Self-healing Materials

Self-healing materials are smart materials that can intrinsically repair damage leading to longer lifetimes, reduction of inefficiency caused by degradation and material failure.
Applications include shock absorbing materials, paints and anti-corrosion coatings and more recently, conductive self-healing materials for circuits and electronics.

1. SELF-HEALING SELF-HEALING
MATERIALSMATERIALS
Cristina Resetco
Polymer and Materials Science

2. Motivation: Self-healing materials are smart materials that can
intrinsically repair damage leading to longer lifetimes, reduction of
inefficiency caused by degradation and material failure.
Applications: shock absorbing materials, paints and anti-corrosion
coatings.
Outline
(1)Restoration of Conductivity with TTF-TCNQ Charge-Transfer Salts
(2) Self-Healing Materials with Interpenetrating Microvascular
Networks
(3) Coaxial Electrospinning of Self-Healing Coatings
(4) Nanoscale Shape-Memory Alloys for Ultrahigh Mechanical Damping
Self-Healing MaterialsSelf-Healing Materials

3. Self-Healing MaterialsSelf-Healing Materials

4. Self-Healing MaterialsSelf-Healing Materials
a) damage is inflicted on the material
b) a crack occurs
c) generation of a “mobile phase” triggered either by the
occurrence of damage (in the ideal case) or by external
stimuli.
d) damage is removed by directed mass transport towards the
damage site and local mending reaction through
(re)connection of crack planes by physical interactions
and/or chemical bonds
e) after the healing of the damage the previously mobile
material is immobilised again, resulting in restored
mechanical properties
http://www.autonomicmaterials.com/technology/

5. Material DesignMaterial Design
Self-Healing MethodsSelf-Healing Methods

6. Restoration of Conductivity withRestoration of Conductivity with
TTF-TCNQTTF-TCNQ Charge-Transfer SaltsCharge-Transfer Salts
A new microcapsule
system restores
conductivity in
mechanically damaged
electronic devices in
which the repairing agent
is not conductive until its
release.
Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

7. Conductive healing agent is generated upon mechanical damage. Two core
solutions travel by capillary action to the relevant damage site before
forming the conductive salt.
The major advantage of this approach is greater mobility of precursor
solutions compared to suspensions of conductive particles.
Restoration of Conductivity withRestoration of Conductivity with TTF-TCNQTTF-TCNQ Charge-Transfer Charge-Transfer
SaltsSalts
Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.
Tetrathiafulvalene Tetracyanoquinodimethane
tetrathiafulvalene–tetracyanoquinodimethane
Non-conductingNon-conductingConducting

8. Figure 1. Optical microscope images from A) an attempt to
encapsulate crystalline TTF-TCNQ salt in PA, B) MCs containing
powdered TTF-TCNQ salt suspended in PA; inset: ruptured MCs
containing powdered TTFTCNQ salt in PA, C) TTF-PA MCs, and
D) TCNQ-PA MCs. All scale bars are 200mm.
TTF and TCNQ were individually
incorporated into microcapsule cores
as saturated solutions in chlorobenzene
(PhCl), ethyl phenylacetate (EPA), and
phenyl acetate (PA).
Poly(urea-formaldehyde) (PUF)
core–shell microcapsules were
prepared using an in situ
emulsification polymerization in an
oil-in-water suspension.
Microcapsule Synthesis Microcapsule Synthesis
Electron impact mass spectra of the
dried microcapsule core solutions
confirmed the presence of TTF and
TCNQ in the microcapsules.
Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

9. Microencapsulation of DCPD utilizing acid-catalyzed in
situ polymerization of urea with formaldehyde to form
capsule wall.
Microencapsulation by in-situ PolymerizationMicroencapsulation by in-situ Polymerization
Brown, E. et al.; J. Microencapsulation, 2003, vol. 20, no. 6, 719–730

10. When mixtures of TTF and TCNQ microcapsules
were ruptured, a dark-brown color was immediately
observed, indicative of the TTF-TCNQ charge-
transfer salt formation.
IR spectroscopy was used to verify charge-transfer
salt formation.
Figure. Microcapsules crushed between two glass slides: A) 50mg
PAMCs; B) 50mg TTF-PA MCs; C) 50mg TCNQ-PA MCs; D) 50mg each
TTFPA and TCNQ-PA MCs.
Damage and Formation of Charge-Transfer Salt Damage and Formation of Charge-Transfer Salt
Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

11. Figure 7. I–V measurements of analytes on glass slides
measured between two tungsten probe tips spaced
approximately 100mm apart for neat ruptured TTF-PA, TCNQ-
PA, and TTF-PA:TCNQPA in a 1:1 ratio (wt%) microcapsules.
Restoration of Conductivity by TRestoration of Conductivity by TTF-TCNQTF-TCNQ
Charge-Transfer SaltCharge-Transfer Salt
Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

12. Optimization of Precursor ConcentrationOptimization of Precursor Concentration
Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

13. Self-Healing Materials with Interpenetrating Microvascular Self-Healing Materials with Interpenetrating Microvascular
NetworksNetworks
Healing strategy mimics
human skin, in which a minor
cut triggers blood flow from
the capillary network in the
underlying dermal layer to
the wound site.
Key advances in direct-write assembly:
Two fugitive organic inks possess similar
viscoelastic behavior, but different temperature-
dependent phase change responses.
Hansen, C. et al. Adv. Mater. 2009, 21, 1–5.

