An engineer's introduction to mechanophores

Deneke, Naomi; Rencheck, Mitchell L.; Davis, Chelsea S.

doi:10.1039/d0sm00465k

Cited by 55 publications

(80 citation statements)

References 164 publications

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“…[4] It is thus crucial to understand how, when, and where such degrada-applications, [31] but it also may restrict the functionality of a material or result in a permanent loss of mechanical strength. [5] An attractive alternative to the use of mechanophores is therefore nonsacrificial mechanoresponsive motifs, i.e., chemical motifs, (macro)molecules, or assemblies that respond to mechanical stimuli in a defined manner without undergoing covalent bond scission. In fact, the application of mechanical stimuli can readily elicit conformational changes in individual molecules or polymer chains, disrupt aggregates of molecules, or trigger the disassembly of associated noncovalent binding motifs.…”

Section: Introductionmentioning

confidence: 99%

“…[ 30 ] An irreversible response can be desirable for some applications, [ 31 ] but it also may restrict the functionality of a material or result in a permanent loss of mechanical strength. [ 5 ]…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, research efforts directed toward the investigation and development of mechanoresponsive materials has drawn ever increasing attention. [ 2,3,5–8 ] Polymers that translate mechanical stresses into a defined response are thought to be useful for many different applications, including as tamper‐proof packaging materials, [ 9 ] as degradable plastics, [ 10,11 ] or for structural health monitoring. [ 12 ]…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

From Molecules to Polymers—Harnessing Inter‐ and Intramolecular Interactions to Create Mechanochromic Materials

Traeger

Kiebala

Weder

et al. 2020

Macromol. Rapid Commun.

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tion occurs to avoid catastrophic materials failure and to possibly redirect degradation processes into useful responses. Consequently, research efforts directed toward the investigation and development of mechanoresponsive materials has drawn ever increasing attention. [2,3,5-8] Polymers that translate mechanical stresses into a defined response are thought to be useful for many different applications, including as tamper-proof packaging materials, [9] as degradable plastics, [10,11] or for structural health monitoring. [12] One possibility to render polymers mechanoresponsive is the integration of so-called mechanophores. The latter generally feature a weak covalent bond that undergoes either homo-or heterolytic cleavage upon experiencing a force that exceeds a certain threshold. [1,5,7,13,14] These motifs are covalently incorporated into a polymer and serve as predefined weak links that preferentially break or transform in response to an applied mechanical force. [1,6,14-16] Widely investigated mechanophores include spiropyrans, 1,2-dioxetanes, and Diels-Alder adducts. [16-18] The rate constants, threshold forces, and transition state bond-lengths and energies of many mechanophores have been well-characterized via techniques such as single-molecule force spectroscopy (SMFS), [19-22] force-modified potential energy surface modeling, [23] and in situ activation using sonication. [2,22,24] The insights gained in such studies have driven advancements in the field of mechanoresponsive materials and the mechanical activation has, for example, been harnessed to promote thermodynamically unfavorable reactions, [19] affect the intra-or intermolecular transfer of protons, [20,25,26] release small molecules, [27] initiate the depolymerization of the surrounding material, [10,28] or elicit changes in the material's color or fluorescence. [16,17,29] The fact that the active bond or functional group of a mechanophore is typically cleaved irreversibly can limit its utility. Some mechanophores can be returned to their original state through an additional stimulus such as light or heat, but unless the mechanophore undergoes a nonscissile cleavage (e.g., a ring-opening reaction, such as in spiropyrans), the reversal is generally hampered by kinetic factors that leave the mechanophore in its cleaved state. [30] An irreversible response can be desirable for some

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

From Molecules to Polymers—Harnessing Inter‐ and Intramolecular Interactions to Create Mechanochromic Materials

Traeger

Kiebala

Weder

et al. 2020

Macromol. Rapid Commun.

