Insight into the Permeation Selectivity of Calix[n]arene-Based Langmuir−Blodgett Films:  Importance of Headgroup Association and the Solid Phase

• Published in: Langmuir 1998-10, Vol.14 (22), p.6545-6549
• Main Authors: Hendel, Robert A, Zhang, Lan-hui, Janout, Vaclav, Conner, Mark D, Hsu, James T, Regen, Steven L
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Langmuir blodgett films; Surface physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la9806496

This paper reports the design and synthesis of 5,11,17,23,29,35-hexaacetyl-37,38,39,40,41,42-hexakis(1-hexadecyloxy)calix[6]arene (2) and 5,11,17,23-tetraamideoxime-25,26,27,28-tetrakis(1-hexadecyloxy)calix[4]arene(3), plus a detailed comparison of the membrane properties of corresponding Langmuir−Blodgett films with those assembled from 5,11,17,23,29,35-hexaamideoxime-37,38,39,40,41,42-hexakis(1-hexadecyloxy)calix[6]arene (1a). Surface pressure−area isotherms that were recorded for 1a and 2 over a pure water subphase at 25 °C showed significant hysteresis that was eliminated after two compression−expansion cycles; the limiting area in both cases was ca. 162 Å2/molecule. In sharp contrast, 3 showed no hysteresis at 25 °C and a limiting area of 107 Å2/molecule. Careful examination of the dependence of surface viscosity on temperature has provided compelling evidence for a solid-analogous to liquid-analogous phase transition occurring at 31 and 28 °C for monolayers of 1a and 2, respectively. Permeation measurements that were made across Langmuir−Blodgett (LB) films [four monolayers supported on poly[1-(trimethylsilyl)-1-propyne] with respect to helium and nitrogen] revealed high selectivity in the case of 1a and much lower selectivity with 2 and 3 at ambient (21−23 °C) temperatures. The implications of these findings, in terms of the further development of LB films as membranes for gas separations, are briefly discussed.