Effect of Endfunctionality of Reactive Polymers on the Reaction Kinetics at Immiscible Polymer Interfaces: A Monte Carlo Study

Reactions at the interface of two immiscible polymers containing different reactive groups at either one end or both ends are studied with Monte Carlo (MC) simulations. The MC simulation shows that the copolymer concentration at the interface is shown to dramatically increase during the early stage of reaction and then levels off at a constant value. The effect of endfunctionality, i. e., the effect of the number of endfunctional groups, is also investigated. While the saturation value of interfacial coverage is proportional to the initial reactive polymer density for the case of mono-endfunctional polymer, the simulation results with di-endfunctional polymers show that the saturation copolymer coverage is not exactly proportional to the initial reactive polymer density in the case of high concentrations of the initial reactive polymer. This is believed to be caused by the change of conformation of block copolymers formed at the interface due to reaction: the fraction of loop conformation decreases while the tail fraction increases with a large amount of initial reactive di-endfunctional polymer. Also, the experimentally determined time-dependent interfacial fracture toughness, which is, in turn, related to the copolymer coverage at the interface, is in good qualitative agreement with the simulation results.We are very grateful to the financial support from the Brain Korea 21 program endorsed by the Ministry of Education and the National Research Laboratory Fund by the Ministry of Science and Technology, Korea

Effect of dicarboxy terminated polystyrene on strengthening immiscible polystyrene/poly(methyl methacrylate) interface

The fracture toughness between polystyrene (PS)/poly(methyl methacrylate) (PMMA) reinforced with reactive polymers, poly(glycidyl methacrylate) (PGMA) and dicarboxy or monocarboxy terminated PS (dcPS and mcPS), was measured by the asymmetric fracture test. Molecular weight effect of mcPS, although the molecular weight distribution is rather polydisperse, on the maximum achievable fracture toughness, Gmax qualitatively agreed with the results of the monodisperse case4,5). In the case of dcPS with Mw 142 K, Gmax reached ca. 170 J/m2 which is nearly 8 times higher than that of mcPS of molecular weight of about 150K. From the mechanical point of view, dcPS with a degree of polymerization (N) greater than the ratio of chain breaking force to monomeric friction force (fb/fmono) is more effective in enhancing the interfacial adhesion than mcPS since it provides two stitches to the interface. It was also shown by Monte Carlo simulation on reactive polymer system that the di-endfunctional polymers are more effective than mono-endfunctional polymers in reinforcing the week interface between immiscible polymers.This work was supported by the Korea Science and Engineering Foundation (KOSEF) under Grant 94-0520-02-3. We are very grateful to the financial support from the Brain Korea 21Program through the Ministry of Education of Korea

Induced Infiltration of Hole-Transporting Polymer into Photocatalyst for Staunch Polymer–Metal Oxide Hybrid Solar Cells

For efficient solar cells based on organic semiconductors, a good mixture of photoactive materials in the bulk heterojunction on the length scale of several tens of nanometers is an important requirement to prevent exciton recombination. Herein, we demonstrate that nanoporous titanium dioxide inverse opal structures fabricated using a self-assembled monolayer method and with enhanced infiltration of electron-donating polymers is an efficient electron-extracting layer, which enhances the photovoltaic performance. A calcination process generates an inverse opal structure of titanium dioxide (<70 nm of pore diameters) providing three-dimensional (3D) electron transport pathways. Hole-transporting polymers was successfully infiltrated into the pores of the surface-modified titanium dioxide under vacuum conditions at 200 °C. The resulting geometry expands the interfacial area between hole- and electron-transport materials, increasing the thickness of the active layer. The controlled polymer-coating process over titanium dioxide materials enhanced photocurrent of the solar cell device. Density functional theory calculations show improved interfacial adhesion between the self-assembled monolayer-modified surface and polymer molecules, supporting the experimental result of enhanced polymer infiltration into the voids. These results suggest that the 3D inverse opal structure of the surface-modified titanium dioxide can serve as a favorable electron-extracting layer in further enhancing optoelectronic performance based on organic or organic–inorganic hybrid solar cell

Enhanced Electrochemical Stability of a Zwitterionic-Polymer-Functionalized Electrode for Capacitive Deionization

In capacitive deionization, the salt-adsorption capacity of the electrode is critical for the efficient softening of brackish water. To improve the water-deionization capacity, the carbon electrode surface is modified with ion-exchange resins. Herein, we introduce the encapsulation of zwitterionic polymers over activated carbon to provide a resistant barrier that stabilizes the structure of electrode during electrochemical performance and enhances the capacitive deionization efficiency. Compared to conventional activated carbon, the surface-modified activated carbon exhibits significantly enhanced capacitive deionization, with a salt adsorption capacity of ∼2.0 × 10^–4 mg/mL and a minimum conductivity of ∼43 μS/cm in the alkali-metal ions solution. Encapsulating the activated-carbon surface increased the number of ions adsorption sites and the surface area of the electrode, which improved the charge separation and deionization efficiency. In addition, the coating layer suppresses side reactions between the electrode and electrolyte, thus providing a stable cyclability. Our experimental findings suggest that the well-distributed coating layer leads to a synergistic effect on the enhanced electrochemical performance. In addition, density functional theory calculation reveals that a favorable binding affinity exists between the alkali-metal ion and zwitterionic polymer, which supports the preferable salt ions adsorption on the coating layer. The results provide useful information for designing more efficient capacitive-deionization electrodes that require high electrochemical stability

Dendrite-Free Lithium Deposition for Lithium Metal Anodes with Interconnected Microsphere Protection

A lithium (Li) metal anode is required to achieve a high-energy-density battery, but because of an undesirable growth of Li dendrites, it still has safety and cyclability issues. In this study, we have developed a microsphere-protected (MSP) Li metal anode to suppress the growth of Li dendrites. Microspheres could guide Li ions to selective areas and pressurize dendrites during their growth. Interconnections between microspheres improved the pressurization. By using an MSP Li metal anode in a 200 mAh pouch-type Li/NCA full cell at 4.2 V, dendrite-free Li deposits with a density of 0.4 g/cm³, which is 3 times greater than that in the case of bare Li metal, were obtained after charging at 2.9 mAh/cm². The MSP Li metal enhanced the cyclability to 190 cycles with a criterion of 90% capacity retention of the initial discharge capacity at a current density of 1.45 mA/cm²