Running away from thermodynamics to promote or inhibit crystal growth

Abstract

Impurities/additives may be either detrimental or beneficial to many different crystal growth applications. Determined to a great extent by thermodynamics, their effects are hardly avoided once supersaturation, temperature, pH, and impurity content are established. In this work we introduce the rate of supersaturation variation R(sigma) as a new variable that can dramatically influence crystal growth relatively to steady-state conditions. We show that the crystal growth of a model protein can be accelerated, retarded, or even suppressed by altering R(sigma). Our results provide insight into the mechanism by which fast supersaturation variation prevents the adsorption equilibrium from being restored. When impurity adsorption onto kink sites gets delayed, crystal growth is enhanced and a "purifying" effect takes place. If, instead, impurity desorption from kink sites gets delayed, then a "poisoning" effect takes place. The same rationale is used to elucidate fundamental challenges that inspired this work. Included in this list are the nonlinear acceleration kinetics of growth layers and the growth rate hysteresis. While attenuating impurity incorporation, the purifying effect is expected to be important for the production of high quality lattices during single crystal growth. On the other hand, the poisoning effect opens new possibilities for crystal growth inhibition during pathological mineralization.