Poly(sulfobetaine)-Based Diblock Copolymer Thin Films in Water/Acetone Atmosphere: Modulation of Water Hydration and Co-nonsolvency-Triggered Film Contraction

Abstract

The water swelling and subsequent solvent exchange including co-nonsolvency behavior of thin films of a doubly thermo-responsive diblock copolymer (DBC) are studied via spectral reflectance, time-of-flight neutron reflectometry, and Fourier transform infrared spectroscopy. The DBC consists of a thermo-responsive zwitterionic (poly(4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate)) (PSBP) block, featuring an upper critical solution temperature transition in aqueous media but being insoluble in acetone, and a nonionic poly(Nisopropylmethacrylamide) (PNIPMAM) block, featuring a lower critical solution temperature transition in water, while being soluble in acetone. Homogeneous DBC films of 50−100 nm thickness are first swollen in saturated water vapor (H 2 O or D 2 O), before they are subjected to a contraction process by exposure to mixed saturated water/acetone vapor (H 2 O or D 2 O/acetone-d6 = 9:1 v/v). The affinity of the DBC film toward H 2 O is stronger than for D 2 O, as inferred from the higher film thickness in the swollen state and the higher absorbed water content, thus revealing a pronounced isotope sensitivity. During the co-solvent-induced switching by mixed water/acetone vapor, a two-step film contraction is observed, which is attributed to the delayed expulsion of water molecules and uptake of acetone molecules. The swelling kinetics are compared for both mixed vapors (H 2 O/acetone-d6 and D 2 O/acetone-d6) and with those of the related homopolymer films. Moreover, the concomitant variations of the local environment around the hydrophilic groups located in the PSBP and PNIPMAM blocks are followed. The first contraction step turns out to be dominated by the behavior of the PSBP block, whereas the second one is dominated by the PNIPMAM block. The unusual swelling and contraction behavior of the latter block is attributed to its co-nonsolvency behavior. Furthermore, we observe cooperative hydration effects in the DBC films, that is, both polymer blocks influence each other's solvation behavior.

KCl-Modulated Hydration and Subsequent Thermoresponsive Behavior of Poly(sulfobetaine)-Based Diblock Copolymer Thin Films

“…The film surface is smoother than it is in the as-prepared samples (see RMS roughness values S q in Figure S3). Such changes are attributed to the rearrangement of the polymer chains after D 2 O hydration, as seen in our previous studies. , …”

“…The synthesis of the monomers, chain transfer agent, and block copolymer was reported before. , Water was purified by a Millipore Milli-QPlus water purification system (resistivity 18 MΩ × cm). 2,2,2-Trifluoroethanol (TFE, Roth, 99.8%), potassium chloride (KCl, Sigma-Aldrich, 99%), and deuterated water (D 2 O, Deutero GmbH, 99.95%) were used as received.…”

Ambient Environment Adaptive Elastomer Constructed by Microphase Separation and Segment Complexation of Triblock Copolymers

“…Hydrogen-bonding complexation of PAA segments from SAS and PEO segments from SES make these FT-IR adsorption differences before and after association. − Under scrutiny, the wideness and shape of CO and C–O–C FT-IR adsorption bands of complex samples present variation because PAA segments of SAS triblock copolymers have different lengths and their complexation with PEO have different hydrogen-bonding degrees. The peak shift and the integration of CO FT-IR absorbance are further analyzed by Gaussian fit. , The changes in the wideness and shape of the character peaks are visually discernible in Figure S6.…”

“…The peak shift and the integration of C�O FT-IR absorbance are further analyzed by Gaussian fit. 44,45 The changes in the and 106 °C (PAA of T g ). 33, 43 T g of the PAA/PEO complex is dependent on the composition: the higher PEO content has the lower T g .…”

Effect of Magnesium Salts with Chaotropic Anions on the Swelling Behavior of PNIPMAM Thin Films

“…Stimuli-responsive polymers open a wide field of applications due to their unique properties. − For most applications, the polymers require a certain mechanical stability while exhibiting a fast response to the stimuli. This balance between stability and responsiveness can be achieved by using thin films , and is especially needed when designing nanodevices such as nanoswitches or gas sensors. − The response of thin films fabricated from stimuli-responsive polymers is shown to derive often from a conformational change, which can be achieved by temperature, − light, , ionic strength, , pressure, pH, , or by changing the environment. , An example for a thermoresponsive polymer is poly­( N -isopropylmethacrylamide) (PNIPMAM), which features a lower critical solution temperature in water at about 44 °C. , Moreover, PNIPMAM films are capable of temperature-modulated swelling under the influence of surrounding water vapor and exhibit cononsolvency behavior in various water-organic solvent mixtures. − These properties make PNIPMAM a promising candidate for application in nanodevices, such as nanoswitches or humidity sensors. , …”