title: Exceptional gas permeation selectivity of a glued Langmuir-Blodgett bilayer by pH control.
abstract: The monolayer properties of 5,11,17,23,29,35-hexakis[(N,N,N-trimethylamonium)-N-methyl-37,38,39,40,41,42-hexakis-n-hexadecyloxy-calix[6]arene hexachloride (1) have been characterized over aqueous solutions of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) as a function of pH. At high pH values (e.g., pH 10), such monolayers show relatively low surface viscosities. At low pH (e.g., pH 4.4), these monolayers exhibit relatively high surface viscosities. The barrier properties of single Langmuir-Blodgett bilayers of 1, which have been ionically cross-linked (i.e., "glued together") with PAA were found to correlate with changes in surface viscosity. Thus, bilayers that were fabricated under low pH conditions exhibited high permeation barriers and high permeation selectivity with respect to He and N(2). Given the extreme thinness of these glued bilayers (ca. 6 nm), the optimized He/N(2) selectivity of ca. 1000 is extraordinary. These results, taken together, demonstrate the feasibility of fine tuning the surface viscosity of monolayers of 1, and also the barrier properties of corresponding glued bilayers, by adjusting the pH of an aqueous subphase that contains a weak polyacid.
authors.affiliation: Department of Chemistry and Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
authors.forename: Junwei
authors.initials: J
authors.lastname: Li
authors.forename: Vaclav
authors.initials: V
authors.lastname: Janout
authors.forename: Donald H
authors.initials: DH
authors.lastname: McCullough
authors.forename: James T
authors.initials: JT
authors.lastname: Hsu
authors.forename: Quoc
authors.initials: Q
authors.lastname: Truong
authors.forename: Eugene
authors.initials: E
authors.lastname: Wilusz
authors.forename: Steven L
authors.initials: SL
authors.lastname: Regen
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D047250:Calixarenes / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D015394:Molecular Structure; D011109:Polymethacrylic Acids / Q000737:chemistry*; D013499:Surface Properties; D013997:Time Factors; D014783:Viscosity
chemical_list: C510838:5,11,17,23,29,35-hexakis((N,N,N-trimethylamonium))-N-methyl-37,38,39,40,41,42-hexakis-n-hexadecyloxy-calix(6)arene hexachloride; D000180:Acrylic Resins; D005740:Gases; D008567:Membranes, Artificial; D011109:Polymethacrylic Acids; D047250:Calixarenes; C030613:polymethacrylic acid; C006903:carbopol 940