Dynamical Properties of Concentrated Suspensions of Block Copolymer Stars in Shear Flow

Jaramillo-Cano, Diego; Camargo, Manuél; Likos, Christos N.; Gârlea, Ioana C.

doi:10.1021/acs.macromol.0c01365

Cited by 9 publications

(8 citation statements)

References 51 publications

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“…The weak PE block should change its ionization depending on the pH, resulting in a reversible pH-responsive electrostatically cross-linked gel. Systematic studies of similar coacervate gels are scarce in the literature, ,,, despite the numerous simulations of physical gels composed of neutral telechelic polymers or soft patchy particles. − Yet, none of the existing studies explicitly incorporated the effects of ionization equilibrium and exchange of small ions.…”

Section: Introductionmentioning

confidence: 99%

Electrostatically Cross-Linked Reversible Gels—Effects of pH and Ionic Strength

et al. 2021

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Mixing of oppositely charged macromolecules can, under certain conditions, lead to the formation of electrostatically cross-linked coacervate gels. In this simulation study, we determine the conditions under which equimolar mixtures of oppositely charged monodisperse four-armed star copolymers with charged end-blocks are able to form such coacervate gels. The cationic charged blocks consist of quenched charges, whereas the anionic blocks contain pH-responsive weak acid groups. We used the Grand-reaction method to determine the phase stability, equilibrium composition, and structural properties of these systems in equilibrium with a supernatant solution at various pH levels and salt concentrations. Depending on the pH and hence on the charge state of the polyanion blocks, we observed the emergence of three regimes: a solution, a sol of isolated star clusters, and a gelpercolating network of stars. Moreover, we demonstrate that the charge state of the stars in the gel phase can be well described by the ideal Henderson–Hasselbalch (HH) equation, despite the presence of strong interactions violating ideality. We can backtrace this surprising result to two deviations from the ideal titration behavior that almost quantitatively cancel each other. This observation explains why various experiments on coacervate gels can be well described by the HH equation, even though the basic assumptions of ideality are clearly violated.

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Section: Introductionmentioning

confidence: 99%

Electrostatically Cross-Linked Reversible Gels—Effects of pH and Ionic Strength

et al. 2021

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“…A hybrid simulation (MD-MPCD) approach has been applied to a variety of soft-matter systems such as colloids, 28) polymer solutions, 29) polymer gels, 30) and bacteria in concentrated suspensions. 31) Among variations of MPCD, the stochastic rotation dynamics (SRD) method conserves the local energy, linear momentum, and mass at the cell level; thus, the Navier-Stokes equation is satisfied, and hydrodynamic interactions are reproduced down to the size of a collision cell.…”

Section: Simulation Techniques With Hydrodynamic Interactionsmentioning

confidence: 99%

Self-Assembly Behaviors and Flow Properties of Amphiphiles by Mesoscale Simulations with Hydrodynamic Interactions

Kobayashi

2022

J. Soc. Rheol., Jpn

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Amphiphilic molecules or colloids such as surfactants and Janus particles with hydrophobic and hydrophilic parts can spontaneously self-assemble in a variety of morphologies in their solutions. Coarse-grained simulations can be used to investigate the behavior of molecules inside these complex fluids and clarify the origin of rheology. However, the choice of essential degrees of freedom and kinetic equations for their dynamics must be carefully considered. Indeed, the hydrodynamic interactions play essential roles for the dynamics of solutions. This article overviews a few simulation techniques that are suitable to the problems mentioned above. The results for surfactant aqueous solutions under confinement and Janus colloid dispersions under shear are exhibited as well as typical examples.

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“…The determination of the microstructure of colloidal dispersions under shear is an important problem for both its relevance in their theoretical study and many applications from atmospheric science [1], chemistry [2], preparation of emulsions [3,4] and industrial products [5], and plasmas [6]. The information about the spatial arrangement of a suspension of particles in a continuous liquid medium is encoded in the pair correlation function g(r, t) or equivalently, via a Fourier transform, in the structure factor S(k, t).…”

Section: Introductionmentioning

confidence: 99%

Solution to the two-body Smoluchowski equation with shear flow for charge-stabilized colloids at low to moderate Péclet numbers

Riva,

Banetta,

Zaccone

2022

Preprint

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We developed an analytical theoretical method to determine the microscopical structure of weakly to moderately sheared colloidal suspensions in dilute conditions. The microstructure is described by the static structure factor, obtained by solving the stationary two-body Smoluchowski advectiondiffusion equation. The singularly perturbed PDE problem is solved by performing an angular averaging over the extensional and compressing sectors and by the rigorous application of boundarylayer theory (intermediate asymptotics). This allows us to expand the solution to a higher order in Péclet with respect to previous methods. The scheme is independent of the type of interaction potential. We apply it to the example of charge-stabilized colloidal particles interacting via the repulsive Yukawa potential and study the distortion of the structure factor. It is predicted that the distortion is larger at small wavevectors k and its dependence on P e is a simple power law. At increasing P e, the main peak of the structure factor displays a broadening and shift towards lower k in the extensional sectors, which indicates shear-induced spreading out of particle correlations and neighbor particles locally being dragged away from the reference one. In the compressing sectors, instead, a narrowing and shift towards high k is predicted, reflecting shear-induced ordering near contact and concomitant depletion in the medium-range. An overall narrowing of the peak is also predicted for the structure factor averaged over the whole solid angle. Calculations are also performed for hard spheres, showing good overall agreement with experimental data. It is also shown that the shear-induced structure factor distortion is orders of magnitude larger for the Yukawa repulsion than for the hard spheres.

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Dynamical Properties of Concentrated Suspensions of Block Copolymer Stars in Shear Flow

Cited by 9 publications

References 51 publications

Electrostatically Cross-Linked Reversible Gels—Effects of pH and Ionic Strength

Electrostatically Cross-Linked Reversible Gels—Effects of pH and Ionic Strength

Self-Assembly Behaviors and Flow Properties of Amphiphiles by Mesoscale Simulations with Hydrodynamic Interactions

Solution to the two-body Smoluchowski equation with shear flow for charge-stabilized colloids at low to moderate Péclet numbers

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