Molecular Dynamics Simulations of Polyelectrolyte Brushes:  From Single Chains to Bundles of Chains

Sandberg, Daniel J.; Carrillo, Jan‐Michael Y.; Dobrynin, Andrey V.

doi:10.1021/la702203c

Cited by 82 publications

(87 citation statements)

References 54 publications

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“…There is also a regime with solvent-filled holes (H) defects. These four different structures have been previously predicted (14,22,(25)(26)(27)(28)(29) and observed (4,12,14,17) in a variety of grafted systems. The region denoted as M þ NA corresponds to micelles together with highly stretched individual polymers and has never been observed before.…”

Section: Resultssupporting

confidence: 58%

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Tagliazucchi

Cruz

Szleifer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

165

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The competition between chemical equilibrium, for example protonation, and physical interactions determines the molecular organization and functionality of biological and synthetic systems. Charge regulation by displacement of acid-base equilibrium induced by changes in the local environment provides a feedback mechanism that controls the balance between electrostatic, van der Waals, steric interactions and molecular organization. Which strategies do responsive systems follow to globally optimize chemical equilibrium and physical interactions? We address this question by theoretically studying model layers of end-grafted polyacids. These layers spontaneously form self-assembled aggregates, presenting domains of controlled local pH and whose morphologies can be manipulated by the composition of the solution in contact with the film. Charge regulation stabilizes micellar domains over a wide range of pH by reducing the local charge in the aggregate at the cost of chemical free energy and gaining in hydrophobic interactions. This balance determines the boundaries between different aggregate morphologies. We show that a qualitatively new form of organization arises from the coupling between physical interactions and protonation equilibrium. This optimization strategy presents itself with polyelectrolytes coexisting in two different and well-defined protonation states. Our results underline the need of considering the coupling between chemical equilibrium and physical interactions due to their highly nonadditive behavior. The predictions provide guidelines for the creation of responsive polymer layers presenting self-organized patterns with functional properties and they give insights for the understanding of competing interactions in highly inhomogeneous and constrained environments such as those relevant in nanotechnology and those responsible for biological cells function.aggregates | charge regulation | local pH | responsive surfaces T he competition between physical interactions and chemical equilibrium is a challenging problem in physics, chemistry, and biology. A ubiquitous example of this competition in synthetic and life systems is the control of the charge state by protonation that regulates enzymatic activity (1), switches ionconductivity in biological (2) and synthetic channels (3), induces self-assembly (4-7), and determines the properties of technologically important polyelectrolyte layers (8, 9). These processes occur in confined inhomogeneous environments, where molecular organization is restricted and competition among interactions is augmented. The optimization of charge state by protonation depends not only on the solution pH but also on the local environment (10, 11). Therefore, it is imperative to understand whether the molecular organization is determined by the independent optimization of the acid-base equilibrium and the physical interactions, or if there are phenomena that arise exclusively from their coupling. This understanding is particularly relevant today given the large number of systems...

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Section: Resultssupporting

confidence: 58%

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Tagliazucchi

Cruz

Szleifer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

165

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“…As expected, the R g with side chains is slightly bigger than R g of pure backbones and the difference keeps increasing as the side chain length increases. The R g of PNB 25 -g-PLA 5 shows distinctively increased size compared to its neighbors, which is comparable with the size of PNB 25 -g-PLA 19 . (Figure 5e) It should be noted that this does not indicate the structural details of two polymers are the same.…”

Section: Resultsmentioning

confidence: 63%

Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies

Zhang¹,

Carrillo²,

Ahn³

et al. 2014

Macromolecules

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We have used small angle neutron scattering (SANS) measurement and atomistic molecular dynamics (MD) simulations to investigate the conformation of bottlebrush polymers with poly(norbornene) (PNB) backbone and different sizes of poly(lactide) (PLA) side chains (PNB 25 -g-PLA 5 , PNB 25 -g-PLA 10 , and PNB 25 -g-PLA 19 ). At early stage of simulations, stretched side chains with visible spatialcorrelations of about 30 Å were observed. The experimentally measured SANS data, on the other hand, does not exhibit any correlation peaks in the corresponding length scale indicating a compact form rather than a stretched-hairy polymer conformation. As the simulation continued, the spatial correlations between side chains disappeared after about 40 ns of chain relaxation, and the scattering intensity calculated for the simulated structure becomes reasonably close to the measured one. Statistical approach is used to overcome the time scale limitation and search for optimal conformation space, which also provides a good agreement with the experimental data. Further coarse-grained simulation results suggest that the side chain conformation strongly depends on the solubility competition among side chain, backbone, and solvent. Significant changes of backbone dynamics due to the side chain encapsulation have been revealed and discussed.

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“…At low coverages of MHA ligands, the van der Waals interactions among the alkyl chains may compete with electrostatic repulsions and cause ligands to form bundles. 47,[54][55] Additionally, the model predicts a single, presumably average, adsorption constant for the QD/AQ system, whereas there are several possible binding geometries (for example, through sulfonate group, through the oxygen lone pair, or through the pi system of AQ). We believe that the photoinduced electron transfer yield, as measured by the PL of the samples in the presence of AQ, is a sensitive enough probe of these interactions to warrant a model that treats both the QD surface and the ionic species in solution with molecular-level detail.…”

Section: Discussionmentioning

confidence: 99%

Control of the Redox Activity of PbS Quantum Dots by Tuning Electrostatic Interactions at the Quantum Dot/Solvent Interface

Weinberg

Nepomnyashchii

et al. 2016

J. Am. Chem. Soc.

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This paper describes the control of electron exchange between a colloidal PbS quantum dot (QD) and a negatively charged small molecule (9,10-anthraquinone-2-sulfonic acid sodium salt, AQ), through tuning of the charge density in the ligand shell of the QD, within an aqueous dispersion. The probability of electron exchange, measured through steady-state and time-resolved optical spectroscopy, is directly related to the permeability of the protective ligand shell, which is a mixed monolayer of negatively charged 6-mercaptohexanoate (MHA) and neutral 6-mercaptohexanol (MHO), to AQ. The composition of the ligand shell is quantitatively characterized by (1)H NMR. The dependence of the change in Gibbs free energy, ΔGobs, for the diffusion of AQ through the charged ligand shell and its subsequent adsorption to the QD surface is well-described with an electrostatic double-layer model for the QD/solvent interface. Fits of the optical data to this model yield an increase in the free energy for transfer of AQ from bulk solution to the surface of the QD (where it exchanges electrons with the QD) of 154 J/mol upon introduction of each additional charged MHA ligand to the ligand shell. This work expands the set of chemical parameters useful for controlling the redox activity of QDs via surface modification and suggests strategies for the use of nanoparticles for molecular and biomolecular recognition within chemically complex environments and for design of chemically stable nanoparticles for aqueous photocatalytic systems.

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Molecular Dynamics Simulations of Polyelectrolyte Brushes: From Single Chains to Bundles of Chains

Cited by 82 publications

References 54 publications

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies

Control of the Redox Activity of PbS Quantum Dots by Tuning Electrostatic Interactions at the Quantum Dot/Solvent Interface

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