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. 2019 Feb 1;24(3):542.
doi: 10.3390/molecules24030542.

'Seeing' Strain in Soft Materials

Zhiyong Xia  1 , Vanessa D Alphonse  2 , Doug B Trigg  3 , Tim P Harrigan  4 , Jeff M Paulson  5 , Quang T Luong  6 , Evan P Lloyd  7 , Meredith H Barbee  8 , Stephen L Craig  9
Affiliations

'Seeing' Strain in Soft Materials

Zhiyong Xia et al. Molecules. .

Abstract

Several technologies can be used for measuring strains of soft materials under high rate impact conditions. These technologies include high speed tensile test, split Hopkinson pressure bar test, digital image correlation and high speed X-ray imaging. However, none of these existing technologies can produce a continuous 3D spatial strain distribution in the test specimen. Here we report a novel passive strain sensor based on poly(dimethyl siloxane) (PDMS) elastomer with covalently incorporated spiropyran (SP) mechanophore to measure impact induced strains. We have shown that the incorporation of SP into PDMS at 0.25 wt% level can adequately measure impact strains via color change under a high strain rate of 1500 s-1 within a fraction of a millisecond. Further, the color change is fully reversible and thus can be used repeatedly. This technology has a high potential to be used for quantifying brain strain for traumatic brain injury applications.

Keywords: impact strain; mechanophore; poly(dimethyl siloxane); spiropyran; strain sensing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Incorporation of SP (spiropyran) into PDMS (poly(dimethyl siloxane)) network structure. (b) Changing between SP and MC (merocyanine) during uniaxial mechanical deformation.
Figure 2
Figure 2
Effects of PDMS (poly(dimethyl siloxane)) mixing ratios on color change quasi-static tensile test. The top row shows blue color (B%) and true stress plotted against true strain and the dark arrows show the onset point for blue color change. The bottom row shows the B% plotted against true stress.
Figure 3
Figure 3
Schematic showing the calculation of end-to-end distance with fixed valence angles. The α is the bond angle and b is the bond length.
Figure 4
Figure 4
Schematic showing the chain contour length and mean end-to-end distance. Lower mixing ratio led to higher crosslinking density and thus smaller average molecular weight between crosslinks (Mc¯).
Figure 5
Figure 5
(a) Color change in SP-PDMS during and after impact at an impact speed of 100 m/s. The arrow shows the projectile impact direction. (b) Von Mises strain contours during the impact process via (top row) and high-speed video (bottom row). The PDMS (poly(dimethyl siloxane)) had a mixing ratio of 10:1 with 0.25% SP (spiropyran).
Figure 6
Figure 6
(a) Color change in SP-PDMS (spiropyran-poly(dimethyl siloxane)). (b) FEA shows the formation of the high strain areas on the surface of the specimen during the early impact. (c) Effective strain envelope based on FEA (finite element analysis) versus time. The strain levels are the maximum Von Mises strain that each material point experiences over the history of the impact. The highest strain locus is shown by the red color.
See this image and copyright information in PMC

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