Excluded volume effects in compressed polymer brushes: A density functional theory

Chen, Cangyi; Tang, Ping; Qiu, Feng; Shi, An‐Chang

doi:10.1063/1.4916133

Cited by 16 publications

(19 citation statements)

References 55 publications

(78 reference statements)

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“…These structural properties may also be predicted theoretically. For monodisperse brushes, theoretical approaches such as self-consistent field theory (SCFT), − classical density functional theory (DFT), − and polymer reference interaction site model − have proven to be successful and provided physical insights into the molecular origin of the measured structures. Making use of computer simulations, detailed configurations of monomers subject to various solvent–monomer or matrix–monomer interactions are realized.…”

Section: Introductionmentioning

confidence: 99%

Structural and Dynamical Coupling in Solvent-Free Polymer Brushes Elucidated by Molecular Dynamics Simulations

Chang

2021

Langmuir

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We investigate the chain configuration and segmental dynamics in interacting solvent-free polymer brushes using molecular dynamics simulations. The brush systems are designed to mimic the interstitial space between a pair of neighboring polymer-grafted nanoparticles in solvent-free nanoparticle–organic hybrid materials. Each brush consists of uniformly grafted chains formed by a given number of monomer beads. In monodisperse systems, two opposing brushes have the same chain length and grafting density. In mixed conditions, we consider binary systems with two surfaces being separately grafted with polymers of distinct chain lengths at different grafting densities as well as bidisperse systems with polymers of two different lengths being tethered to the surfaces at a fixed grafting density. We demonstrate that the brush configuration and interpenetration are both governed by the need that monomer beads have to uniformly fill the space. For systems with longer chain lengths and/or higher grafting densities, the larger interwall separation yields more stretched brush conformations and reduced extents of interbrush mixing. As a result, the polymer configurational entropy is generally decreased and the segment-to-segment relaxation dynamics is slowed down accordingly. The grafting of chains at a high density not only makes the relaxation dynamics deviate from the standard Rouse prediction but also leads to distinct relaxation times for the free and tethered segments. The more slowly relaxing tethered segments play a more important role in determining the overall end-to-end fluctuations. Moreover, the two distinct relaxation processes are consistent with the two-stage decay in the Rouse mode fluctuation autocorrelation function. In the presence of brush bidispersity, the collaboration between polymers of different lengths is evidently observed in the brush profiles. The variations of the chain configuration for the two polymers are complementary, and the associated relaxation dynamics of the two species are significantly coupled.

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Section: Introductionmentioning

confidence: 99%

Structural and Dynamical Coupling in Solvent-Free Polymer Brushes Elucidated by Molecular Dynamics Simulations

Chang

2021

Langmuir

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“…To date, a significant amount of modeling effort is put into the brush system with an implicit or explicit solvent or melt. For surfaces tethered with monodisperse polymers, the chain distribution is widely explored using the polymer self-consistent field theory (SCFT), − classical DFT, − polymer reference interaction site model (PRISM), − Monte Carlo (MC), ,, and MD simulations. ,− In addition to the monodisperse systems, mixed polymer brushes also attract attention. Among the theoretical studies, for a given solvent condition mixed brushes are considered as bidisperse/binary, ,− ternary, , or fully polydisperse with a specified length distribution (e.g., Schulz–Zimm distribution), − to name just a few.…”

Section: Introductionmentioning

confidence: 99%

Entropic Effects in Solvent-Free Bidisperse Polymer Brushes Investigated Using Density Functional Theories

Tai

Pan

2019

Langmuir

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Solvent-free polymer-functionalized nanoparticles form a special type of colloid composed of inorganic cores self-suspended by their grafted coronas. In the absence of intervening solvent molecules, the fluidity of the system is provided by these tethered polymers as they fill the space.Here, we study the structure and interaction of neighboring polymer-grafted surfaces in the solvent-free condition using mean-field density functional theories. For opposing flat surfaces, the brush configuration and the associated energy landscape are semianalytically investigated given the incompressibility of the tethered entropic chains. The effect of brush polydispersity (including variations in both chain length and surface grafting density) is considered by two bidisperse models corresponding to different physical scenarios: one for opposing brushes uniformly mixed with two species at a fixed grafting density, and the other for opposing brushes with distinct chain lengths and grafting densities. The space-filling capabilities of the neighboring coronas differ not only by their ratio of radii of gyration for the composing polymers but also by their ratio of grafting densities. We show that the system energy depicts a steric repulsion as the brushes are compressed, which is typical for hairy particles in a solvent. However, as the interwall separation increases, the cooperative stretching of the chains leads to an entropic attraction between them, a unique characteristic of solventless systems. The corresponding brush profiles change from a bell-like shape to a more step-function-like feature as the interwall spacing increases significantly. The interwall separation associated with the overall free energy minimum therefore characterizes the favorable interparticle spacing for solvent-free polymer-functionalized particles. The limiting accessible parameter space of polymer sizes and grafting densities subjected to the space-filling constraint is comprehensively explored for representative interparticle spacing characterizing the compressed, relaxed, and stretched regimes for a given polymer species, respectively. Such information would be useful for guiding the design of experimental solvent-free polymerfunctionalized nanoparticles.

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“…With the assumption of uniform densities in x and y directions, we define the brush height as 41 The local volume fraction of the α-component isThe adsorption of the competitive components in the mixture solvent is analyzed by the relative excess adsorption quantity A α e , 25 here, φ α stands for the volume fraction of the α component in the mixed solvent, while φ α,0 is the corresponding value in bulk.…”

Section: Model and Theorymentioning

confidence: 99%

Polymer Brushes Immersed in Two-Component Solvents with Pure Volume Exclusion: Effect of Solvent Molecular Shape

Zhang

Yang

et al. 2019

ACS Omega

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Polymer brushes have wide application in surface modification. We study dense, short polymer brushes immersed in a mixing solvent under athermal conditions using the classical density functional theory. The brush polymer is short so that the equilibrium behavior of the brush deviates far from the scaling laws for infinite brush chains. The excluded volume interaction is the only interaction in the system. We compare the excluded volume effect of solvent molecules of different shapes. Two types of mixing solvents are considered: solvent composed of linear oligomers and monomers, or that of spherical particles and monomers. The effects of grafting density, solvent molecular size, and solvent number density on the brush height, the density profiles, the relative excess adsorption, and the brush–solvent interface width are systematically analyzed. In the adsorption aspect, the spherical particles have stronger ability than the linear oligomers do to penetrate through the brush layer and gather at the substrate. In the screening aspect, the oligomers are more capable of screening the excluded volume interaction between the brush chains than the spherical particles. The brush–solvent interface width decreases monotonically with increasing oligomer length, but it has a minimum with the increasing spherical particle size. Our research differentiates the attractive-interaction-induced phenomenon and the volume-exclusion-induced phenomenon in dense brush systems and exhibits the difference in the antifouling properties of the brushes contacting solvent molecules of different shapes.

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Excluded volume effects in compressed polymer brushes: A density functional theory

Cited by 16 publications

References 55 publications

Structural and Dynamical Coupling in Solvent-Free Polymer Brushes Elucidated by Molecular Dynamics Simulations

Structural and Dynamical Coupling in Solvent-Free Polymer Brushes Elucidated by Molecular Dynamics Simulations

Entropic Effects in Solvent-Free Bidisperse Polymer Brushes Investigated Using Density Functional Theories

Polymer Brushes Immersed in Two-Component Solvents with Pure Volume Exclusion: Effect of Solvent Molecular Shape

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