From ambient- and high-pressure density measurements, we report the volume expansivities and isothermal compressibilities of four room-temperature ionic liquids and 1-methylimidazole at temperatures between 298.2 and 343.2 K and pressures to 206.9 MPa. The compounds studied are 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), 1-octyl-3-methylimidazolium tetrafluoroborate ([C8mim][BF4]), and N-butylpyridinium tetrafluoroborate ([NBuPy][BF4]). The density is affected by the natures of the anion, cation, and substituents on the cation, with lower densities observed for longer alkyl chains. Density decreases fairly linearly with increasing temperature but at a rate less than that for molecular organic compounds. In addition, the high-pressure measurements reveal that ionic liquids are significantly less compressible than organic solvents, with isothermal compressibility values similar to that of water. The high-pressure density data can be adequately described by the Tait equation.

We report in this paper the successful production of stable high-concentration graphene dispersions in low-boiling-point, low-polarity conventional organic solvents (chloroform and THF) by liquid-phase noncovalent exfoliation of graphite assisted with a hyperbranched polyethylene (HBPE) as the stabilizer. In the exfoliation process, HBPE adsorbs onto the surface of exfoliated graphene flakes, providing steric stabilization against their restacking. A systematic investigation on the effects of exfoliation conditions, including the solvent and the amounts of graphite and HBPE, has been conducted. Graphene dispersions with the concentration up to 0.18 mg/mL in chloroform and 0.045 mg/mL in THF have been obtained. It is also demonstrated that the dispersions can be further concentrated by solvent evaporation to give highly concentrated stable dispersions at 3.4 mg/mL. Through their characterizations with transmission electron microscopy, atomic force microscopy, and Raman spectroscopy, the majority of the graphene products is found to be high-quality, defect-free, few-layer graphene flakes with the layer number between 2 and 4 and the lateral dimension in the range of 0.2–0.5 μm. The dispersions can be fabricated into flexible conductive free-standing graphene films and be used to prepare graphene/ethylene copolymer composites through solution blending, which show significant enhancements in both thermal and mechanical properties.

In numerous applications in microfluidics, cell growth, soft lithography, and molecular imprinting, the surface of poly(dimethylsiloxane) (PDMS) is modified from a hydrophobic methyl-terminated surface to a hydrophilic hydroxyl-terminated surface. In this study, we investigated molecular structural and orientational changes at the PDMS-air interface in response to three commonly used surface modification processes: exposure to long-wavelength ultraviolet light (UV), exposure to short-wavelength UV that generates ozone (UVO), and exposure to oxygen plasma (OP). The surfaces of two PDMS compositions (10:1 and 4:1 of base polymer/curing agent) were probed during modification, using monolayer-sensitive IR + visible sum frequency generation (SFG) vibrational spectroscopy, with two different polarization combinations. During PDMS surface modification, the peak intensities of CH3 side groups and CH2 cross-link groups decreased, while peak intensities of Si-OH groups increased. There was no significant change in the average orientation of the CH3 groups on the PDMS surface during modification. The concentration of CH3 groups on the surface decreased exponentially with time, for all three UV, UVO, and OP modification processes, with first order kinetics and time constants of approximately 160, 66, and 0.3 min, respectively. At steady state, residual CH3 groups were detected at the PDMS surface for UV and UVO treatments; however, there were negligible CH3 groups detected after OP modification.

In this communication we describe a new chemical encapsulation and release platform using 3D microfabricated nanoliter scale containers with controlled porosity. The containers can be fabricated of magnetic materials that allow them to be remotely guided using magnetic fields. The favorable attributes of the containers that include a versatile highly parallel fabrication process, precisely engineered porosity, isotropic/anisotropic chemical release profiles, and remote magnetic guiding provide an attractive platform for engineering spatially controlled chemical reactions in microfluidic systems.

No abstract