ASSEMBLY AND DISASSEMBLY OF LANGMUIR-BLODGETT-FILMS ON POLY[1-(TRIMETHYLSILYL)-1-PROPYNE] - THE UNIQUENESS OF CALIX[6]ARENE MULTILAYERS AS PERMEATION-SELECTIVE MEMBRANES
Ra. Hendel et al., ASSEMBLY AND DISASSEMBLY OF LANGMUIR-BLODGETT-FILMS ON POLY[1-(TRIMETHYLSILYL)-1-PROPYNE] - THE UNIQUENESS OF CALIX[6]ARENE MULTILAYERS AS PERMEATION-SELECTIVE MEMBRANES, Journal of the American Chemical Society, 119(29), 1997, pp. 6909-6918
series of calix[6]arene-based surfactants have been synthesized, which
contain amide oxime head groups on their upper rim and 5,5-dimethylhe
xyl (I), n-octyl (II), n-dodecyl (III), and n-hexadecyl (IV) groups on
their lower rim. Composite membranes that were fabricated from Langmu
ir-Blodgett (LB) multilayers derived from each surfactant plus poly[1-
(trimethylsilyl)-1-propyne] (PTMSP) cast film showed a significant inc
rease in their selectivity toward helium and nitrogen, relative to bar
e PTMSP. In sharp contrast, analogous composites that were prepared wi
th LB multilayers of conventional single chain surfactants [arachidic
acid (AA), cadmium arachidate (AA/Cd2+), and stearoamideoxime (SA)] ex
hibited permeation properties that were identical with those of bare P
TMSP. When a polymeric surfactant [poly(1-octadecene-co-maleic anhydri
de), POM] was used fdr LB film construction, a modest increase in sele
ctivity was observed. These findings, together with an analysis of rep
resentative composites by X-ray photoelectron spectroscopy, provide co
mpelling evidence for the presence of intact, calix[6]arene-based LB a
ssemblies on the surface of PTMSP; with the conventional single chain
surfactants, however, disassembly and absorption into the bulk phase o
f the support is favored. The results of this study highlight the need
for having individual surfactant molecules span individual pores on t
he surface of the support and strong intermolecular forces between nei
ghboring surfactants to produce relatively defect-free LB films.