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In polymers, the equilibrium state is achieved when the chains have access to the maximum number of conformational states, which allows them to explore a larger conformational space, leading to an increase in the entropy of the system. Preparation of thin polymer films using the spin-coating technique results in polymer chains being locked in a nonequilibrium state with lower entropy due to possible stretching of chains during the process. Allowing enough time for recovery results in the relaxation of the spin-coating-induced molecular recoiling stress. Annealing such a film generates entropy due to its inherent irreversibility. We employed the dewetting technique to determine the molecular recoiling stress relaxation time in poly-(tertbutyl styrene) thin films. Furthermore, we qualitatively differentiated the metastable states achieved by the polymer film using entropy generation in a relaxing polymer film as an effect of thermal entropy and associated it with the conformational entropy of polymer chains utilizing the molecular recoiling stress relaxation time. This enabled us to explain molecular recoiling stress relaxation using a rather simplistic approach involving segmental level molecular rearrangements in polymer chains by attaining transient metastable states through an entropically activated process driving toward equilibrium. [ABSTRACT FROM AUTHOR]

Polymers when confined to a dimension comparable to the length scale of polymer chain coils such as thin films, often lead to molecular relaxation processes distinct from their bulk counterpart. Often observed as thermal and mechanical responses such relaxation has been frequently associated with the squeezing of polymer chains having conformations trapped far from thermodynamic equilibrium and subsequently generating processing‐induced molecular recoiling stress. Relaxation in polymer films can be modified by tuning the molecular recoiling stress, which is directly influenced by the preparation conditions of the polymer thin films. Hence a comprehensive understanding of the genesis and relaxation of molecular recoiling stress becomes necessary. Here, we provide insights into the nonequilibrium nature observed in polymer thin films, focusing majorly on the investigations into the molecular recoiling stress using the dewetting technique. The impact of various factors like temperature of dewetting, thickness of films, molecular weight of polymers, and physical aging affecting the relaxation of molecular recoiling stress is discussed. In addition, discussions on the possible mechanisms of relaxation and modification of molecular recoiling stress by varying the spin‐coating speed and addition of plasticizers are also provided. An alternate approach which gives a new perspective into the relaxation of molecular recoiling stress considering the entropy generated during the dewetting of polymer films is also included. The present work is expected to give the reader a comprehensive understanding of the characteristics of molecular recoiling stress relaxation occurring in polymer thin films. [ABSTRACT FROM AUTHOR]

Designing metal–organic framework (MOF)-based solid nanoparticles to stabilize Pickering emulsions by fine-tuning their hydrophobicity and lipophobicity is vital for essential applications and fundamental understanding. We demonstrate in situ grafting of palmitic acid in UiO-66 MOF through its linker defects. Our designed and activated nanoparticles (denoted as UP′) stabilized the Pickering emulsions of n-heptane-in-water. Furthermore, we showed how UP′ stabilized emulsion droplets disperse in media by covering each tiny droplet with a nanoscale layer made of UP′. To support our claim, we carried out the freeze-drying process to remove the liquid part from the emulsion, leaving behind the solid shell-like microstructures that we further characterized through several microscopic techniques. The stable n-heptane-in-water emulsion was confirmed by dilution (drop test), conductivity, zeta potential, and theoretical surface electrostatic potential measurements. Rheological studies indicate that the Pickering emulsions of n-heptane-in-water stabilized by UP′ are much more resistant to deformation and flow imparting higher (mechanical) stability and shelf-life. Pickering emulsions stabilized by UP′ emerged as a versatile way to design smart functional materials of UiO-66 through engineering linker defects that may have potential applications in interfacial catalysis, dye or contaminant separation, etc. [ABSTRACT FROM AUTHOR]

Recently, inorganic perovskite materials have been attracting increasing attention owing to their exceptional structural, electronic, and optical characteristics in photovoltaic technology. Ca3AsI3 is a semiconductor material that shares similarities with the group of inorganic metal halide perovskites. Ca3AsI3 possesses a perovskite crystal structure that is cubic, which is classified under the space group Pm-3m (no. 221). Our research aims to analyze how the optical and electronic properties of Ca3AsI3 are influenced by spin–orbit coupling (SOC) and strain using the first-principles density-functional theory. The inorganic Ca3AsI3 perovskite has an electronic band structure that possesses a direct bandgap of roughly 1.58 eV at the Γ(gamma)-point. However, when the SOC relativistic effect is introduced, this value decreases to around 1.27 eV. As the level of compressive strain is increased, the bandgap becomes narrower, whereas with increasing tensile strain, the bandgap becomes wider. It has been observed through analysis of the dielectric functions, absorption coefficient, and electron loss function of these materials that the optical properties give Ca3AsI3 the ability to effectively absorb visible light. According to the study, the dielectric constant peaks of Ca3AsI3 shift toward a lower photon energy (redshift) as the level of compressive strain increases. On the other hand, when subjected to increased tensile strain, these peaks have a tendency to shift toward a higher photon energy (blueshift), as per the same study. Modifying the energy gap of Ca3AsI3 perovskites to suit optoelectronic and solar cell needs could be achieved by using techniques involving the SOC effect and by applying strain. These approaches have the potential to enable utilization of Ca3AsI3 in such applications in the future. [ABSTRACT FROM AUTHOR]