Understanding the mechanism of cracking during the drying of aqueous colloidal dispersions is important to preventing film failure. While most of the reported work has dealt with stable aqueous dispersions, a few studies have focused on flocculated systems. The latter especially assumes importance because the role of particle packing in the mechanism of cracking is not completely understood. In this work, we study the cracking of colloidal films cast from flocculated aqueous dispersions of alpha-alumina. Here, the extent of flocculation is controlled by varying the pH of the dispersion and characterized in terms of the final packing volume fraction of the dried film. The influence of varying the close-packed volume fraction on the critical cracking thickness and critical cracking stress is measured. The measurements are compared with the model predictions based on Griffith's energy balance, and good agreement is found between theory and experiments, suggesting that the model is universal and applies equally well to stable as well as flocculated systems.

SUMMARYAn effective means for rapid multiplication of plant species of clonal origin is micro propagation. Various in vitro studies have been reported on different species of patchouli, one such method of propagation that can be usefully employed to produce relatively uniform plantlets in a short time is via in vitro culture but there is limited effort to study direct organogenesis, which supports cultivation by providing true type plants in large numbers.Therefore this study determines the effect of different concentrations of growth hormones on patchouli, micropropagation and rapid multiplication stages of patchouli plant within a short time with good results of micropropagation stages for regeneration of patchouli were successfully initiated.