Structure of pH-Responsive Polymer Brushes Grown at the Gold–Water Interface: Dependence on Grafting Density and Temperature

Abstract

ethyl methacrylate) (PDMAE-MA) brushes have been grown by surface-initiated atom transfer radical polymerization (SI-ATRP) from the gold−water interface at different grafting densities, and neutron reflectivity has been used to characterize the response of the brush structures to changes in pH and temperature. Low-density brushes show the greatest response to changes in pH, with the swelling of the highest density brushes essentially independent of pH. The scaling exponent of the swelling ratio with grafting density changes from β ∼ −0.7, which is typical for neutral brushes, at pH 10, to β ∼ −1.4, at pH 3, reflecting the change in the dominant contribution to the osmotic pressure in the brush. At low pH, the osmotic pressure due to the counterions of the charged segments exceeds that of the segmental excluded volume, except in the highest density brushes, resulting in the pH-dependent swelling response of all but the highest density brushes. At pH 10, increasing temperature causes a partial collapse of the brushes with a transition temperature in the range 30−40 °C. The transition is associated with the dehydration of the hydrophilic segments. The magnitude of the deswelling decreases with increasing grafting density, reflecting the decreasing volume fraction of water in the brush.

Swelling Behavior and Nanomechanical Properties of (Peptide-Modified) Poly(2-hydroxyethyl methacrylate) and Poly(poly(ethylene glycol) methacrylate) Brushes

“…In agreement with earlier reported observations on e.g. poly(2-(dimethylamino)ethyl methacrylate) 17,37 and PNIPAm 38 brushes, the swelling ratios were also found to decrease with increasing grafting density. The grafting density dependence of the swelling ratio decreases from PHEMA to PPEGMA 6 to PPEGMA 10 .…”

“…The swelling ratios are similar for all the polymers with most of the values between 1.5 and 3.5, which are comparable to values reported for other hydrophilic polymer brushes. 19,21,22,37 For samples with lower grafting density and smaller film thicknesses (i.e. shorter ATRP reaction times), the swelling ratios were found to increase to ~ 5.…”

Temperature responsive behavior of polymer brush/polyelectrolyte multilayer composites

“…The choice of this block copolymer was motivated by the design of a neutral, temperature responsive part coupled with a charged block, which serves as a substrate for efficient PE adsorption. The charged nature of the PDMAEMA in Milli-Q water (pH B 5.5; pK a B 7.5 26 ) makes it a suitable candidate for this purpose; in addition, the pH and temperature responsiveness of this polymer 27,28 might enhance the control of system properties and its applicability as a smart coating material. The presence of PNIPAM ensures the temperature responsive behavior even in the case of strong complexation between the polyelectrolyte brush and free PE chains.…”

Stimuli-Responsive Polyelectrolyte Brushes As a Matrix for the Attachment of Gold Nanoparticles: The Effect of Brush Thickness on Particle Distribution

“…Neutral polymer brushes and polyelectrolyte brushes are widely used for the modification of surfaces, due to their advantageous specific properties, such as mechanical and chemical stability, their adsorption behavior [1] and permeability [2] and the possibility to tune their structure by varying external stimuli. For instance, the structure of a weak polyelectrolyte brush depends on pH [3][4][5][6][7][8], temperature [9][10][11], salt [12][13][14][15] and solvent [16][17][18]. More precisely, the swelling/shrinking of the studied poly-(N,N-(dimethylamino ethyl) methacrylate) (PDMAEMA) brushes can be manipulated by adjusting the pH of the surrounding environment to values below and above the pK A .…”