Details

• Dr. Alexander E.S. Van Driessche, Institut des Sciences de la Terre Grenoble, CNRS, França
• Date: Jan, 27, 2016 12:00 am
• Place: Sala d’Actes del Institut de Ciències de la Terra Jaume Almera(ICTJA)
• Location: C/ Solé i Sabarís s/n, Barcelona
• Further information: Angels Canals Sabaté, Facultat de Geologia – UB

Abstract

Understanding the growth of crystalline materials from impure media is of relevance to a wide array of research areas, such as: (bio)mineralization, protein crystallography, pharmaceutical compounds and construction materials, to name just a few. Although great advances have been made in our comprehension of mineral growth from solution in the last decade, we are still confronted with one important unresolved paradox: the prevailing conditions in natural growth environments, being low supersaturation and highly heterogeneous solution composition, are prone to induce growth cessation, even so, crystals are formed. Unavoidably, this raises the question of how crystals manage to grow in those adverse conditions. Hence, to address this matter we have studied crystal growth at low driving force in the presence of impurities using kinetic Monte Carlo simulations (in silico). As a first step we revisited the most frequently used impurity model, called step pinning, introduced in the 50s by Cabrera and Vermilyea (CV). We found that the blocking of elementary steps is not solely determined by the Gibbs-Thomson effect, as assumed by the CV. As such this model only applies in the case of effectively large impurities with long surface residency times (e.g. polypeptides during biomineralization). In the case of point impurities, much higher impurity densities are required to induce step blocking because thermal fluctuations drive the system past the limit implied by the Gibbs Thomson effect. These fluctuations also dominate step advanced in the low supersaturation regime leading up to growth cessation. Recent experimental and simulation results show that multilayer steps can “boost” the forward fluctuations and help escape the crystal surface from the so-called death zone. The obtained insights from these works will be discussed as a possible model to explain (bio)mineral growth from natural solutions (e.g. highly inhomogeneous) at low supersaturations. The advantages and disadvantages of using in silico versus in situ studies will be also briefly discussed.