Homopolymer Brushes Research Articles

Polymer brushes based on N-methacryloxysuccinimide as platform for versatile post-polymerization modification

In this contribution we present a method for the surface-initiated atom-transfer radical polymerization of active esters based on N-methacryloxysuccinimide and post-polymerization modification in mild conditions. The obtained active ester brushes show quantitative conversion under amidation conditions with various primary amines, including 1-amino-2-propanol, fluorine containing amines and amine-containing fluorophores. Amidation reaction with propargyl amine offers the possibility to introduce a second functionality in the homopolymer brushes. This widens the ability of polymer analogous reactions with functionalized compounds. The effectiveness of the amidation reaction was deeply studied utilizing spectroscopic ellipsometry, infrared reflection-absorption and X-ray photoelectron spectroscopies, contact angle goniometry and surface energy analysis. As validated by functionalized homopolymer brushes, hierarchical block copolymer brushes containing active ester monomer units also undergo quantitative conversion with primary amines. Furthermore, resulting polymer brushes containing fluorophores were studied by fluorescent microscopy to further investigate their film structure and homogeneity.

Sequential Brush Grafting for Chemically and Dimensionally Tolerant Directed Self-Assembly of Block Copolymers

We report a method for the directed self-assembly (DSA) of block copolymers (BCPs) in which a first BCP film deploys homopolymer brushes, or "inks", that sequentially graft onto the substrate's surface via the interpenetration of polymer molecules during the thermal annealing of the polymer film on top of existing polymer brushes. By selecting polymer "inks" with the desired chemistry and appropriate relative molecular weights, it is possible to use brush interpenetration as a powerful technique to generate self-registered chemical contrast patterns at the same frequency as that of the domains of the BCP. The result is a process with a higher tolerance to dimensional and chemical imperfections in the guiding patterns, which we showcase by implementing DSA using homopolymer brushes for the guiding features as opposed to more robust cross-linkable mats. We find that the use of "inks" does not compromise the line width roughness, and the quality of the DSA as a lithographic mask is verified by implementing a robust "dry lift-off" pattern transfer.

Phase Behaviors of ABA Star Polymer and Nanoparticles Confined in a Sphere with Soft Inner Surface.

The phase behaviors of an ABA star polymer and nanoparticles confined in a sphere with soft inner surface, which is grafted with homopolymer brushes have been studied by the self-consistent field theory (SCFT). The morphologies of mixture in the center slice of sphere were focused. Two cases are considered: one is that the nanoparticles interact with the B blocks and the other is that the nanoparticles preferentially wet the B blocks. Under the two conditions, through changing the block ratio of the ABA star polymer, the concentration and radius of the nanoparticles, the phase behaviors of the mixtures confined the soft sphere are studied systematically. With increasing the concentration of nanoparticles, the entropy and the steric repulsive interaction of nanoparticles, and the nanoparticle density distributions along the perpendicular line through the center of sphere are plotted. The phase diagram is also constructed to analyze the effects of the nanoparticle volume fraction and radius on morphologies of ABA star polymers, and to study the effect of confinement on the phase behaviors. The results in this work provide a useful reference for controlling the ordered structures in experiment, which is an effective way to fabricate the newly multifunctional materials.

The direction of influence of specific ion effects on a pH and temperature responsive copolymer brush is dependent on polymer charge

The effect of electrolyte identity on the conformation of homopolymer brushes of poly(2-(2-methoxyethoxy) ethyl methacrylate) (PMEO2MA) and poly(2-(diethylamino)ethyl methacrylate) (PDEA), as well as a P(MEO2MA-co-DEA) copolymer brush of 90:10 mol% composition has been examined. PMEO2MA is a thermoresponsive polymer with a lower critical solution temperature of ~28 °C, PDEA a weak polybase with an apparent pKa of ~7.5, while the copolymer brush exhibits both pH and temperature responsive behaviour. Brushes were synthesised using surface initiated ARGET ATRP. The effect of temperature at low and high pH in the presence of different electrolytes on the thickness of the P(MEO2MA-co-DEA) 90:10 mol% brush was tracked with ellipsometry and the polymer volume fraction profile was elucidated with neutron reflectometry. The effect of each electrolyte on the copolymer brush conformation as the temperature changes could be switched by changing the pH from low (charged DEA segments) to high (uncharged DEA segments). The overall behaviour of the copolymer in each salt was PDEA-like at low pH, and MEO2MA-like at high pH. At low pH a reverse Hofmeister effect was observed, while at high pH a direct Hofmeister effect was observed.

