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UNIVERSITY OF WATERLOO
Waterloo Institute for Nanotechnology (WIN); Department of Chemical Engineering; Department of Physics & Astronomy
Prof. Mark W. Matsen

Block copolymer research has progressed enormously in the last couple decades to the point where there is impressive agreement between experiment and theory. This is demonstrated by the comparison between the experimental [1] and SCFT [2] phase diagrams for diblock copolymer melts shown in the two figures to the right. Initially the absence of a perforated-lamellar (PL) morphology from the SCFT phase diagram was attributed to a shortcoming in the theory, but it has since been realized [3] that the experimental PL phase was only metastable and converts to the gyroid (G) morphology given sufficient time. The remaining difference regarding the nature of the disorder-order transition (ODT) was attributed to the omission of fluctuation effects by the mean-field SCFT.

In principle, Monte Carlo simulations provide the most straightforward way of accounting for fluctuation effects. However, early simulations struggled to detect any definitive signature of the ODT. We originally overcame this problem with the introduction of a new order parameter [4], but now we get sufficiently good statistics with parallel tempering that we can detect to ODT from a spike in the heat capacity [5]. The resulting Monte Carlo phase diagram is shown to the right. Consistent with experiments, the disordered phase is found to exhibit direct first-order transitions to each of the ordered morphologies. This surprisingly includes small regions where the PL phase spontaneously forms. This may be a result of the relatively short chains (N=30) used in the simulations.