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Growing Inorganic Membranes in Microfluidic Devices: Chemical Gardens Reduced to Linear Walls
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posted on 2015-12-03, 00:00 authored by Bruno
C. Batista, Oliver SteinbockThe
hollow precipitate tubes in chemical gardens conserve the nonequilibrium
conditions present during their formation and are an important example
of molecular processes causing complex macroscopic self-organization.
We report a greatly simplified experimental model of these structures
that is based on the formation of an inorganic membrane in a microfluidic
device. Within this device, we induce the precipitation of Mn(OH)2 and other metal hydroxides at the reactive interface of steadily
injected NaOH and MnCl2 solutions. The resulting precipitate
wall extends along the entire length of the reactor channel and can
be positioned at will, and its width increases strictly in the direction
of the metal solution. These thickening dynamics obey a square root
law. The corresponding effective diffusion coefficient is proportional
to [OH–], shows a sigmoidal dependence on [Mn2+], and also depends on the precipitating metal ion. The precipitate
wall is permeable to methylene blue and strongly adsorbs methyl orange.
Electron and optical microscopy reveals decaying micrometer-sized
perturbations and a 40 μm thick gel-like layer on the surface
exposed to the Mn2+ solution. The wall growth is also followed
by in situ Raman spectroscopy. Potential applications toward materials
and origins-of-life research are discussed.
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Potential applicationsmicrofluidic devicereactor channelOHmetal ionnonequilibrium conditionsChemical Gardens Reduced40 μ mMicrofluidic DevicesRaman spectroscopyformationsigmoidal dependencemetal hydroxideswall growthwidth increasesmetal solutionInorganic Membranesreactive interfacechemical gardensLinear WallsThediffusion coefficientsquare root lawMnCl 2 solutions
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