Cyclic Water Storage Behavior of Doubly Thermoresponsive Poly(sulfobetaine)-Based Diblock Copolymer Thin Films

Abstract

The cyclic swelling and collapse behavior of a doubly thermoresponsive diblock copolymer thin film, consisting of a zwitterionic poly­(sulfobetaine), poly­(N,N-dimethyl-N-(3-methacrylamidopropyl)-ammoniopropane sulfonate) (PSPP), and a nonionic poly­(N-isopropylmethacrylamide) (PNIPMAM) block, is investigated in situ at three characteristic temperatures with time-of-flight neutron reflectometry. With increasing temperature, the thin film becomes less hydrophilic, which leads to a decreased but faster water uptake. This response of the block copolymers in the thin-film geometry differs greatly from their known aqueous solution behavior. In the cyclic experiments at constant temperature, the behavior is reproducible in terms of mesoscopic parameters such as swelling ratio and water content, even though Fourier transform infrared spectroscopy reveals altered swelling mechanisms, which are attributed to a complex interplay between different water species. Thus, the overall reduced hydrophilicity affects the overall swelling behavior of the thin film but not the hydration of particular functional groups of the diblock copolymer PSPP-b-PNIPMAM.

Solvation Behavior of Poly(sulfobetaine)-Based Diblock Copolymer Thin Films in Mixed Water/Methanol Vapors

“…These water enrichment layers are formed during swelling in water vapor due to attractive interactions between the D 2 O molecules and the native hydrophilic SiO 2 layer on top of the Si substrate, as reported in earlier studies for other polymers. [23][24][25]69 During the H 23,26 One should note here that the swelling ratios of the DBC thin films in both experiments A and B lie in between the swelling ratios of the corresponding PSPE and PNIPMAM homopolymer thin films, which were swollen in H 2 O vapor (d/d ini (PSPE) = 1.82 and d/d ini (PNIPMAM) = 1.07). 26 During the methanol exchange, in both experiments A and B, the film thickness is lower in mixed water/methanol vapors than in pure water vapors, and both thin films reach a similar degree of swelling Analogously to the water swelling, the results during the methanol exchange might point to a higher affinity of the DBC to H 2 O.…”

“…The longer time needed for equilibration during the H 2 O swelling is attributed to the increase of the diffusion pathways of the solvent molecules with film thickness. 25 The methanol exchange is induced by changing the gas flow from a 100 vol % water flow to a 70/30 vol % water/methanol flow. As a consequence, the DBC undergoes a complex contraction process.…”

Poly(sulfobetaine) versus Poly(N-isopropylmethacrylamide): Co-Nonsolvency-Type Behavior of Thin Films in a Water/Methanol Atmosphere

“…In previous work, we investigated a doubly thermoresponsive, so-called “schizophrenic” diblock copolymer (DBC) that consisted of a zwitterionic poly­(sulfobetaine) block, exhibiting an upper critical solution temperature (UCST), , and a nonionic poly­( N -isopropyl­acrylamide) (PNIPAM) or poly­( N -isopropylmethacrylamide) (PNIPMAM) block, featuring a lower critical solution temperature (LCST). − Its response to temperature strongly differed in thin film geometry and in aqueous solution. This is mainly attributed to the increased polymer concentration and the resulting shift of the phase transition temperatures. , Remarkably, their film thicknesses and incorporated water contents varied in different isotope water vapor atmospheres (H 2 O and D 2 O). This is attributed to the marked H-D isotope sensitivity of the poly­(sulfo-betaine)s, ,, whereas PNIPMAM exhibits a rather minor H/D isotope sensitivity …”

“…This is mainly attributed to the increased polymer concentration and the resulting shift of the phase transition temperatures. 20,21 Remarkably, their film thicknesses and incorporated water contents varied in different isotope water vapor atmospheres (H 2 O and D 2 O). This is attributed to the marked H-D isotope sensitivity of the poly(sulfobetaine)s, 15,16,22 whereas PNIPMAM exhibits a rather minor H/D isotope sensitivity.…”

Double hydrophilic copolymers – synthetic approaches, architectural variety, and current application fields

“…Water-soluble polymers are very attractive materials, and they find applications in various fields from cosmetics, detergents, water treatment, or coatings. 5,221–225 This is mostly due to favourable interactions with other materials, e.g. , complex formation or even stabilising effects to improve solubility.…”