Stucture and dynamics of a microphase separating block copolymer melt.

A block copolymer melt is quenched from the disordered state to a temperature ($T_{q})$ below the order-to-disorder transition ($T_{ODT})$. The structure and dynamics of the melt is studied as a function of quench time using Small-Angle X-ray Scattering (SAXS) and X-ray Photon Correlation Spectroscopy (XPCS) respectively. For $T_{q}$ well below $T_{ODT}$, we observe that the broad SAXS peak corresponding to the disordered state transforms into a sharp peak indicating the formation of the ordered state. The ordering process is accompanied by an increase in the XPCS relaxation time. On the other hand, for $T_{q}$ close to $T_{ODT}$, the static structure factor remains unchanged and the melt remains disordered. However, even though the structure remains unchanged, the XPCS relaxation time increases and then reaches a plateau. Finally, we have shown that microphase separation can be stimulated in the above case of $T_{q}$ close to $T_{ODT}$. In order to do so, the melt is first taken to a temperature, $T'< T_{q}$, where microphase separation would eventually occur. After holding the melt at $T'$ for a short period of time, it is taken to $T_{q}$. At this time the melt is still disordered. However, in contrast to a direct quench to $T_{q}$, this procedure eventually results to the formation of a micrphase-separated state.