Reorientation of Crystalline Block Copolymer Membranes by Phospholipid Hybridization

Block copolymer (BCP) self-assembly and crystallization determine their fundamental mechanical, optical, and transport properties. Multiple physical and chemical routes to control BCP self-assembly have been developed over the years. In contrast, modulating the crystallization behavior, particularly crystallite size and orientation, has received considerably less attention. This paper underpins that 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipid additives enable precise control of BCP crystallization via a combination of interfacial and confinement effects. The assembly and crystallization behavior of methoxy-poly(ethylene glycol)-b-poly(ϵ-caprolactone) (mPEG-b-PCL) hybridized with DPPC was elucidated in solid-supported dry-film forms. mPEG-b-PCL/DPPC hybrid films coassemble into multilamellar structures with BCP and lipid domains stacked in registry across the film thickness. With small amounts of DPPC (3 wt %), mPEG-b-PCL/DPPC hybrid films unexpectedly exhibit nonadditive thermal conductivity, reaching ∼0.1 W m^-1K^-1, a value considerably lower than pure BCP or DPPC films. Hybridization alters DPPC chain packing and induces specific PCL crystallite orientation at the nanoscale. PCL chains on the folding plane of an orthorhombic lattice optimize molecular interactions with vertically aligned DPPC alkyl chains by orienting PCL crystallites at a 20° tilt. These results enable new applications of polymeric systems in which switchable crystallization routes are used to tune heat transport.