学术来访
Mass Transport and Mechanics of Ultrathin Membranes (2017.5.16)
Title： Mass Transport and Mechanics of Ultrathin Membranes
Invited Speaker：Dr. Luda Wang
Department of Mechanical Engineering
Massachusetts Institute of Technology
Venue: Chemistry Building,A717
Time: 4:00 pm, May 16, 2017
Abstract:
Membranes act as selective barriers and play an important role not only in large scale applications, such as chemical and gas purification, seawater desalination, and power generation, but also at other scales, such as in biological filtering, micro/nano fabrication, and sensing. The ideal membranes should allow desired species to easily pass through (high permeance) and effectively block undesired species (high selectivity). The membranes should also be chemically resistant and mechanically robust. To achieve these properties, we explore atomically thin materials in membrane transport and applications. To exploit the theoretical limit of membrane selectivity, we made ångström-sized pores in pristine graphene (micron scale) and achieved molecular sieving for standard gases at selectivity of around 2 orders higher than the best commercial membranes. Interestingly, gas permeance through these porous graphene membranes fluctuates stochastically and can be tuned by gold nano-clusters deposited on the membrane, which is the first demonstration of gas flow control across ångström-sized pores. Graphene made by chemical vapor deposition (CVD) is suitable for larger scale applications. Several membrane applications involve high pressure, e.g. water desalination by reverse osmosis or power generation by pressure retarded osmosis. However, the ability of CVD graphene membranes to withstand high pressure is unclear. Our study shows that polycrystalline CVD graphene at macroscale (centimeter scale) is strong enough to sustain ultra-high pressure (100 bar), suggesting the feasibility for applications requiring high pressure. In summary, through studying the mass transport mechanisms and mechanical properties of graphene and 2D composite materials, we have made advances towards engineering of the next generation membranes that have high selectivity and high permeance, and can withstand high pressure.
