Glass - Back to the Future!

Presenting Author:
Lisa Klein

article posted 14 April 2916

Lisa C. Klein is a Professor in the Department of Materials Science and Engineering at Rutgers University, the State University of New Jersey. She has a BS in Metallurgy and a PhD in Ceramics from the MSE Department at the Massachusetts Institute of Technology. She is an Editor for the Journal of the American Ceramic Society. The focus of Klein's research activities is the synthesis and processing of ceramics and glasses using the sol-gel process.

Phase Separation in Melting Gels

Lisa C. Klein
Materials Science & Engineering, Rutgers University Piscataway, NJ 08854, USA

Melting gels are a special class of organically-modified silica hybrid nanocomposites. Their thermal behavior is that they are rigid at room temperature, flow around 100C (temperature T1 ) and consolidate around 150°C (temperature T2, where T2>T1). Consolidation indicates when crosslinking is complete. However, before consolidation, the process of softening, becoming rigid, and softening again can be repeated many times. Once heated to T2, the melting gels are organic-inorganic hybrid glasses.

Several families of melting gels exist that involve the mixing of mono-substituted and di-substituted siloxanes. For example, phenyltrimethoxysilane (PhTMS-Figure 1) and diphenyl dimethoxysilane (DPhDMS-Figure 2) mixtures produce melting gels. The process for preparing melting gels is given in the flow chart (Figure 3).

Before consolidation, the melting gels exhibit glass transition behavior at temperatures below 0°C. The structure of the gels before consolidation and after consolidation has been investigated using 9-ID USAXS at the Advanced Photon Source, Argonne National Laboratory, X-ray energy 17.5 keV and X-ray flux 1013 photon s-1 mm-2 (Dr. Fan Zhang, NIST). To better understand the structure, a third component is being added that is tetrafunctional, for example, tetramethyl orthosilicate.

The goal is to find the limit of the melting gel behavior. When too much tetrafunctional silane is added, the mixture shows liquid-liquid immiscibility and two glass transition temperatures. The limit is shown on the ternary diagram in Figure 4.

Figure 4: Ternary Diagram

Financial support of the National Science Foundation (NSF) through the Award #1313544, Materials World Network, SusChEM: Hybrid Sol-Gel Route to Chromate-free Anticorrosive Coatings is acknowledged, along with the contributions of Andrei Jitianu, Lehman College-City University of New York.