Transcript ELECTROACTIVE MATERIALS

PART 2
ELECTRORHEOLOGICAL
SUSPENSIONS
ELECTRORHEOLOGICAL
SUSPENSIONS
 SUMMARY
– Review of electrorheological suspensions
(ERS)
– Classification of ERS
– Mechanisms of the ER effect proposed
by several researchers
– potential applications
– modelling
ELECTROACTIVE MATERIALS
 An
electro-active material is a
suspension where a semiconductive
material (particulate or liquid) is
dispersed in a dielectric liquid
medium.
 The rheological properties change in
reversible form by several orders of
magnitude under external electric
fields.
ELECTROACTIVE MATERIALS
 Since
the rheological properties can
be easily controlled within a wide
range, many scientific and
technological applications may be
developed.
T. Hao , Adv. Colloid Interface Sci. 1-35, 97 (2002)
H. Block, J.P. Kelley, J. Phys. D, 1661, 21(1988)
A. P. Gast, C. F.Zukoski,Adv. Colloid Interface Sci.153,30(1989)
T.C. Halsey Science 761,23(1992)
POTENTIAL APLICATIONS
 Clutch,
brake and damping systems,
actuators, fuel injections systems
 Joints and hands of robotic arms
 photonic crystals.
 Microswitches.
 Mechanical-electronic interfaces
C. F.Zukoski, Annu.Rev.Matter.Sci.23(1993)45
T.C. Halsey Science 23(1992) 761
Schematic illustration of structure
change of ERS
E
Before an external
electric field is applied
Structure of an
electrorheological
material after an electric
field is applied
ERF Phenomena
E
With Electric field (E)
DC ó AC
Without Electric Field
+
Increase in Viscosity
Continue experimental
4. Estructural arrangement observations
Classification of Electrorheological Materials
ERF
Dispersed
Phase
Liquid Phase
Additive
Water
Anhydrous
Liquid
Solid
Homogeneous
Fluid
Heterogeneous
Fluid
Liquid
Crystalline
Emulsion
a
Microemulsion
Inorganic
Oxide
Non-Oxide
Organic
Polymeric
Experimental Characteristics
of an Electrorheological fluid
Liquid Phase
Particle
Relative dielectric
2
constant
-10
-16
Conductivity (S/m) 10 to10
Viscosity at
0.01 to 10
no electric field Pa.s
2
to10000
-7
10
ER
Suspension
-9
10 to10
0.1 to 10
-16
CRITICAL PARAMETERS
 Electric
Field Strength, E
– two effects in competition for explain the
changes in the yield stress, y, after
applying the electric field
 Frequency
of Electric Field, 
– DC is mostly used to generate detectable
ER effect
– AC is used to study the ER mechanisms
– ER effect is function of  through  and 
 Particle
Conductivity, 
CRITICAL PARAMETERS
 Particle
Dielectric Property,
– the polarization depends on .
– the electric double layer overlap is the
reason
– the dielectric constant changes with
electrolytes
 Particle
Volume Fraction, 
– y and  depend on , and exhibit a
maximum
– Percolation theory was used to
CRITICAL PARAMETERS
 Temperature
– Changes the polarizability of ERF
because changes  and .
– Impact particle thermal motion
 Liquid
medium
– sedimentation, viscosity, conductivity
and permitivity of liquid causes
pronounced differences for the ER
effect.
 Water
content
FORCES RELEVANT TO THE
ER EFFECT
 After
ER fluid is submitted to an
electric field the particles should be
polarized and appears a electrostatic
force. However hydrodynamic,
Brownian, van der Waals, DLVO and
other forces act too.
 Dimensionless groups that describe
the relative importance of those
forces. Eg.
– Mason, Mn = 6/(0smE2)
PHASE TRANSITION
 As
increase the ERS changes from a
disordered state to coexistence with a
crystalline phase
 Laser diffraction method and confocal
scanning laser microscopy were
employed to determine the crystal
structure within fibrilated columns
POLARZATION PROCESS
 Four
kinds of polarization exist
– electronic
– atomic
– Debye
– Interfacial
 The
dielectric constant is  = E + A +
D + I
Results
Rheological properties
Viscosity vs shear rate
4
10
Relative viscosity
SF-14 20 wt %
10
3
10
2
10
1
10
0
10
10
3
10
2
10
1
10
0
-1
10
-2
10
-1
10
0
10
1
-1
a
Shear rate (s )
10
2
4
SF-14 (A-1100) 20 wt %
E = kV/mm
0.25
0.50
0.75
1.0
1.5
2.0
2.5
Relative viscosity
10
10
3
10
E = kV/mm
0.25KV
0.5 KV
0.75KV
1.0 KV
1.5 KV
2.0 KV
2.5 KV
-1
10
-2
10
-1
10
0
10
1
10
2
-1
Shear rate (s )
b
10
3
Continue results
Shear stress vs shear rate
10
4
10
4
SF-14 (A-1100) 20 wt %
10
3
10
2
10
1
10
0
10
3
10
2
1
10
0
10
-1
10
-1
10
E = kV/mm
0.0 V
0.25
0.5
0.75
1.0
1.5
2.0
2.5
10
E = kV/mm
0.O KV
0.25KV
0.5 KV
0.75KV
1.0 KV
1.5 KV
2.0 KV
2.5 KV
 (Pa)
 (Pa)
SF-14 20 wt %
-2
10
-1
10
0
10
1
-1
Shear rate (s )
a
10
2
10
3
-2
10
-1
10
0
10
1
10
2
10
3
10
-1
Shear rate (s )
b
Model of ER suspensions
 = y + plastic
Bingham model
plastic = 0 [1-
Krieger-Dougherty
.
 = y + 0  [1- /m]
J. W. Goodwin et.al. J Phys. Chem. B, 1997, 101, 1961-1967
L. Rejon. PhD Thesis, 1998, UNAM.
.

