Structure of Monodisperse and Bimodal Brushes

Currie, E.P.K.; Wagemaker, Marnix; Stuart, M.A. Cohen; Well, A.A. van

doi:10.1021/ma990936w

Cited by 33 publications

(39 citation statements)

References 28 publications

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“…This effect should not be confused with the deviation from the parabolic density profile near the edge of the bare brush caused by Gaussian fluctuations of weakly stretched terminal parts of the chains. The latter effect has been observed experimentally [28] and in numerical SCF-calculations [1,8] but is not accounted for by the "quasi-classical" approximation used in our analysis.…”

Section: Continuous Distributions: One-phase Brushsupporting

confidence: 47%

“…Small amounts of additives may have a strong effect on the conformation, and as a result, on the protective properties of brushes. Understanding of such effects 28 The European Physical Journal E is important in order to predict the efficiency of protection obtained from grafted polymeric layers: in practical applications of grafted polymers (including biological ones) the solution always contains small organic molecules, proteins or/and surfactants which can exhibit specific interactions and association with polymer chains. Grafted polymeric layers find also an important application in chromatography.…”

Section: Introductionmentioning

confidence: 99%

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Grafted polymers with annealed excluded volume: A model for surfactant association in brushes

Currie

Fleer

Stuart

et al. 2000

The European Physical Journal E - Soft Matter

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We present an analytical self-consistent-field (SCF) theory for a neutral polymer brush (a layer of long polymer chains end-grafted to a surface) with annealed excluded volume interactions between the monomer units. This model mimics the reversible adsorption of solute molecules or aggregates, such as small globular proteins or surfactant micelles, on the grafted chains. The equilibrium structural properties of the brush (the brush thickness, the monomer density profile, the distribution of the end segments of the grafted chains) as well as the overall adsorbed amount and the adsorbate density profile are analyzed as a function of the grafting density, the excluded volume parameters and the chemical potential (the concentration) of the adsorbate in the solution. We demonstrate that, when the grafting density is varied, the overall adsorbed amount always exhibits a maximum, whereas the root-mean-square brush thickness either increases monotonically or passes through a (local) minimum. At high grafting densities the chains are loaded by adsorbed aggregates preferentially in the distal region of the brush, whereas in the region proximal to the grafting surface depletion of aggregates occurs and the polymer brush retains an unperturbed structure. Depending on the relative strength of the excluded volume interactions between unloaded and loaded monomers both the degree of loading of the chains and the polymer density profile are either continuous or they exhibit a discontinuity as a function of the distance from the grafting surface. In the latter case intrinsic phase separation occurs in the brush: the dense phase consists of unloaded and weakly extended chains and occupies the region proximal to the surface, whereas a more dilute phase consisting of highly loaded and strongly extended chains forms the periphery of the brush.

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Section: Continuous Distributions: One-phase Brushsupporting

confidence: 47%

Section: Introductionmentioning

confidence: 99%

Grafted polymers with annealed excluded volume: A model for surfactant association in brushes

Currie

Fleer

Stuart

et al. 2000

The European Physical Journal E - Soft Matter

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“…This approach has on many occasions shown excellent agreement with experimentally determined density profiles 22 and with molecular dynamics simulations, 23 For weak polyelectrolytes such as PDMAEMA, the charge or degree of dissociation will depend on the pH, the ionic strength and on the local electrostatic potential. This is modelled by a two state model.…”

Section: Numerical Self-consistent Field Theory Simulationsmentioning

confidence: 77%

Switching the Interpenetration of Confined Asymmetric Polymer Brushes

et al. 2016

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The interpenetration of two polymer brushes on approaching flat surfaces has been investigated. When compacting polymer brushes with an asymmetric charge on each surface, one neutral and the other weakly charged, we find that the brush interpenetration becomes a parameter that can be controlled by the pH of the hydrating solution. The switching between high and low degrees of brush interpenetration was investigated with numerical selfconsistent field theory (nSCF) and experimentally using a sample environment which combines neutron reflectometry with a surface force type apparatus. Initially, a pair of uncharged poly(ethylene oxide), PEO, brushes are examined, where one of the brushes is 2 deuterated to distinguish it from a hydrogenous counter-part. We find in both nSCF and these experiments that there is no significant overlap between the brushes as both compact into polymer blocks with little hydration. However, when a weak polyelectrolyte poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, brush is confined against a deuterated neutral PEO brush and the pH of the hydrating solution is below the polycation's pKa of 7.5, then the presence of charged groups on the PDMAEMA allows significant interpenetration to occur between the two polymer brushes on contact. This interpenetration remains once the polymer brushes dehydrate due to the confining pressure that is applied. Raising the pH to a value above the pKa, removes the charges from the polyelectrolyte brush resulting in little to no interpenetration between the two brushes. Therefore, by simply adjusting the pH of the hydrating solution the interpenetration state between polymer brush pairs can be switched when one brush is a weak polyelectrolyte. Since polymer brushes are widely investigated and used to reduce friction between solid surfaces, this effect may have significant implications in the design and operation of polymer brushes with controllable friction properties.

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“…Also, the maximum values are very similar, although the maximum for the bimodal brush is shifted to a lower grafting density (0.03-0.05 nm −2 ) compared to the monomodal brush (0.05-0.06 nm −2 ). This can be due to extended stretching of the long chains of the bimodal brush, at low grafting density, imposed by the dense short-chain layer near the surface [22,23]. It would yield more sites at the long chains available for adsorption and therefore more ternary adsorption at lower grafting density, compared to the monomodal PEO 770 brush.…”

Section: Bimodal Peo Brushmentioning

confidence: 99%

“…In this way the proximity of the surface is covered with a dense PEO layer, which should prevent primary adsorption. The structure of bimodal PEO brushes has been investigated using NR and SCF calculations with three different PEO chain lengths at different ratios of long and short chains and at different grafting densities [22,23]. The results show distinct regions of short chains (close to the surface) and long chains (protruding through the proximal layer into the water).…”

Section: Introductionmentioning

confidence: 99%