Enhancement of Mechano-Sensitivity for Spiropyran-Linked Poly(dimethylsiloxane) via Solvent Swelling

Abstract

Spiropyran (SP) is a mechanophore that undergoes changes in chemical structure and thus in optical character when subjected to a force. Incorporation of SP into polymer chains enables optical detection of stress/strain and damage in the material under load. However, the mechano-sensitivity of SPlinked polymers is in general insufficient for many applications. Attempts have been made to enhance the mechano-sensitivity of SP-linked polymers via modification of the chemical structure of the SP mechanophore or the mesostructure of the polymer matrix.In the present study, we explore how the mechano-sensitivity of SP incorporated in a poly(dimethylsiloxane) (PDMS) network is influenced by the pre-swelling of PDMS with an organic solvent (xylene). The effect of PDMS swelling on the optical property of the mechanophore was investigated by measuring the fluorescence intensity from the SP-linked PDMS in situ during uniaxial deformation using a custom-built opto-mechanical measurement setup. The results suggest that a longer swelling time causes a decrease in the initial fluorescence, a decrease in the activation onset strain, and an increase in the activation slope, resulting in enhanced apparent mechano-sensitivity. For instance, the 15 min pre-swollen SP-linked PDMS showed an 8.3-fold increase in mechano-sensitivity relative to the unswollen reference. Such effect is not limited to uniaxial extension but also observed in other modes of deformation, such as compression and bending. When corrected against the variation in sample thickness during uniaxial extension, and pre-strain and initial fluorescence intensity due to solvent swelling, the SP fluorescence intensity vs true strain (or chain entropy) curves obtained at various degrees of initial swelling collapse into a single curve, which suggests that the swellingenhanced mechano-sensitivity is due to the pre-strain of the network and a decrease in initial fluorescence intensity caused by the pre-swelling.

Mechanochromophore‐Linked Polymeric Materials with Visible Color Changes

“…[109] A more direct approach to enhancing the mechano-sensitivity by pre-stretching the polymer network was via swelling the polymers in solvents. [179] But how to use this solvent swelling strategy in real applications remains unanswered, with regard to the concerns of solvent leakage, volatility, and toxicity.…”

Aggregation-Induced Emissive Silicone Elastomer with Multiple Stimuli Responsiveness

“…Following this idea, a series of fluorescent silicone elastomers have been developed in the past few years. The unique photoelectric properties of fluorescent silicone materials endow them with broad application prospects in the fields of organic light-emitting diodes, , probes, , bioimaging, , and thin-film chemical sensors. , …”

“…The unique photoelectric properties of fluorescent silicone materials endow them with broad application prospects in the fields of organic light-emitting diodes, 12,13 probes, 14,15 bioimaging, 16,17 and thin-film chemical sensors. 18,19 Physical doping of fluorescent molecules into a silicone elastomer substrate is the simplest method to prepare fluorescent silicone materials. 20,21 However, fluorescent mole-cules directly physically doped into the matrix tend to aggregate and disperse unevenly.…”

Design and synthesis of mechanochromic poly(ether-ester-urethane) elastomer with high toughness and resilience mediated by crystalline domains

“…11 This mechanically induced color change could serve as a sensor for mechanical deformation or stress in a polymer sample. This strategy has been applied to develop a wide variety of polymeric elastomers, including polyurethanes, [12][13][14] polydimethylsiloxane, [15][16][17] polyacrylate elastomers, [18][19][20][21][22] etc. As reported, the mechanochromic response sensitivity, the effect of polymer chain alignment and relaxation on the SP-MC reaction and the color activation energy of elastomers have been investigated in detail.…”

“…As reported, the mechanochromic response sensitivity, the effect of polymer chain alignment and relaxation on the SP-MC reaction and the color activation energy of elastomers have been investigated in detail. 16,23,24 Unfortunately, it is uncommon to develop mechanochromic elastomers that possess high toughness and excellent resilience. As we know, high energy dissipation contributes to improving the toughness of polymers, while energy dissipation will decrease the elasticity of polymer elastomers and the transfer efficiency of external forces in polymer chains.…”