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John Sebastian


Current Position:  Senior Research Specialist, 3M Personal Safety Division
Advisors: Prof. R.A. Register and Prof. W. W. Graessley 
Undergraduate Institution: University of Notre Dame 

Ph.D. Thesis Research: 
We examine the interrelation between flow and structure in body-centered cubic (BCC) block copolymer melts and solutions.  At temperatures below TODT, the rheology-morphology relation may be divided into three regimes:  a Newtonian plateau, a critical stress region, and a simple shear-thinning region.  In the Newtonian plateau present at low shear stresses, the flow mechanism is due to the creeping motion of defects in the large-scale grain structure which manifests itself as a finite viscosity on the order of 108 – 109 Poise.  As the stress is increased to a critical level, a transition occurs where the viscosity abruptly falls several orders of magnitude as the BCC lattice is continuously broken down until a shear-disordered metastable state is attained.  In this metastable state the block copolymer acts as a rheologically simple shear-thinning polymer equivalent to when it is disordered by heating above its TODT.