Paper Highlighting certain applications of Halloysite Clay.

1. Institute for Micromanufacturing
Louisiana Tech University
Clay Nanotubes for Controlled Release
y
of Active Agents
Yuri Lvov and Elshad Abdullayev
Halloysite tubules clay of 50 nm diameter
H ll it t b l l f di t
with 15 nm lumen, and ca 1000 nm length.
Tiny tubular containers to keep loaded chemicals for a long time
and release them in coating defects
29th Biennial Western Coating Symposium,
Las Vegas, NM, October 25-28, 2009

2. Carbon Nanotubes versus Halloysite
Parameter Halloysite CarbonTubes
Diameter / length 50 / 1000 nm 2 / 1000 nm
Inner Lumen Diameter 15 nm 1 nm
Biocompatibility Biocompatible Poisonous
Price / availability ca $6 per kg / tons $200,000 per kg / grams
Patents 8-10 ca 300
Publications
P bli ti 26 and 12 of th
d f them – ours ca 50 000
50,000
Researchers / companies Applied Minerals Inc., hundreds companies
LaTech, China and labs

3. Schematic Representation
15 nm
0.2 -1.0
μm
7Å
Oxygen
7Å OH group
Dragon Mine UT
Mine, Aluminium
Applied Minerals, Inc Silicon
End on View of Kaolinite /
Halloysite
Halloysite occurs i nature as h d t d mineral th t h
H ll it in t hydrated i the formula of Al2Si2O5(OH)4.2H2O
l that has th f l f
which is similar to kaolinite except for the presence of an additional water monolayer
between the adjacent layers. It forms by kaolinite layer rolling due to the action of
hydrothermal processes.

4. Potential Applications of
pp
Halloysite as Nanocontainer
1) Paint with anti-fouling properties where marine biocide was loaded.
Delivery of herbicides, insecticides, fungicides and anti-microbials
2) Release of anticorrosion agents
3) Plastic fillers
4) Specific ion adsorbent, hydrogen storage
) p , y g g
5) Drug sustained release (cosmetics), fertilizers, food additives, fragrance
6) Templating nanoparticle synthesis
7) Use in advanced ceramic materials bio-implants
materials, bio implants
8) Catalytic materials and molecular sieves.

5. Halloysite Mi
H ll it Microscopy images
i

6. Halloysite
0.5
DV [10-3 cm3*Å-1*g-1]
0.4
*
0.3
0.2
0.1
0.0
0 50 100 150 200
Pore diameter [nm]
Pore size distribution of halloysite nanotubes obtained
from N2 adsorption measurements analyzed with BET Zeta potential for silica (blue) , halloysite (middle
model curve) and alumina (red) nanoparticles

7. Halloysite - biocompatible “green” nanoparticles
CLSM images of HNTs
(functionalised by APTES)
intracellular uptake by HeLa cells.
(Up) Hoechst-fluorescence of
nuclei (blue) (left) and FITC-
fluorescence (green) of
(g )
HNTs+APTES (right). (down)
Transmission image of HeLa cells
and (down) FITC Fluorescence
HNTs+APTES and HeLa nuclei
(blue) overlayed images (right).
Applied Minerals Inc Dragon Mine
Inc.,
Making halloysite tube fluorescent with aminopropyl triethoxysilane-FITC
Trypan Blue test of
HNTs in HeLa (and
MCF-7 tissue cells. %
MCF 7 ti ll
Cell Viability vs HNTs
concentration for 24-
48-72 hours. It is
much less toxic than
usual table salt -
NaCl ( which kills
cells at concentration
of 5 µg/ml )

8. Halloysite nanotubes in paint
H ll it t b i i t
Protective chemicals (corrosion inhibitors, antifouling agents) slowly release from the
halloysite t b
h ll it tubes when cracks occurred.
h k d

9. General procedure for preparation of
halloysite-paint composite

10. Halloysite-Paint composite
y p
tensile properties
2.5 3
0% halloysite
1% halloysite
2 2% halloysite 2.5
a)
5% halloysite 0%
Stress (MPa
Stress (MPa)
10% halloysite 2 1%
1.5 30% halloysite
2%
1.5 5%
1
10%
1
0.5
0.5
0
0
0 5 10 15 20 25 30
0 10 20 30 40 50
Strain (%)
Strain (%)
Halloysite is readily mixed with a variety of metal protective coatings, which
is an important advantage of this material. Above pictures describe stress-
strain characteristics of halloysite-paint comopsites with different halloysite
halloysite paint
concentration. Epoxy (left) and Polyurethane (right) paints were used in this
experiment.

11. Paint-halloysite composite
y p
surface properties
100
90 P ol
yurethane
C o n ta ct a n g le
80
P ol
yepoxy
70
60
50
40
0 2 4 6 8 10
H aloysi concentrati (w t% )
l te on
Water contact angles on paint
halloysite nanocomposite surfaces

12. Paint Resistance to rapid
p
deformation
7
A366 Fe alloy
6
2024 Al alloy
Deformation energy (J)
5
e
4
3
D
2
1
0
0 2 4 6 8 10 12
Halloysite concentration (%)

13. Paint dh i
P i t adhesion test
t t

14. Adhesion t t on 2024 Al
Adh i test
Epoxy
Polyuret
hane

15. Controlling Release Rates
• Release rate may be controlled by geometry of
halloysite nanotubes (tubes with smaller internal
diameters provide longer release)
• Rate can also be controlled through:
1) formation of stoppers at tube endings
2) encapsulation of nanotubes by layer-by-layer (LbL)
nanoassembly of polyelectrolytes

