Dr. John M. Sebastian
Status: Senior Research Engineer
at 3M
Advisors: Prof. R.A. Register and
Prof. W. W. Graessley
Undergraduate Institution: University
of Notre Dame
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.
see Group Research
Focus