Densification of a polymer glass under high-pressure shear flow

 

The study “Densification of a polymer glass under high-pressure shear flow” conducted by Istanbul Technical University Department of Physics Engineering member Prof. Dr. H. Özgür Özer was published in journal of “Physical Review B, (American Physical Society)”.

 

Prof. Dr. H. Özgür Özer,  Department of Physics Engineering, Istanbul Technical University, 34469, Maslak, Sariyer, Istanbul, Turkey

Owen Brazil, School of Physics, CRANN & AMBER, Trinity College, Dublin D02 PN40, Ireland

Benjamin Watts, Laboratory for Synchrotron Radiation-Condensed Matter, Paul Scherrer Institute, 5232 Villigen, Switzerland

John B. Pethica, School of Physics, CRANN & AMBER, Trinity College, Dublin D02 PN40, Ireland

Graham L. W. Cross, School of Physics, CRANN & AMBER, Trinity College, Dublin D02 PN40, Ireland, and Adama Innovations LLC, CRANN, Trinity College, Dublin 2, Ireland

The properties of glasses can change significantly as they evolve toward equilibrium. Mechanical deformation appears to influence this physical aging process in conflicting ways, with experiments and simulations showing both effects associated with rejuvenation away from and overaging toward the equilibrium state. Here we report a significant densification effect in a polymer undergoing shear flow under high pressure. We used the high-aspect ratio geometry of the layer compression test to measure the uniform and homogeneous accumulation of plastic strain during isothermal confined compression of a deeply quenched film of polystyrene glass. Combined scanning transmission x-ray microscopy (STXM) and atomic force microscopy confirmed defect-free deformation leaving up to 1.2% residual densification under conditions of confined uniaxial strain. At higher peak strain, plastic shear flow extruded glass from below the compressing punch under conditions of a high background pressure. A further density increase of 2% was observed by STXM for a highly thinned residual thickness of polymer that nevertheless showed no signs of crystallization or internal strain localization. While the confined uniaxial densification can be accounted for by a simple elastic–plastic constitutive model, the high-pressure extrusion densification cannot.