Fabrication of Porous Carbon/TiO₂ Composites through Polymerization-Induced Phase Separation and Use As an Anode for Na-Ion Batteries

Polymerization-induced phase separation of nanoparticle-filled solution is demonstrated as a simple approach to control the structure of porous composites. These composites are subsequently demonstrated as the active component for sodium ion battery anode. To synthesize the composites, we dissolved/dispersed titanium oxide (anatase) nanoparticles (for sodium insertion) and poly­(hydroxybutyl methacrylate) (PHBMA, porogen) in furfuryl alcohol (carbon precursor) containing a photoacid generator (PAG). UV exposure converts the PAG to a strong acid that catalyzes the furfuryl alcohol polymerization. This polymerization simultaneously decreases the miscibility of the PHBMA and reduces the mobility in the mixture to kinetically trap the phase separation. Carbonization of this polymer composite yields a porous nanocomposite. This nanocomposite exhibits nearly 3-fold greater gravimetric capacity in Na-ion batteries than the same titanium oxide nanoparticles that have been coated with carbon. This improved performance is attributed to the morphology as the carbon content in the composite is five times that of the coated nanoparticles. The porous composite materials exhibit stable cyclic performance. Moreover, the battery performance using materials from this polymerization-induced phase separation method is reproducible (capacity within 10% batch-to-batch). This simple fabrication methodology may be extendable to other systems and provides a facile route to generate reproducible hierarchical porous morphology that can be beneficial in energy storage applications

Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

Photoresponsive thin films are commonly encountered as high performance coatings as well as critical component, photoresists, for microelectronics manufacture. Despite intensive investigations into the dynamics of thin glassy polymer films, studies involving reactions of thin films have typically been limited by difficulties in decoupling segregation of reacting components or catalysts due to the interfaces. Here, thin films of coumarin polyesters overcome this limitation where the polyester undergoes predominately cross-linking upon irradiation at 350 nm, while chain scission occurs with exposure to 254 nm light. Spectroscopic ellipsometry is utilized to track these reactions as a function of exposure time to elucidate the associated reaction kinetics for films as thin as 15 nm. The cross-linking appears to follow a second order kinetic rate law, while oxidation of the coumarin that accompanies the chain scission and enables this reaction to be tracked spectroscopically appears to be a first order reaction in coumarin concentration. Because of the asymmetry in the coumarin diol monomer and the associated differences in local structure that result during formation of the polyester, two populations of coumarin are required to fit the reaction kinetics; 10–20% of the coumarin is significantly more reactive, but these groups appear to undergo chain scission/oxidation at both wavelengths. These reaction rate constants are nearly independent (within 1 order of magnitude) of film thickness down to 15 nm. There is maximum rate at a finite thickness for the 254 nm exposure, which we attribute to constructive interference of the UV radiation within the polymer film, rather than typical confinement effects; no thickness dependence in reaction rates is observed for the 350 nm exposure. The utilization of a single polymer with two distinct reactions enables unambiguous investigation of thickness effects on reactions