Salt-Dependent Phase Transition Behavior of Doubly Thermoresponsive Poly(sulfobetaine)-Based Diblock Copolymer Thin Films.

The water vapor-induced swelling, as well as subsequent phase-transition kinetics, of thin films of a diblock copolymer (DBC) loaded with different amounts of the salt NaBr, is investigated in situ. In dilute aqueous solution, the DBC features an orthogonally thermoresponsive behavior. It consists of a zwitterionic poly(sulfobetaine) block, namely, poly(4-(N-(3'-methacrylamidopropyl)-N,N-dimethylammonio) butane-1-sulfonate) (PSBP), showing an upper critical solution temperature, and a nonionic block, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), exhibiting a lower critical solution temperature. The swelling kinetics in D2O vapor at 15 °C and the phase transition kinetics upon heating the swollen film to 60 °C and cooling back to 15 °C are followed with simultaneous time-of-flight neutron reflectometry and spectral reflectance measurements. These are complemented by Fourier transform infrared spectroscopy. The collapse temperature of PNIPMAM and the swelling temperature of PSBP are found at lower temperatures than in aqueous solution, which is attributed to the high polymer concentration in the thin-film geometry. Upon inclusion of sub-stoichiometric amounts (relative to the monomer units) of NaBr in the films, the water incorporation is significantly increased. This increase is mainly attributed to a salting-in effect on the zwitterionic PSBP block. Whereas the addition of NaBr notably shifts the swelling temperature of PSBP to lower temperatures, the collapse temperature of PNIPMAM remains unaffected by the presence of salt in the films.

3D printed spherical environmental chamber for neutron reflectometry and grazing-incidence small-angle neutron scattering experiments.

In neutron scattering on soft matter, an important concern is the control and stability of environmental conditions surrounding the sample. Complex sample environment setups are often expensive to fabricate or simply not achievable by conventional workshop manufacturing. We make use of state-of-the-art 3D metal-printing technology to realize a sample environment for large sample sizes, optimized for investigations on thin film samples with neutron reflectometry (NR) and grazing-incidence small-angle neutron scattering (GISANS). With the flexibility and freedom of design given by 3D metal-printing, a spherical chamber with fluidic channels inside its walls is printed from an AlSi10Mg powder via selective laser melting (SLM). The thin channels ensure a homogeneous heating of the sample environment from all directions and allow for quick temperature switches in well-equilibrated atmospheres. In order to optimize the channel layout, flow simulations were carried out and verified in temperature switching tests. The spherical, edgeless design aids the prevention of condensation inside the chamber in case of high humidity conditions. The large volume of the sample chamber allows for high flexibility in sample size and geometry. While a small-angle neutron scattering (SANS) measurement through the chamber walls reveals a strong isotropic scattering signal resulting from the evenly orientated granular structure introduced by SLM, a second SANS measurement through the windows shows no additional background originating from the chamber. Exemplary GISANS and NR measurements in time-of-flight mode are shown to prove that the chamber provides a stable, background free sample environment for the investigation of thin films.

Effect of Trapped Solvent on the Interface between PS-b-PMMA Thin Films and P(S-r-MMA) Brush Layers.

The orientation of block copolymer (BCP) features in thin films can be obtained by spin-coating a BCP solution on a substrate surface functionalized by a polymer brush layer of the appropriate random copolymer (RCP). Although this approach is well established, little work reporting the amount and distribution of residual solvent in the polymer film after the spin-coating process is available. Moreover, no information can be found on the effect of trapped solvent on the interface between the BCP film and RCP brush. In this work, systems consisting of poly(styrene)-b-poly(methyl methacrylate) thin films deposited on poly(styrene-r-methyl methacrylate) brush layers are investigated by combining neutron reflectivity (NR) experiments with simulation techniques. An increase in the amount of trapped solvent is observed by NR as the BCP film thickness increases accompanied by a significant decrease of the interpenetration length between the BCP and RCP, thus suggesting that the interpenetration between grafted chains and block copolymer chains is hampered by the solvent. Hybrid particle-field molecular dynamics simulations of the analyzed system confirm the experimental observations and demonstrate a clear correlation between the interpenetration length and the amount of trapped solvent.

Morphology Tuning of ZnO/P3HT/P3HT- b-PEO Hybrid Films Deposited via Spray or Spin Coating.

Hybrid films of zinc oxide (ZnO) and poly(3-hexylthiophen-2,5-diyl) (P3HT) show promising characteristics for application in hybrid bulk-heterojunction solar cells (HBSCs). However, the incompatibility of ZnO and P3HT may lead to a reduced interface area, thus reducing the probability of exciton separation and consequently lowering solar cell efficiencies. Here, a diblock copolymer P3HT- b-poly(ethylene oxide) (PEO) is introduced to improve the interface between ZnO and P3HT. ZnO is synthesized via a block copolymer assisted sol-gel approach, and the used zinc precursor is directly incorporated into the PEO blocks. Thus, the possibility of aggregation is reduced for both the inorganic and the organic components, and a good intermixing is ascertained. Two deposition methods, namely, spray and spin coating, are compared with respect to the resulting film structure, which is investigated with scanning electron microscopy and time-of-flight grazing-incidence small-angle neutron scattering measurements. Both the surface and inner morphologies reveal that the spin coated samples possess smaller and less diverse domain sizes than the sprayed films. Due to the advantage of spray coating in large-scale production, the morphology of the sprayed samples is tailored more meticulously by changing the weight fraction of ZnO in the films. The sprayed hybrid films show smaller domains and less aggregation with decreasing the amount of ZnO. This reveals that both the deposition method and composition of the ZnO/P3HT/P3HT- b-PEO hybrid films play an important role for tailoring the film morphology and thus for improving the performance of HBSCs in future application.