Cross-Linked Block Copolymer/Ionic Liquid Self-Assembled Blends for Polymer Gel Electrolytes with High Ionic Conductivity and Mechanical Strength

Poly­(propylene oxide)–poly­(ethylene oxide)–poly­(propylene oxide) (PPO–PEO–PPO) block copolymers (BCPs) with cross-linkable end groups were synthesized, blended with an ionic liquid (IL) diluent, and cross-linked to form polymer gel electrolytes. The IL prevented crystallization of PEO at high concentrations, enabling fast ion transport. In addition, the IL was selective for the PEO block, inducing strong microphase separation in what are otherwise disordered or weakly ordered BCP melts. Cross-linking the BCPs in the presence of the IL resulted in the formation of solid, elastic gels with high ionic conductivitiesgreater than 1.0 mS/cm at 25 °C for some compositions. However, it was found that neither the presence or absence of microphase separation nor the BCP composition of the microphase separated gels substantially influenced ionic conductivity. Increasing the cross-link density through the use of phase-selective PEO- and PPO-based cross-linking reagents was also evaluated. It was revealed that confinement of cross-links to the PPO rich domains through the use of PPO-based diacrylates enhanced the mechanical strength of the gels without detriment to the ionic conductivity. Conversely, cross-linking in the PEO-rich domains through the use of PEO-based acrylates significantly reduced conductivity. Isolation of cross-links within a minor nonconducting domain in a microphase separated gel is a viable strategy for mechanical property enhancement without a large sacrifice in conductivity, effectively decoupling ionic conductivity and mechanical strength. This approach yielded solid-like gel electrolytes fabricated from BCPs that can be produced inexpensively, with ionic conductivities of 0.64 mS/cm at 25 °C and a frequency independent storage modulus of approximately 400 kPa

Nanostructured Block-Random Copolymers with Tunable Magnetic Properties

It was recently shown that block copolymers (BCPs) produced room-temperature ferromagnetic materials (RTFMs) due to their nanoscopic ordering and the cylindrical phase yielded the highest coercivity. Here, a series of metal-containing block-random copolymers composed of an alkyl-functionalized homo block (C₁₆) and a random block of cobalt complex- (Co) and ferrocene-functionalized (Fe) units was synthesized via ring-opening metathesis polymerization. Taking advantage of the block-random architecture, the influence of dipolar interactions on the magnetic properties of these nanostructured BCP materials was studied by varying the molar ratio of the Co units to the Fe units, while maintaining the cylindrical phase-separated morphology. DC magnetic measurements, including magnetization versus field, zero-field-cooled, and field-cooled, as well as AC susceptibility measurements showed that the magnetic properties of the nanostructured BCP materials could be easily tuned by diluting the cobalt density with Fe units in the cylindrical domains. Decreasing the cobalt density weakened the dipolar interactions of the cobalt nanoparticles, leading to the transition from a room temperature ferromagnetic (RTF) to a superparamagnetic material. These results confirmed that dipolar interactions of the cobalt nanoparticles within the phase-separated domains were responsible for the RTF properties of the nanostructured BCP materials

Binary Short-Range Colloidal Assembly of Magnetic Iron Oxides Nanoparticles and Fullerene (nC₆₀) in Environmental Media

Colloidal assembly of nC₆₀ fullerene with naturally abundant magnetic iron oxide NPs will affect their fate and transformation in environmental media. In solution, fullerene association to aggregating iron oxide NPs/clusters greatly enhanced the overall colloidal stability. Development of depletion-mediated structured fullerene layers between pure and surface modified γFe₂O₃ NPs possibly resulted in such stabilization. Here, we also report that on air–water interface, association of fullerene to pure and humic acid (HA7) coated γFe₂O₃ NPs led to the formation of ordered assemblies, e.g., binary wires and closed-packed “crystalline” and “glassy” structures in the presence and absence of electrolytes suggesting immobilization of the former. The interaction of fullerene to Fe₃O₄ NPs and clusters also produced ordered assemblies along with amorphous aggregates. Fullerene interaction with Fe₃O₄ NPs in low concentration of HA1 and Na⁺ at pH 6 formed dendritic growth and polycrystalline circular assemblies on air–water interface. HRTEM study further revealed that the monolayer circular assemblies were highly ordered but structural degeneracy was evident in multilayers. Therefore, interfacial assemblies of fullerene with iron oxide NPs resulted in short-range periodic structures with concomitant immobilization and reduction in availability of the former, especially in soils or sediments rich in the latter

Kinetics of Ion Transport in Perovskite Active Layers and Its Implications for Active Layer Stability

Solar cells fabricated using alkyl ammonium metal halides as light absorbers have the right combination of high power conversion efficiency and ease of fabrication to realize inexpensive but efficient thin film solar cells. However, they degrade under prolonged exposure to sunlight. Herein, we show that this degradation is quasi-reversible, and that it can be greatly lessened by simple modifications of the solar cell operating conditions. We studied perovskite devices using electrochemical impedance spectroscopy (EIS) with methylammonium (MA)-, formamidinium (FA)-, and MA_<i>x</i>FA_1–<i>x</i> lead triiodide as active layers. From variable temperature EIS studies, we found that the diffusion coefficient using MA ions was greater than when using FA ions. Structural studies using powder X-ray diffraction (PXRD) show that for MAPbI₃ a structural change and lattice expansion occurs at device operating temperatures. On the basis of EIS and PXRD studies, we postulate that in MAPbI₃ the predominant mechanism of accelerated device degradation under sunlight involves thermally activated fast ion transport coupled with a lattice-expanding phase transition, both of which are facilitated by absorption of the infrared component of the solar spectrum. Using these findings, we show that the devices show greatly improved operation lifetimes and stability under white-light emitting diodes, or under a solar simulator with an infrared cutoff filter or with cooling