Conformational transitions of adsorption-responsive single diblock copolymers in homopolymer brushes.

Using self-consistent field calculations, we examine the effect of brush polydispersity on conformational transitions of single adsorption-active diblock copolymer chains embedded in inert polydisperse brushes. To represent the polydispersity, we adopt the continuous Schulz-Zimm chain length distributions, and three typical distributions are chosen such that a wide range of polydispersity is covered. A phase diagram of the diblock copolymer switches has been constructed showing that the first order phase transitions occupy a larger space in the case of polydisperse brushes. We further characterize these first order phase transitions by specifying their transition points, transition widths and transition barriers, where the latter two are particularly important as they determine the performance of the polymer switches. Our calculation indicates that polydispersity has different effect on the switching behavior depending on the lengths of both the active block and the inert block of the copolymer switch chain. In general, polydispersity improves the switching performance in the case of short active blocks, i.e. shorter or not very longer than the average length of the brush chains, and the corresponding energy barrier is smaller than a few kBT. In contrast, monodisperse brushes have the advantages when these two blocks are particularly long, i.e., lower transition barriers and fast switching. Notably, when the inert block approaches the average length of the brush chains, the transition barrier becomes almost zero in any case for monodisperse brushes, while a large finite value is still observed for that in polydisperse brushes. The complex interplay between the brush polydispersity and the switch behavior is attributed to the wide-range repulsions generated by the polydisperse brushes.

Benchtop Preparation of Polymer Brushes by SI-PET-RAFT: The Effect of the Polymer Composition and Structure on Inhibition of a Pseudomonas Biofilm

We report a high-throughput method for producing surface-tethered polymeric brushes on glass substrates via surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT). Due to its excellent oxygen tolerance, SI-PET-RAFT allows brush growth using low reagent volumes (30 μL) without prior degassing. An initial 28 homopolymer brush library was successfully prepared and screened with respect to their antifouling performance. The high-throughput approach was further exploited to expand the library to encompass statistical, gradient, and block architectures to investigate the effect of monomer composition and distribution using two monomers of disparate performance. In this manner, the degree of attachment from Gram-negative Pseudomonas aeruginosa (PA) bacterial biofilms could be tuned between the bounds set by the homopolymer brushes.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method.

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Tunable Assembly of Block Copolymer Tethered Particle Brushes by Surface-Initiated Atom Transfer Radical Polymerization.

A strategy to synthesize SiO2-g-PMMA/PMMA-b-PS mono- and bimodal block copolymer particle brushes by surface-initiated atom transfer radical polymerization (SI-ATRP) from silica particles is presented. First, PMMA blocks were prepared by normal ATRP with controlled degree of polymerizations and grafting density. In a second step, the PS block was synthesized through a chain extension using low parts per million of Cu catalyst. Variation of the SiO2-g-PMMA-Br macroinitiator concentration had a pronounced effect on the modality of the chain extension product. In the limit of small concentration, partial termination resulted in bimodal brush architectures, while more uniform brush architectures were observed with increasing concentration of macroinitiator. Brush nanoparticles with bimodal architectures assembled into string-like aggregates that bore a resemblance to structures found in systems comprised of sparse (homopolymer) brush particles. The unexpected effect of modality on structure formation points to opportunities in controlling microstructures in brush particle materials.

Interplay of Composition, pH, and Temperature on the Conformation of Multi-stimulus-responsive Copolymer Brushes: Comparison of Experiment and Theory.

Poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA), a thermoresponsive polymer with a lower critical solution temperature of ∼28 °C, and poly(2-(diethylamino)ethyl methacrylate) (PDEA), a weak polybase with an apparent pKa of ∼7.5, have been statistically copolymerized using activators continuously regenerated via electron transfer atom transfer radical polymerization to form multi-stimulus-responsive polymer brushes. The stimulus-responsive behavior of these brushes has been investigated with ellipsometry and numerical self-consistent field (nSCF) theory. The pH- and thermoresponsive behaviors of a PDEA homopolymer brush were investigated experimentally in order to benchmark the nSCF theory calculations. nSCF theory was able to reproduce the responsive behavior of PDEA and PMEO2MA homopolymer brushes. Three copolymer compositions (90:10, 70:30, and 50:50 mol % MEO2MA:DEA) were investigated experimentally with pH ramps performed at low and high temperatures and temperature ramps performed at low and high pH. A broader range of compositions were investigated with nSCF theory and compared to the experimental results, with the nSCF calculations able to capture the general behavior of the homopolymer and copolymer brushes. The responsive behavior of each brush to a given stimulus (temperature or pH) was dependent on both the polymer composition and environment (temperature or pH). The influence of pH on the brush increased with higher DEA mol % with a copolymer brush response transitioning from temperature-dominant to pH-dominant. The temperature response of PMEO2MA was completely masked at low and high pH values by the presence of at least 30 mol % polybase in the copolymer.

Surface Nanostructures Based on Assemblies of Polymer Brushes.

Studies on the fabrication of hierarchical surface nanostructures have significantly promoted the development of materials with new surface properties and functionalities. In this Minireview, progress on the fabrication of surface nanostructures based on surface organization of polymer brushes are outlined. In the past decades, self-assemblies of polymer brushes, including homopolymer, block-copolymer and mixed-polymer brushes, have aroused great interest in the fields of chemistry and materials science. Recent studies demonstrate that surface co-assemblies of polymer brushes and free polymer chains on solid surfaces are considered as an efficient approach to the preparation of hierarchical nanostructures. Some typical surface nanostructures and properties achieved through surface co-assembly approach are reviewed in this article. Meanwhile, the fundamental problems in the co-assembly approach are discussed and the potential applications of the hierarchical surface nanostructures are presented.

Synthesis and Hydration Behavior of a Hydrolysis-Resistant Quasi-Choline Phosphate Zwitterionic Polymer.

A hydrolysis-resistant polymer bearing new quasi-choline phosphate (quasi-CP) structures as side groups, poly(2-methacryloyloxyethyl choline methylphosphonate) (PMCPm), was designed and synthesized. Radical polymerization and sub-surface-initiated radical polymerization were used to prepare homopolymer and polymer brush on polymer substrates. Hydrolytic stability and hydrophilicity of the polymer were confirmed by nuclear magnetic resonance and contact angle measurements. Furthermore, the hydration states were investigated using Fourier-transform infrared spectroscopy and differential scanning calorimetry. The similar hydration behavior of PMCPm to poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) sheds light on understanding the interfacial functions of quasi-CP-bearing zwitterionic biomaterials.

Impact of Backbone Composition on Homopolymer Dynamics and Brush Block Copolymer Self-Assembly.

Four series of brush block copolymers (BBCP), with near identical side chain compositions but varying backbone structures, were synthesized to investigate the effect of backbone structure on the process of thermal BBCP self-assembly to photonic crystals (PCs). Each of the self-assembled PC films were examined by reflection measurements, small angle X-ray scattering measurements, and scanning electron microscopy to compare the resulting properties of the polymeric photonic crystal and the nanostructured morphology impacted by the backbone structure. It was found that the composition of the brush backbone within a BBCP has a dramatic effect on the ability of the BBCP to self-assemble into ordered nanostructures and on the local ordering of the nanostructure morphology accessed with higher molecular weight (MW) BBCPs (> 1,500 kg/mol). BBCPs with a norbornene imide-based backbone were able to thermally self-assemble to longer wavelength reflecting PCs and had higher fidelity ordering of lamellar nanostructures with higher MW polymers. By analyzing the melt rheological responses of the backbone compositions, both as linear polymers and homobrush polymers, it was concluded that the inherent fragility of the backbone promotes enhanced local ordering in the lamellar nanostructure morphology as well as access to larger domain sizes.

