(119g) Shear Driven Transition from BCC to Frank-Kasper A15 States in Diblock Polymer Solutions

Amphiphilic diblock oligomers and low molecular weight diblock polymers demonstrate complex phase behavior in solutions where the solvent is preferential to one of the blocks. The nanoscale structures in these crystalline phases give rise to mechanical properties that can drastically affect processing and the fruition of useful applications. It is important to be able to process these materials to control the nanoscale structure and obtain desirable mechanical properties. The goal of this work is to demonstrate the impact of mechanical processing on the rate of phase transitions in an aqueous diblock oligomer system. A Linkam shear stage is used to apply oscillatory shear to aqueous diblock oligomer solutions [Brij-58,C16H33(CH2CH2O)20OH], while real-time structural data is collected via synchrotron small angle x-ray scattering (SAXS). In this work, we demonstrate that mechanical shear processing can be used to control the rate of a phase transition from a metastable BCC state to the equilibrium Frank Kasper A15 state in an aqueous diblock oligomer solution. Under thermal equilibration alone, this transition requires 5 months. By tuning the oscillatory shear conditions, we demonstrate that this transition can be accelerated to occur on the order of minutes.