A liquid crystal form of silicone which toughens under compression.
Courtesy Verduzco Laboratory/Rice University A liquid crystal form of silicone which toughens under compression.

As material science advances, the familiar often becomes foreign. As Paola Antonelli described in the MoMA show "Mutant Materials" back in 1995, materials continue to cross known boundaries of behavior, upsetting our expectations about the ways in which they are supposed to perform.

Rice University researchers have discovered a new form of silicone that meets this description. Although the material is known to be flexible and rubbery, it can be made tough when subjected to repeated stresses in a particular state. When silicone is in a so-called liquid crystal phase, which is in-between a solid and liquid, it will gain increasing strength under repeated pressure. The scientists determined this unusual behavior results from the reorganization of molecular chains from random to organized coil formations.

"The molecules in a liquid crystal elastomer are like rods that want to point in a particular direction," said polymer scientist Rafael Verduzco in a university press release. "In the starting sample, the rods are randomly oriented, but when the material is deformed, they rotate and eventually end up pointing in the same direction. This is what gives rise to the stiffening. It’s surprising that by a relatively gentle but repetitive compression, you can work out all the entanglements and knots to end up with a sample where all the polymer rods are aligned."

Verduzco and his team anticipate the toughened silicone to be applied to a wide variety of products, ranging from electronic displays to self-healing polymers. Since silicone is biocompatible, the material offers a promising substance for human tissue engineering—particularly since the toughening response mimics the reaction of human muscles to stress.

Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.