Growth and etching kinetics of tetragonal lysozyme

Abstract

The morphology and kinetics of the growth and dissolution of lysozyme in aqueous solutions with 2.5% NaCl and at pH=4.5 were studied in-situ with a depth resolution of 300 Å (4 unit cells) by high resolution optical microscopy and digital image processing. The bulk super- or undersaturation, σ, of the solution insidea closed growth cell was controlled by temperature. The growth habit was bound by (110) and (101) faces that grew through layer spreading, although with different growth rate dependencies on supersaturation/temperature. At σ<10 (obtained at higher temperatures) growth was purely kinetically controlled, with impurity effects (macrostep formation and kinetic hindrance) becoming significant for σ<2. At σ10 (lower temperatures), anisotropies in the interfacial kinetics were more pronounced, with interfacial kinetics and bulk transport becoming equally important to the growth morphology. Growth rates were growth-history dependent. The formation of striations (layers of irregularly incorporated solution) was unambiguously correlated with growth temperature variations. Etching exposed dislocations and various high-index faces whose growth morphologies were studied during return to the steady-state growth form. Growth steps were observed to originate from two-dimensional nuclei or from outcrops of growth striations, and from dislocations that preferentially formed in growth sector boundaries.