Dynamical behavior of microgels of interpenetrated polymer networks

Nigro, Valentina; Angelini, Roberta; Bertoldo, Monica; Bruni, Fabio; Ricci, Maria Antonietta; Ruzicka, Barbara

doi:10.1039/c7sm00739f

Cited by 52 publications

(69 citation statements)

References 80 publications

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“…59 This particular kind of microgels has recently gathered a lot of interest because of their intriguing fragility behavior: as the amount of charges increase, these systems exhibit features of strong glass-formers, a rather unique example in soft matter. 16,17 A recent work 60 has put forward the idea that this behavior directly stems from charge effects, which also increase the softness of the particles, as confirmed in the present work. It would thus be very interesting to address the behavior of IPN microgels in future works.…”

Section: Discussionsupporting

confidence: 79%

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Numerical insights on ionic microgels: structure and swelling behaviour

et al. 2019

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Recent progress has been made in the numerical modelling of neutral microgel particles with a realistic, disordered structure. In this work we extend this approach to the case of co-polymerised microgels where a thermoresponsive polymer is mixed with acidic groups. We compare the cases where counterions directly interact with microgel charges or are modelled implicitly through a Debye-Hückel description. We do so by performing extensive numerical simulations of single microgels across the volume phase transition varying the temperature and the fraction of charged monomers. We find that the presence of charges considerably alters the microgel structure, quantified by the monomer density profiles and by the form factors of the microgels, particularly close to the volume phase transition (VPT). We observe significant deviations between the implicit and explicit models, with the latter comparing more favourably to available experiments. In particular, we observe a shift of the VPT temperature to larger values as the amount of charged monomers increases. We also find that below the VPT the microgel-counterion complex is almost neutral, while it develops a net charge above the VPT. Interestingly, under these conditions the collapsed microgel still retains a large amount of counterions inside its structure. Since these interesting features cannot be captured by the implicit model, our results show that it is crucial to explicitly include the counterions in order to realistically model ionic thermoresponsive microgels.

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Section: Discussionsupporting

confidence: 79%

“…Since such a ratio has been previously adopted as a measure of the particle softness, 16,17 this suggests that more charged microgels are softer than less charged or neutral ones, in agreement with experimental findings.…”

Section: Temperature-driven Swelling Of Charged Microgels With Explicsupporting

confidence: 82%

Numerical insights on ionic microgels: structure and swelling behaviour

et al. 2019

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“…Moreover, they are used as model systems in soft matter chemistry and physics, thanks to their phase behavior (volume phase transition) and colloidal properties . The volume phase transition of the temperature‐ and pH‐sensitive IPN microgel made of interpenetrating PNIPAM and polyacrylic acid (PAAc) has been investigated in the last years, as well as the dynamical properties in the concentration region around and above the overlap value, across the volume phase transition temperature at different pH values …”

Section: Introductionmentioning

confidence: 99%

“…[10][11][12][13][14][15] The volume phase transition of the temperature-and pH-sensitive IPN microgel made of interpenetrating PNIPAM and polyacrylic acid (PAAc) has been investigated in the last years, [16][17][18] as well as the dynamical properties in the concentration region around and above the overlap value, across the volume phase transition temperature at different pH values. [19][20][21] Another important issue concerns the role of the electrostatic interactions in determining the stability conditions of the microgel and it is commonly faced by considering the effective interaction potential between two sphere-like particles. [11,12,14,[22][23][24][25][26] For charged particles the potential takes into account the effect of neutralization of the bare charge by counterions.…”

Section: Introductionmentioning

confidence: 99%

Interpenetrating Polymer Network Microgels in Water: Effect of Composition on the Structural Properties and Electrosteric Interactions

et al. 2018

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Microgels of cross-linked interpenetrating polymer networks (IPNs) are very versatile systems combining the properties of colloids and polymers. Herein we study IPN microgels composed of poly(N-isopropylacrylamide) and poly(acrylic acid) to understand how weight composition and reactant concentrations affect their structural, conformational and electrosteric properties in water. The results show that it is possible to drive the formation of microgels with the desired properties by adjusting IPN composition and preparation method during the synthesis. During synthesis, the polymerization of acrylic acid triggers the merging among IPNs via covalent linking, giving rise to microgels with larger mass and size, the effect being larger for higher concentration of the reactants. In addition, a close relation between the microgel internal conformation and the colloidal stability is observed, due to the presence of screened groups inside the microgel.

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“…Significant changes in m k for soft colloids have been reported previously [35,[40][41][42], but the physics underlying this behavior in terms of the interparticle interaction has remained unclear, and perhaps even controversial. It was found that there is a crossover from fragile to strong glasses in deformable microgels when the internal elasticity of the particles decreases.…”

Section: Stiffness Of the Dlvo Potential And Dramatic Fragility Changesmentioning

confidence: 99%

Fragile-to-strong crossover, growing length scales, and dynamic heterogeneity in Wigner glasses

et al. 2020

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Colloidal particles, which are ubiquitous, have become ideal testing grounds for the structural glass transition (SGT) theories. In these systems glassy behavior is manifested as the density of the particles is increased. Thus, soft colloidal particles with varying degree of softness capture diverse glass forming properties, observed normally in molecular glasses. By performing Brownian dynamics simulations for a binary mixture of micron-sized charged colloidal suspensions, known to form Wigner glasses, we show that by tuning the softness of the interaction potential, achievable by changing the monovalent salt concentration, there is a continuous transition between fragile to strong behavior. Remarkably, this is found in a system where the well characterized interaction potential between the colloidal particles is isotropic. We also show that the predictions of the random first order transition (RFOT) theory quantitatively describes the universal features such as the growing correlation length,where φK , the analogue of the Kauzmann temperature, depends on the salt concentration. As anticipated by the RFOT predictions, we establish a causal relationship between the growing correlation length and a steep increase in the relaxation time and dynamic heterogeneity as the system is compressed. The broad range of fragility observed in Wigner glasses, which can be induced by merely changing the salt concentration, is used to draw analogies with molecular and polymer glasses. The large variations in the fragility is found only when the temperature dependence of the viscosity is examined for a large class of diverse glass forming materials. In sharp contrast, this is vividly illustrated in a single system that can be experimentally probed. Our work also shows that the RFOT predictions are accurate in describing the dynamics over the entire density range, regardless of the fragility of the glasses, implying that the physics describing the structural glass transition is universal. arXiv:1909.03463v1 [cond-mat.soft]

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Dynamical behavior of microgels of interpenetrated polymer networks

Cited by 52 publications

References 80 publications

Numerical insights on ionic microgels: structure and swelling behaviour

Numerical insights on ionic microgels: structure and swelling behaviour

Interpenetrating Polymer Network Microgels in Water: Effect of Composition on the Structural Properties and Electrosteric Interactions

Fragile-to-strong crossover, growing length scales, and dynamic heterogeneity in Wigner glasses

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