Upload
amzeit
View
858
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Paper Highlighting certain applications of Halloysite Clay.
Citation preview
Institute for MicromanufacturingLouisiana Tech University
Clay Nanotubes for Controlled Release yof Active Agents
Yuri Lvov and Elshad Abdullayev
H ll it t b l l f 50 di tHalloysite tubules clay of 50 nm diameter 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
Carbon Nanotubes versus Halloysite
Parameter Halloysite CarbonTubesDiameter / length 50 / 1000 nm 2 / 1000 nmDiameter / length 50 / 1000 nm 2 / 1000 nmInner Lumen Diameter 15 nm 1 nmBiocompatibility Biocompatible PoisonousPrice / availability ca $6 per kg / tons $200,000 per kg / gramsPatents 8-10 ca 300 P bli ti 26 d 12 f th 50 000Publications 26 and 12 of them – ours ca 50,000Researchers / companies Applied Minerals Inc., hundreds companies
LaTech, China and labs
Schematic RepresentationSchematic Representation
15 nm
7 Å
0.2 -1.0 μm
7 ÅOxygenOH groupAluminiumDragon Mine UT
End on View of Kaolinite / Halloysite
Silicon
H ll it i t h d t d i l th t h th f l f Al Si O (OH) 2H O
Dragon Mine, UTApplied Minerals, Inc
Halloysite occurs in nature as hydrated mineral that has the formula of Al2Si2O5(OH)4.2H2Owhich is similar to kaolinite except for the presence of an additional water monolayerbetween the adjacent layers. It forms by kaolinite layer rolling due to the action ofhydrothermal processes.
Potential Applications of ppHalloysite 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 agents3) Plastic fillers 4) Specific ion adsorbent, hydrogen storage) p , y g g5) Drug sustained release (cosmetics), fertilizers, food additives, fragrance6) Templating nanoparticle synthesis 7) Use in advanced ceramic materials bio implants7) Use in advanced ceramic materials, bio-implants8) Catalytic materials and molecular sieves.
H ll it Mi iHalloysite Microscopy images
Halloysite
0.4
0.5
*g-1]
0.2
0.3
[10-3
cm
3 *Å-1*
0 50 100 150 2000.0
0.1DV
Pore diameter [nm]
Pore size distribution of halloysite nanotubes obtained from N2 adsorption measurements analyzed with BET model
Zeta potential for silica (blue) , halloysite (middle curve) and alumina (red) nanoparticles
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
Making halloysite tube fluorescent with aminopropyl triethoxysilane-FITC
Trypan Blue test of HNTs in HeLa (and MCF 7 ti ll %
Applied Minerals Inc., Dragon Mine
MCF-7 tissue cells. % Cell Viability vs HNTs concentration for 24-48-72 hours. It is much less toxic than usual table salt -usual table salt NaCl ( which kills cells at concentration of 5 µg/ml )
H ll it t b i i tHalloysite nanotubes in paint
Protective chemicals (corrosion inhibitors, antifouling agents) slowly release from the h ll it t b h k dhalloysite tubes when cracks occurred.
General procedure for preparation ofGeneral procedure for preparation of halloysite-paint composite
Halloysite-Paint composite y ptensile properties
2
2.5
a)
0% halloysite1% halloysite2% halloysite5% halloysite
2.5
3
0%
0.5
1
1.5
Stre
ss (M
Pa
5% halloysite10% halloysite30% halloysite
1
1.5
2
Stre
ss (M
Pa) 0%
1%2%5%10%
0
0.5
0 5 10 15 20 25 30
Strain (%)
0
0.5
0 10 20 30 40 50
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
Strain (%)
strain characteristics of halloysite paint comopsites with different halloysite concentration. Epoxy (left) and Polyurethane (right) paints were used in this experiment.
