Ultrastable nanostructured polymer glasses

Conceptually, glasses are liquids that have lost their ability to flow 1 . They are typically formed by cooling from the liquid state 2,3 . If the liquid is cooled at sufficiently high rates, crystallization can be circumvented beyond the melting temperature. Eventually, on further cooling, molecular motions become progressively slower, and the molecules are unable to adequately sample equilibrium configurations in the experimental timescale, as set by the rate of cooling. The temperature at which the liquid falls out of equilibrium is denoted as the glass transition temperature (Tg). The glass transition is a kinetic phenomenon 4 . The slower the rate of cooling during glass formation, the greater is the available time for molecular rearrangement in the liquid state. Consequently, the liquid will be cooled to a lower temperature before it abruptly transforms into a glass. The properties of glasses, hence, depend on the path to the glassy state, and may be tuned by the rate of cooling. From a practical viewpoint, an order of magnitude change in the rate of cooling merely modifies the value of Tg by 3K (ref. 5). Thus, the ability to tune the properties of glasses through the typical route to the vitreous state is restricted, and therefore other routes to the glassy statethose that can bypass the kinetic limitations of glass formationare necessary to induce significant changes in material properties.