Interfacial Force‐Focusing Effect in Mechanophore‐Linked Nanocomposites

Kim, Tae Ann; Lamuta, Caterina; Kim, Hojun; Leal, Cecília; Sottos, Nancy R.

doi:10.1002/advs.201903464

Cited by 33 publications

(41 citation statements)

References 43 publications

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“…Furthermore, the force threshold, being dictated by scissile bond energy, is not amenable to chemical tuning and often the material has already sustained considerable permanent damage when the mechanophore activates, [ 18 ] although recent work has demonstrated that it is possible to lower the strain and stress of activation by incorporating stress‐concentrators in the material, such as voids [ 19 ] or silica nanoparticles. [ 20 ] Mechanochromic photonic materials such as colloidal photonic elastomers are inherently more tuneable and provide continuous mechano‐sensing output, yielding grayscale mechanographs. However, such materials have limited dynamic range restricted to imaging only small strains, and cannot give any insights on the mechanical processes at molecular length scales, where mechanical damage initiates.…”

Section: Introductionmentioning

confidence: 99%

Cephalopod‐Inspired High Dynamic Range Mechano‐Imaging in Polymeric Materials

Clough

Gucht

Kodger

et al. 2020

Adv Funct Materials

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Cephalopods, such as squid, cuttlefish, and octopuses, use an array of responsive absorptive and photonic dermal structures to achieve rapid and reversible color changes for spectacular camouflage and signaling displays. Challenges remain in designing synthetic soft materials with similar multiple and dynamic responsivity for the development of optical sensors for the sensitive detection of mechanical stresses and strains. Here, a high dynamic range mechano‐imaging (HDR‐MI) polymeric material integrating physical and chemical mechanochromism is designed providing a continuous optical read‐out of strain upon mechanical deformation. By combining a colloidal photonic array with a mechanically responsive dye, the material architecture significantly improves the mechanochromic sensitivity, which is moreover readily tuned, and expands the range of detectable strains and stresses at both microscopic and nanoscopic length scales. This multi‐functional material is highlighted by creating detailed HDR mechanographs of membrane deformation and around defects using a low‐cost hyperspectral camera, which is found to be in excellent agreement with the results of finite element simulations. This multi‐scale approach to mechano‐sensing and ‐imaging provides a platform to develop mechanochromic composites with high sensitivity and high dynamic mechanical range.

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Section: Introductionmentioning

confidence: 99%

Cephalopod‐Inspired High Dynamic Range Mechano‐Imaging in Polymeric Materials

Clough

Gucht

Kodger

et al. 2020

Adv Funct Materials

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“…The fractional activation of HT-CD in the matrix is quite small, and we hypothesized that the mechanochromic response could be enhanced in two ways. First, by placing the mechanophore at the particle-matrix interface to take advantage of stress concentration effects, [21,23] and, second, by using a more mechanically labile mechanophore. [45] For the latter purpose, we targeted the head-to-head coumarin dimer (HH-CD, Figure 3a).…”

mentioning

confidence: 99%

Molecular Damage Detection in an Elastomer Nanocomposite with a Coumarin Dimer Mechanophore

Zhang

Lund

Gossweiler

et al. 2020

Macromol. Rapid Commun.

