Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
We investigate the influence of thermal history on the deformation and fracture of a poly(vinyl cyclohexane)-poly(ethylene)-poly(vinyl cyclohexane) (PCHE-PE-PCHE) CEC triblock copolymer (M=107,000 g/mol; wt(PE)=0.29). Ordered thin films of CEC are bonded to ductile copper grids, deformed in tension and then examined by transmission electron and atomic force microscopy. We find that the deformation and fracture mechanisms of CEC depend significantly on the thermal history. The CEC thin films undergo crazing and the crazes break down to form cracks at low strains when the films are prepared by slow cooling (- 0.5 C/min) from 190 C, where both PCHE and PE domains are rubbery. On the contrary, after being quenched to room temperature from 190 C, the CEC films become ductile with a change in deformation mechanism to competing shear deformation zones and crazing. Both physical aging of the PCHE domains and different semi-crystalline microstructures of the PE domains may play a role in determining these mechanisms and the resultant ductility or brittleness.
*Supported in part by the NSF-DMR-MRSEC Program under the UCSB MRL.