A new family of molten salts is reported, based on the N-alkyl, N-alkyl pyrrolidinium cation and the bis-(trifluoromethane sulfonyl)imide anion. Some of the members of the family are molten at room temperature, while the smaller and more symmetrical members have melting points around 100°C. Of the room-temperature molten salt examples, the methyl butyl derivative exhibits the highest conductivity; at 2 × 10 -3 S/cm this is the highest molten salt conductivity observed to date at room temperature among the ammonium salts. This highly conductive behavior is rationalized in terms of the role of cation planarity. The salts also exhibit multiple crystalline phase behavior below their melting points and exhibit significant conductivity in at least their higher temperature crystal phase. For example, the methyl propyl derivative (mp ) 12°C) shows ion conductivity of 1 × 10 -6 S/cm at 0°C in its higher temperature crystalline phase.

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.

Penetrant permeability coefficients in high-free-volume, glassy poly(1-trimethylsilyl-1propyne) [PTMSP] increase systematically with increasing concentration of nonporous, nanoscale fumed silica [FS]. For example, the permeability of PTMSP containing 40 wt % FS to methane is 180% higher than that of the unfilled polymer. Gas and vapor solubility in the nanocomposites are unaffected by FS at concentrations of up to 50 wt %. Penetrant diffusion coefficients in PTMSP increase with increasing FS content, and the enhanced permeability in the nanocomposites is due to this rise in diffusivity. These results are qualitatively similar to behavior previously observed when FS was added to another stiffchain polyacetylene, poly(4-methyl-2-pentyne) [PMP]. However, in contrast to PMP, the permeability of PTMSP to relatively small gases increases more upon filling than that of larger penetrants. This results in a reduction in vapor/permanent-gas selectivity for filled PTMSP. In fact, mixed-gas n-butane/methane selectivity is 64% lower in PTMSP containing 50 wt % FS than in pure PTMSP. These results, combined with penetrant diffusion coefficients on the order of 10 -3 cm 2 /s in filled PTMSP, suggest an escalating influence of free phase transport mechanisms such as Knudsen diffusion as FS concentration in the polymer increases.

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The addition of nanoscale, nonporous fumed silica [FS] particles to size-selective poly(2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene) [AF2400] systematically increases penetrant permeability coefficients, similar to behavior previously observed in vapor-selective polyacetylenes, but contrary to results in traditional filled polymer systems. Permeability coefficients of large penetrants increase more than those of small molecules in filled AF2400, thereby decreasing the size selectivity of this polymer. AF2400 is readily plasticized by n-butane, whereas AF2400 containing 40 wt % FS exhibits antiplasticization behavior, suggesting that filler addition alters AF2400 to allow n-butane molecules to be accommodated in the polymer without significant swelling and subsequent plasticization of the matrix. Both filled and unfilled AF2400 have essentially the same gas solubility coefficients, so all of the increase in penetrant permeability in filled AF2400 is a result of increased diffusion coefficients. There is reasonable agreement between diffusion coefficients obtained from transient sorption and steady-state data, both of which increase regularly with increasing FS content. Positron annihilation lifetime spectroscopy reveals that FS addition increases the size of free volume elements in AF2400. Thermal analysis of filled AF2400 shows that FS has no detectable effect on the polymer's glass transition temperature, indicating that FS has little impact on long-range chain mobility.

A number of novel organic ionic compounds based on the pyrrolidinium cation are described which have been found to be ion conductors in their solid states around room temperature. The properties of the compounds are consistent with their exhibiting plastic crystal phases. In order to understand some of the molecular origins of the plastic crystal behaviour and the ion conductivity that it promotes, a number of related compounds based on the imidazolium and ammonium cations are also described which have structural elements in common with the pyrrolidinium cation, but which do not show the plastic behaviour. It is found therefore that the nature of the cation is quite critical to the development of this behaviour. The alkyl methyl pyrrolidinium cation is found to produce plastic crystal phases when the alkyl chains are short, thereby preserving the ability of the cation to rotate with minimal steric hindrance. The ammonium and imidazolium cations of comparable size and structure are less able to produce these plastic phases, in many cases because the low temperature phase proceeds to melt rather than forming a stable rotator phase.

The effects of salt (LiClO4) concentration and plasticizer (tetraglyme) concentration on the room-temperature conductivity and free volume of a polyether-urethane solid polymer electrolyte are studied. The free volume is probed by the positron annihilation lifetime spectroscopy (PALS) technique which uses the oPs pick-off lifetime, tau 3, as an indication of the local electron density and the mean free volume cavity radius. The oPs pick-off intensity, I3, reflects the probability of oPs formation and the relative concentration of free volume cavities in the material. The mean size ( tau 3) and relative number (l3) of free volume cavities decrease with an increase in salt concentration in the host polymer due to the Li+ coordination (effective cross-linking) with the oxygens of the host polymer. The addition of 25 wt% tetraglyme plasticizer to the 1 molal LiClO4/host polymer complex is shown to counter the effective cross-linking resulting in a Tg decreased to a value equal to that of the pure host polymer, increased conductivity, and average free volume cavity size ( tau 3) increased to a value equal to that of the pure host polymer. However, the relative number of free volume cavities (l3) in the plasticized host polymer/salt complex remains fewer than that of the pure host polymer over the concentration range of plasticizer studied, and in a similar manner the density remains greater than that of the pure host polymer. The room-temperature conductivity, free volume, and density behaviour in conjunction with the Tg results suggest that the plasticizer addition leads to Li+ coordination with the oxygens of the plasticizer chains as well as increased mobility of the host polymer chains. The increase in free volume of the host polymer/salt complex caused by the addition of plasticizer is shown to dominate the conductivity behaviour in this system.