Like the simple stretching case, the resistance-changing trend is divided into a steady region (low-strain region) and a sharp-changing region (high-strain region). In the high-strain region, the ∆R/∆ϵ is approximately 2.0 TΩ/%, which is far smaller than under simple stretching. When measured again after relaxation of the applied strain, the resistance at each strain was reproducible as shown by the blue square symbols in Figure 5c. It is not clear at this moment why the resistance-changing trends are divided into two regions for both

simple stretching and more complex straining of bending and stretching. A clue, however, can be deduced from the cracking behavior of the sample. The border between the two regions exists around a 30% strain for the 180-nm-thick Ti/PDMS sample, coinciding with the initiation point of the tilted secondary cracks (ϵ c ≈ 30%). It is inferred that below this strain, the vertical cracks are not fully developed BAY 1895344 and there PF-02341066 mw is still a connected current path, and then all the current paths are severed with the advent of the secondary cracks above the CX-4945 critical strain, which causes a steep resistance increase with a small increase in strain. This was supported by the fact that no significant resistance variation

was observed in the strain range of 0% to 50% for a 250-nm-thick Ti film on PDMS substrate, where only weak vertical cracks appear. Despite many advantages of the cracked Ti film on PDMS substrate as a strain sensor, there still remain issues to be further addressed, including the effects of irregular crack patterns and surface oxide and how to widen the strain-sensing range more, particularly toward the lower strains. Conclusions Thin Ti films with thicknesses of 80 to 250 nm were sputter-deposited on elastomeric PDMS substrates.

All the samples were transparent and highly flexible. Cracks were introduced in the Ti films by both planar and non-planar stretching, but the cracking behaviors differed depending on the applied strain and the Ti film thickness. Vertical cracks were developed at low strains below a critical strain, and beyond it, secondary cracks tilted from the straining direction appeared to intersect the earlier formed vertical cracks. The strain-dependent crack Progesterone patterns led to the strain-dependent resistance. For a 180-nm Ti film on PDMS substrate, a sharp-resistance-changing region appeared over a tensile strain range of 20% above a critical strain of 30%, where a gauge factor of 2 was achieved. It also showed extremely low-power consumption and endured a mixed strain of bending and stretching. These attributes of cracked Ti films on PDMS substrates provide a pathway for the embodiment of an advanced strain sensor with low-cost manufacturability, high transparency and flexibility, and good portability. Author’s information JSN earned his Ph.D. degree in materials science in 2003 from University of Wisconsin-Madison.