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Caption : figure s1 friction measurement between a pdms probe and a glass slide in dry condition: the bottom glass substrate attached in a petri dish travels in x-axis against a stationary pdms probe at a constant sliding velocity and a constant preload. (a) experimental set-up. (b) a representative friction trace at a preload of 200 g and a sliding velocity of 0.1 mm/s. (c) the friction coefficient against the sliding velocity at the preloads of 25, 100, and 200 g. error bars represent standard deviation, though some are smaller than the size of the data point.

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Caption : figure s2 representative friction traces. in dry, (a) smooth sliding was obtained with a p20 substrate at the sliding velocity of 0.05 mm/s under the preload of 100 g, (b) irregular stick-slip friction was presented with a p30 substrate at the sliding velocity of 0.01 mm/s under the preload of 100 g, and (c) stick-slip friction was observed with a p10 substrate at the sliding velocity of 0.1 mm/s under the preload of 25g. in lubricated condition, (d) smooth sliding was obtained in the water with a p10 substrate at the sliding velocity of 0.005 mm/s under the preload of 25 g, (e) irregular stick-slip friction was shown in the water with a p10 substrate at 0.005 mm/s under the preload of 25 g, and (f) stick-slip friction was presented in the water  with a p40 substrate at 0.005 mm/s under the preload of 100 g. 

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Caption : figure s3 the plot of the friction coefficient (between a p10 probe and p25 – p40 substrates) against the sliding velocity. in dry conditions, the friction force was measured at the preloads of (a) 1.962, (b) 0.981, and (c) 0.245 n. in glycerol lubricated conditions, the friction force was examined at the preloads of (d) 1.962, (e) 0.981, (f) 0.245 n. in water lubricated conditions, the friction was tested at the preloads of (g) 1.962, (h) 0.981, and (i) 0.245 n. to improve readability, the friction coefficient between a p10 probe, and p10 and p20 substrates are not included in this figure. error bars represent standard deviation, though some are smaller than the size of the data point.

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Caption : figure s4 the friction force (f_x) against the preload (w) for each substrate at different sliding velocities. in dry condition, the friction force was measured with (a) p10, (b) p20, (c) p30, and (d) p40 substrate. in glycerol-lubricated condition, the friction force was measured with (e) p10, (f) p20, (g) p30, and (h) p40 substrates. in water-lubricated condition, the friction force was measured with (i) p10, (j) p20, (k) p30, and (l) p40 substrate. 

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Caption : figure s5 dynamic viscosity of glycerol (after being exposed in the air for 24 hours) as obtained from the rheometer over shear rates of 0.1 – 650 s<sup>-1</sup>).