Structure and Thermal Response of Thin Thermoresponsive Polystyrene-block-poly(methoxydiethylene glycol acrylate)-block-polystyrene Films

Abstract

Thin thermoresponsive films of the triblock copolymer polystyreneblock-poly(methoxydiethylene glycol acrylate)-block-polystyrene (P(S-b-MDEGA-b-S)) are investigated on silicon substrates. By spin-coating, homogeneous and smooth films are prepared for a range of film thicknesses from 6 to 82 nm. Films are stable with respect to dewetting as investigated with optical microscopy and atomic force microscopy. P(S-b-MDEGA-b-S) films with a thickness of 39 nm exhibit a phase transition of the lower critical solution temperature (LCST) type at 36.5 °C. The swelling and the thermoresponsive behavior of the films with respect to a sudden thermal stimulus are probed with in-situ neutron reflectivity. In undersaturated water vapor swelling proceeds without thickness increase. The thermoresponse proceeds in three steps: First, the film rejects water as the temperature is above LCST. Next, it stays constant for 600 s, before the collapsed film takes up water again. With ATR-FTIR measurements, changes of bound water in the film caused by different thermal stimuli are studied. Hydrogen bonds only form between CO and water in the swollen film. Above the LCST most hydrogen bonds with water are broken, but some amount of bound water remains inside the film in agreement with the neutron reflectivity data. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that the inner lateral structure is not significantly influenced by the different thermal stimuli.

Swelling and Exchange Behavior of Poly(sulfobetaine)-Based Block Copolymer Thin Films

“…After the free volume is filled, further water uptake leads to swelling of the polymer chains and an increase in the film thickness. − By increasing the complexity of the stimuli-responsive polymer, for example, by using amphiphilic BCPs, the water uptake behavior becomes more complex. , Introducing a glassy hydrophobic block into the polymer increases the mechanical stability of the BCP film morphology but simultaneously hampers the extent of swelling. This happens because overall, the interactions between the hydrophobic block and water molecules are less attractive than the interactions among the hydrophobic blocks. ,,− Moreover, the swelling kinetics are also affected because the water molecules cannot move as freely as in homopolymer films. ,, …”

“…32,46,51−53 Moreover, the swelling kinetics are also affected because the water molecules cannot move as freely as in homopolymer films. 50,52,53 In the present work, we investigate the swelling and exchange behavior of a BCP thin film that consists of a zwitterionic poly(sulfobetaine) block, namely poly(N,Ndimethyl-N -(3-(methacrylamido)propyl)ammoniopropanesulfonate) (PSPP), and a PNIPAM block, PSPP 80 -b-PNIPAM 130 (Figure 1). In aqueous solution, PSPP displays UCST behavior with its clearing point depending strongly on the molar mass.…”

Controlled Hydration, Transition, and Drug Release Realized by Adjusting Layer Thickness in Alginate-Ca2+/poly(N-isopropylacrylamide) Interpenetrating Polymeric Network Hydrogels on Cotton Fabrics

“…In our previous investigations about nanometer thick thermoresponsive polymer films, the TT showed a prominent decrease when the film thickened. 49,50 This behavior was attributed to the influence of the hydrophilic Si substrate on the transition. The hydrophilicity of the substrate shifted the transition to higher temperatures.…”

Molecular Dynamics of Swollen Poly(2-vinylpyridine) Brushes

“…changes in the surface properties. Many experiments studied structural changes in the morphology and the effects on the surface properties. − In contrast, the present work addresses the question of how the molecular dynamics, i.e., glassy dynamics, of a polymer brush is affected by swelling with tetrahydrofuran (THF), a good solvent for P2VP. Since each P2VP chain segment carries a dipole moment, broadband dielectric spectroscopy (BDS) allows for the measurement of the segmental relaxation, i.e., the dynamic glass transition.…”