A computational method for extracting crystallization growth and nucleation rate data from hot stage microscope images

A novel algorithm for the computer based analysis of a sequence of optical microscope images of a crystallization has been developed to extract growth and nucleation data. The algorithm subtracts grayscale pixel values in corresponding positions on successive images, thereby locating pixels relating to new growth which are then either assigned to newly identified (nucleated) crystals or digitally “grown” onto existing crystals. Thus the algorithm tracks the natural processes of nucleation and growth. The result is a series of maps which identify pixels with specific crystals by an assigned number (label) which remains the same for each crystal from image to image, thereby enabling the growth of any crystal (which can be of any shape) to be tracked. These maps are able to be analysed (again by computer) to extract unimpinged crystal size and number information, and hence provide crystal growth rate, nucleation rate and solid fraction data, and crystal size distributions. The method is mainly demonstrated for the isothermal crystallization of tripalmitin from the melt, but an example of isothermal crystallization of sucrose from aqueous solution is also presented.