self-healing materials

SELF-HEALING SELF-HEALING MATERIALSMATERIALS

Cristina ResetcoPolymer and Materials Science

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

Self-Healing MaterialsSelf-Healing Materials

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/

Material DesignMaterial Design

Self-Healing MethodsSelf-Healing Methods

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.

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-Charge-Transfer SaltsTransfer Salts

Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

Tetrathiafulvalene Tetracyanoquinodimethane

tetrathiafulvalene–tetracyanoquinodimethane

Non-conducting Non-conducting Conducting

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.

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

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.

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.

Optimization of Precursor ConcentrationOptimization of Precursor Concentration

Moore, J. et al. Adv. Funct. Mater. 2010, 20, 1721–1727.

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.

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.

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.

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

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

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

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

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

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.

Dissipation of mechanical energy by reversible transformation between Austenite and Martensite due to stress.

San Juan, J. et al. Nature Nanotech., Vol. 4, 2009.

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.

Comparison of High Damping MaterialsComparison of High Damping Materials

Merit index = E1/2 ΔW/πWmax

W – dissipated energy per stress-release cycleΔW- maximum stored energy per unit volumeE – Young’s modulus San Juan, J. et al. Nature Nanotech., Vol. 4, 2009.

What is Next ?What is Next ?

Go Nano !