow, requires the development of accurate methods to correctly include hydrodynamic effects due to the suspension in a solvent. In the present work, we generalize Multi-Particle Collision Dynamics (MPCD) to be able to deal with soft, polymeric colloids. Our methods build on the knowledge of the monomer density profile that can be obtained from monomer-resolved simulations without hydrodynamics or from theoretical arguments. We hereby propose two different approaches. The first one simply extends the MPCD method by including in the simulations effective monomers with a given density profile, thus neglecting monomer-monomer interactions. The second one considers the macromolecule as a single penetrable soft colloid (PSC), which is permeated by an inhomogeneous distribution of solvent particles. By defining an appropriate set of rules to control the collision events between the solvent and the soft colloid, both linear and angular momenta are exchanged. We apply these methods to the case of linear chains and star polymers for varying monomer lengths and arm number, respectively, and compare the results for the dynamical properties with those obtained within monomer-resolved simulations. We find that the effective monomer method works well for linear chains, while the PSC method provides very good results for stars. These methods pave the way to extend MPCD treatments to complex macromolecular objects such as microgels or dendrimers and to work with soft colloids at finite concentrations.

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A new look at effective interactions between microgel particles

Cited by 118 publications

References 58 publications

Spontaneous deswelling of microgels controlled by counterion clouds

Spontaneous deswelling of microgels controlled by counterion clouds

Atomic scale investigation of the volume phase transition in concentrated PNIPAM microgels

Multi-particle collision dynamics for a coarse-grained model of soft colloids

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