Assembly and Disassembly of Langmuir−Blodgett Films on Poly[1-(trimethylsilyl)-1-propyne]:  The Uniqueness of Calix[6]arene Multilayers as Permeation-Selective Membranes

• Published in: Journal of the American Chemical Society 1997-07, Vol.119 (29), p.6909-6918
• Main Authors: Hendel, Robert A, Nomura, Eisaku, Janout, Vaclav, Regen, Steven L
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja970980w

A series of calix[6]arene-based surfactants have been synthesized, which contain amide oxime head groups on their upper rim and 5,5-dimethylhexyl (I), n-octyl (II), n-dodecyl (III), and n-hexadecyl (IV) groups on their lower rim. Composite membranes that were fabricated from Langmuir−Blodgett (LB) multilayers derived from each surfactant plus poly[1-(trimethylsilyl)-1-propyne] (PTMSP) cast film showed a significant increase in their selectivity toward helium and nitrogen, relative to bare PTMSP. In sharp contrast, analogous composites that were prepared with LB multilayers of conventional single chain surfactants [arachidic acid (AA), cadmium arachidate (AA/Cd2+), and stearoamideoxime (SA)] exhibited permeation properties that were identical with those of bare PTMSP. When a polymeric surfactant [poly(1-octadecene-co-maleic anhydride), POM] was used for LB film construction, a modest increase in selectivity was observed. These findings, together with an analysis of representative composites by X-ray photoelectron spectroscopy, provide compelling evidence for the presence of intact, calix[6]arene-based LB assemblies on the surface of PTMSP; with the conventional single chain surfactants, however, disassembly and absorption into the bulk phase of the support is favored. The results of this study highlight the need for having individual surfactant molecules span individual pores on the surface of the support and strong intermolecular forces between neighboring surfactants to produce relatively defect-free LB films.