Ultrafast layer-by-layer assembly of PDMS for boosting the H2 separation of a P84 membrane

BTDA-TDI/MDI (P84) has been widely applied in gas separation, however, pinholes or defects on P84 membrane surfaces were formed in the membrane preparation process and directly weaken its separation performance. Herein, we developed an ultrafast polydimethylsiloxane (PDMS) layer-by-layer assembly strategy via spraying method to heal the defects of the P84 membrane. Firstly, a very short assembly time 20-30 s was achieved by a UV-curing method. Secondly, both the PDMS spraying concentration and cycle times were optimized to strengthen the healing ability of PDMS. The P84-PDMS membrane with 3 wt % PDMS spraying concentration and 2 spraying cycle times significantly improve the H2/CH4 selectivity from 62.99 to 231.92 with a satisfactory H2 permeance (20.85 GPU). The layer-by-layer PDMS assembly strategy for healing defects of P84 membrane displays outstanding comprehensive abilities, with an easy manufacturing based upon ultrafast curing and excellent gas separation performance based on the defect-free membrane structure.

Continuous MOF Membrane-Based Sensors via Functionalization of Interdigitated Electrodes

Three M-MOF-74 (M = Co, Mg, Ni) metal-organic framework (MOF) thin film membranes have been synthesized through a sensor functionalization method for the direct electrical detection of NO2. The two-step surface functionalization procedure on the glass/Pt interdigitated electrodes resulted in a terminal carboxylate group, with both steps confirmed through infrared spectroscopic analysis. This surface functionalization allowed the MOF materials to grow largely in a uniform manner over the surface of the electrode forming a thin film membrane over the Pt sensing electrodes. The growth of each membrane was confirmed through scanning electron microscopy (SEM) and X-ray diffraction analysis. The Ni and Mg MOFs grew as a continuous but non-defect free membrane with overlapping polycrystallites across the glass surface, whereas the Co-MOF-74 grew discontinuously. To demonstrate the use of these MOF membranes as an NO2 gas sensor, Ni-MOF-74 was chosen as it was consistently fabricated as the best thin and homogenous membrane, as confirmed by SEM. The membrane was exposed to 5 ppm NO2 and the impedance magnitude was observed to decrease 123× in 4 h, with a larger change in impedance and a faster response than the bulk material. Importantly, the use of these membranes as a sensor for NO2 does not require them to be defect-free, but solely continuous and overlapping growth.

Arbitrarily Patterned Active Wrinkles in Highly Stretched Substrate-Free Dielectric Elastic Membrane

Dynamic wrinkle patterns provide an effective approach for on-demand tuning of membrane optical and mechanical properties to realize a smart membrane. Related applications depend on forming and controlling of a sophisticated wrinkling region. Herein, by using strip-structured electrode couples, we enable regular and ordered wrinkling patterns in an arbitrarily shaped region in a pre-stretched substrate-free dielectric elastic membrane. By considering the electromechanical coupling in a substrate-free hyperelastic membrane, the winkling condition and wavelength are predicated theoretically. Supported by the theoretical results, a series of experimental and numerical demonstrations are realized. The method proposed in this work provides a general framework for forming controllable highly ordered wrinkling patterns in a complex/large area of a substrate-free membrane, which could provide useful guidance for the application of dielectric elastomers in intelligent materials and structures.

Novel Composite Membranes Based on Polyaniline/Ionic Liquids for PEM Fuel Cells Applications

The modern development of (PEMFCs) is still faced by several obstacles such as membrane cost and performance. Perfluorosulfonic acid membranes (e.g. Nafion of DuPont) are currently the most successful in PEMFCs. PEMFCs usually operate at temperatures around 80°C and at atmospheric pressure. Higher temperature operation (T >100°C) is preferred and has several advantages including enhanced fuel cell kinetics, improved catalysts tolerance for contaminants and recovery of useful heat. However, the high-temperature operation is not permitted using Nafion membranes as they dehydrate and their proton conductivity dramatically decreases, thus, lowering the fuel cell efficiency. Therefore, this work aims at developing a Nafion-free membrane that would successfully operate at higher temperatures and with reasonable proton conductivity (preferably higher than 10-3 S/cm). In this study, novel solid proton conductors based on polyaniline (PANI) and ionic liquids (ILs) are proposed as membranes in PEMFCs. PANI-IL composite membranes are fabricated using porous polytetrafluoroethylene (PTFE) as support. The composite membrane was evaluated for its proton conductivity. The results showed a high proton conductivity range of 0.01 to 0.02 S/cm when a 3.7 wt % of the ionic liquid (IL)[1-Hexyl-3-Methylimidazolium Tricyanomethanide] was used.