14. Direct-Write Assembly with Dual Fugitive InksDirect-Write Assembly with Dual Fugitive Inks
(a) Epoxy substrate is leveled for writing
(b) Wax ink (blue) is deposited to form one network
(c) Pluronic ink (red) is deposited to separate networks
(d) Wax ink is deposited to form 2nd microvascular network
(e) Wax ink vertical features are printed connecting to both
networks
(f) Void space is filled with low viscosity epoxy
(g) After matrix curing, pluronic ink is removed
(h) Void space from previous pluronic network is re-infiltrated with
epoxy
(i)Wax ink from both microvascular networks is removed
(j) Networks are filled with resin (blue) in one network and
hardener (red) in the second network
Hansen, C. et al. Adv. Mater. 2009, 21, 1–5.

15. Once a crack contacts the microvascular network, epoxy resin and
hardener wick into the crack plane due to capillary forces.
Repeated Repair CyclesRepeated Repair Cycles
Healing Efficiency
Hansen, C. et al. Adv. Mater. 2009, 21, 1–5.

16. Coaxial Electrospinning of Self-Healing CoatingsCoaxial Electrospinning of Self-Healing Coatings
Healing agent encapsulated in a bead-on-string structure
and electrospun onto a substrate.
AdvantagesAdvantages
Park, J. et al. Adv. Mater.
2010, 22, 496–499

17. One-Step Coaxial Electrospinning EncapsulationOne-Step Coaxial Electrospinning Encapsulation
Spinneret contains two
coaxial capillaries
Two viscous liquids are fed
through inner and outer
capillaries simultaneously
Electro-hydro-dynamic
forces stretch the fluid
interface to form coaxial
fibers due to electrostatic
repulsion of surface charges
Park, J. et al. Adv. Mater. 2010, 22, 496–499

18. Figure. SEM images of a) the core–shell bead-on-string morphology and b) healing agent released from the
capsules when ruptured by mechanical scribing. c) Fluorescent optical microscopic image of sequentially spun
Rhodamine B (red) doped part A polysiloxane precursor capsules and Coumarin 6 (green) doped part B capsules.
d) TEM image of as-spun bean-on-fiber core/sheath structure.
Core–Shell Bead-on-String StructuresCore–Shell Bead-on-String Structures
Park, J. et al. Adv. Mater.
2010, 22, 496–499

19. Self-healing by
polycondensation of
hydroxyl-terminated
PDMS and PDES
crosslinker catalyzed
by organotin.
Self-Healing after Microcapsule RuptureSelf-Healing after Microcapsule Rupture
Park, J. et al. Adv. Mater. 2010, 22, 496–499

20. Figure. SEM images of scribed region of the self-healing sample after healing a) 458
crosssection and b) top view of the scribed region on a steel substrate.
Self-Healing by PolymerizationSelf-Healing by Polymerization
Figure 2. Control and self-healing coating samples that were stored under ambient
conditions for 2 months after 5 days salt water immersion.
Park, J. et al. Adv. Mater.
2010, 22, 496–499.c

21. Nanoscale Shape-Memory Alloys for Nanoscale Shape-Memory Alloys for
Ultrahigh Mechanical DampingUltrahigh Mechanical Damping
Nanoscale Pillars of shape-memory alloys exhibit
mechanical damping greater than any bulk material.
San Juan, J. et al. Nature Nanotech., Vol. 4, 2009.

22. Dissipation of mechanical energy by reversible
transformation between Austenite and Martensite
due to stress.
San Juan, J. et al. Nature Nanotech., Vol. 4, 2009.

23. Size Effect of Cu-Al-Ni NanopillarsSize Effect of Cu-Al-Ni Nanopillars
(2) Stabilization of martensite by
small pillars that relieve elastic energy
at the surface by crossing the entire
specimen
(1) Stabilization of austenite by
elimination of martensite nucleation
sites
Cu-Al-Ni pillars were produced
by focused ion beam (FIB)
micromachining of surface
sections of Cu-Al-Ni crystals.
San Juan, J. et al. Nature Nanotech., Vol. 4, 2009.
Figure. SEM image of Cu–Al–Ni pillar, mean
diameter of 900 nm.

24. Comparison of High Damping MaterialsComparison of High Damping Materials
Merit index = E
1/2
ΔW/πWmax
W – dissipated energy per stress-release cycle
ΔW- maximum stored energy per unit volume
E – Young’s modulus San Juan, J. et al. Nature Nanotech., Vol. 4, 2009.

25. What is Next ?What is Next ?
Go Nano !