화학공학소재연구정보센터
Journal of Membrane Science, Vol.318, No.1-2, 397-404, 2008
Selective rejection of a water-soluble nerve agent stimulant using a nanoporous lyotropic liquid crystal-butyl rubber vapor barrier material: Evidence for a molecular size-discrimination mechanism
The selective vapor rejection performance of a "breathable", cross-linked lyotropic liquid crystal (LLC)-butyl rubber (BR) composite membrane with a type I bicontinuous cubic (Q(I)) morphology was studied for a water-soluble chemical nerve agent simulant, dimethyl methylphosphonate (DMMP). The thickness-normalized DMMP vapor flux of this nanoporous Q(I)-phase LLC-BR membrane, which has a 3D interconnected water nanopore network, was found to be (2.5 +/- 0.4) x 10(1) g m(-2) day(-1) mu m with a driving force of 0.333 torr at 25 degrees C. This DMMP vapor penetration level is the same low level as that observed for dense, cross-linked BR films under the same testing conditions. This LLC-BR material also has a very high thickness-normalized water vapor flux ((5.9 +/- 0.3) x 10(3) g m(-2) day(-1) mu m at 16.87 torr, the normal partial pressure of water at 25 degrees C), whereas cross-linked BR has effectively no water vapor permeation. Consequently, the LLC-BR material was found to have two-orders of magnitude higher water/DMMP molar selectivity than cross-linked pure BR and commercial BR gloves. The Q(I)-phase LLC-BR material also exhibited more than one order of magnitude higher water/DMMP molar selectivity than previously reported H-II-phase LLC-BR composites with 1D water nanopores. The percent rejection of DMMP vapor was measured to be 99.91% in a cross-flow system for the Q(I)-phase LLC-BR membrane. Since DMMP is highly water-soluble (614 g (LH2O)(-1)), the separation selectivity in this LLC-BR material cannot be due to low solubility of DMMP in the aqueous LLC nanopores (i.e., a solution-diffusion mechanism). Instead, the mechanism of DMMP rejection in this LLC-BR membrane appears to be molecular size-discrimination through the water nanopore network, which appears to have an effective gap size of < 0.57 nm. This effective pore size is slightly smaller than that previously observed for the analogous BR-free Q(I)-phase LLC material (0.75 nm) when used in high-pressure liquid water filtrations. (c) 2008 Elsevier B.V. All rights reserved.