Co-Nonsolvency Transition of Poly(N-isopropylacrylamide) Brushes in a Series of Binary Mixtures

Abstract

Co-nonsolvency occurs if a mixture of two good solvents causes the collapse or demixing of polymers into a polymer-rich phase in a certain range of compositions of these two solvents. In this work, we systematically study the co-nonsolvency behavior of poly­(N-isopropylacrylamide) brushes of different grafting densities in a series of alcohol–water binary mixtures with increasing hydrophobic parts ranging from methanol to 1-butanol by using ellipsometry. We report a strong collapse transition by increasing the alcohol concentration in the water-rich phase, which is enhanced for longer-chain alcohols. The analysis of the thermodynamic properties of the alcohol–water series displays that an increasing demixing tendency between alcohol and water is correlated with an enhancement of the collapse transition of the brush. The increase of grafting density weakens the transition behavior but does not shift the solvent composition point of maximum brush collapse, which is in agreement with the predictions of a recently proposed mean-field model based on the preferential adsorption concept. Among the fully miscible solvents, the most sensitive switching behavior of the brush is found for 1-propanol while 1-butanol already displays a miscibility gap at higher volume fractions.

FRET‐Integrated Polymer Brushes for Spatially Resolved Sensing of Changes in Polymer Conformation

“…This intensity,w ith respect to the surrounding area, then decreased in the presence of "good" solvents (35 % EtOH > water > EtOH). [21] Thep hotobleaching therefore offers ap otential way of spatially visualising polymer brush conformation on photobleached patterns.T he fluorescence spectra of the polymer brush surfaces in different aqueous…”

“…Fort he polymer brush, the magnitude of the differences in I 521 /I 581 are expected to be shifted due to ad egree of permanent FRET that occurs between chains,but the trend in the ratios should be similar. It was found that for the FRET,t ypical co-nonsolvency transitions were exhibited (i.e., FRET ratios consistent with collapsed polymers at intermediate volume fractions of alcohol in water [21] ). Particularly,t he onset of FRET was at greater volume fractions of alcohol for MeOH > EtOH > 1-PrOH (Figure 3), which matches known co-nonsolvency trends.C rucially,b yd irectly comparing to polymer brush height, there were clear similarities between the onset of…”

“…Herein, we introduce Fçrster resonance energy transfer (FRET) chemistry into ultrathin (< 70 nm) poly(N-isopropyl acrylamide) (PNIPAM) polymer brush surfaces for use as in-liquid optical sensors of polymer conformation under different stimuli. The PNIPAM was chosen due to its exceptional sensitivity to various stimuli, including subtle changes in liquid mixture compositions (co-nonsolvencye ffects-polymer collapse at intermediate mixing ratios of two good solvents [21] ), and their ability to be assembled into well-defined polymer brushes.T he polymer chains were assembled into dense and homogenously smooth polymer brushes on planar quartz surfaces by ag rafting-to approach. Thes urfaces exhibited strong fluorescence,w ith ab rush thickness in water of approximately 65 nm.…”

Multifunctional, complex polymers for functional and stimuli-responsive coatings

“…As we discuss in a separate Chapter, PNIPAM has a co-non-solvent behavior in a mixture of water and alcohols such as methanol, ethanol or isopropanol. [168][169][170] At room temperature, PNIPAM polymer chains are found to be swollen in water or one of these alcohols, while they become collapsed in a methanol-water mixture. The co-non-solvency behavior is affected by the physical constraints on the polymer chains; in fact, the conformational transition of PNIPAM chains occur in 10-20 vol.% methanol when the polymer is free in solution, and in 30 vol.% methanol in water for gels and brushes.…”

“…[171][172][173] The origin of co-non-solvency is still under debate, as shown in Figure 2.19. [174][175][176][177] Irrespective of the exact explanation regarding its origin, the manifestation of the phenomenon of co-non-solvency is well established and has been widely observed for 2 different combinations of polymers, solvents and co-solvents. 172,[178][179][180][181] Co-non-and cosolvency of polymer brushes is of interest e.g., for surfaces with tunable friction and adhesion properties in smart drug releasing devices, for the pick-up and release of nanoparticles, regulation of channel permeability in fluidics, as well as sensing devices.…”