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SUMMARY:Self-assembled Precipitate Membranes and the Implications for Life
  - Yang Ding (Department of Chemical Engineering\, University of Cambridge
 )
DTSTART:20181123T130000Z
DTEND:20181123T140000Z
UID:TALK112414@talks.cam.ac.uk
CONTACT:Joseph Ibrahim
DESCRIPTION:Far from the thermodynamic equilibrium\, many precipitation re
 actions can create complex membrane structures.   Such membranes are of gr
 eat research interest in fields ranging from chemical engineering to geoph
 ysics\, and even biology where they are thought to have played a vital rol
 e in the origin of life. Usually\, the transport of chemicals by combined 
 buoyancy\, osmotic and diffusive mechanisms\, support the precipitation re
 action. In order to study these transport processes across a growing selec
 tive membrane\, we use a chemical-garden reaction in a micro-fluidic react
 or. We focus on two studies in a horizontal Hele-Shaw cell:  one where the
  flow is driven by the membrane itself and another where flow is forced by
  a pump. In the first\, we examine the changes of the membrane morphology 
 associated with the concentration of reactants. We also survey the growth 
 rate of membrane\, which is determined by the osmotic flow as well as by c
 oncentration effects. The motion of the fluid is visualized in order to un
 derstand the transport process. The pressure inside the membrane structure
  is measured and different patterns of pressure changes are identified. A 
 pressure-concentration model is proposed to explain the harmonic pressure 
 changes of this system. In the second study\, with externally-forced flow\
 , the growth of a wavy precipitate membrane is observed.  We establish tha
 t its growth is controlled by transverse diffusion and dispersion of ions.
  We develop a precipitation model\, taking into account diffusion of ions 
 through the precipitate and through an adjacent gel layer. Results from ou
 r theory are in excellent agreement with the measurements\, and show that 
 a wavy precipitate surface can enhance the transverse transport of ions.
LOCATION:JDB Seminar Room\, CUED
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