Swelling of multi-responsive spherical polyelectrolyte brushes across a wide range of grafting densities

Multi-stimulus responsive weak polyelectrolyte brushes were grafted by surface-initiated atom transfer radical polymerization from spherical silica nanoparticles across a wide range of grafting densities approaching the limit of close packing of grafting sites: a regime not previously explored in the brush swelling literature. Brushes consisted of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) homopolymers or poly(2-(dimethylamino)ethyl methacrylate)-r-poly(4-metharyloyloxyazobenzene) random copolymers P (DMAEMA-r-MOAB) and were subjected to pH-, temperature-, and photoisomerization-induced swelling and deswelling. Homopolymer brushes were prepared at grafting densities ranging from 0.12 to 1.4 nm−2 and number average degrees of polymerization ranging from 300 to 1200. Two copolymer brushes with 8 mol% and 13 mol% of the nonionizable, photoresponsive MOAB units were compared with homopolymer brushes prepared at similar grafting densities and degrees of polymerization. Dynamic light scattering was used to measure the hydrodynamic radius of grafted nanoparticles, and thus brush thickness, in water. Brush swelling in response to increased DMAEMA protonation followed a single scaling behavior across the full range of degrees of polymerization and grafting densities. Incorporating azobenzene-containing MOAB comonomers introduced a modest photoresponsive control of brush swelling and decreased the brush thickness relative to the comparable PDMAEMA homopolymer brush, without affecting the scaling with respect to protonation. PDMAEMA brushes exhibited a pH-dependent lower critical solution temperature behavior, resulting in a thermal collapse of up to 50% upon heating. This work demonstrates that scaling behaviors previously tested at low grafting densities hold for extremely high grafting densities and that they are unaffected by moderate nonionizable comonomer content.

Controlled grafting of polymer brush layers from porous cellulosic membranes

Dense polymer brushes on porous supports present powerful routes toward fouling-resistant coatings and ultra-thin, mechanically-stable selective layers. However, characterization of polymer chains grafted from nonideal, planar substrates often relies on indirect methods to determine the length, density, and location of polymeric brushes. In this study, we explore new methods to control and characterize the properties of polymer brush layers. Starting from hand-cast cellulose films and commercial cellulose membranes, we use surface-initiated atom transfer radical polymerization to graft polymeric chains. We tailor brush density and simultaneously stabilize the support by varying the proportions of initiator and crosslinker esterified to the cellulose substrate. On films with grafted polyacrylic acid (PAA) chains, we use the silver-binding method to determine brush density. We analyze brush growth behavior by directly cleaving chains from the surface of films for analysis by size exclusion chromatography, uniquely observing the divergence of two distinct populations of differing length beyond a certain molecular weight. Such behavior would be important to consider if the alignment of block copolymer layers is absolutely necessary in an application. By controlled contact of polymerization solution with the top surface, we show that brush growth can be partially directed to the top surface for asymmetric cellulose membranes with relatively low molecular weight cutoffs. In a semi-quantitative method to locate brush growth, depleted uranium was bonded to grafted PAA chains, and targeted emission x-ray spectroscopy was conducted for comparison of uranium content in various regions. Finally, we used our developed methods and findings to inform the synthesis of homopolymer and diblock copolymer brush layers, which we then used as selective layers in pressure-driven filtration and diffusion cell experiments.

Design, Synthesis, and Application of a Difunctional Y-Shaped Surface-Tethered Photoinitiator.

