Modeling mechanophore activation within a crosslinked glassy matrix

Silberstein, Meredith N.; Min, Kyoungmin; Cremar, Lee D.; Degen, Cassandra M.; Martı́nez, Todd J.; Aluru, N. R.; White, Scott R.; Sottos, Nancy R.

doi:10.1063/1.4812581

Cited by 52 publications

(46 citation statements)

References 21 publications

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“…For all experiments the onset of mechanical activation occurs at a larger strain than the yield peakas is consistent with other literature on SP-linked PMMA (Table 1). 12,24 Like the yield strain, the onset of activation strain increases with increasing strain rate and is larger for compression than for tension. The trend for strain at the onset of activation is in fact more exaggerated than the trend for yield strain (quadratic vs log strain rate).…”

Section: Resultsmentioning

confidence: 99%

Mechanoactivation of Spiropyran Covalently Linked PMMA: Effect of Temperature, Strain Rate, and Deformation Mode

et al. 2015

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Polymer multifunctionality can be designed through the incorporation of chemical groups termed "mechanophores" that have a specific chemical transformation in response to applied force. The behavior of mechanophorelinked polymers depends on synthetic factors such as the choice of the mechanophore, the polymer chemistry, and the mechanophore linking architecture and on externally imposed factors such as temperature, loading mode, and loading rate. While many papers have explored changing polymer architecture, relatively few have systematically looked at these external factors, particularly temperature and loading mode. These external factors are critical for practical application of mechanophore-linked polymers, particularly for damage detection in engineering materials. Here, we use a single synthetic system to quantify the influence of these externally imposed factors. In particular, the mechanophore spiropyran (SP) is covalently bonded into lightly cross-linked poly(methyl methacrylate) (PMMA). SP is a mechanophore that has a distinct color and fluorescence change when activated through force to the merocyanine state, making it ideal for in situ studies. We monitor and analyze the full field fluorescence of SP-PMMA samples during mechanical loading under tension and compression, over 3 decades of strain rate, and over a 60°C range in temperature. Typical SP mechanoactivation response exhibits three distinct regimes: minimal change through yield, followed by rapid intensity increase, and approach to a steady state. Stress has a strong influence on the rate of increase in SP activation, where stress increase by temperature decrease or strain rate increase substantially raises the SP activation rate. Uniaxial compression displays a qualitatively similar response to that of uniaxial tension. However, a longer flat region is observed in the case of compression as compared to tension corresponding with the larger yield strain.

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Section: Resultsmentioning

confidence: 99%

Mechanoactivation of Spiropyran Covalently Linked PMMA: Effect of Temperature, Strain Rate, and Deformation Mode

et al. 2015

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“…Silberstein et al found a non-equilibrium state resulting in local force fluctuations in glassy polymers. 5 The MD simulation results showed good agreement between the onset of strain softening (first kink) and the onset of mechanophore activation. Based on the damage analysis in the MD simulation, there are micro cracks when the local strain is 8%, associated with the observed initial kink point of the stress-strain curve.…”

Section: B Strain Based Damage Evaluation To Predict Failurementioning

confidence: 70%

“…[1][2][3][4] Mechanophores, which are covalently linked into polymers, is a result of the transmission of external forces at the macroscale to the debonding of covalent links at the molecular level. [4,5] Therefore, itprovides a novel means for designing smart materials with self-sensing capability. Cho et al [6,7] have developed a cyclobutane-based mechanophore comprised of carbon-carbon covalent bonds that transform into cinnamate groups and emit visible fluorescence under external loading.…”

Section: Introductionmentioning

confidence: 99%

A novel statistical spring-bead based network model for self-sensing smart polymer materials

Zhang

Koo

Liu

et al. 2015

Smart Mater. Struct.

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This paper presents a multiscale modeling approach to simulate the self-sensing behavior of a load sensitive smart polymer material. A statistical spring-bead based network model is developed to bridge the molecular dynamics simulations at the nanoscale and the finite element model at the macroscale. Parametric studies are conducted on the developed network model to investigate the effects of the thermoset crosslinking degree on mechanical response of the self-sensing material. The comparison between experimental and simulation results shows that the multiscale framework is able to capture the global mechanical response with adequate accuracy and the network model is also capable of simulating the self-sensing phenomenon of the smart polymer. Finally, the molecular dynamics simulation and network model based simulation are implemented to evaluate damage initiation in the self-sensing material under monotonic loading. Nomenclature I= fluorescence intensity density = original length of the ith spring = variation of the spring length N = number of springs in this subzone = number of actual potential crosslinked covalent bonds = number of all potential crosslinked covalent bonds = loading strain = equivalent strain in the ith spring ̅ = average equivalent strain in the bead-centered subzone = crosslinking degree Keywords: spring-bead model, network model, statistical distribution of crosslinking degree, self-sensing smart material

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“…In contrast to the extensive efforts devoted to syntheses of MCR polymers, very few models have been developed to reveal intricate interplays between mechanical forces and chemical reactions in MCR polymers. Recently, elastic and viscoelastic models for MCR glassy polymers [23] and elastomers [24,25] have been reported. While these models are consistent with some experimental data, they fail to explain other important experimental phenomena.…”

Section: Introductionmentioning

confidence: 99%

Mechanochemically Responsive Viscoelastic Elastomers

Takaffoli

Zhang

Parks

et al. 2016

Journal of Applied Mechanics

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Mechanochemically responsive (MCR) polymers have been designed to possess unconventional properties such as changing colors, self-healing, and releasing catalysts under deformation. These properties of MCR polymers stem from a class of molecules, referred to as mechanophores, whose chemical reactions can be controlled by mechanical forces. Although extensive studies have been devoted to the syntheses of MCR polymers by incorporating various mechanophores into polymer networks, the intricate interactions between mechanical forces and chemical reactions in MCR polymers across multiple length and time scales are still not well understood. In this paper, we focus on mechanochemical responses in viscoelastic elastomers and develop a theoretical model to characterize the coupling between viscoelasticity and chemical reactions of MCR elastomers. We show that the kinetics of viscoelasticity and mechanophore reactions introduce different time scales into the MCR elastomers. The model can consistently represent experimental data on both mechanical properties and chemical reactions of MCR viscoelastic elastomers. In particular, we explain recent experimental observations on the increasing chemical activation during stress relaxation of MCR elastomers, which cannot be explained with existing models. The proposed model provides a theoretical foundation for the design of future MCR polymers with desirable properties.

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Modeling mechanophore activation within a crosslinked glassy matrix

Abstract: II. METHODS The continuum activation model developed herein relies on two smaller scale simulation methods (molecular a)

Cited by 52 publications

References 21 publications

Mechanoactivation of Spiropyran Covalently Linked PMMA: Effect of Temperature, Strain Rate, and Deformation Mode

Mechanoactivation of Spiropyran Covalently Linked PMMA: Effect of Temperature, Strain Rate, and Deformation Mode

A novel statistical spring-bead based network model for self-sensing smart polymer materials

Mechanochemically Responsive Viscoelastic Elastomers

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