| In the 1950s, Conmar Robinson described a beautiful set of
experiments showing that synthetic polypeptides spontaneously form liquid
crystals in organic solvents supporting the helical conformation. Other
rodlike polymers prove more convenient when it comes to applications,
especially structural ones, but the polypeptides continue to teach us
fundamental lessons. These sometimes transcend the domain of liquid crystal
physics. For example, the special alignments available to cholesteric
mesophases permit the apparent release of topological constraints that
impede diffusion in isotropic solutions. This is done by RAISING the
concentration slightly. No comparable option exists in random flight polymer
solutions. Optical tracer diffusion measurements in the vicinity of the
isotropic-to-liquid crystal phase boundary thus inform on the nature of
entanglements in polymer solutions.
Like any great teacher, polypeptides also inspire students to try
new ideas. Thus, we embarked on a series of experiments to confine
polypeptides to the surface of colloidal particles. (Most students have
probably dreamed of imprisoning their teachers, but an academic
administrator might have predicted the outcome: polypeptides are no more
easily corralled than cats...or professors!) With some effort, we have
succeeded to place polypeptides on the desired silica colloids. The
resultant structures physically resemble influenza virus particles, which
also feature a polypeptide (protein) shell on a colloidal-sized core.
Although the functionality of our hybrid silica-polypeptide is far less
powerful (and not at all dangerous) these disease-inspired materials do
retain some features of their natural counterparts, especially the ability
to expand or contract in response to stimulus. They can perform other
tricks, especially when equipped with magnetic inclusions. |