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Cover of Scientific American , October 2003. Actuator driven by thermal expansion of water and air. Source: www.ritsumei.ac.jp. A chemical reaction with methanol creates heat in the NiTi alloy wire, which causes it to shrink - thus lifting a weight. Example of negative thermal expansivity!. - PowerPoint PPT Presentation
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Cover of Scientific American, October 2003
Source: www.ritsumei.ac.jp
Actuator driven by thermal expansion of water and air
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.
Example of negative thermal expansivity!
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)
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
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
AB
C
D
EC
Measuring Force of Attraction to a Polymer Surface
Pulling on the AFM probe tip
Pushing on AFM probe tip