A Facile method to fabricate double gyroid as a polymer template for nanohybrids

Here, we suggest a facile method to acquire double gyroid (DG) phase from the self-assembly of chiral block copolymers (BCPs∗), polystyrene-b-poly(l-lactide) (PS-PLLA). A wide region for the formation of DG can be found in the phase diagram of the BCPs∗, suggesting that helical phase (H∗) from the self-assembly of BCPs∗ can serve as a stepping stone for the formation of the DG due to an easy path for order-order transition from two-dimensional to three-dimensional (network) structure. Moreover, the order-order transition from metastable H∗ to stable DG can be expedited by blending the PS-PLLA with compatible entity. Unlike the conventional way for blending BCP with homopolymer, PS-PLLA blends are prepared by using styrene oligomer (S) to fine-tune the morphologies of the blends at which the molecular weight ratio of the S and compatible PS block (r) is less than 0.1. Owing to the use of the low-molecular-weight oligomer, the increase of BCP chain mobility in the blends significantly reduces the transformation time for the order-order transition from H∗ to DG. Consequently, by taking advantage of degradable character of the PLLA, nanoporous gyroid SiO₂ can be fabricated using hydrolyzed PS-PLLA blends as a template for sol-gel reaction followed by removal of the PS matrix.