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Pdms 12.1 Crack !EXCLUSIVE! 51

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Pdms 12.1 Crack 51

in this work, cnts were synthesized by cvd method and dispersed in pdms to form the pdms/cnts nanocomposite by solution mixing method. the prepared samples with different concentrations of cnts were subjected to tensile tests and the mechanical properties of the samples were studied. meanwhile, the electrical properties of these samples were characterized by four-point probe and impedance analyzer. the results indicate that both the mechanical properties and electrical properties of the samples showed a good linear relation with the content of cnts. moreover, the electrical properties of the samples were significantly improved, and the values of the samples with concentration of cnts over 0.5 wt % were found to be larger than that of pure pdms. finally, a tactile sensor based on pdms/cnts nanocomposite was fabricated and its piezoresistive properties were studied by bending and stretching experiments. the fabricated tactile sensor showed excellent piezoresistive properties under various strains. in addition, the conductivity of the tactile sensor was also found to be dependent on the applied strain, which indicates its potential use in wearable electronic skins.

to investigate the crack-generation behaviors on nanoscale films, the ti films on pdms substrates with and without straining were compared. the morphology and crack-generation behaviors of ti films on pdms substrates were examined at the microscale using an optical microscope (olympus bx 51, olympus corporation, tokyo, japan). the pdms substrates were immersed into a ti thin film solution (ti-1100 solution, ot&t manufacturing corporation, seoul, korea) for a given period of time and the ti-1100 films were then dried and annealed at 150° c for 15 minutes. before straining, the samples were scanned with an optical microscope to measure the average crack width. the samples were then stretched with the tensile tester to generate cracks and to examine the crack-generation behaviors. in addition, scanning electron microscopy (sem, hitachi s4800, hitachi high-tech, tokyo, japan) was utilized to closely observe individual cracks. to compare the crack-generation behaviors of ti films on pdms substrates with and without straining, the average crack width, the orientation of the cracks, and the distribution of the cracks in the ti film were measured after straining. by comparing the microscale crack-generation behaviors with the nanoscale crack-generation behaviors, the mechanism of crack-generation in the ti films on pdms substrates is discussed.

the microcracks formed on the ti films on pdms substrates by straining the samples at a constant strain rate of 2.5 × 10−3/s, as shown in figure 5 a. the straining led to the simultaneous formation of both primary and secondary cracks (figure 5 a). the dimension of the primary cracks increased with increasing film thickness. the microcracks in the 250-nm-thick ti film were observed in the magnified sem image presented in figure 5 b. as shown in the inset, the primary cracks that originated from an initial pinhole were developed into well-defined cracks. these results suggest that the cracks can be easily formed at a high strain rate by using a slow strain rate of 2.5 × 10−3/s. therefore, it can be concluded that the primary cracks are spontaneously generated and grow under the residual tensile stress during the film deposition, which is released by the formation of the secondary cracks. the fabrication flow of the crack sensor is illustrated in fig. 3 a. the crack sensor consists of a flexible piezoresistive substrate, a parylene-c spacer, and a crack tip formed on the pdms surface. the piezoresistive substrate is fabricated using pdms and silver electrodes by the lift-off process. the electrode layer and parylene-c spacer layers are then laminated on the substrate by hot-pressing the substrate to the spacer layer and the top layer, respectively. finally, the crack sensor is cut into squares, and then the crack tip is made by cutting it from the top layer using a glass blade. the crack tip is fabricated by laser-machining the layer above the parylene-c spacer layer and then by scribing the layer from the crack tip to the parylene-c spacer layer along the scribed path. the crack sensor is fixed on the substrate with the pdms (figure 3 b). the crack sensor is used to measure the contraction of cardiomyocytes, which is induced by drugs. the cell contraction induces a localized stress in the crack sensor. the change of resistance of the crack sensor is detected by a wheatstone bridge circuit by adjusting the output voltage and by a four-probe method by measuring the change in the resistance of the crack sensor. the crack sensor is mounted on the pdms substrate using a vacuum method and epoxy resin. in addition, the flexible sensor is packaged by poly(methyl methacrylate) (pmma) as the cover and fixed on the pdms substrate by epoxy resin, as shown in figure 3 c. finally, the crack sensor is secured to the pdms substrate by a pdms pillar so that the crack sensor can contract and expand independently. the crack sensor is placed on the pdms substrate after the pdms pillar is formed by casting pdms on the ti layer on the substrate. 5ec8ef588bأهلا-بالعالم/

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