Nanoconfined crystal growth and dissolution

Nanoconfined crystal growth and dissolution Confinement in crystal growth and dissolution consists of multiple phenomena. The most apparent one is the finite-size effect of not having infinite space to diffuse in solution, or grow the crystal. But confinement also include highly non-trivial effects such as the surface-surface interactions due to overlapping electric double layes and steric effects as the surfaces come closer (around ten and a few Debye lengths, respectively). Moreover, in extremely close contact (few water molecules), the growth stops as if the two surfaces were in contact due to the water becoming highly ordered and thus expensive to remove in terms of (free) energy. Only the first of these effects have been modelled in a satisfying manner previously. We have developed a new microscopic model of crystal growth and dissolution which incorporates the effect of the overlapping double-layers. The simulation results of with the model agrees with thermodynamic theory and with recent experimental results. The experiments use optical microscopy to study the nanoconfined, interface between growing crystals and glass. By the use of microfluidics and high resolution imaging techniques we have for the first time been able to study confined crystal growth atom-layer by layer. The results from the project will hopefully be used to predict and control salt weathering and crystal growth in nanoconfinement.

Growth and dissolution at stressed, confined crystal surfaces have been discussed for 150 years. The existence of a nanoconfined water film at the stressed interface that mediates crystallization, dissolution and material transport has been thoroughly con firmed experimentally, theoretically and by simulation. We have recently performed experiments showing that nanoconfined growth surfaces are rough. This contradicts theoretical results that predict smooth nanoconfined growth surfaces. We will explain the discrepancies between experiment and theory and suggest two hypotheses that will guide the project: 1. Nanoconfined crystal growth/dissolution roughness is controlled by lower energy state and lower activation energy to growth/dissolution of molecules in surface separations smaller than 1 nm. The net outcome may be to enhance the growth rate or reduce the dissolution rate in load bearing contact points relative to other parts of the surface at separations of more than 1 nm and thus to destabilize surface s that would otherwise be flat. 2. By changing the fluid ionic properties, pH and crystal surface properties the disjoining pressure between nanoconfined surfaces may be reduced sufficiently to expel the water film confined between the reactive surfaces and nanoconfined crystal growth/dissolution stops. We propose that the only way to obtain a new, fundamental understanding is to combine and quantitatively compare experiments, simulation and theory. The microfluidic/imaging and AFM experiments, the kine tic Monte Carlo and Molecular Dynamics simulations and the continuum theory that we propose to employ will also put us in a unique position internationally to perform both fundamental and applied research in this area in the future.