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resistance that result from dispersing stiffer particulates or fibers into the softer polymer matrix. [2,3] In high performance polymer composites, mechanical performance is often determined by how stress transfer from the matrix to the filler either prevents or facilitates the formation of voids, depending on the mechanism of toughening. [4,5] Stress overload can lead to the scission of covalent bonds or chain slippage and induce irreversible structural changes at the molecular, mesoscopic, and macroscopic levels, [6-8] ultimately leading to catastrophic material failure. Therefore, damage detection in polymer composites has long been an active area of study from both fundamental and applied perspectives. Currently, damage detection in composites is mostly achieved through techniques such as ultrasonics, computerized vibro-thermography, x-ray tomography and infrared thermography. [9] These techniques are non-destructive, and in some cases they have been applied in combination with methods for repairing the damage, such as resin injection and the use of reinforcing patches. [9] In addition, higher resolution techniques such as scanning electron microscopy and transmission electron microscopy have been used in post-mortem damage analysis in composites. [10,11] These methods have been quite successful, but they require that material damage has progressed to the point of nanoscale to mesoscale defects in order to be detected, and they do not directly probe the nature of the specific molecular events that are responsible for damage initiation and/or propagation. Polymer mechanochemistry offers exciting opportunities for stress-sensing and damage detection in polymer composites through incorporating mechanophores, which are molecular units that react in response to force. [12,13] By embedding different mechanophores, materials can be endowed with stress-responsive properties that include changes in modulus, [14,15] color, [16-19] and electronic properties. [20] Recent years have seen increased efforts to utilize mechanophores in bulk composites, [21-27] and mechanophores that provide irreversible optical responses to mechanical events are promising candidates to characterize the molecular stresses caused by wear or fatigue (Figure 1a). [12,28] But, to the best of our knowledge, mechanochromophores have Molecular force probes that generate optical responses to critical levels of mechanical stress (mechanochromophores) are increasingly attractive tools for identifying molecular sites that are most prone to failure. Here, a coumarin dimer mechanophore whose mechanical strength is comparable to that of the sulfur-sulfur bonds found in vulcanized rubbers is reported. It is further shown that the strain-induced scission of the coumarin dimer within the matrix of a particle-reinforced polybutadiene-based co-polymer can be detected and quantified by fluorescence spectroscopy, when cylinders of the nanocomposite are subjected to unconstrained uniaxial stress. The extent of the scission suggests that the coumarin dimers are mol...

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“…What is already known is that the stress transfer within the complex composites determines the overall mechanical properties, a build-in sensitive stress probe thus would be helpful for understanding their complex mechanical behaviors. [26][27][28] Herein, with the dispersion of different surface-modified Janus nanofillers (sheets or hollow spheres) into the 1,2-dioxetane containing Semi-IPNs, a new kind of mechanochemiluminescent Semi-IPNs nanocomposites with enhanced mechanical properties and stress-reporting capability were developed. Comprehensive characterizations based on fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electronic microscope (SEM), and tensile tests demonstrated that the hierarchically crosslinked structures, including H-bond interactions mediated by Janus nanoparticles and chemical crosslinking within Semi-IPNs, jointly contributed to excellent mechanical properties of the composites.…”

Section: Doi: 101002/marc202000442mentioning

confidence: 99%

Semi‐IPNs Reinforced with Silica Janus Nanoparticles and Their Stress Sensing with Mechanoluminescent Probe

Mou-cheng

Yuan

Yang

et al. 2020

Macromol. Rapid Commun.

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A series of nanocomposite elastomers are prepared by dispersing surface‐modified silica Janus nanoparticles into semi‐interpenetrating network (Semi‐IPN) of polyurethane/polyethyl methacrylate. Benefiting from the hierarchically crosslinked structures that consist of physical interlocking mediated by hydrogen‐bond‐rich silica Janus nanoparticles and permanent crosslinking by Semi‐IPN, these elastomers exhibit excellent mechanical properties. Moreover, the Janus nanosheet is found more effective in strengthening and toughening the Semi‐IPN, in comparison to Janus hollow sphere. Since 1,2‐dioxetane is covalently embedded in these elastomers as a mechanoluminescent stress probe, stress transfer between the polymer and Janus nanoparticles and the toughening mechanism can be illuminated, which offer exciting opportunities to study the failure process of complex polymer nanocomposites with high spatial and temporal resolution.

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Interfacial Force‐Focusing Effect in Mechanophore‐Linked Nanocomposites

Cited by 33 publications

References 43 publications

Cephalopod‐Inspired High Dynamic Range Mechano‐Imaging in Polymeric Materials

Cephalopod‐Inspired High Dynamic Range Mechano‐Imaging in Polymeric Materials

Molecular Damage Detection in an Elastomer Nanocomposite with a Coumarin Dimer Mechanophore

Semi‐IPNs Reinforced with Silica Janus Nanoparticles and Their Stress Sensing with Mechanoluminescent Probe

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