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Membrane-based CO$_2$ removal from exhaust streams has recently gained much attention as a means of reducing emissions and limiting climate change. Novel membranes for CO$_2$ removal include so called facilitated transport membranes (FTMs), which offer very high selectivities for CO$_2$ while maintaining decent permeabilities. Recently, these FTMs have been scaled up from laboratory level to plant-sized pilot modules with promising results. However, the molecular details of CO$_2$ transport in these has not yet been fully unraveled. In this work, experimental studies were combined with quantum-mechanical ab initio molecular dynamics simulations to gain insight into the underlying molecular mechanism of CO$_2$ permeation through FTMs. Various compositions of polyvinyl alcohol (PVA) as the membrane matrix with polyvinyl amine (PVAm), monoethanolamine (MEA), or 4-amino-1-butanol (BA) as carrier molecules were experimentally tested. Our experiments revealed that water was essential for the CO$_2$ transport and a transport superposition was achieved with a mixed composition of PVAm and MEA in PVA. Furthermore, sorption measurements with PVA were conducted with humidified N$_2$ and CO$_2$ to quantify water sorption-induced swelling and its contribution to the gas uptake. As the carbonic acid--amine interaction is assumed to cause transport facilitation, electronic structure-based ab initio molecular dynamics simulations were conducted to study the transport of CO$_2$ in the form of carbonic acid along PVAm polymer chains. In particular, the necessity of local water for transport facilitation was studied at different water contents. The simulations show that transport is fastest in the system with low water content and does not happen in the absence of water., Comment: 34 pages, 9 figures

Drops deposited on rough and hydrophobic surfaces can stay suspended with gas pockets underneath the liquid, then showing very low hydrodynamic resistance. When this superhydrophobic state breaks down, the subsequent wetting process can show different dynamical properties. A suitable choice of the geometry can make the wetting front propagate in a stepwise manner leading to {\it square-shaped} wetted area: the front propagation is slow and the patterned surface fills by rows through a {\it zipping} mechanism. The multiple time scale scenario of this wetting process is experimentally characterized and compared to numerical simulations., Comment: 7 pages, 5 figures