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

Abstract

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.

A 7 nm Thick Polymeric Membrane With a H2/CO2 Selectivity of 200 That Reaches the Upper Bound

“…Experimental methods that were used to (i) synthesize 5,11,17,23,29,35hexakis[(N,N,N-trimethylamonium)-N-methyl-37,38,39,40,41,42-hexakis-nhexadecyloxy-calix[6]arene chloride (i.e., Calix), (ii) deposit Langmuir-Blodgett (LB) bilayers of PAA-crosslinked Calix, 1 and 2 onto poly[1-(trimethylsilyl)-1-propyne] (PTMSP) supports or silicon wafers (silylated with n-octadecyltrichlorosilane, OTS), (iii) quantify gas permeabilities, and (iv) measure film thicknesses by ellipsometry were similar to those that have previously been described. [1][2][3] Ellipsometry measurements were made using VASE ellipsometer (J.A. Woollam Co., Inc., Lincoln, NE), equipped with variable wavelength ( from 250-1700nm) and angle of incidence (15º-90º) system, a λ of 632.8nm and an incidence angle of 70º were chosen for measurements.…”

Hyperthin Membranes for Gas Separations via Layer‐by‐Layer Assembly

“…To be able to deposit PEMs on PTMSP, the surface of PTMSP must be made hydrophilic and have a high density of charged groups. In our early studies, we used the Langmuir‐Blodgett deposition method to modify the surface of PTMSP . Because self‐assembly methods are much simpler (e. g., adsorbing a monolayer of branched poly(ethyleneimine), b ‐PEI onto PTMSP), we carried out a detailed study to determine whether there were any advantages to the more laborious LB method.…”

“…In our early studies, we used the Langmuir-Blodgett deposition method to modify the surface of PTMSP. [37][38][39][40][41][42] Because self-assembly methods are much simpler (e. g., adsorbing a monolayer of branched poly(ethyleneimine), b-PEI onto PTMSP), we carried out a detailed study to determine whether there were any advantages to the more laborious LB method. Thus, a Langmuir-Blodgett monolayer of a poly(1-octadecene-alt-N,N,N-trimethylammonium-Nethylmaleimide) chloride (POMTMA) was compared with a self-assembled monolayer of branched poly(ethyleneimine) (b-PEI) as anchor layers, using PEMs formed from PDDA and PSS as a test case ( Figure 5).…”

Building molecular frameworks with tailored pore structures

“…Porous architectures based on surfactant or polymeric vesicular structures, 1,2 polymeric worm-like micelles, 3 metalligand coordination networks 4-7 and hydrogen-bonded host frameworks [8][9][10][11] are illustrative of this growing interest. Applications include drug delivery, [12][13][14] in which bioactive molecules are trapped inside the pores of materials designed to release their contents at targeted sites, highly specific separations of small molecules based on materials having pore sizes and structure with molecular-scale uniformity, 15 and heavy metal encarceration for toxic remediation. 16 Tailor-made porous architectures may also serve as chemical storage media, and as nanoscale reaction compartments that guide or constrain reaction pathways for molecules contained inside the pores, generating novel materials not attainable through conventional methods.…”