IJTC2006 -12331 ORIGINS OF PRESSURE AND VISCOSITY OSCILLATION WITH FILM THICKNESS IN ULTRA THIN LUBRICATING FILMS

ABSTRACT Both pressure and viscosity have been observed via molecular simulation to oscillate with film thickness in ultra thin lubricating films. This oscillation may need to be considered in lubricated system design for applications that operate in the thin film lubrication regime. Oscillatory behavior occurs when the thickness of the lubricant is on the same order of magnitude as the fluid molecules themselves. It has been suggested by many researchers that this oscillation is related to the layering that occurs in confined fluids. In the present work, this relationship between molecular configuration and oscillation in fluid properties is further investigated. A quantifiable relationship is identified which may enable prediction of oscillatory effects based on fluid atom size and wall separation

G-quadruplex organic frameworks

Two-dimensional covalent organic frameworks often π stack into crystalline solids that allow precise spatial positioning of molecular building blocks. Inspired by the hydrogen-bonded G-quadruplexes found frequently in guanine-rich DNA, here we show that this structural motif can be exploited to guide the self-assembly of naphthalene diimide and perylene diimide electron acceptors end-capped with two guanine electron donors into crystalline G-quadruplex-based organic frameworks, wherein the electron donors and acceptors form ordered, segregated π-stacked arrays. Time-resolved optical and electron paramagnetic resonance spectroscopies show that photogenerated holes and electrons in the frameworks have long lifetimes and display recombination kinetics typical of dissociated charge carriers. Moreover, the reduced acceptors form polarons in which the electron is shared over several molecules. The G-quadruplex frameworks also demonstrate potential as cathode materials in Li-ion batteries because of the favourable electron- and Li-ion-transporting capacity provided by the ordered rylene diimide arrays and G-quadruplex structures, respectively

Defect Engineering Of Porous Aromatic Frameworks Via End Capping Improves Dioxane Removal From Water

Amorphous porous organic polymers show promise for energy-efficient adsorptive separations, but it is difficult to understand or improve their performance through intentional structural modification. Herein, we report the synthesis of porous aromatic frameworks (PAFs) with pore structures tailored by the incorporation of a monofunctionalized end-capping monomer that disrupts framework topology. Combining experimental characterization with molecular simulations, we show that this defect engineering strategy yields less densely crosslinked networks, which leads to pore collapse and the presence of unique adsorption sites. These defect-engineered PAFs exhibit enhanced removal of 1,4-dioxane, an important environmental pollutant, from water. Increasing the concentration of end-capping monomers produces PAFs with narrower pore size distributions and improved 1,4-dioxane uptake. These results illustrate that defect engineering can effectively modulate polymer connectivity and porosity for applications in selective adsorptive separations. This technique avoids post-synthetic treatments and presents another approach to tailor amorphous polymeric adsorbents

A combined experimental and quantum chemical study of CO₂ adsorption in the metal–organic framework CPO-27 with different metals

A first principles study of CO₂ adsorption is presented for a group of metal–organic frameworks (MOFs) known as CPO-27-M, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. These materials consist of one-dimensional channels with a high concentration of open metal sites and have been identified as among the most promising MOFs for CO₂ capture. In addition, extensive, high-pressure, experimental adsorption results are reported for CO₂, CH₄, and N₂ at temperatures ranging from 278 K to 473 K. Isosteric heats of adsorption were calculated from the variable-temperature isotherms. The binding energies of CO₂ calculated using an MP2-based QM/MM method are in good agreement with those obtained from experiments. The relative CO₂ binding strengths for the different transition metals can be explained by the relative strength of electrostatic interactions caused by the effective charge of the metal atom in the direction of the open metal site induced by incomplete screening of 3d electrons. The Mn, Fe, Co, Ni, and Cu versions of CPO-27 are predicted to be anti-ferromagnetic in their ground states. Selectivities for CO₂ over CH4 or N₂ were calculated from the experimental isotherms using ideal adsorbed solution theory