Post on 18-Dec-2015
Chang T., Zhang H., Guo Z., Guo X. Chang T., Zhang H., Guo Z., Guo X.
Gao HuajianGao Huajian
2014.04.222014.04.22
All pics from internet
Provides the most straightforward way for actuation and energy conversion.
Generally induced by an external source of energy.
Lack of intrinsic mechanism similar to downhill flow of water.
Barreiro et al., Science 320, 775 (2008) Fennimore et al., Nature 424, 408 (2003)
Kudernac et al., Nature 479, 208 (2011)
Thermal Electronic
vdW 0 vV V Tk
B vdWν zo 2 za 2
0
1 1
2 ( , ) ( , ) l ml m l m
k kk dq dq
m q q q q
0.0 0.5 1.0 1.5 2.03
4
5
6
7
8
ki
v
ke
v
Pot
entia
l coe
ffici
ents
(e
V/a
tom
/K)
Stiffness coefficient (kvdW
)
Guo Z, Chang T, Guo, X, Gao H, J Mech Phys Solids 60, 1676 (2012).
kvdW
kvdW0.5kvdW
B
C
D
Soft Hard
A
0.0 2.5 5.0 7.5 10.0
-30
-15
0
15
30 C
Vel
ocity
(nm
/ns)
Time (ns)
-25
0
25
50
kc = 0.48/4.8/7.7/9.6/12.0/14.4/14.4 nN/nm
k = 0.0096/0.096/0.144/0.192/0.24/0.288/0.096 nN/nm2
Dis
plac
emen
t (nm
)
B
A larger driving force can be generated by a larger stiffness gradient or a smaller local stiffness.
0.0 0.2 0.4 0.60
2
4
6
8
10
12A
0.801/2.403 300K 2.403/4.005 300K 0.801/4.005 300K 0.801/4.005 500K
Dis
plac
emen
t (nm
)
Time (ns)
0.0 0.2 0.4 0.60
6
12
18
24
30
36B
Vel
ocity
(nm
/ns)
Time (ns)
0 2 4 6 8
-30
-15
0
15
30
Vel
ocity
(nm
/ns)
Time(ns)
-12
-6
0
6
12C
Dis
plac
emen
t(nm
)
SuperpositionTemperature
Accel – Stable – DeaccelShuttles like a pendulum
Soft Hard
Durotaxis was first observed in living cells.
Active sensing
Lo et al., Biophys J 79, 144 (2000)
Water droplets undergo reverse durotaxis.
Wetting
Discher et al, Science 310, 1139 (2005)
Style et al., Proc. Natl. Acad. Sci. U.S.A. (2013)
Nanodurotaxis:Nanodurotaxis:
Neither Neither active sensing active sensing nornor wettingwetting
Stiffness gradient induces a bias van der Waals potential
0 3 6 9 12 15-48.51
-48.48
-48.45
-48.42
Inte
rlaye
r P
oten
tial (
meV
/ato
m)
Stiffness (nN/nm)
A
21.23
-6.79
-3.04
-0.20 -0.81 -0.30
2.37
5.99
-12.97
13.19
-5.49
-1.72
0.63
-0.34 -0.66
1.91
5.43
-12.02
-15
-10
-5
0
5
10
15
20
1st/2nd/3rd/4th rings (52 atoms each)on harder side
Inner region
1st/2nd/3rd/4th rings (52 atoms each)on softer side
Inte
rlaye
r F
orce
(pN
) Stiffness jump Stiffness gradient
B
Driving force comes mainly from the unbalance edge force
1st/2nd/3rd/4th ring at the rear end
4th/3rd/2nd/1st ring at the front end
Inner part
Unbalanced edge force/Net driving force6.29 pN/5.48 pN1.27 pN/0.93 pN
Partly (less) from thermal atomic vibration, as shown by Guo et al, JMPS (2012).
Partly (more) from out-of-plane deformation of substrate.
Contributions to edge force from substrate atoms at different position.
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
4.005 nN/nm Soft Hard
Su
bst
rate
De
form
atio
n (
nm
)
Longitudinal position
Contact area
0.801 nN/nm
Functional graded material
Marerial interface
Nanoporous array
*Chang T., Zhang H., Guo Z., Guo X. Chang T., Zhang H., Guo Z., Guo X.
*Gao HuajianGao Huajian
*2014.04.222014.04.22