MSE Colloquium: Dr. Lisa Klein, Processing and Applications of Melting Gels
A characteristic of so-called silica-based melting gels is that the gels, which are rigid at room temperature, are able to soften and re-soften at temperatures around 110oC. However, after consolidation at temperatures higher than 150oC, the gels no longer re-soften. In other words, the network formation proceeds to such a degree, that the rigid gel is a hybrid glass, a silica glass with residual organic groups directly bonded to silicon. Many systems of melting gels have been investigated, for example, phenyltriethoxysilane (PhTES)-diphenyldiethoxysilane (DPhDES). The influence of di-substituted versus mono-substituted alkoxides on the softening behavior, the temperature of consolidation and ultimate thermal decomposition have been studied. The glass transition temperature decreases as the amount of di-substituted alkoxide increases. The consolidation temperature does the opposite, meaning it increases as the amount of di-substituted alkoxide increases, while the thermal decomposition temperature is unchanged (>500°C).
Hybrid organic-inorganic materials made by the sol-gel process are not simple physical mixtures of the inorganic and organic components. In particular, the hybrid gels are nonporous, even without high temperature treatment. This suggests a variety of applications where melting gels can replace low temperature sealing glasses and epoxies. The properties of melting gels that have been studied include their dielectric strength1, their hermeticity and barrier properties2, their resistance to attack by salt spray in corrosion studies3, their ability to be imprinted and textured4, and their role as Au-nanoparticle hosts.
1 L. Gambino, A. Jitianu, and L. C. Klein, “Dielectric Properties of Organically Modified Siloxane Melting gels”, J. Non-crystalline Solids 358, 2012, 3501-3504. 2 A. Jitianu and L. C. Klein, “Encapsulating Battery Components with Melting Gels” Ceramic Transactions 250: Advances in Materials Science for Environmental and Energy Technologies III, eds. T. Ohji,, J. Matyas, N. J. Manjooran, G. Pickrell, A. Jitianu,, American Ceramic Soc., Westerville, OH, 2014, pp. 279-286. 3 M. Aparicio, A. Jitianu, G. Rodriguez, A. Degnah, K. Al-Marzoki, J. Mosa, L. C. Klein “Corrosion Protection of AISI 304 Stainless Steel with Melting Gel Coatings”, Electrochimica Acta 202, 2016, 325-332. 4 L. C. Klein, B. McClarren and A. Jitianu, “Silica-Containing Hybrid Nanocomposite “Melting Gels” Thermec 2013 Symposium on Advanced Protective Coatings/Surface Engineering, ed. B. Mishra, M. Ionescu. And T. Chandra, Materials Science Forum, Trans Tech Publishers, Vol. 783-786, 2014, pp. 1432-1437.
Lisa C. Klein obtained a BS in Metallurgy in 1973 and a PhD in Ceramics in 1977 from the Material Science and Engineering Department at the Massachusetts Institute of Technology. With Rutgers since 1977, she became a full Professor in 1987. The focus of Klein's activities is the synthesis and processing of ceramics and glasses using the sol-gel process, emphasizing processing studies on the conditions for forming gels for optical applications, membranes, organic-inorganic hybrids and electrochemical devices. In particular, Klein has explored the use of the sol-gel process in the preparation of solid electrolytes for smart windows. She serves as an Editor for the Journal of the American Ceramic Society.