Optical characterization and confocal fluorescence imaging of mechanochromic acrylate polymers

Abstract

Optical characterization and confocal fluorescence imaging of mechanochromic acrylate polymers. "J. Appl. Phys. 117, 043103 (2015 The development of mechanochromic molecules has opened new pathways for the study of localized stress and failure in polymers. Their application as stress or temperature diagnostics, however, requires suitable measurement techniques capable of detecting the force-and temperature-sensitive chemical species with high spatial resolution. Confocal imaging techniques offer excellent spatial resolution but the energy input during these measurements can itself affect the activation state of the mechanochromic species. Here, we present a systematic study of the effects of laser-based imaging on the activation and fluorescence behavior of mechanochromic spiropyran (SP) integrated into poly(methyl acrylate) (PMA) and poly(methyl methacrylate) matrices using a confocal Raman microspectrometer. Localized stress and temperature activation were studied by means of high-rate compressive loading and dynamic fracture. Laser illumination of SP in PMA revealed a strong excitation wavelength-and power-dependence. Suitable correction functions were established and used to account for the observed laser effects. The presented study demonstrates that confocal imaging using conventional Raman spectrometers is a powerful characterization tool for localized stress analysis in mechanochromic polymers, offering quantifiable information on the activation state with high spatial resolution. However, laser-mechanophore interactions must be well understood and effects of laser excitation and exposure times must be taken into consideration when interpreting the obtained results.

Mechanochemical tools for polymer materials

“…Another class of polymers that are well studied in polymer mechanochemistry are poly(urethanes) (PU), because of their highly-tunable properties. 43,50,74,92,104,[148][149][150][151][152][153][154][155][156][157][158][159][160] Their synthesis is based on a Process in solution PMA, 35,56,62,63,67,84,[137][138][139][140][141][142] PMMA, 143 PEA, 144 PnBA, 144 PiBA, 144 PtBA, 144 PS, 145,167 copolymers, 167,168,171 PCL, 146,147 polybutadiene 68,123,170 Controlled/living polym. (SET-LRP, ATRP, ROP, ROMP, RAFT, etc.. .…”

“…Besides material design, external parameters like temperature, 182 solvent, 74 strain rate, 148,159,182,224 and laser excitation 140 impact the force at which the mechanophore activates; presumably by modifying activation barriers for the reaction. Such sensitivity to the environment should be kept in mind if a quantitative interpretation of the mechanochemical response is desired.…”

Cu(0)-Mediated Living Radical Polymerization: A Versatile Tool for Materials Synthesis

“…In the same field, Osswald and co-workers presented a systematic study of the effects of laser-based imaging on the activation and fluorescence behavior of mechanochromic spiropyran (SP) integrated into PMA and PMMA matrixes utilizing a confocal Raman microspectrometer . The mechanophore-bearing PMAs were synthesized via SET-LRP following the procedure of Moore and co-workers that was described previously .…”

“…Laser illumination of SP in PMA revealed strong excitation wavelength and power dependence while suitable correction functions were established and utilized to account for the observed laser effects. It was demonstrated that if the laser–sample interactions are well understood the confocal imaging techniques can offer quantifiable information on the activation state of mechanochromic material systems with extremely high spatial resolution . In addition, Craig and co-workers reported high mechanophore content polyester–acrylate ABA block copolymers allowing access to stable, mechanophore-rich polymers of various molecular weights. , Finally, Stoddart described the synthesis of of cyclobis­(paraquat- p -phenylene)-derived [2]­rotaxane initiators and their use in the SET-LRP of MA, leading to well-defined polymers with exactly one mechanical interlocked molecule (MIM) per polymer chain …”

“…384 In the same field, Osswald and co-workers presented a systematic study of the effects of laser-based imaging on the activation and fluorescence behavior of mechanochromic spiropyran (SP) integrated into PMA and PMMA matrixes utilizing a confocal Raman microspectrometer. 385 The mechanophore-bearing PMAs were synthesized via SET-LRP following the procedure of Moore and co-workers that was described previously. 384 Laser illumination of SP in PMA revealed strong excitation wavelength and power dependence while suitable correction functions were established and utilized to account for the observed laser effects.…”