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