Rheology and calorimetry of microtextured colloidal polycrystals with embedded laponite nanoparticles

We investigate the rheological properties of copolymer-nanoparticle aqueous solutions and their connection to the thermodynamic and structural behavior. The samples are formed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer micellar solutions with embedded anisotropic colloidal laponite nanoparticles. The concentrated micellar solutions exhibit a temperature induced phase transition from fluid to crystal. Addition of laponite nanoparticles is found to promote the formation of polycrystallized micellar micrograins, above the transition temperature, instead of a cubic monocrystal. This polycrystallization is associated with the confinement of the nanoparticles, which play the role of impurities, in interstices between the micrograins. The analysis and comparison of the experimental data show that the presence of nanoparticles above the transition temperature has the effect to gradually reduce storage modulus and the enthalpy needed to gel the same amount of copolymer concentration as the nanoparticles are gradually added due to very efficient copolymer adsorption on the nanoparticles. It was also noticed that compartmentalization of nanoparticles influences the onset of transition seen in the evolution of viscoelastic moduli. Indeed the transition temperature point displays a nonmonotonous variation with the particle concentration which could point to inefficient nanoparticle segregation at higher concentrations. (c) 2017 The Society of Rheology.