Mixed homopolymer brushes have unique interfacial properties that can be exploited for both fundamental studies and applications in technology. Herein, the synthesis of a new catechol-based biomimetic Y-shaped binary photoinitiator (Y-photoinitiator) and its applications for surface modification with polymer brushes through both "grafting to" and "grafting from" strategies are reported. The "leg" of the Y consists of a catechol group as surface anchoring moiety. The arms are photoinitiator moieties that can be "addressed" independent of each other by radiation of different wavelengths. Using ultraviolet and visible light successively, each arm of the Y-photoinitiator was activated, thereby allowing the synthesis of Y-shaped block copolymer brushes with dissimilar polymer chains. The suitability of the Y-photoinitiator for surface modification was first investigated using N-vinylpyrrolidone and styrene as the model monomers for successive UV-photoiniferter-mediated polymerization and visible-light-induced polymerization, respectively. Switching of the wetting properties of the Y-shaped block copolymer brush poly( N-vinylpyrrolidone)- block-poly(styrene) (PVP- b-PS)-grafted surfaces by contact with different solvents was also investigated. To further exploit this novel Y-photoinitiator for the preparation of functional interfaces, Y-shaped block copolymer brushes poly(1-(2-methacryloyloxyhexyl)-3-methylimidazolium bromide)- block-poly( N-vinylpyrrolidone- co-glycidyl methacrylate) (PIL(Br)- b-P(NVP- co-GMA)) were also prepared and subsequently functionalized with the cell-adhesive arginine-glycine-aspartic acid (RGD) peptides by reaction with the glycidyl groups (PILPNG-RGD). The PILPNG-RGD grafted surfaces showed excellent cell-adhesive, bacteriostatic, and bactericidal properties. Thus, it can be concluded that further exploitation of this novel Y-photoinitiator for graft polymerization should allow the preparation of a wide range of functional interfaces with tailored properties.

Sequential and one-pot post-polymerization modification reactions of thiolactone-containing polymer brushes.

Thiolactone chemistry has garnered significant attention as a powerful post-polymerization modification (PPM) route to mutlifunctional polymeric materials. Here, we apply this versatile chemistry to the fabrication of ultrathin, multifunctional polymer surfaces via aminolysis and thiol-mediated double modifications of thiolactone-containing polymer brushes. Polymer brush surfaces were synthesized via microwave-assisted surface-initiated polymerization of DL-homocysteine thiolactone acrylamide. Aminolysis and thiol-Michael double modifications of the thiolactone-functional brush were explored using both sequential and one-pot reactions with bromobenzyl amine and 1H,1H-perfluoro-N-decyl acrylate. X-ray photoelectron spectroscopy and argon gas cluster ion sputter depth profiling enabled quantitative comparison of the sequential and one-pot PPM routes with regard to conversion and spatial distribution of functional groups immobilized throughout thickness of the brush. While one-pot conditions proved to be more effective in immobilizing the amine and acrylate within the brush, the sequenital reaction enabled the fabrication of multifunctional, micropattterned brush surfaces using reactive microcontact printing.

Fabrication of Amphiphilic Nanoparticles via Mixed Homopolymer Brushes and NMR Characterization of Surface Phase Separation

“Patchy particles”, where the surface is anisotropically patterned through variation in the surface composition, can assemble into different colloidal crystal structures as well as act as interface stabilizers, heterogeneous reaction catalysts, and targeted drug delivery agents. Patchy nanoparticles (NPs) can be formed by adsorbing two chemically different polymer chains that will spontaneously phase separate. Although there is growing interest in polymer-based patchy nanoparticles, the majority of the studies have been theoretical rather than experimental due to difficulties in preparing significant quantities of nanoparticles with controlled polymer ratios. Likewise, characterization of the phase separation on the nanoparticle surface is challenging. Here we simultaneously overcome the synthesis and characterization hurdles by developing a facile, versatile protocol to produce sufficient quantities of patchy NPs for quantitative solid-state NMR measurements of the patch fractions, degree of phase separation, and morphology. Monodisperse 3.5 nm ZrO2 nanocrystals with polystyrene (PS) and poly(ethylene oxide) (PEO) ligands, covering the entire possible composition range, were reproducibly prepared through a simple exchange process. This approach has the advantage of well-defined polymer molecular weights and NP sizes, allowing experimental validation of theoretical predictions for nanophase separation in NPs with mixed homopolymer brushes. Upon exposure to a nonselective solvent, the nanoparticles assemble into different morphologies, namely micelles and vesicles, as a function of the PEO:PS ratios.

