Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing.

In contrast to the performance of traditional filled polymer systems, penetrant permeability coefficients in high-free-volume, glassy poly(4-methyl-2-pentyne) (PMP) increase systematically and substantially with increasing concentration of nonporous, nanoscale fumed silica (FS). For instance, the permeability of PMP containing 40 wt % FS to methane is 2.3 times higher than that of the unfilled polymer. Gas and vapor uptake in the PMP/FS nanocomposites is essentially unaffected by the presence of up to 40 wt % FS, while penetrant diffusion coefficients increase regularly with increasing filler content. This increase in diffusivity is responsible for elevated permeability in the PMP/FS nanocomposites. The addition of FS to PMP augments the permeability of large penetrants more than that of small gases, consistent with a reduction in diffusivity selectivity. Consequently, vapor selectivity in the nanocomposites increases with increasing FS concentration. Activation energies of permeation in PMP decrease with increasing FS content, suggesting that penetrant diffusive jumps require less energy at higher filler concentrations. Positron annihilation lifetime spectroscopy (PALS) reveals that FS subtly increases the free volume in PMP available for molecular transport. The accessible free volume measured by PALS correlates favorably with relative penetrant permeability in the nanocomposites. Transmission electron microscopy confirms that the FS nanoparticles are relatively well dispersed in PMP.

The pure-gas permeation and sorption properties of poly [1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] [PTMSDPA] are presented and compared to those of poly(1-trimethylsilyl-1-propyne) [PTMSP], poly(4-methyl-2-pentyne) [PMP], and poly(1-phenyl-1-propyne) [PPP]. PTMSDPA is more permeable to large, condensable vapors (e.g., n-butane) than to small, permanent gases (e.g., hydrogen). Such behavior is also observed in PTMSP and PMP but not in PPP. PTMSDPA has lower fractional free volume (0.26) and gas permeabilities than PTMSP and PMP. However, relative to conventional glassy polymers, PTMSDPA is a highly permeable, high free volume, glassy material. For example, the oxygen permeability coefficient of PTMSDPA is 1200 × 10 -10 cm 3 (STP)‚cm/(cm 2 ‚s‚cmHg) at 25 °C. As temperature increases, the permeability in PTMSDPA increases for light gases (helium, hydrogen, and nitrogen) and decreases for more condensable gases. In contrast, the permeabilities of PTMSP and PMP decrease with increasing temperature for both light gases and more condensable hydrocarbons. n-Butane and propane sorption isotherms for PTMSDPA are concave to the penetrant relative pressure axis, consistent with dual-mode sorption behavior. Hydrocarbon sorption levels decrease in the order PTMSP > PMP > PTMSDPA > PPP, in agreement with the ranking of the fractional free volumes of the materials.

The results provide support for Kanter's organizational empowerment theory in the Chinese nurse population. Nurses who view their work environments as empowering are more likely to provide high quality care. Enhancing empowerment in a supportive environment would allow nurses to experience satisfaction with their jobs.

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Objectives Uunder the background of global climate change, the variations of streamflow and sediment discharge in the Yellow River would continue with the

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