1. Cover of Scientific American, October 2003

2. Source: www.ritsumei.ac.jp Actuator driven by thermal expansion of water and air

3. V.H. Ebron et al., Science (2006) 311, 1580 A chemical reaction with methanol creates heat in the NiTi alloy wire, which causes it to shrink - thus lifting a weight and doing work. Example of negative thermal expansivity being exploited to convert chemical energy into work

4. Weak Nano-scale Forces Can be Measured The AFM probe is exceedingly sharp so that only a few atoms are at its tip! Sensitive to forces on the order of nano-Newtons. Atomic force microscope (AFM)

5. AFM tips from NT-MDT. See www.ntmdt.ru Tips for Scanning Probe Microscopy Radius of curvature ~ 10 nm Ideally, one of the atoms at the tip is slightly above the others. The tip is on a cantilever, which typically has a spring constant on the order of k = 10 N/m. Modelled as a simple spring: F = kz where z is the deflection in the vertical direction. F

6. Measuring Force of Attraction to a Polymer Surface Pulling on the AFM probe tip Pushing on AFM probe tip

7. Physics of a “Bubble Jet” Printer How much work is required to create a droplet of ink?

9. Measuring Attractive Forces at the Nano-Scale A = approach B = “jump” to contact C = contact D = adhesion E = pull-off Tip deflection  Force Vertical position A B C DE C

11. Adhesive properties Force spectroscopy experiments Force (nN) Distance (nm)

12. v = 10 µm/s Contact t = 1 s F = 0.5 Kg ε Strain σ Typical Tack Curve v d = 0.1 - 500 µm/s Adhesion energy Stress Fibrillation σpσp

13. 6 fibrils F_max D_max F_max: Maximum adhesive force ; D_max: Maximum deformation 1 2 3 4 56 F_max = 3.5 +/- 0.2 nN; D_max = 300 +/- 20 nm Average over 16 FS curves Stretching Polymer Molecules Distance (nm) Force (nN)

14. 0 Distance (nm) A E D C B f* Force Spectroscopy Principles Force-distance curves:  Force-distance curves: obtained from a force spectroscopy expt. Analysis of F-d curves:  Analysis of F-d curves: to deduce adhesive force (f*) of the tip- sample system, and its elastic and viscoelastic properties

15. Stress (MPa) Strain fibril detachment 1mm Cavitation homogeneous deformation 02461010 8 0 0. 8 0. 6 0. 4 0. 2 A.Roos & C. Creton, ESPCI, Paris Cavity growth Fibrillation Evolution of Structure

16. 0% laponite F_max = (3.5 +/- 0.2); D_max = (300 +/- 20) Average over 16 FS curves