PMMA-b-PNIPAM Thin Films Display Cononsolvency-Driven Response in Mixed Water/Methanol Vapors

Abstract

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.

Co-Nonsolvency Effect in Solutions of Poly(methyl methacrylate)-b-poly(N-isopropylacrylamide) Diblock Copolymers in Water/Methanol Mixtures

“…This difference is ascribed to the steric hindrances resulting from the dense packing of the PNIPAM blocks near the PMMA cores of the micelles. The T CP values of the identical PMMA- b -PNIPAM in H 2 O/CH 3 OH at 10 g L –1 were previously shown to have a similar dependency on the methanol volume fraction but shifted downward by ∼2.5 °C . Moreover, the decrease in the light transmission becomes slightly broader with increasing CD 3 OD volume fraction, and finite values are reached above T CP .…”

Fundamentals and Applications of Polymer Brushes in Air

“…Even in spin-coated polymer films, where polymer migration to the surface is not hindered by grafting, solvent-enriched layers have been observed at the polymer–air interface in experiment. 85 , 86 …”

Flexible Sample Environment for the Investigation of Soft Matter at the European Spallation Source: Part II—The GISANS Setup

“…This ensures that the 3D printed material is not hit by the incident nor the scattered neutron beam (which would produce unnecessary background). It was shown with the previous chamber design that the 3D printed material yields a strong scattering signal when directly hit, but it generates no detectable background otherwise [43,45,46]. As such, NR and GISANS measurements with no measurable background contribution from the chamber itself were already demonstrated.…”

“…2021, 11, x FOR PEER REVIEW 8 of 15 conclusion, the presented gas flow system allows for the study of a broad and well-controlled temperature and humidity range despite the large chamber volume and generous window sizes. This system was already used in neutron scattering experiments that investigated thin-film responses under changing atmospheric compositions, which also demonstrated the use of solvents other than water [45,46]. The setup currently runs without a feedback loop, as set humidity (via the flow rates) and temperature values are reached accurately.…”

“…Overall, we are able to accurately track the thickness via the spectral reflectance setup attached to the chamber lid, allowing for complementary in situ spectral reflectance measurements during GISANS or NR measurements. The setup was already used during a recent NR study and proved to be an important tool to measure the film thickness and refractive index in situ [46].…”