Dr. Karnail's Talk

Aug 06, 2009 - 14:30

Aug 06, 2009 - 16:00

Creativity Hall (Room No 118)

Seminars

Dr. Karnail Singh

Abstract: Understanding the mechanism of film formation in latex dispersions is essential for the success of many industrially important products such as paints coatings dhesives caulks and sealants etc. In recent times the environmental concerns (due to VOCs emission) have forced a change in paint/coating technologies from traditional organic based formulations to present day water based dispersions. Hence the latex where dispersing media is water has become an attractive alternative to the traditional formulations. However the water-based dispersions suffer with the problem of cracking. It has been observed that while drying these aqueous dispersions show an intricate pattern of cracks. Further not only the paints/coatings but the more classical systems such as mud also show this fascinating array of cracks. In the first part of the research work we have addressed the issue of cracking in drying dispersion. Here based on the magnitude of compressive strain at the maximum attainable capillary pressure two distinct regimes for obtaining crack free films have been identified. In the first regime which we call as Strain-Limited the maximum crack free thickness (referred to as CCT) decreases with the increase in particle rigidity. In the second regime which is referred to as Stress-Limited the CCT increases with the increase in particle rigidity contrary to the expectations. Film formation in strain-limited regime leads to impermeable films where as the film formation in stress limited regime yields crack free porous films. In the next part film formation in Latex-Blends has been investigated. These blends are also the water-based dispersions containing soft (low Tg) and hard (high Tg) polymer particles. In these blends soft particles coalesce to fill the voids and the hard ones give mechanical strength to the final film. Here an experimental technique to measure the critical stresses in the film has been developed. The effect of various parameters such as relative volume fraction (soft/hard) rigidity etc. on critical stress and film formation has been investigated. An existing model for dispersions with homogenous particles has been extended to blends and compared with extensive experimental data. In the final part of the research work we have studied the phenomenon of cracking in flocculated dispersions. Here the critical cracking thickness (CCT) and critical cracking stress (CCS) were measured for aqueous dispersions of -Alumina over almost the entire range of pH values. We have shown that the theory developed for stable dispersions is equally capable of describing the cracking mechanism in flocculated dispersions as well.Biosketch of the speaker: Karnail Singh graduated from our department with a doctoral degree in December 2008. His PhD work was on “Understanding Film Formation Mechanism in Latex Dispersions”. His research work was well appreciated both in the academia as well as in the industry. A news story on his work appeared in a leading Indian Newspaper DNA. His work was also reported in Physics Web & Physics World the leading website and magazine of the Institute of Physics (IOP) publishing house. Not only this a news article on his work had also formed the subject matter on the homepage of our institute website. He has published his research work in high Impact journals such as PRL Langmuir and has also given presenation on this work in national as well as international conferecnes. Before joining our department he was a Masters student in the department of Chemical Engineering at UICT from where he graduated in 2002. He also obtained his Batchelor’s degree in Chemical Enginner from Mumbai University in 2000. Currently Karnail is working as a Research Engineer at GE’s John F. Welch Technology Centre in Bangalore. His current area of research is Reaction Engineering and Catalysis.