Analytical Self-Consistent-Field Model of Weak Polyacid Brushes

Lyatskaya, Yu.V.; Leermakers, F.A.M.; Fleer, G.J.; Zhulina, Ekaterina B.; Birshtein, T.M.

doi:10.1021/ma00114a009

Cited by 194 publications

(294 citation statements)

References 12 publications

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“…There is, however, an alternative definition, termed the total thickness in what follows, that can be obtained using the distance from the surface at which the polymer density profile vanishes. 32 That is, h tot such that z ≥ h tot implies ρ p (z) = 0. Lyatskaya et al 32 showed that the two definitions of thickness are generally not equivalent for weak polyelectrolyte layers.…”

Section: Discussionmentioning

confidence: 99%

“…3, has been similarly predicted for grafted polymer layers of weak polyelectrolytes. In the latter case, scaling considerations, selfconsistent field theory, and molecular theory [32][33][34]39 have all provided the same qualitative picture. The maximum has been experimentally observed.…”

Section: B Reentrant Swelling: the Role Of Ph And Salt Concentrationmentioning

confidence: 93%

“…31 Moreover, increasing the salt concentration can lead to swelling of a grafted weak polyelectrolyte layer. 32 Theoretical calculations have predicted the thickness of grafted weak polyelectrolyte layers to have a maximum as a function of the salt concentration. 33,34 This behavior has been confirmed by experimental findings.…”

Section: Introductionmentioning

confidence: 99%

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Non-monotonic swelling of surface grafted hydrogels induced by pH and/or salt concentration

Longo

Cruz

Szleifer

2014

The Journal of Chemical Physics

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We use a molecular theory to study the thermodynamics of a weak-polyacid hydrogel film that is chemically grafted to a solid surface. We investigate the response of the material to changes in the pH and salt concentration of the buffer solution. Our results show that the pH-triggered swelling of the hydrogel film has a non-monotonic dependence on the acidity of the bath solution. At most salt concentrations, the thickness of the hydrogel film presents a maximum when the pH of the solution is increased from acidic values. The quantitative details of such swelling behavior, which is not observed when the film is physically deposited on the surface, depend on the molecular architecture of the polymer network. This swelling-deswelling transition is the consequence of the complex interplay between the chemical free energy (acid-base equilibrium), the electrostatic repulsions between charged monomers, which are both modulated by the absorption of ions, and the ability of the polymer network to regulate charge and control its volume (molecular organization). In the absence of such competition, for example, for high salt concentrations, the film swells monotonically with increasing pH. A deswelling-swelling transition is similarly predicted as a function of the salt concentration at intermediate pH values. This reentrant behavior, which is due to the coupling between charge regulation and the two opposing effects triggered by salt concentration (screening electrostatic interactions and charging/discharging the acid groups), is similar to that found in end-grafted weak polyelectrolyte layers. Understanding how to control the response of the material to different stimuli, in terms of its molecular structure and local chemical composition, can help the targeted design of applications with extended functionality. We describe the response of the material to an applied pressure and an electric potential. We present profiles that outline the local chemical composition of the hydrogel, which can be useful information when designing applications that pursue or require the absorption of biomolecules or pH-sensitive molecules within different regions of the film.

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Section: Discussionmentioning

confidence: 99%

Section: B Reentrant Swelling: the Role Of Ph And Salt Concentrationmentioning

confidence: 93%

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Non-monotonic swelling of surface grafted hydrogels induced by pH and/or salt concentration

Longo

Cruz

Szleifer

2014

The Journal of Chemical Physics

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“…The root-mean-square thickness of polyacid close to its pK a has been predicted theoretically to exhibit a maximum in its swelling when exposed to salt [48]. This maximum occurs with 10 Ð3 volume fraction salt (or approximately 0.05 M), and was attributed to the charging effect of salt on a weak electrolyte at low salt concentrations combined with Ôsalting outÕ at higher concentrations, whereby counterion condensation causes the chains to become less charged.…”

Section: Pdmaema Comb and Brush Behaviour In Salt Solutionsmentioning

confidence: 98%

Determination of the molar mass of surface-grafted weak polyelectrolyte brushes using force spectroscopy

Al-Baradi

Tomlinson

Zhang³

et al. 2015

Polymer

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The molar mass and dispersity of a polycation, poly[2-(dimethyl amino)ethyl methacrylate)] (PDMAEMA) grafted from a poly(methyl methacrylate) (PMMA) backbone, was measured by single-molecule force spectroscopy (SMFS) and shown to be consistent with results from gel permeation chromatography for the same comb polymer in aqueous solution. Comparison was then made between the comb polymer and PDMAEMA brushes that were grown from the substrate, as a function of the pH and ionic strength of the surrounding medium, and the limits of reliable characterization of the polymers are determined. A large discrepancy was observed between the responses of the comb and brush layer at low pH when the PDMAEMA molecules are extended from the supporting substrate. Here it is believed that the atomic force microscope (AFM) tip can penetrate the comb layer and selectively desorb side-chains of the comb. In the case of the well solvated PDMAEMA brushes at high pH, the tip preferentially selects larger chains, resulting in an over-estimate of the brush molar mass. The addition of salt also influenced the molar mass obtained by this technique. It is believed that salted brushes did not adhere well to the AFM tip, with subsequent desorption resulting in an underestimate of the molar mass. However, SMFS was shown to be capable of demonstrating the effect of salt on brush conformation, with greater swelling after the addition of a small amount of NaCl, but a significant decrease when 100 mM is added.

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“…35 This is the result of the local electrostatic potential being significantly different between these two locations and leads to substantial deviations from the parabolic density profile. However, an increase in the ionic strength leads to a more uniform distribution in the degree of dissociation and the density profile reassumes its parabolic shape.…”

Section: Numerical Self-consistent Field Theory Simulationsmentioning

confidence: 99%

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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Analytical Self-Consistent-Field Model of Weak Polyacid Brushes

Cited by 194 publications

References 12 publications

Non-monotonic swelling of surface grafted hydrogels induced by pH and/or salt concentration

Non-monotonic swelling of surface grafted hydrogels induced by pH and/or salt concentration

Determination of the molar mass of surface-grafted weak polyelectrolyte brushes using force spectroscopy

Switching the Interpenetration of Confined Asymmetric Polymer Brushes

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