Mechanically activated rupture of single covalent bonds: evidence of force induced bond hydrolysis.

We have used temperature-dependent single molecule force spectroscopy to stretch covalently anchored carboxymethylated amylose (CMA) polymers attached to an amino-functionalized AFM cantilever. Using an Arrhenius kinetics model based on a Morse potential as a one-dimensional representation of covalent bonds, we have extracted kinetic and structural parameters of the bond rupture process. With 35.5 kJ mol−1, we found a significantly smaller dissociation energy and with 9.0 × 102 s−1 to 3.6 × 103 s−1 also smaller Arrhenius pre-factors than expected for homolytic bond scission. One possible explanation for the severely reduced dissociation energy and Arrhenius pre-factors is the mechanically activated hydrolysis of covalent bonds. Both the carboxylic acid amide and the siloxane bond in the amino-silane surface linker are in principle prone to bond hydrolysis. Scattering, slope and curvature of the scattered data plots indicate that in fact two competing rupture mechanisms are observed

Mechanochemistry Induced Using Force Exerted by a Functionalized Microscope Tip

Atomic-scale mechanochemistry is realized from force exerted by a C-60-functionalized scanning tunneling microscope tip. Two conformers of tin phthalocyanine can be prepared on coinage-metal surfaces. A transition between these conformers is induced on Cu(111) and Ag(100). Density-functional calculations reveal details of this reaction. Because of the large energy barrier of the reaction and the strong interaction of SnPc with Cu(111), the process cannot be achieved by electrical means.National Natural Science Foundation of China [21522301, 21373020, 21403008, 61321001, 21433011, 11304107, 61371015]; Ministry of Science and Technology [2014CB239302, 2013CB933404, 2017YFA0205003]; Deutsche Forschungsgemeinschaft [Sonderforschungsbereich 677]SCI(E)ARTICLE3911769-117735

Experimental Polymer Mechanochemistry and its Interpretational Frameworks

Polymer mechanochemistry is an emerging field at the interface of chemistry, materials science, physics and engineering. It aims at understanding and exploiting unique reactivities of polymer chains confined to highly non-equilibrium stretched geometries by interactions with their surroundings. Macromolecular chains or their segments become stretched in bulk polymers under mechanical loads or when polymer solutions are sonicated or flow rapidly through abrupt contractions. An increasing amount of empirical data suggests that mechanochemical phenomena are widespread wherever polymers are used. In the past decade, empirical mechanochemistry has progressed enormously, from studying fragmentations of commodity polymers by simple backbone homolysis to demonstrations of self-strengthening and stress-reporting materials and mechanochemical cascades using purposefully designed monomers. This progress has not yet been matched by the development of conceptual frameworks within which to rationalize, systematize and generalize empirical mechanochemical observations. As a result, mechanistic and/or quantitative understanding of mechanochemical phenomena remains, with few exceptions, tentative. In this review we aim at systematizing reported macroscopic manifestations of polymer mechanochemistry, and critically assessing the interpretational framework that underlies their molecular rationalizations from a physical chemist's perspective. We propose a hierarchy of mechanochemical phenomena which may guide the development of multiscale models of mechanochemical reactivity to match the breadth and utility of the Eyring equation of chemical kinetics. We discuss the limitations of the approaches to quantifying and validating mechanochemical reactivity, with particular focus on sonicated polymer solutions, in order to identify outstanding questions that need to be solved for polymer mechanochemistry to become a rigorous, quantitative field. We conclude by proposing 7 problems whose solution may have a disproportionate impact on the development of polymer mechanochemistry

Mechanochemical Triggers for Self -Healing Polymers

198 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Mechanochemical triggers based on the electrocyclic ring opening of both trans and cis substituted benzocyclobutenes was studied. The products of mechanically-accelerated ring opening were studied by trapping experiments. Ultrasound induces ring opening at 10°C, whereas thermal activation only took place at temperatures over 105°C. It was found that the substitution pattern around the four-membered ring influenced the rotational preference for ring opening. 13C labeling studies indicate that while the trans isomer prefers to open in a conrotatory manner, the cis isomer prefers to open in a disrotatory manner. It is proposed that these rotational preferences are a result of the efficiency of stress release; mechanical activation is greatest for those pathways which most efficiently relieve the applied force upon transformation from substrate to products.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Mechanochemical Triggers for Self -Healing Polymers

198 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Mechanochemical triggers based on the electrocyclic ring opening of both trans and cis substituted benzocyclobutenes was studied. The products of mechanically-accelerated ring opening were studied by trapping experiments. Ultrasound induces ring opening at 10°C, whereas thermal activation only took place at temperatures over 105°C. It was found that the substitution pattern around the four-membered ring influenced the rotational preference for ring opening. 13C labeling studies indicate that while the trans isomer prefers to open in a conrotatory manner, the cis isomer prefers to open in a disrotatory manner. It is proposed that these rotational preferences are a result of the efficiency of stress release; mechanical activation is greatest for those pathways which most efficiently relieve the applied force upon transformation from substrate to products.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD