Dr. Yuval Vidavsky, SibleySchool of Mechanical and Aerospace Engineering Cornell University, willgive a Candidate Lecture on Wednesday, March 18th 2020,at 16:00.
The title of the talk will be: The Importance ofBreaking Bonds.
Chalk talk (faculty members only) will take placeon Thursday, March 19th 2020, at 15:00 at the facultyroom.
Application of force on polymeric materials ultimately causes chemical bond scission and usually
results in destructive behaviors such as failure, fatigue and abrasion. Hence, it is often desirable to
prevent processes that result in bond scission. However, with the proper material design, bond
breaking can generate beneficial features with tailor-made behaviors.
In this talk, I will present the incorporation of spiropyran mechanochromic functionality in bisphenol A
polycarbonate that is synthesized by the addition of dihydroxyspiropyran as bisphenol monomer. This
copolymer demonstrates the high glass transition temperature, toughness and stiffness that are
associated with polycarbonate, while boasting the desired mechanochromic activity at room
temperature. The mechanochemical bond scission and isomerization of spiropyran to merocyanine are
thoroughly investigated by measuring the fluorescence in situ while stretching the material. Evaluation
of the mechanochromic response to changes in stress, deformation and time shows a complex
dependence on the combination of these factors and provides new insights regarding the stress
accumulation in polymer chains.
In addition, I will present a polymeric system with metal-ligand crosslinking, which is based on the
ionic interaction of divalent metal cations with carboxylate anions grafted on polymer backbones. The
metal-ligand crosslinking increases the stiffness and strength and reduces ductility. In addition, by
attaching different types or number of neutral ligands to the metal center, the metal-carboxylate
interactions could be modulated, thus allowing to fine-tune the mechanical properties of the
Insights gained from this work can be used for the rational design of mechano-active polymers with
wide range of targeted mechanical properties and application.