We report the chain conformations of polymer molecules accommodated at the solid-polymer melt interfaces in equilibrium. Polystyrene “Guiselin” brushes (adsorbed layers) with different molecular weights were prepared on Si substrates and characterized by using x-ray and neutron reflectivity. The results are intriguing to show that the adsorbed layers are composed of the two different nanoarchitectures: flattened chains that constitute the inner higher density region of the adsorbed layers and loosely adsorbed polymer chains that form the outer bulklike density region. In addition, we found that the lone flattened chains, which are uncovered by the additional prolonged solvent leaching ($\sim 120$ days), are reversibly densified with increasing temperature up to $150°\mathrm{C}$. By generalizing the chain conformations of bulks, we postulate that the change in probabilities of the local chain conformations (i.e., trans and gauche states) of polymer molecules is the origin of this densification process.

We report the origin of the effect of nanoscale confinement on the local viscosity of entangled polystyrene (PS) films at temperatures far above the glass transition temperature. By using marker x-ray photon correlation spectroscopy with gold nanoparticles embedded in the PS films prepared on solid substrates, we have determined the local viscosity as a function of the distance from the polymer-substrate interface. The results show the impact of a very thin adsorbed layer ($\sim 7\mathrm{nm}$ in thickness) even without specific interactions of the polymer with the substrate, overcoming the effect of a surface mobile layer at the air-polymer interface and thereby resulting in a significant increase in the local viscosity as approaching the substrate interface.

Organic–inorganic hybrid lead halide perovskites (e.g., CH₃NH₃PbX₃, X = Cl, Br, I) hold great promise in optoelectronic devices, e.g., solar cells. High-performance devices have been realized by controlling the perovskite surface morphology, grain size, and degree of crystallinity. However, the role of the components during film formation and crystallization remains mysterious. Here, we show the management of perovskite intermediates to construct perovskite films with uniform perovskite crystals and controlled surface morphology using methylammonium acetate (MAAc) to retard the reaction between PbI₂ and MAI in the solution. The formation of MAPbI₃ was allowed via the exchange of I⁻ anions from the neighboring MAI molecules to the perovskite intermediate phases replacing Ac⁻ anions. A highly efficient perovskite solar cell with a power conversion efficiency of 18.09% was achieved. The experimental and theoretical studies reveal that perovskite intermediates play an important role in facilitating homogeneous nucleation or modulating the crystallization kinetics. These results also provide important progress towards the understanding of perovskite intermediate phases for advancing the building of perovskite semiconductors.