View full text Add to dashboard Cite

show abstract

“…[ 3–6 ] Polymers have been designed to respond to diverse types of inputs, including thermal, optical, magnetic, chemical, mechanical, and electrical. [ 1,2,7–9 ] Among these options, the ability to respond to electrical stimuli offers unique advantages in terms of on/off response time, ease of application within a bulk polymer, and relevance for energy conversion technologies. [ 10 ]…”

Section: Introductionmentioning

confidence: 99%

Can Polyelectrolyte Mechanical Properties be Directly Modulated by an Electric Field? A Molecular Dynamics Study

Raiter

Vidavsky

Silberstein

2020

Adv Funct Materials

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Multifunctionality in polymers facilitates their application in emerging technologies. Electrical fields are a preferred stimulus because of the speed and ease of application to bulk polymers. While a wide range of electrically triggered actuators are developed, and electrically controlled adhesion between gels is demonstrated, modification of bulk mechanical properties via electrical stimuli remains elusive. Polymers with covalently incorporated ionic charge (polyelectrolytes) should be well suited to achieving this goal since the mechanical properties depend on electrostatic interactions and these charges are intrinsically susceptible to electric fields. Molecular dynamics simulations are utilized here to investigate whether electric fields can modulate the mechanical properties of polyelectrolytes and to understand the governing mechanisms. Mechanical property modulation by electric field is found to be sensitive to the charge distribution—charges must be tightly attached to the polymer backbone, and responsivity is greater if a single backbone contains both positive and negative charges. The dominant mechanisms are reorientation and stretching of the polymer chains, which also elongate the ionic clusters to maintain strong electrostatic interactions throughout deformation. These insights are critical for future experimental realization of polymers with electric field regulated mechanical properties.

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“…The reliance on macroscopic response is not in line with the fact that microscopic forces are unevenly distributed and manifested at the molecular level via a range of molecular mechanisms. [3][4][5] Recent advances in polymer mechanochemistry [6,7] provide a useful opportunity to probe strain-induced transformations at the microscopic level. For example, it would be useful to know when molecular bond breakage occurs, long before we observe micro and macro cracks developing.…”

mentioning

confidence: 99%

Onset of Mechanochromic Response in the High Strain Rate Uniaxial Compression of Spiropyran Embedded Silicone Elastomers

Shannahan

Lin

Berry

et al. 2020

Macromol. Rapid Commun.

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The molecular processes that accompany dynamic mechanical response to large deformations at high strain rate (≈1000 s−1 or higher) underlie the early stages of damage in materials, but understanding of material response in this regime is typically limited to macroscopic constitutive equations. Here, spiropyran mechanophores are embedded in very short, stress‐bearing strands in silicone elastomers, and their mechanochromic response to uniaxial compression is explored in a Split Hopkinson Pressure (or Kolsky) Bar. At strain rates of 1000 s−1, the onset of mechanochromism occurs at lower strains, but higher stresses, than in the same materials under quasi‐static loading. Similar to quasi‐static loading, however, a negligible effect of mechanophore structure on the critical strain for colorimetric onset is observed. The results suggest that nonequilibrium, inhomogeneous local tension distributions in the elastomers lead to greater stress in individual strands than at the same strains under equilibrium loading, but that within the regions of force concentration, mechanochromic onset is determined primarily by a limiting local strain threshold.

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An engineer's introduction to mechanophores

Abstract: Mechanophores are force-responsive molecules that have the potential to serve as stress sensors in various material systems. This review discusses recent scientific advances and critical challenges facing engineers regarding implementation of mechanophores in polymeric materials.

Cited by 55 publications

References 164 publications

From Molecules to Polymers—Harnessing Inter‐ and Intramolecular Interactions to Create Mechanochromic Materials

From Molecules to Polymers—Harnessing Inter‐ and Intramolecular Interactions to Create Mechanochromic Materials

Can Polyelectrolyte Mechanical Properties be Directly Modulated by an Electric Field? A Molecular Dynamics Study

Onset of Mechanochromic Response in the High Strain Rate Uniaxial Compression of Spiropyran Embedded Silicone Elastomers

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