16. Benzotriazole release
characteristics
100
90
80
70 BTA release from halloysite
R elease (%)
BTA diffusion into water
60
50
40
30
20
10
0 100
0 10 20 30 40 50 90
Time (hrs) 80
R elease (%) 70
60
50
40
30
20
10
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Time (hrs)

17. Formation of stoppers at tube
pp
endings

18. TEM with elemental analysis
Free
Halloysite
Overlap mapping image Oxygen mapping
Nitrogen mapping
g pp g
(Nitrogen and Oxygen)
(Nit dO )
0.2m 0.2m

19. Halloysite Tubes as Nanocontainers for Anticorrosion Coating
with Benzotriazole
100
Blank
0.04
0 04 mM
80 0.4 mM
R ele as e (% )
2.0 mM
60 4.0 mM
8.0 mM
40 20.0 mM
Tube stopper formation
20
0
0 120 240 360 480
Time (min)
Benzotriazole release with
different stoppers at the tube ends
CCD images (top) and current density maps (bottom) of Al coated with sol gel layer immersed in
sol-gel
0.1 NaCl after 0, 4.5 and 10 h; left- without halloysite, and right -doped with benzotriazole loaded
halloysite nanotubes

20. Anticorrosion coating by using
g y g
halloysite
Two copper strips were painted
with oil based blue paint (ECS-
34 powder, blue, produced by
Tru-Test
Tru Test manufacturing
company) for corrosion
resistance testing. Halloysite
nanotubes loaded with
benzotriazole was mixed with
paint before painting sample
(A). Both of the strips were
artificially scratched and
exposed to highly corrosive
media containing 24 g/l NaCl,
3.8 g/l CaCl2, and 2 g/l Na2SO4
for 10 days.
Images show that coated with only paint is covered with green rust while no evidences of rust is visible for the
sample that is covered with the paint containing halloysite. Corrosive media, that samples were exposed to for 10
p p g y , p p
days, was also analyzed for Cu (II) content. Copper in corrosive media were detected by UV-Vis spectrophotometer,
and 120 ppm of copper ion was observed in the media where sample (B) was exposed while no copper was detected
in the media of sample (A).

21. Corrosion inhibition kinetics
C i i hibiti ki ti
0.7 16
centration (ppm)
B en z o tria o le m ass (  g )
0.6
(
12
0.5
0.4
Fresh water 8
0.3 Usual paint coating
az
Salty water
Cu( II) conc
Paint h ll
P i t - halloysite composite
it it
0.2
4
0.1
0
C
0
0 3 6 9 12 15 18 21
0 5 10 15 20 25 30 35
Time (hrs) Time (days)
Kinetics of BTA deposition on Cu surface Kinetics of corrosion process, studied by
studied by QCM. Process follows 1st tracking f th C (II)
t ki of the Cu(II) concentration in
t ti i
order kinetics with the constants of 0.012 corrosive media
and 0.0033 for fresh and salty waters
respectively

22. Anticorrosion coating by using
g y g
halloysite
Copper strips were painted with
polyurethane paint from top side and
epoxy paint from the back side and
artificially scratched. Strip at (a) painted
with usual paint while strip at (b) had
halloysite loaded with benzotriazole
admixed with epoxy paint. Strips were
exposed to water containing 30 g/l NaCl.
(a) (b)
(a) After 9 days of exposure and
(b) after 35 days of exposure into
corrosive liquid.

23. Encapsulation of nanotubes byy
LbL assembly of polyelectrolytes
50
PEI 7
PEI PEI
40 PAA
6
Layer thicknes s (nm)
30
5
mV)
20 Sample 1
Zeta potential (m
10 Sample 2 4 PEI
Sample 3
0 PAA
Sample 4 3
1 2 3 4 5 6
-10 Sample 5
2
-20 Sample 6 PAA
-30 1 PEI
-40 PAA PAA 0 PEI
PAA
-50 1 2 3 4 5 6 7
Number of layers No of layer
Alteration of surface charge during LbL assembly as well
as deposition of 7 nm SiO2 nanoparticles on halloysite
surface clearly indicates that the assembly was
performed successfully. An average thickness of
PEI/PAA bilayer is 2.2 nm. PEI - poly(ethyleneimine),
PAA - poly(acrylic acid)
100 nm

24. Conclusions
C l i
1. The capability of naturally occurring clay nanotubes as a
nanocontainers for protective agents (e.g., corrosion inhibitors)
p g ( g, )
was demonstrated. Inhibitors may be kept in such
nanocontainers for long time and released in the defect points
within hours. Efficiency of paint coating with benzotriazole
halloysite was demonstrated for copper, aluminum, and iron.
y pp , ,
2. Once loaded with protective agents, halloysite nanotubes can be
modified by formation of stoppers at tube endings to extend
inhibitor release rate.
3.
3 Halloysite nanotubes are readily mixed with variety of polymers
and paints. Physical properties of halloysite / paint composites
were improved.

25. Acknowledgements
A k l d t
 Andre Zeitoun, Applied Minerals,
Inc, NY
 H. Möhwald, D. Shchukin, Max
Planck Inst, Potsdam, Germany
 K. Ariga, National Inst Materials
Science, Tsukuba, Japan
The work was supported by Louisiana Board of Regents ITRS-2009
grants