– []
m
/m]
– []
m
BKD Model
4
10
SF-14 (A1100) 20 wt %
3
 (Pa)
10
2.5 Kv/mm
2
10
Experimental
Model
0.5 Kv/mm
1
10
-1
10
0
1
2
10
10
10
-1
Shear rate (s )
3
10
Kinetic chain model. [ Martin, J.E.;
Odinek, J. J. Rheol. 1995, 39, 995].
 The
kinetics of aggregation and
fragmentation follows a
phenomenological expression

dN (t )
k 
N (t ) 2 

1 

dt
N (t )  N (t ) 2 max 
maximum stable size of the chains
N(t)max,
 The
aggregation process is induced
by the dipolar forces and hence the
kinetic constant k is given by

k M  k 0 M (8 0 f  2 E0 /  0 )
2
 This
model predicts a viscosity
proportional to the electric field
squared and to inverse shear rate
according to

 1
3 6
2
2

 0  f   E0 
10
is the volume fraction of particles
A rheological kinetic model for
electrorheological suspensions

  ´ ( , D)  2G0 ´ ( , D) D
 ´( , D)  A 1 0
dA
1
' 
' 
 (1  A)  k0 ( 0  A)WF  k1 ( 0  A)WE
dt


E
WF
  :D
WE  E  P

    p  (1   )  f
 0 
2
E
2
k0 
'
k0
1  k 2  0  2 E 2
k1  k1 
'
k ( /   A) : D
dA
(1  A)

 0 0
 k1 (0 /  E  A) 0 
dt

1  k 2  0  2  E 2
2
 E2



For weak electric fields and low shear rates, the
viscosity grows slowly as a function of time with
rate proportional to E*E. Under strong electric
fields, the viscosity growth with time is
exponential, and at long times the viscosity
approaches the limit
  0 (E / 0 )   E
At short times and in the case where , the model
gives the proportionality of the characteristic time
for structure formation with the viscosity and
t  / E
electric field, i.e.,.
2
c
Strong flow limit

 
0
1  2b t
Initially, the reference viscosity is the zero
shear-rate viscosity. Asymptotic analysis
of the model shows that at long times, for
weak electric fields, the viscosity
decreases with a rate proportional to
 1/( t )
 whereas under strong electric fields, the
E
viscosity is proportional to





t
In the latter case, the ratio of the electric
field to the shear rate controls the
viscosity decrease with time.
Weak flow
 E (1  k1 0 2  E 2 )

E
 k1 0   2 E 2
0
 y  G0
 y 0  G0
(1  k1 0  2 E 2 )(1  k 2  0 2 E 2 )
 / 


 y   y 0 k1k 2   0 2  E 2
Conductivity contributions to the
electrorheological effect.
k0
k 
1  k 2 (1  k 3 E )  0 2 E 2
'
0
k1'  k1 (1  k3 E)
   p  (1   ) f
10000
r
A
1000
S100=0.08
E (kV/mm)
0.5
1.0
1.5
100
0
200
400
600
time (s)
800
1000
1200
Influence of electric field
strength on ER response
 Red
100000
(E)
10000
1000
100
10
0.0
0.5
1.0
E (kV/mm)
1.5
2.0
=0.03
 Black
=0.16 
Silicon 100
 DOP
 TCP
 There are
two effects
in
Influence of fraction of particles
on ER response
 Black
(E)
100000
10000
1000
100
10
0.0
0.1

E=0.5
 Red
E=1.0
 Green
E=1.5
 Blue
E=2.0
 Silicon
100  DOP
 TCP
Comparison between
experimental data and model
predictions
E = kV/mm
0.5
1.5
2.0
3
10
L
2
10
S100,  = 0.03
6
p/L = 1 x 10
1
10
0
10
-6
-5
-4
-3
10 1x10 1x10 10
-2
10
-1
10
Mn
0
10
1
10
2
10
3
10
Comparison between
experimental data and model
predictions
10
2
 = 0.03
Yield stress (Pa)
2
S100, R = 0.99
2
DOP, R = 0.96
2
TCP, R = 0.97
1
10
0
10
-2
10
-1
2
E
10
Comparison between
experimental data and model
predictions
10
2
 = 0.03
Yield stress (Pa)
2
S100, R = 0.99
2
DOP, R = 0.96
2
TCP, R = 0.97
1
10
0
10
-2
10
-1
2
E
10