Self-assembly of block copolymers in ionic liquids: Mixed pluronics- structure, rheology and use as wearable electronics

The goal of this work is to understand and control hierarchical nanostructure formation by block-copolymer self-assembly in ionic liquids. A viable technological application is wearable electronics. The structural and rheological properties of a model series of binary Pluronic block copolymer mixtures dissolved in a protic ionic liquid are studied as a strategy to modulate and control the soft solid behavior of amphiphilic block copolymers in ionic liquids. The softness is controlled via tuning the mixture composition of Pluronic block copolymers P123 and F127 self-assembled in deuterated ethylammonium nitrate (dEAN). Equilibrium microstructures are studied by linear viscoelasticity and small angle neutron scattering (SANS) measurements, while the shear induced microstructures are probed by rheo-SANS in the radial direction (1-3 plane of flow) under steady shear flow. We find that mixing block copolymers yields mixed micelles, where the micelle radius is nearly constant despite the very different block lengths of the components. At higher concentrations, these micelles arrange into body centered cubic (BCC) or face centered cubic (FCC) lattice depending on the mixing ratio. These cubic phases are formed by quiescently heating the mixture systems from the liquid region of the phase diagram, i.e., inverse melting. Under steady shear flow, increasing shear rate induces three structural transitions: polydisperse FCC lattice at low shear rates, formation of HCP layers at intermediate shear rates, shear-melting at high shear rates, with dependence on the mixing ratio. This study enables modifying the structural, and hence rheological, properties of Pluronic block copolymers in ionic liquid solvent through polymer mixing, providing guidance for formulation and processing. The use of these materials in making novel, ionoelastomers for applications in wearable electronics will be presented.