The swelling and solvation of 100−200 nm thin films of a diblock copolymer consisting of a short poly(methyl methacrylate) (PMMA) block and a long poly(N-isopropylacrylamide) (PNIPAM) block are investigated in mixed water/methanol vapors. The processes are followed in real time using spectral reflectance (SR), time-offlight neutron reflectometry (ToF-NR), and Fourier transform infrared (FT-IR) spectroscopy, applying two neutron scattering contrast variation sequences. After hydration in pure water vapor, the vapor composition (relative to a flow rate of 1 L/ min ≙ 100%) is changed to 70% water (D 2 O/H 2 O) and 30% methanol (CH 3 OH/ CD 3 OH). Upon the mixed vapor stimulus, a two-step response is found, in which an initially enhanced swelling of the films is followed by a contraction. Differences in the solvent exchange kinetics found in ToF-NR experiments coincide with characteristic changes in the FT-IR spectra. While the initially enhanced swelling of the films is driven by the absorption of methanol, the film contraction is related to the release of both solvents, with almost no further change in solvent composition. In analogy to the coil-to-globule transition encountered in the polymer solution, these film response characteristics are attributed to the cononsolvency behavior of PNIPAM in water/methanol mixtures.

The temperature-dependent phase behavior and self-assembly behavior in aqueous solution of the thermoresponsive amphiphilic diblock copolymer PMMA21-b-PNIPAM283 made of a short permanently hydrophobic poly­(methyl methacrylate) block and a long thermoresponsive poly­(N-isopropylacrylamide) are studied. Turbidimetry, dynamic light scattering (DLS), and synchrotron small-angle X-ray scattering (SAXS) provide temperature-dependent structure information. A lower critical solution temperature (LCST) behavior with a cloud point T CP = 31.1 °C in dilute solution is observed. Below T CP, spherical core–shell micelles are present, having a small PMMA core and a hydrated PNIPAM shell with a radial gradient of water content. Below T CP, the micelles are interpenetrated and show a weak correlation with each other. As the temperature approaches T CP, the micellar core shrinks and thus, the aggregation number decreases, revealing that the PMMA blocks are still mobile. Moreover, the micellar shell dehydrates above T CP and the micelles notably contract. They form clusters, which grow and transform into large compact aggregates as temperature is raised far above T CP.

The self-assembly of the thermoresponsive amphiphilic diblock copolymer PMMA 21 -b-PNIPAM 283 is studied in different water/methanol mixtures. It consists of a short hydrophobic poly(methyl methacrylate) block and a long thermoresponsive poly(N-isopropylacrylamide) block. Adding methanol as a cosolvent causes the PNIPAM block, which is soluble in both pure water and pure methanol, to collapse due to the so-called cononsolvency effect. Meanwhile, the addition of methanol reduces the incompatibility of the PMMA block with water. By means of turbidimetry and differential scanning calorimetry, the solvent-composition-dependent phase diagram is constructed. Dynamic light scattering and synchrotron radiation-based small-angle X-ray scattering provide structural information at 20 °C in dependence on the solvent composition. In water-rich solvent mixtures, self-assembled spherical core−shell micelles are formed. The internal structure of the micelles is adjusted by the solvent compositions in two ways: methanol softens the PMMA micellar core, while it causes the shrinkage of the PNIPAM micellar shell. In methanol-rich solvent mixtures beyond the miscibility gap, the copolymers are molecularly dissolved chains. They are collapsed near the coexistence line, while they become random coils as the methanol content increases. We propose that the internal morphology of the micelles and the conformation of the dissolved chains depend strongly on the solvent composition, as a consequence of the superposed co-nonsolvency effect of PNIPAM and the overall enhanced solvation of PMMA when adding methanol.

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.

To systematically add functionality to nanoscale polymer switches, an understanding of their responsive behavior is crucial. Herein, solvent vapor stimuli are applied to thin films of a diblock copolymer consisting of a short poly(methyl methacrylate) (PMMA) block and a long poly(N‐isopropylmethacrylamide) (PNIPMAM) block for realizing ternary nanoswitches. Three significantly distinct film states are successfully implemented by the combination of amphiphilicity and co‐nonsolvency effect. The exposure of the thin films to nitrogen, pure water vapor, and mixed water/acetone (90 vol%/10 vol%) vapor switches the films from a dried to a hydrated (solvated and swollen) and a water/acetone‐exchanged (solvated and contracted) equilibrium state. These three states have distinctly different film thicknesses and solvent contents, which act as switch positions “off,” “on,” and “standby.” For understanding the switching process, time‐of‐flight neutron reflectometry (ToF‐NR) and spectral reflectance (SR) studies of the swelling and dehydration process are complemented by information on the local solvation of functional groups probed with Fourier‐transform infrared (FTIR) spectroscopy. An accelerated responsive behavior beyond a minimum hydration/solvation level is attributed to the fast build‐up and depletion of the hydration shell of PNIPMAM, caused by its hydrophobic moieties promoting a cooperative hydration character.