Quantifying the Interactions in the Aggregation of Thermoresponsive Polymers: The Effect of Cononsolvency

Abstract

The aggregation kinetics of thermoresponsive core-shell micelles with a poly(N-isopropyl acrylamide) shell in pure water or in mixtures of water with the cosolvents methanol or ethanol at mole fractions of 5% is investigated during a temperature jump across the respective cloud point. Characteristically, these mixtures give rise to cononsolvency behavior. At the cloud point, aggregates are formed, and their growth is followed with time-resolved small-angle neutron scattering. Using the reversible association model, the interaction potential between the aggregates is determined from their growth rate in dependence on the cosolvents. The effect of the cosolvent is attributed to the interaction potential on the structured layer of hydration water around the aggregates. It is surmised that the latter is perturbed by the cosolvent and thus the residual repulsive hydration force between the aggregates is reduced. The larger the molar volume of the cosolvent, the more pronounced is the effect. This framework provides a molecular-level understanding of solvent-mediated effective interactions in polymer solutions and new opportunities for the rational control of self-assembly in complex soft matter systems.

Synthesis and solution properties of a temperature-responsive PNIPAM–b-PDMS–b-PNIPAM triblock copolymer

“…SAXS/SANS studies have been published on a variety of block copolymers such as the diblock copolymer poly(methoxy diethylene glycol acrylate)-block-polystyrene (PS), 5 the diblock copolymer PS-PNIPAM 6 , deuterated polystyrene and poly(n-hexyl methacrylate) (PnHMA), 7 poly(2-isopropyl-2-oxazoline)-b-poly(2-ethyl-2-oxazoline), 8 C18EO100 9 , polyethylene oxide -poly(2-vinylpyridine) 10 , polyethylene oxide -PNIPAM, 11,12 and PNIPAMpoly(n-butyl acrylate) 13,14 and on triblock copolymers such as (LCP, poly(4-cyanobiphenyl-4-oxyundecylacrylate)) 'A' endblock and a deuterated polystyrene 'B' midblock, 15 PS-PMDEGA-PS, 16,17 and PS-PNIPAM-PS 18 . The most studied class of temperature-responsive polymers are poly(ethylene oxide-block-propylene oxide-blockethylene oxide) PEO-PPO-PEO triblock copolymers known as Pluronics ® .…”

Solubility behaviour of random and gradient copolymers of di- and oligo(ethylene oxide) methacrylate in water: effect of various additives

“…No cononsolvency effect (i.e. lower compatibility of the polymer with the solvent at a certain range of solvent composition) is observed for these copolymers in the water-ethanol system in contrast to other temperature responsive polymers like PNIPAM 32,36,86,87 or other thermoresponsive polymers with nitrogen atoms as the source of hydrogen bonding. 38 This can be a result of no preference to form water-ethanol interactions rather than water-polymer or polymer-polymer interactions in this system.…”

Collapse in two good solvents, swelling in two poor solvents: defying the laws of polymer solubility?

“…For example, when a polymer is well soluble in a solvent and a small amount of cosolvent is added in the same binary solution, the polymer undergoes a coil-globule transition. While the recent literature generally associates co-non-solvency with the LCST polymers [5][6][7][8][9][10][11][12][13][14][15]17], the term co-non-solvency was first coined for a UCST system of polystyrene solvation in a mixture of cyclohexane and N,N-dimethylformamide (DMF) [35]. There are a wide range of polymers, both LCST and UCST, that show the phenomenon of co-non-solvency when they are disolved in appropriate mixtures of solvent and cosolvent.…”

“…Smart responsive polymers are becoming increasingly important as high-performance multifunctional soft materials [1][2][3][4]. A polymer is considered to be smart responsive when a small change in external stimuli can drastically alter its structure, function and stability [5][6][7][8][9][10][11][12][13][14][15][16][17]. Because of this fast responsiveness to external stimuli, these systems serve as suitable candidates to tune polymer properties for desired applications [1,2].…”