Network phases in thin films of diblock polymers

Ordered bicontinuous network phases formed from self-assembled block polymers exhibit nanoscale domains that intertwine in all three dimensions, providing a unique platform for soft-materials engineering. Although many such phases have been formed or theorized across different types of soft matter, only two network phases—O⁷⁰ and double gyroid—are stable in neat diblock polymer melts. Additional degrees of freedom are necessary to open up windows of stability for other network phases, and one such approach is to introduce boundary effects by geometrically confining the polymers. However, the effects of such confinement on network phases are not well-understood. In this work, we use self-consistent field theory to model the equilibrium morphology and free energy of various stable and metastable network-phase thin films. In particular, we evaluate the relative stability of different phases and orientations as a function of system parameters including film thickness, block fraction, segregation strength, and conformational asymmetry, providing insight into the ways that confinement can alter the phase behavior of a network-forming block polymer system relative to the bulk.