Anion-Specific Effects on the Behavior of pH-Sensitive Polybasic Brushes

Willott, Joshua D.; Murdoch, Timothy J.; Humphreys, Ben A.; Edmondson, Steve; Wanless, Erica J.; Webber, Grant B.

doi:10.1021/acs.langmuir.5b00116

Cited by 60 publications

(111 citation statements)

References 78 publications

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“…At higher pH values, closer to and above the p K a , the percentage of charged monomer decreases. 10 For both the hydrophilic and hydrophobic polymers, the variation in overall brush thickness is nonmonotonic, as expected from existing theories 11 , 19 and experiments 3 , 5 for weak polyelectrolyte brushes.…”

Section: Resultssupporting

confidence: 79%

Behavior of Weak Polyelectrolyte Brushes in Mixed Salt Solutions

et al. 2018

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Hydrophilic and hydrophobic weak polybasic brushes immersed in aqueous solutions of mixed salt counterions are considered using a mean-field numerical self-consistent field approach. On top of the solvent quality of the polymer, the counterion–solvent interactions are accounted for by implementing Flory–Huggins interaction parameters. We show that ion specificity within the brush can bring about large changes in conformation. It is found that the collapse transition of hydrophobic, weak polyelectrolyte brushes features an intermediate two-phase state wherein a subset of chains are collapsed in a dense layer at the substrate, while the remainder of chains are well-solvated and strongly stretched away from the it. Besides pH and ionic strength, solvent quality of counterions and the composition of ions in the solvent are important control parameters for the behavior of polyelectrolyte brushes. Increasingly hydrophobic counterions penetrate deeper within the brush and stabilize the collapsed region, while hydrophilic counterions do the opposite.

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Section: Resultssupporting

confidence: 79%

Behavior of Weak Polyelectrolyte Brushes in Mixed Salt Solutions

et al. 2018

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“…Cleaned wafers and sensors (see ESI †) were amine-functionalised at room temperature via exposure to APTES vapour at <5 mbar for 30 min before being annealed for a further 30 min in air at 110 °C. [39][40][41] Bromine functionalisation of the APTES layer was then performed by immersion of the wafers and QCM sensors in a solution of BIBB (0.26 mL) and anhydrous triethylamine (0.30 mL) in anhydrous THF (10 mL) under a N2 atmosphere for 60 min. [39][40][41] Brush Polymerisation via ARGET ATRP…”

Section: Surface Initiator-functionalisationmentioning

confidence: 99%

Specific ion modulated thermoresponse of poly(N-isopropylacrylamide) brushes

Humphreys

Willott

Murdoch

et al. 2016

Phys. Chem. Chem. Phys.

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The influence of specific anions on the equilibrium thermoresponse of poly(N-isopropylacrylamide) (pNIPAM) brushes has been studied using in situ ellipsometry, quartz crystal microbalance with dissipation (QCM-D) and static contact angle measurements between 20 and 45 °C in the presence of up to 250 mM acetate and thiocyanate anions in water. The thickness and changes in dissipation exhibited a broad swelling transition spanning approximately 15 °C from collapsed (high temperatures) to swollen conformation (low temperatures) while the brush surface wettability changed over approximately 2 °C. In the presence of the kosmotropic acetate anions, the measured lower critical solution temperature (LCST) by the three techniques was very similar and decreased linearly as a function of ionic strength. Conversely, increasing the concentration of the chaotropic thiocyanate anions raised the LCST of the pNIPAM brushes with variation in the measured LCST between the three techniques increasing with ionic strength. The thickness of the pNIPAM brush was seen to progressively increase with increasing thiocyanate concentration at all temperatures. It is proposed that specific ion binding of the chaotropic thiocyanate anion with pNIPAM amide moieties increases the electrostatic intra- and intermolecular repulsion within and between pNIPAM chains. This allows the brush to begin to swell at higher temperatures and to an overall greater extent.

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“…In the presence of monovalent salt solutions, the swelling of weak polybasic brushes (and gels 26 ) is high for strongly hydrated anions, like CH 3 COO – and Cl – , whereas weakly hydrated anions, like NO 3 – and SCN – , result in much less swelling and even complete collapse of the brush layer. 24,27,28…”

Section: Introductionmentioning

confidence: 99%

Combined Experimental and Theoretical Study of Weak Polyelectrolyte Brushes in Salt Mixtures

et al. 2019

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The swelling behavior of a hydrophobic poly(2diisopropylamino)ethyl methacrylate (PDPA) brush immersed in aqueous solutions of single and mixed salts has been investigated using ellipsometry and numerical self-consistent field (nSCF) theory. As a function of solution ionic strength, the osmotic and salted brush regimes of weak polyelectrolyte brushes as well as substantial specific anion effects in the presence of K + salts of Cl – , NO 3 – , and SCN – are found. For solutions containing mixtures of NO 3 – and Cl – , the brush swelling is the same as one would expect on the basis of the concentration-weighted average of the brush behavior in the single salt solutions. However, in mixtures of SCN – and Cl – , the swelling response is more complicated and substantial divergence from ideal behavior is observed. Mean-field theory shows excellent qualitative agreement with the ellipsometry findings. nSCF reveals that for the SCN – /Cl – cases the swelling behavior of the PDPA brush most likely arises from the predominant localization of the weakly hydrated SCN – within the brush compared to the more strongly hydrated Cl – .

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Anion-Specific Effects on the Behavior of pH-Sensitive Polybasic Brushes

Cited by 60 publications

References 78 publications

Behavior of Weak Polyelectrolyte Brushes in Mixed Salt Solutions

Behavior of Weak Polyelectrolyte Brushes in Mixed Salt Solutions

Specific ion modulated thermoresponse of poly(N-isopropylacrylamide) brushes

Combined Experimental and Theoretical Study of Weak Polyelectrolyte Brushes in Salt Mixtures

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