Influence of polymer shape on depletion potentials and crowding in colloid–polymer mixtures

Lim, Wei Kang; Denton, Alan R.

doi:10.1039/c5sm02863a

Cited by 20 publications

(34 citation statements)

References 79 publications

(138 reference statements)

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“…Close agreement between polymer field theory predictions and the potentials output by our simulations, which use as input the penetration free energy predicted by the same theory, not only validates the ellipsoidal polymer model, but also confirms the self-consistency of the field theories. We emphasize, however, that our approach, unlike the field theories, can be applied also in the colloid limit [116].…”

Section: Resultsmentioning

confidence: 99%

“…A mixture of hard nanospheres and nonadsorbing polymers is characterized by the number densities of the two species, n n and n p , the nanosphere radius R n , and the rms radius of gyration R g of free (uncrowded) polymer. In the colloid limit (R g < R n ), in which the polymer coils are impenetrable to particles, the effective polymer size must be calibrated in order to consistently and accurately account for the polymer excluded volume [116]. In the protein limit (R g ≫ R n ), in which polymer penetration supplants excluded volume, it is instead the penetration energy that must be calibrated, as explained below (Sec.…”

Section: B Polymer-nanoparticle Mixturesmentioning

confidence: 99%

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Depletion-induced forces and crowding in polymer-nanoparticle mixtures: Role of polymer shape fluctuations and penetrability

Lim

Denton

2016

The Journal of Chemical Physics

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Depletion forces and macromolecular crowding govern the structure and function of biopolymers in biological cells and the properties of polymer nanocomposite materials. To isolate and analyze the influence of polymer shape fluctuations and penetrability on depletion-induced interactions and crowding by nanoparticles, we model polymers as effective penetrable ellipsoids, whose shapes fluctuate according to the probability distributions of the eigenvalues of the gyration tensor of an ideal random walk. Within this model, we apply Monte Carlo simulation methods to compute the depletion-induced potential of mean force between hard nanospheres and crowding-induced shape distributions of polymers in the protein limit, in which polymer coils can be easily penetrated by smaller nanospheres. By comparing depletion potentials from simulations of ellipsoidal and spherical polymer models with predictions of polymer field theory and free-volume theory, we show that polymer depletion-induced interactions and crowding depend sensitively on polymer shapes and penetrability, with important implications for bulk thermodynamic phase behavior.

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Section: Resultsmentioning

confidence: 99%

Section: B Polymer-nanoparticle Mixturesmentioning

confidence: 99%

Depletion-induced forces and crowding in polymer-nanoparticle mixtures: Role of polymer shape fluctuations and penetrability

Lim

Denton

2016

The Journal of Chemical Physics

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“…Nevertheless, for our system the AO polymer model has several drawbacks. Treating polymers as spherical objects is by itself a crude approximation, as is a neglect of polymer shape fluctuations [9][10][11]51 . We also note that water is a good solvent for PEG, i.e., even the ideal polymer model that the AO aims to simplify, is inappropriate for our system.…”

Section: Comparing With Ao Theorymentioning

confidence: 99%

“…A colloidal dispersion with non-adsorbing polymers form an especially useful model system. Various theoretical models of particle-polymer mixtures have been utilized in previous work, aiming to quantify the various interactions and to establish how they affect the macroscopic properties [5][6][7][8][9][10][11] . Several experimental methods are available to elucidate the structure of particlepolymer mixtures, which can then be compared with the model predictions [12][13][14][15][16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

Theoretical predictions of structures in dispersions containing charged colloidal particles and non-adsorbing polymers

Xie

Turesson

Woodward

et al. 2016

Phys. Chem. Chem. Phys.

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We develop a theoretical model to describe structural effects on a specific system of charged colloidal polystyrene particles, upon the addition of non-adsorbing PEG polymers. This system has previously been investigated experimentally, by scattering methods, so we are able to quantitatively compare predicted structure factors with corresponding experimental data. Our aim is to construct a model that is coarse-grained enough to be computationally manageable, yet detailed enough to capture the important physics. To this end, we utilize classical polymer density functional theory, wherein all possible polymer configurations are accounted for, subject to a mean-field Boltzmann weight. We make efforts to counteract drawbacks with this mean-field approach, resulting in structural predictions that agree very well with computationally more demanding simulations. Electrostatic interactions are handled at the fully non-linear Poisson-Boltzmann level, and we demonstrate that a linearization leads to less accurate predictions. The particle charge is an experimentally unknown parameter. We define the surface charge such that the experimental and theoretical gel point at equal polymer concentration coincide. Assuming a fixed surface charge for a certain salt concentration, we find very good agreement between measured and predicted structure factors across a wide range of polymer concentrations. We also present predictions for other structural quantities, such as radial distribution functions, and cluster size distributions. Finally, we demonstrate that our model predicts the occurrence of

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“…Crowding agents modify the eigenvalue probability distributions and, in turn, the rms radius of gyration and asphericity of a polymer. As in our previous studies of crowding of RW polymers in a θ solvent [63][64][65], our model extends the classic Asakura-Oosawa-Vrij (AOV) model of colloid-polymer mixtures [66,67], which idealizes nonadsorbing polymers as effective spheres of fixed size (radius of gyration). Although qualitatively describing depletion-induced demixing of colloid-polymer mixtures, the AOV model completely neglects polymer conformational fluctuations, the influence of crowding on polymer size and shape, and the penetrability of polymers by smaller colloids (nanoparticles).…”

Section: A Coarse-grained Model Of Polymer Coilmentioning

confidence: 88%

Influence of solvent quality on conformations of crowded polymers

Davis

Denton

2018

The Journal of Chemical Physics

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The structure and function of polymers in confined environments, e.g., biopolymers in the cytoplasm of a cell, are strongly affected by macromolecular crowding. To explore the influence of solvent quality on conformations of crowded polymers, we model polymers as penetrable ellipsoids, whose shape fluctuations are governed by the statistics of self-avoiding walks, appropriate for a polymer in a good solvent. Within this coarse-grained model, we perform Monte Carlo simulations of mixtures of polymers and hard-nanosphere crowders, including trial changes in polymer size and shape. Penetration of polymers by crowders is incorporated via a free energy cost predicted by polymer field theory. To analyze the impact of crowding on polymer conformations in different solvents, we compute average polymer shape distributions, radius of gyration, volume, and asphericity over ranges of polymer-to-crowder size ratio and crowder volume fraction. The simulation results are accurately predicted by a free-volume theory of polymer crowding. Comparison of results for polymers in good and theta solvents indicates that excluded-volume interactions between polymer segments significantly affect crowding, especially in the limit of crowders much smaller than polymers. Our approach may help to motivate future experimental studies of polymers in crowded environments, with possible relevance for drug delivery and gene therapy.

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Influence of polymer shape on depletion potentials and crowding in colloid–polymer mixtures

Cited by 20 publications

References 79 publications

Depletion-induced forces and crowding in polymer-nanoparticle mixtures: Role of polymer shape fluctuations and penetrability

Depletion-induced forces and crowding in polymer-nanoparticle mixtures: Role of polymer shape fluctuations and penetrability

Theoretical predictions of structures in dispersions containing charged colloidal particles and non-adsorbing polymers

Influence of solvent quality on conformations of crowded polymers

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