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George Scherer

George W. Scherer

William L. Knapp '47 Professor of Civil Engineering
Professor of Civil and Environmental Engineering

S.B., Ceramics, Massachusetts Institute of Technology, 1972
S.M., Ceramics, Massachusetts Institute of Technology, 1972
Ph.D., Materials Science, Massachusetts Institute of Technology, 1974

Room: E319 Engineering Quad
Phone: 609-258-5680
Email: scherer@princeton.edu

Webpage: Materials Research Group

Honors and Awards

  • National Academy of Engineering, 1997
  • Ralph K. Iler Award, American Chemical Society, 1995
  • Sosman Award, American Ceramic Society, 1994
  • Richard M. Fulrath Award, American Ceramic Society, 1990
  • Ross Coffin Purdy Award, American Ceramic Society, 1986
  • G.W. Morey Award, American Ceramic Society, 1985

Concurrent University Appointments

  • Faculty, Princeton Institute for the Science and Technology of Materials Associated Faculty, Department of Chemical Engineering

Publications

Research Areas

Research Interests

Our research generally explores the behavior of porous materials, ranging from gels and polymers to stone and cement. We have elucidated the structure and mechanical properties of aerogels using a combination of computer simulation and novel experimental techniques. We study the growth of crystals of ice and salt in stone in order to understand - on a molecular level - the processes responsible for deterioration of monuments and sculpture. Recently, we have begun a major effort to understand the anomalous properties of aqueous solutions in extremely small pores (in cement, for example), where the molecular packing is affected by proximity of the pore walls.

Art and monument conservation. In cement and concrete, we are interested in the mechanisms of degradation brought about by freeze-thaw cycles and precipitation of salt in the pores. We are studying the sites where nucleation occurs, and the paths along which the crystals grow. We are also measuring the interfacial energies between ice, salt, and stone. With this information, we will be able to predict the magnitudes of the stresses that result from crystallization. This program involves a broad range of approaches, from computer simulation of crystal nucleation, to experimental studies of freezing in porous materials, to fabrication of frost-resistant concrete (by exploiting our understanding of the nature of nucleation).

We are also studying gels (called consolidants) that are used by art conservators to "heal" damage done to stone by exposure to the elements. Unfortunately, these gels can do more harm than good, if their physical properties are not properly matched to those of the material being infiltrated. Therefore, we are developing a palette of new consolidants that can be chosen to match the thermal expansion, elastic modulus, optical characteristics, and permeability of the original material. This can be done by preparing suspensions of nanoscale particles of oxides other than silica, so that the properties can be tuned to meet the need.

Sol-gel processing. Inorganic gels are used for making films, fibers, filters, catalytic substrates, and sensors, among other things. In most cases, it is essential to control the pore size and/or surface area of the material. The final structure is drastically altered from that of the original gel due to shrinkage during drying and heat treatment. We have shown that the final density can be predicted on the basis of properties measured on the original wet gel.

Characterizing the structure of a highly porous gel is an important but difficult problem, because most techniques impose stresses on the material that can alter the pore size distribution. One of the gentlest methods is nitrogen sorption; however, the interpretation of the sorption isotherm in such sparse networks is subtle. The adsorbed species can develop a liquid/vapor interface with zero curvature at a stage when condensation has occurred in very few of the pores, causing serious errors in the apparent pore size distribution when the conventional analysis is applied. We have developed a theory that accounts for this phenomenon, but further theoretical development and experimental verification are required.


A salt-damaged slab of Indiana limestone. The bottom of the stone was in contact with a bath containing a solution saturated with sodium sulfate, which was allowed to wick up into the stone for 42 days. As the water evaporated, crystals of salt precipitated in the pores of the stone and generated stresses large enough the cause cracking. Stress from salt precipitation is the major cause of deterioration of monuments in the Mediterranean basin.