Transcript Nano-Impact Jonathan P. Rothstein Mechanical and Industrial Engineering University of Massachusetts Amherst, MA, USA.

Nano-Impact
Jonathan P. Rothstein
Mechanical and Industrial Engineering
University of Massachusetts
Amherst, MA, USA
Making a Better Bulletproof Vest
•
A group of researchers at Univ. Del. have impregnated Kevlar vests with a nanoparticle
colloidal suspension resulting in a dramatic improvement in projectile impact.
•
The addition of a very small amount of fluid increased performance equivalent to
doubling the number of Kevlar sheets while not changing flexibility of fabric. Why?
Kevlar
Kevlar & Nanoparticle Suspension
Lee, Wetzel and Wagner J. Material Science (2003)
Nanoparticle Suspensions
Viscosity [pa.s]
•
1000
The nanoparticle (d = 13nm)
suspensions are shear thickening –
the faster you shear or stretch them
more viscous (thick) they become.
The dramatic increase in viscosity
dissipates energy as the Kevlar
fibers are pulled out by the impact of
the bullets.
100
10
1
0.1
1
10
100
1000
-1
Shear Rate [s ]
10000
Extensional Viscosity [pa.s]
•
Increasing
Stretch Rate
1000
100
10
0
1
2
Strain
3
4
5
Why Size Matters
1mm Particles
100nm Particles
10nm Particles
• For large particles the fluid remains Newtonian like air or water below 30wt%
• Above 30% interactions between and collisions of particles result shear thickening and
elastic effects – particles interact to form large aggregate structures
• For nanoparticles, the effect of nanoparticle addition can be observed at concentrations
closer to 1wt% - why?
• Surface area increases with reduced particle size resulting in enhanced interparticle
interactions
• At same volume fraction smaller particles are packed closer together – electrostatic
interactions are stronger and diffusion is faster so they interact more frequently.
Copying Nature – Biomimetic Superhydrophobic Surfaces
•
The leaves of the lotus plant are superhydrophobic – water beads up on the surface of
the plant and moves freely with almost no resistance making the leaves self-cleaning.
Water Drops on a Lotus Leaf
•
The surface of the lotus leaf has 10mm sized bumps which are coated by 1nm sized
waxy crystals which make the surface extremely hydrophobic - repel water.
•
The water does not wet the entire surface of the leaf, but only the tops of the large scale
roughness.
•
Synthetic superhydrophobic surfaces have designed to produce stain-resistant clothing
and coatings for buildings and windows to make them self-cleaning.
Drop Motion on a Superhydrophobic Surfaces
•
Droplets don’t wet, but roll down superhydrophobic surfaces.
• Water-based stains don’t adsorb.
• Dirt is picked up by rolling drop as it moves.
Using Superhydrophobic Surfaces to Reduce Drag
•
We are currently using superhydrophobic surfaces
to develop a passive, inexpensive technique that can
generate drag reduction in both laminar and
turbulent flows.
•
This technology could have a significant impact on
applications from microfluidics and nanofluidics to
submarines and surface ships.
•
How does it work? The water touches only the tops
of the post and a shear-free air-water interfaces is
supported – effectively reducing the surface area.
d
•
Currently capable of reducing drag by over 70% in
both laminar and turbulent flows!
w
Carbon Nanotubes
PDMS
60μm
Why Size Matters
•
To support larger and larger pressures and pressure drops, the spacing of the
roughness on the ultrahydrophobic surfaces must be reduced into the nanoscale.
p  pw  pa 
•
4 cos(  a )
w
Currently developing processing techniques for large area nanofabrication of
ultrahydrophobic surfaces with precise patterns of surface roughness.
Nano Imprint Lithography (NIL)
• Uses enormous pressures to replicate
pattern from master onto polymer film.
Create master
through e-beam or
photo lithography
Capillary Force Lithography (CFL)
• Uses surface tension to draw molten
polymer film into master.
Form replica in polymer
through CFL or NIL
~100nm ~10nm
water
air
polymer
Can These Surfaces Have a Real Impact?
• Current Energy Resources – Fossil Fuels
• Increasing scarcity
• Increasing cost
• Dangerous to maintain security
• Ocean-going vessels accounted for 72% of all U.S.
imports in 2006
• Technology could be employed to make ships more
efficient or faster
• Friction drag accounts for 90% of total drag
experienced by a slow moving vessel
• A 25% reduction in friction drag on a typical
Suezmax Crude Carrier could…
• Save $5,500 USD / day in #6 fuel oil
• Prevent 43 metric tons of CO2 from entering the
atmosphere each day
60μm
The GENMAR GEORGE T
(Japan Universal Shipbuilding, Tsu shipyard)
Nanoparticle Encapsulation
•
Nanoparticle shells can be formed around spherical droplets
•
•
A.D. Dinsmore, et al., Science 298, 1006 (2002), Y. Lin, et al., Science 299, 226 (2003)
Shells are porous at lengthscales much smaller than size of nanoparticle.
