Weijia Wen
Department of Physics and Institute of Nano Science and Technology
The Hong Kong University of Science and Technology
HONG KONG
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Outline:
Introduction to Electrorheological effect
Display from electrorheological suspension
Paperlike thermochromic display
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Electrodes
E
liquid
Dielectric particles
ER fluid is a kind of colloid
consisting of dielectric
particles suspended in a
nonconducting liquid. It can
change from liquid
state to solid state abruptly.
dipole-dipole interaction model
E
+ ++
+
+ p +
+
+
--
--
-
+ ++
+
+
+
p
+
+
--
--
f∼εE·P/r4=εE2/r4
-
Polarized induced by E-field
Chain formation
Column formation
Electrode
E>>0
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Structural evolution of ER suspension
under an external electric field
E=0
Random distribution
E
E>0
Form chains
E>>0
Form columns
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E
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Display principle
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Nanoparticles used for display
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b
a
100nm
1µm
6
c
d
Volume %
5
4
3
2
1
0
10
100
P a rtic le S iz e (n m )
1000
Illustration of the mechanism for the storage mode display
left and right panels show the cases without and with applied electric
field, respectively
Incident
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Incident
Scattering
Reflection
ITO Electrodes
Dielectric nanoparticles
Transmission
Top-views of field-induced patterns formed by nanoparticles
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Top electrode
bottom
electrode
a
E=0
Field area
E>>0
b
pixel
c
d
Pattern formation with different electrode configurations
+
electrode
+
+
-
nanoparticles
-
-
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Electric field is applied across the top and bottom electrodes
Electric field formed by the planar electrodes
Optical transmission characteristics of nanoparticle-based
suspension at different field strengths
50
300 µm
45
60µm
Transmittance (%)
40
ITO
35
E7
30
300µm
E8
E6
E5
E4
10 µm
25
E3
20
E2
15
10
E1
5
0
400
E0
500
600
Wavelength(nm)
700
800
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Images viewed through the display panel
Viewed through
the display panel
a
Display panel
Without electric field
b
Original color panel
With electric field
c
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Display panels formed with different backgrounds
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a
c
b
d
luminous powder to the suspension
The drawback of nanoparticle-based ER display presented above is the classic
tendency of particles to agglomerate together irreversibly, the flocculation effect.
Diagram of the synthesis of
silica core-gold shell particles
reduction
Hydrolysis
Condensation
Surface
functionalization
Reduction
Shell growth
Shell growth
Results: particle shapes by TEM
Dyed
particles
Gold
shell
Dispersion in oil
2As
2C
Polydimethylsioxane (PDMS)-based conducting composite
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(a)
Nano or micro-conducting
particles
10µm
PDMS + conducting particles
(b)
1µm
SEM pictures of the cured conductive composite and powders:
(a) Ag+PDMS (84wt%); (b) C+PDMS 28wt%
Electrode fabricated with PDMS/Carbon conducting composite
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(b)
(a)
AZ 4620
Substrate
C+PDMS
(c)
PDMS
(d)
Hot plate
Process flow chart illustrating the patterning of conductive PDMS by soft lithography. (a) Micro-patterning of
the conductive PDMS, (b) –(d) SEM pictures showing the various fabricated conductive patterns.
Electrode fabricated with PDMS/Silver conducting composite
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100μm
(d)
(f)
silver powder
(e)
Silver +PDMS
Micro-heater from PDMS conducting composite
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Schematic illustration of the micro-heater. The three-dimensional helicalpatterned structure is made from silver micro-particles-PDMS composite.
Inset: a SEM picture of the micro-heater whose line width is 25
Temperature of the micro-heater’s central heating part plotted
as a function of the input voltage.
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o
Temperature (C )
300
250
200
150
100
50
0
0.5 mm
0.0
0.5
1.0
1.5
2.0
2.5
Voltage (V)
The two insets are IR pictures showing the thermal distributions at specific applied
voltages. The bright spot on the right panel is a high temperature region with a
temperature of ~250 0C
Response time
Time dependent temperature variations of the micro-heater
square pulse
240
V=2.5v
o
Temperature (C )
270
210
180
V=2.0v
150
V=1.5v
120
90
V=1.0v
60
V=0.5v
30
0
20
40
60
80 100 120 140 160
Time (s)
The right inset tabulates the temperature rise and decay times, defined at
points where the temperature is 80% of the stabilized value.
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Integration of multiple micro-heaters to form a thermal display
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(a)
(b)
display
cell
electrode
(b) shows the infrared images of the digits are displayed, demonstrating the
ease and flexibility of operations.
Fabrication of thermochromic composite
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thermochromic nanopowder
+
PDMS
cured thermochromic
thin film
liquid-like composite
reeled film
Fabrication processing for paperlike thermochromic display
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Thermochromic composite
PDMS + Ag
composite
AZ4620
substrate
Hot plate
Structure of thermochromic thin film display
22mm
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groove
thermochromic
composite
V
top view
silver-PDMS
composite
I
bottom view
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Display panel with flexible character
Image appears when power turns on
The display is wrapped on a column
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(b)
(a)
curved film
voltage off
voltage on
(a) shows the display film when no input signal is applied,
(b) shows the logo image to be correctly displayed when
a voltage heating pulse train is applied
Display degree plotted as a function of applied voltage
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display degree (%)
(b)
120
100
(c)
6V
8V
10V
12V
14V
voltage off
80
60
(a)
40
20
0
2
4
6
8
10
12
14
16
18
20
time (s)
The five curves on the left correspond to a step function voltage of various height,
while the one on the right corresponds to what happens after the voltage is turned
off. The insets show the logo images at various display degrees. The image in inset
C is blurred due to overheating
Power consumption of the display under
different t/T ratios of the heating pulse train.
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0.19
power (w)
0.18
0.17
0.16
0.15
0.14
0.13
0.12
0.0
0.1
0.2
0.3
t/T
0.4
0.5
The duty cycle is fixed at 50Hz. The table gives the best voltage values (for
achieving an accurate image) associated with the various values of t/T ratio.
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