Chapter 6
Ultrasound as Mechanical Force
Abstract Acoustic cavitation invariably combines chemical and mechanical effects
that stem from bubble collapse in liquids. Strategies to harness preferentially the role
of mechanochemistry in sonochemistry have been invented and developed in recent
years, demonstrating enormous versatility from synthesis and catalysis to biology
and analytical monitoring. Most cases involve polymers containing weak bonds that
can be fragmented by sonication. The effects are dependent largely on both the nature
of substrates and the strength of cavitational collapse.
6.1 Introduction: What Mechanochemistry Is
Mechanochemistry is the branch of chemistry that deals with the mechanical activation of molecules and materials. These everyday actions and phenomena, such as
stretching, milling and grinding, date back to the origins of human civilization and
have long been used to induce chemical reactions. In fact, rubbing sticks together
to make fire is probably one of the earliest mechanochemical transformations to
have been discovered by man. According to IUPAC definitions, a mechanochemical reaction involves a chemical reaction that is induced by the direct absorption of
mechanical energy (Fernández-Bertran 1999). Some authors have argued that this
rather broad definition is inappropriate and that the term should only be used when
mechanical energy directly breaks strong bonds, for example, in polymers or in
single molecule (Kaupp 2009). This restriction may mislead some readers as the literature often alludes to mechanochemistry in the broader sense. After all, nature itself
harnesses mechanotransduction processes to transform mechanical force into chemical/biochemical signals. The motion of cells and bacteria, the interactions of cells with
their environment, ion channel opening in membranes and conformational changes
in biomolecules are all manifestations of chemical responses induced by weak forces
(Gillespie and Walker 2001; Chalfie 2009). Mechanical effects that induce changes in
atomic positions and molecular structure, which are characteristic of polymorphism
and conformational equilibria, for instance, could then be accurately described in
terms of mechanophysics (Kaupp 2009). This semantic distinction is not usually
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2018
J.-M. Lévêque et al., Organic Sonochemistry, Ultrasound and Sonochemistry,
https://doi.org/10.1007/978-3-319-98554-1_6
87
Ultrasound as Mechanical Force
Abstract Acoustic cavitation invariably combines chemical and mechanical effects
that stem from bubble collapse in liquids. Strategies to harness preferentially the role
of mechanochemistry in sonochemistry have been invented and developed in recent
years, demonstrating enormous versatility from synthesis and catalysis to biology
and analytical monitoring. Most cases involve polymers containing weak bonds that
can be fragmented by sonication. The effects are dependent largely on both the nature
of substrates and the strength of cavitational collapse.
6.1 Introduction: What Mechanochemistry Is
Mechanochemistry is the branch of chemistry that deals with the mechanical activation of molecules and materials. These everyday actions and phenomena, such as
stretching, milling and grinding, date back to the origins of human civilization and
have long been used to induce chemical reactions. In fact, rubbing sticks together
to make fire is probably one of the earliest mechanochemical transformations to
have been discovered by man. According to IUPAC definitions, a mechanochemical reaction involves a chemical reaction that is induced by the direct absorption of
mechanical energy (Fernández-Bertran 1999). Some authors have argued that this
rather broad definition is inappropriate and that the term should only be used when
mechanical energy directly breaks strong bonds, for example, in polymers or in
single molecule (Kaupp 2009). This restriction may mislead some readers as the literature often alludes to mechanochemistry in the broader sense. After all, nature itself
harnesses mechanotransduction processes to transform mechanical force into chemical/biochemical signals. The motion of cells and bacteria, the interactions of cells with
their environment, ion channel opening in membranes and conformational changes
in biomolecules are all manifestations of chemical responses induced by weak forces
(Gillespie and Walker 2001; Chalfie 2009). Mechanical effects that induce changes in
atomic positions and molecular structure, which are characteristic of polymorphism
and conformational equilibria, for instance, could then be accurately described in
terms of mechanophysics (Kaupp 2009). This semantic distinction is not usually
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2018
J.-M. Lévêque et al., Organic Sonochemistry, Ultrasound and Sonochemistry,
https://doi.org/10.1007/978-3-319-98554-1_6
87