A: Scanning electron microscope of a dried
10-μm-diameter colloidosome composed of
0.9- μm-diameter polystyrene spheres.
Nanoparticles At Interfaces
oil-nanoparticle
suspension,
w/ droplets
• Nanoparticles can be functionalized, cross linked or
sintered to make shell permanent, strengthen shell or
change shell permeability.
water droplet:
mm
to
mm
nm
Nano-Encapsulation for Drug Delivery
Drug Concentration in Patient
• By making the holes between nanoparticles approximately the same size as the
drug you want to administer you can get a constant release rate – avoids spikes in
dosage.
Standard Diffusion Based Drug Delivery
Nano-Encapsulated Drug Delivery
Time
• Can also allow encapsulation of hydrophobic drugs which are difficult to get into
you mostly water body.
Stabilization of Encapsolated Colloidosomes
(From Weitz et al.)
Elasticity of Polyelectrolyte Stabilized Shell
Strength of Sintered Shell
Dimpled
Fractured
• Depending on how shell is stabilized, the
properties of colloidosome can vary greatly
• Colloidosomes can be extremely strong, tough,
long-lived and porous.
• This makes them excellent for encapsulation of
flavors, fragrances, cells or pharmaceuticals.
Why Particles Adsorb to Interfaces
[Pickering (1907); Pieranski PRL 45, 569 (1980)]
I. Particle (P) away from interface:
(Oil)
P
Interfacial Area = A
surface tension
Energy = AO/W + 4R2P/O
(Water)
II. Particle sitting astride the interface (half-in, half-out):
Energy = (A-R2)O/W + 2R2P/O + 2R2P/W
• If |P/O – P/W| < O/W/2, then adsorption reduces surface energy.
Cylindrical Droplets and Colloidosomes
• Ultimate goal is to develop a method for self-assembly of rigid cylinders
• Uses include low-weight additives for tough composite materials, encapsulation and
release of drugs, and food additives.
• Jets are created using micro and nanofluidic devices and the interface is populated by
nanoparticles
Jet Encapsulation
• 300nm diameter PMMA particles now added to hexadecane phase
• Particles diffuse very quickly to oil-water interface (tD << 1s) and jam the interface
hexadecane (continuous)
10 mm
Nanoclay Reinforced Nylon – How to Make a Better Fishing Line
Nylon 6 with 3wt% Nanoclay
100000
G'
G''
G'
G''
G ' and G '' [Pa]
10000
Nylon 6
Nylon 6
Nylon 6 / Montmorillonite
Nylon 6 / Montmorillonite
1000
100
10
1
o
Tref = 230 C
0.1
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
Angular Frequency [rad/s]
• Nylon adsorbs strongly to surface of the clay montmorillinite which is a disk with a radius
of 10nm and a thickness of 2nm.
10nm
• Viscous modulus not greatly affected by addition of clay.
2nm
• Elastic modulus increased by orders of magnitude at low frequencies (solid-like response).
Effect of Nanoparticles on Entangled Polymer Melts
•
To relieve stress, entangled polymers can reptate past each other
polymer chain
tube
Brownian
motion
rept
reptates free
of original
tube and
constraints
entanglement point
•
Adsorption of polymers to nanoparticle additives locks polymer together producing
long-range order, reducing mobility and increasing elasticity and viscosity.
nanoparticle
Brownian
motion
polymer adsorption sites
Only free
ends can
reptate free of
original tube
and contraints
Toughness and Stiffness of Nanoclay Reinforced Nylon 6
• Due to enormous surface area available for
adsorption, very small amounts of
nanoparticles are needed to produced very
large effects on material properties of solids.
16
Increased wt% of
nanoclay (0-8wt%)
Toughness (KN/m)
14
• Addition of nanoclay increases
modulus, but reduces toughness
12
10
• Addition of macroscopic particles
or fibers increases toughness, but
reduces modulus
8
Increased Clay Dispersion
6
4
2
0
2.5
3
3.5
4
4.5
Modulus (GPa)
5
5.5
• Currently looking at synergistic
interaction of multiple
lengthscale particles and fibers
Nanotechnology in Tissue Engineering – Cartilage Replacement
www.healthsolutionsgroup.com
•
Over 15 million people worldwide suffer
from knee-joint failure each year due to
cartilage deterioration and 1 million
spinal surgeries are needed every year
•
When cartilage breaks down, the
resulting contact of bones causes pain,
swelling, and loss of movement.
www.allaboutarthritis.com
•
As observed over the past 250 years,
normal (hyaline-type) cartilage is not
known to repair itself.
•
Mechanism not fully understood, but
cartilage cells, chondrocytes, are
sparsely distributed in tissue with poor
vasculature, and actually continue to
deteriorate after a traumatic incident
 osteoarthritis.
Current Treatments
•
Because cartilage doesn’t have vasculature and cannot repair itself, accepted treatments
have been mostly mechanical in their approach.
• Joint lubricants:
• Simple and effective at short-term pain relief but do not address cause of the
problem or repair any damage.
• Debridement/lavage/microfracture:
• Small lesions are repaired by shaving or shaping contour of cartilage.
• Microfracture penetrates subchondral plate (bone) and actually causes growth of
fibrocartilage – a lesser form, not desirable.
• Total joint replacement:
• Addresses problem and generally allows full repair, but
• Very invasive procedure, native tissue removed
• Prostheses do not last a lifetime in active patients.
www.hughston.com/hha/
ACT Methods
•
A popular tissue engineering approach has been to introduce new cells, via
autologous chondrocyte transplantation/implantation (ACT/ACI).
•
Some of the earliest work by Benya and Shaffer (1982) showed it was possible to
isolate and culture chondrocytes.
• More interesting result was that when cultured in vitro, the cells differentiated
and changed their phenotype to produce a lesser quality collagen.
Genzyme ACT method: FDA approved 1997
biomed.brown.edu
Important to tissue engineering:
Cells will differentiate purely based
on mechanical stimulus.
Hydrogels – Self Assembly
•
Hydrogels have applications in drug delivery and tissue engineering
•
Regenerating cartilage and other tissue requires scaffolds with similar modulus and
other mechanical properties → Need to develop stiffer, tunable hydrogels
•
We are currently looking at Polylactide-Polyethylene Oxide-Polylactide triblock
copolymers.
•
Systems are biocompatible with a hydrophobic ends (PLA)
??? and a hydrophilic center
(PEO) which self-assembles in water and can form a gel under the right conditions
1-10
100
1000
10,000 [kPa]
amorphous
hydrogel
crystalline
Hydrogel
Gelation
CMC
Triblock
Copolymer
hyaline
cartilage
Micelle
Gel
Reinforced
Through
Addition of
Nanoparticles
Rheology of Hydrogels
•
100000
Elastic Modulus (Pa)
10000
1000
The hydrogels formed are very stiff
with elastic modulus on the order of
1-10 kPa.
•
100
10
Within range of moduli of several
human tissues including cartilage.
1
72L
58L
72R
60R
0.1
0.01
0.001
0.0001
0.01
0.1
1
10
•
100
•
Frequency (Hz)
R-Lactide
Amorphous Core
L-Lactide
Crystalline Core
Gels formed from polymers with
higher degree of polymerization
maintain a high storage modulus even
at physiological temperatures (370C).
•
In-vivo applications feasible.
Rheological response of these
polymers can be easily tuned by
varying the crystallinity or block
length of PLA or through addition of
nanoparticles.
Khaled et al. Biomaterials (2003)
Effect of Nanoparticle Addition on Rheology of Hydrogel
10000
Elastic modulus (Pa)
1000
100
10
78R
78R
78R
78R
1
78R
25%
25% + laponite 1%
25% + laponite 1.5%
25% + laponite 2.5%
Laponite
Clay
Nanoparticles
0.1
1
10
100
Frequncy (Hz)
•
PEO adsorbs very strongly to laponite
•
Result is an additional, stronger network junction that increases modulus
•
Only a very small amount of laponite (1%) is required to gel the neat polymer
•
Dramatic modulus enhancement is observed shows great promise
•
However, laponite is non-ideal because it is not FDA approved for in-vitro use
•
Currently looking for the ‘right’ nanoparticle
Hydroxyapatite (HAP) Nanoparticles
•
•
•
•
Hydroxyapatite (a type of Calcium phosphate) is a mineral found in bone and enamel
Bioactive material capable of bonding to living tissue
HAP nanowhiskers are 20-80 nm in width but up to 100’s of nm in length, and they
have a high tendency to aggregate
Can HAP serve as a new junction point? Initial results are promising, but still a work in
progress … still iterating on particle size, shape, surface functionality, etc.
Acknowledgements
Support
Students
NSF- National Science Foundation
ONR – Office of Naval Research
UMASS MRSEC
UMASS CHM
3M Non-Tenured Faculty Award
Jia Ou
Erik Miller
Robert Daniello
Michael Martell
Manoj Chellamuthu
Collaborators
Tony Dinsmore
Surita Bhatia
Greg Tew
Tom McCarthy