Cononsolvency Transition of Polymer Brushes: A Combined Experimental and Theoretical Study

Abstract

In this study, the cononsolvency transition of poly(N-isopropylacrylamide) (PNiPAAm) brushes in aqueous ethanol mixtures was studied by using Vis-spectroscopic ellipsometry (SE) discussed in conjunction with the adsorption-attraction model. We proved that the cononsolvency transition of PNiPAAm brushes showed features of a volume phase transition, such as a sharp collapse, reaching a maximum decrease in thickness for a very narrow ethanol volume composition range of 15% to 17%. These observations are in agreement with the recently published preferential adsorption model of the cononsolvency effect.

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

“…We found that σ ≈0.19 chains/nm 2 , consistent with previously reported densely grafted PNIPAM brushes. [25] This emphasises the utility of our macromolecular anchoring approach of carboxylate end‐group PNIPAM polymers, from a melt, for assembling dense PNIPAM brush surfaces. Importantly, the surfaces exhibited fluorescence excitation spectra consistent with NBD's excitation wavelength at 454 nm (Figure 1 F ), where the emission showed clear Rhod B emission in the dry state (Figures 1 G and S3), indicating strong FRET pairing.…”

“…These surfaces were investigated under co‐nonsolvency conditions, which causes PNIPAM to collapse at intermediate mixing ratios of two “good” solvents. [25] Common co‐nonsolvency systems for PNIPAM include mixtures of short‐chain alcohols with water. This effect was pursued as it offers an intriguing possibility for chemosensing of small compositional changes in aqueous liquids that causes dramatic changes in PNIPAM conformation.…”

Physics of the nuclear pore complex: Theory, modeling and experiment

“…With further increase of the transport protein concentration, more protein can enter the FG nup film therefore leading to a moderate layer swelling as predicted theoretically and observed experimentally. The effect of concentration dependent protein non-monotonic layer compactification and swelling, although very moderate for large particles such as the transport proteins, is much more pronounced for small particles or mixed solvents, and are related to a phenomenon known in polymer science as ''co-non-solvency'' [226,227]. The morphologies of FG nup and transport assemblies in channel-like geometry of the NPC are discussed in Sections 3.4.5 and 3.5.…”

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

“…We found that s % 0.19 chains/nm 2 ,consistent with previously reported densely grafted PNIPAM brushes. [25] This emphasises the utility of our macromolecular anchoring approach of carboxylate endgroup PNIPAM polymers,from amelt, for assembling dense PNIPAM brush surfaces.I mportantly,t he surfaces exhibited fluorescence excitation spectra consistent with NBDse xcitation wavelength at 454 nm (Figure 1F), where the emission showed clear Rhod Be mission in the dry state (Figures 1G and S3), indicating strong FRET pairing.T his was confirmed by confocal laser scanning microscopy (CLSM) measurements of the surfaces with both the acceptor channel (width between 560 nm and 700 nm, with l exc = 543 nm) and donor channel (width between 490 and 560 nm, with l exc = 458 nm), after asquare section was photobleached at l exc = 543 nm for 40 minutes (Figure 1Hand I, respectively). It was clearly seen that where the acceptor was bleached there was significant enhancement of the donor fluorescence (Figure S4), validating the FRET pairing for the polymer brush surface.T he polymer brush surfaces have the FRET donor in closest proximity to the quartz, with the Rhod Be xtended outwards finishing with the CTAo nt he solvent side.T his architecture ensures changes in FRET pairing should be reflective of both the polymer brush height, and the individual mixing of chains amongst their neighbours (i.e., am ultidimensional probe of the polymer conformation).…”