Swelling of Planar Polymer Brushes in Solvent Vapors

The swelling of densely grafted planar homo- and copolymer brushes in solvent vapors was studied by the dissipative particle dynamics method. It is shown that the distribution of the solvent inside the polymer film is inhomogeneous with the explicit maximum at the polymer–vapor interface. The value of the maximum does not depend on the grafting density and is mainly defined by the concentration of solvent vapors. At the same time, the distribution function of the free ends in homopolymer brush swollen in vapors of a good solvent is closer to the respective function in dry (solvent-free) brush: it has a rather narrow maximum at the upper border of the brush. In case of copolymer brushes, the swelling in vapors of a selective solvent can be accompanied by separation, the character of which is defined by the sequence of polymer segments (random or gradient) and also by the mean fraction of the segments of different types. The distribution function of free ends in the copolymer brush is calculated.

Friction and adhesion control between adsorbed layers of polyelectrolyte brush-grafted nanoparticles via pH-triggered bridging interactions

HypothesisAdsorption of polyelectrolyte brush-grafted nanoparticles (BGNPs) produces a heterogeneous interface with sub-monolayer surface coverage resulting from lateral electrostatic repulsions that limit packing. As a result, the interaction forces between opposing BGNP layers include an adhesive cross-surface BGNP-substrate bridging force that depends on the interparticle spacing, particle size, and strength of electrostatic interactions. We hypothesize that BGNPs with pH-responsive, annealed polyelectrolyte brushes can undergo controlled changes in surface area coverage through post-adsorption swelling or de-swelling into non-equilibrium layer conformations and that such changes in surface coverage can switch off or switch on particle intercalation, bridging attractions, and enhanced energy dissipation upon sliding. This work aims to characterize the nature of surface forces in heterogeneous BGNP adsorbed layers and to utilize pH-sensitive bridging forces as a mechanism to tune friction and adhesion. ExperimentsColloidal probe atomic force microscopy (CP-AFM) is used to measure normal and lateral forces between negatively charged silica surfaces with adsorbed pH-responsive cationic BGNPs. The BGNPs are poly(2-dimethylaminoethyl methacrylate) brush-grafted silica nanoparticles. Adhesion force and friction analysis is complemented by simultaneous quartz-crystal microbalance and ellipsometry measurements under conditions that render the particles strongly charged and swollen (acidic) or weakly charged and de-swollen (basic). FindingsAdsorbed BGNPs can be swollen or de-swollen via pH rinses, enabling direct control of surface coverage and bridging interactions. Transitions from adhesive bridging contacts with high friction to non-adhesive contacts with low friction forces occur when adsorbed BGNP layers are switched from a de-swollen/weakly charged state to a swollen/highly charged state. The ability to controllably shift the character of normal and lateral forces via coverage-mediated bridging interactions is a unique feature of adsorbed nanoparticulate brush constructs and highlights their potential to condition surfaces with additional functionality compared to dense, planar homopolymer brushes.

The role of copolymer composition on the specific ion and thermo-response of ethylene glycol-based brushes

Thermoresponsive ethylene glycol based comb-polymer brushes were studied as a function of copolymer composition in aqueous electrolyte solutions. Homopolymer poly oligo(ethylene glycol) methyl ether methacrylate (POEGMA300) and statistical copolymer brushes with 60 mol% OEGMA300 and 40 mol% (di(ethyleneglycol) methyl ether methacrylate) (MEO2MA) underwent a monotonic swollen to collapsed transition with increasing temperature. Neutron reflectometry and ellipsometry measurements showed that the higher ethylene glycol content of the homopolymer brush led to a higher degree of swelling for a given temperature, with the transition occurring over a wider temperature range than the copolymer brush. Dynamic atomic force microscopy force measurements revealed minimal impact of probe velocity on normal interaction forces for the homopolymer brush. In contrast, a significant increase in both repulsion and adhesion was observed for the copolymer brush. Exposure to potassium thiocyanate solutions increased the degree of swelling at any given temperature while potassium acetate showed the opposite behaviour for both brush compositions. However, the homopolymer brushes displayed a greater increase in swelling due to thiocyanate and reduced collapse due to acetate.