Insight into the Permeation Barrier of Glued Langmuir−Blodgett Bilayers

Abstract

Permeation measurements have been made for He, CO2, and N2 across single Langmuir-Blodgett (LB) bilayers derived from 1,2,4,5-tetrakis[(N-(undecanoamidoethyl)-N,N-dimethyl ammonium) methyl]benzene tetrabromide (2) and 1,2,4,5-tetrakis[(N-(perfluoroundecanoamidoethyl)-N,N-dimethyl ammonium)methyl]benzene tetrabromide (3) in the absence and in the presence of entrapped poly(acrylic acid) (PAA). In the absence of PAA, single LB bilayers of 3 show a higher permeance for He and N2 but a lower permeation rate of CO2, as compared with analogous LB bilayers made from 2. The relatively low permeation rate of CO2 for the former has been attributed to reduced associative interactions with the fluorocarbon-rich bilayer. The same behavior has also been observed for LB bilayers containing PAA, formed under conditions that yield glued bilayers of 2 and 3 having similar diffusional pathways, as judged by He/N2 selectivities. These results, together with the fact that glued bilayers of 2 (having a thinner PAA layer as compared with those made from 3) exhibit lower He and N2 permeances, provide compelling evidence that the main barrier for gas transport is the combination of surfactant plus PAA and not simply a thin PAA layer that is encased within the surfactant bilayer.

Yield strength of glued Langmuir–Blodgett films determined by friction force microscopy

“…1 LB films have served as a low-cost solution to adeptly functionalize otherwise inert substrates for applications such as biosensors, 2,3 organic light-emitting diode devices, 4,5 thin film transistors, 6 organic photovoltaic cells, 7,8 lubricants for microelectromechanical devices (MEMS), 9 and permeation-selective barriers. 10 LB films can also function as efficient filters for molecular gas phase separations 11 and display permeation selectivity to several generally inert gases such as He, N 2 , and CO 2 . 12 Film quality and mechanical stability are critical parameters in the development of all such applications.…”

“…13 Glued LB films displayed increased relative surface viscosities and molecular area as shown by surface pressure-area isotherms. 6,11 Both of these observations, however, are indirect assessments of LB film strength. Therefore, there exists a need for quantitative characterization and qualitative ranking of the stability and the structural strength of the LB films.…”

Engineering membranes with macrocycles for precise molecular separations

“…167 Regen and coworkers have intensely investigated the gas permeability of surfactant-like calix[n]arenes-containing membranes by the Langmuir-Blodgett (LB) method. [168][169][170][171][172][173][174][175][176][177][178][179] Such membranes would act like molecular sieves and the presence of multiple hydrocarbon chains structure in each surfactant would enhance the cohesiveness of these assemblies, thereby minimizing the defect formation. In order to improve the stability of the LB membrane, the head of calixarene-based surfactants have been designed with specific groups, such as disulfide moieties for photo-cross-linking, amide oxime groups for hydrogen bonding, quaternary ammonium-based groups for ionic crosslinking.…”

Challenges and breakthroughs in recent research on self-assembly

“…This tiling strategy provides a versatile design of patterns upon appropriate selection of component molecules. A unique fabrication technique for LB films in the out-plane direction was recently developed by Regen and coworkers, and is known as the 'glued LB film' [732][733][734]. They developed glued LB films through polyanion bridging of cationic amphiphiles at an LB interlayer and investigated gas permeability through the glued LB films (figure 90).…”