Paint-halloysite composite y psurface properties
90
100le
P olyurethaneP olyepoxy
60
70
80
tact a
ng P olyepoxy
40
50
60
Con
0 2 4 6 8 10
H alloysite concentration (w t% )
Water contact angles on paint halloysite nanocomposite surfaces
Paint Resistance to rapid pdeformation
6
7
A366 Fe alloy
5
6
ener
gy (J
)
2024 Al alloy
3
4D
efor
mat
ion
e
1
2D
00 2 4 6 8 10 12Halloysite concentration (%)
P i t dh i t tPaint adhesion test
Adh i t t 2024 AlAdhesion test on 2024 Al
Epoxy
Polyurethane
Controlling Release Rates
• Release rate may be controlled by geometry ofRelease rate may be controlled by geometry of halloysite nanotubes (tubes with smaller internal diameters provide longer release)
Rate can also be controlled through:• Rate can also be controlled through:
1) formation of stoppers at tube endings
2) encapsulation of nanotubes by layer-by-layer (LbL)2) encapsulation of nanotubes by layer-by-layer (LbL) nanoassembly of polyelectrolytes
Benzotriazole release characteristics
80
90
100
BTA release from halloysite
30
40
50
60
70
Rel
ease
(%)
BTA release from halloysiteBTA diffusion into water
0
10
20
0 10 20 30 40 50
Time (hrs) 8090
100
203040506070
Rel
ease
(%)
01020
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Time (hrs)
Formation of stoppers at tube ppendings
TEM with elemental analysisFree
Halloysite
TEM with elemental analysis
Nitrogen mappingOverlap mapping image(Nit d O )
Oxygen mappingg pp g (Nitrogen and Oxygen)
0.2m 0.2m
Halloysite Tubes as Nanocontainers for Anticorrosion Coating Halloysite Tubes as Nanocontainers for Anticorrosion Coating with Benzotriazole
100Blank
0 04 mM
40
60
80
Rel
ease
(%)
0.04 mM
0.4 mM
2.0 mM
4.0 mM
8.0 mM
20.0 mM
Tube stopper formation
0
20
0 120 240 360 480
Time (min)
Tube stopper formation
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 inCCD images (top) and current density maps (bottom) of Al coated with sol-gel layer immersed in 0.1 NaCl after 0, 4.5 and 10 h; left- without halloysite, and right -doped with benzotriazole loaded halloysite nanotubes
Anticorrosion coating by using g y ghalloysite
Two copper strips were painted with oil based blue paint (ECS-34 powder, blue, produced by Tru Test manufacturingTru-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,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 pdays, 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).
C i i hibiti ki tiCorrosion inhibition kinetics
0.6
0.7
(
g)
12
16
(ppm
)
0.3
0.4
0.5
azol
e m
ass
Fresh waterSalty water
8
12
cent
ratio
n (
Usual paint coatingP i t h ll it it
0
0.1
0.2
Ben
zotr
ia Salty water
0
4C
u( II
) con
c Paint - halloysite composite
0 3 6 9 12 15 18 21
Time (hrs)
00 5 10 15 20 25 30 35Time (days)
C
Kinetics of BTA deposition on Cu surface Kinetics of corrosion process, studied by t ki f th C (II) t ti istudied by QCM. Process follows 1st
order kinetics with the constants of 0.012 and 0.0033 for fresh and salty waters respectively
tracking of the Cu(II) concentration in corrosive media
Anticorrosion coating by using g y ghalloysite
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
(a) (b)admixed with epoxy paint. Strips were exposed to water containing 30 g/l NaCl.
(a) After 9 days of exposure and(a) After 9 days of exposure and (b) after 35 days of exposure into corrosive liquid.
Encapsulation of nanotubes by yLbL assembly of polyelectrolytes
PEI PEIPEI
20
30
40
50
mV) Sample 1
PAA
5
6
7
s (n
m)
PAAPAA PAA-40
-30
-20
-10
0
10
1 2 3 4 5 6
Zeta
pot
entia
l (m
Sample 2Sample 3Sample 4Sample 5Sample 6
PEI
PAA
PEI
PAAPEI
0
1
2
3
4
Laye
r th
ickn
es
PAA-50
Number of layers
PEI01 2 3 4 5 6 7
No of layer
Alteration of surface charge during LbL assembly as wellas deposition of 7 nm SiO2 nanoparticles on halloysitesurface clearly indicates that the assembly wasperformed successfully. An average thickness ofPEI/PAA bilayer is 2.2 nm. PEI - poly(ethyleneimine),PAA - poly(acrylic acid)100 nm100 nm
C l iConclusions
1. The capability of naturally occurring clay nanotubes as ananocontainers for protective agents (e.g., corrosion inhibitors)p g ( g , )was demonstrated. Inhibitors may be kept in suchnanocontainers for long time and released in the defect pointswithin hours. Efficiency of paint coating with benzotriazolehalloysite was demonstrated for copper, aluminum, and iron.y pp , ,
2. Once loaded with protective agents, halloysite nanotubes can bemodified by formation of stoppers at tube endings to extendinhibitor release rate.
3 Halloysite nanotubes are readily mixed with variety of polymers3. Halloysite nanotubes are readily mixed with variety of polymersand paints. Physical properties of halloysite / paint compositeswere improved.
A k l d tAcknowledgements
Andre Zeitoun, Applied Minerals, Inc, NY
H. Möhwald, D. Shchukin, Max Planck Inst, Potsdam, Germany
K. Ariga, National Inst Materials K. Ariga, National Inst Materials Science, Tsukuba, Japan
The work was supported by Louisiana Board of Regents ITRS-2009 grants