Self-Healing polymer coating

NGUYEN Thi Thanh Tam

Professor Paul V Braun:

•BS degree with distinction at Cornell University•BS degree, with distinction, at Cornell University•PhD in Materials Science and Engineering from UIUC in 1998 •One year postdoctoral appointment at Bell Labs, Lucent Technologies,•Assistant professor of Materials Science and Engineering at UIUC in 1999•Part-time faculty member of the Beckman Institute.•Named a University Scholar by the University of Illinois (2006) •Named a University Scholar by the University of Illinois (2006). from UIUC

Many Awards:k d (200 )•Beckman Young Investigator Award (2001)

•3M Nontenured Faculty Award (2001); •The Robert Lansing Hardy Award from TMS (2002)•Willett Faculty Scholar Award (2002) Willett Faculty Scholar Award (2002) •The Xerox Award for Faculty Research (2004),•The Burnett Teaching Award from the Department of Materials Science and Engineering (2005),

Research interest: a wide range of materials science disciplines, chemistry conducting polymers, nanostructured ceramics,semiconductors, biomaterials , liquid crystals, nanoreactor, drug delivery, semiconductors, biomaterials , liquid crystals, nanoreactor, drug delivery, microelectronics, optical material.

Topic

P l i tiPolymeric coatings:

•Highly stable to species present in the environment

•Protect a substrate from environmental exposure,

When they fail corrosion of the substrate is greatly acceleratedWhen they fail, corrosion of the substrate is greatly accelerated

WHY?WHY?

Microcracking in polymeric composites

Microcracking

Significant compromise of the integrity of structure

Mechanical degradation of fibre- Electrical failure in microelectronic greinforced polymer composites polymeric components

Worldwide cost of corrosion: nearly $ 300 billions/ yeary $ / y

Self-preparation of polymeric component is important

Self-healing coating

What is it?

Self healing coating Automatically repair and prevent corrosion of the •Self-healing coating = Automatically repair and prevent corrosion of the underlying substrate

•Respond without external intervention to environmental stimuli in a •Respond, without external intervention, to environmental stimuli in a productive fashion.

Various approaches for achieving healing functionality

•Encapsulation•Monomer phase separationMonomer phase separation•Reversible chemistry•Nanoparticle phase separation, •Polyionomers•Polyionomers,•Hollow fiber •Microvascular networks.

Encapsulation approach

k d b d b h d l h l f lFirst work discribed by White and al.: autonomic healing of polymer composites

Cracks form in the matrix wherever damage occurs

Ruptures the mucrocapsules, releasing the healing agent into the crack plane through capilary actionagent into the crack plane through capilary action

Contact of healing agent & catalyst, triggering polymerization that bonds the crack faces closed

S R Whit d l N t 2001 409 794 797S.R. White and al. , Nature. 2001, 409, 794-797

Chemistry of this self-healing system

ROMP: living ring-opening methathesis polymerization

Long self-life, low monomer viscosity and volatility, rapid polymerization at RT, low shrinkage upon polymerization

G bb ’ t l t hi h t th i ti it t l t f id f Grubbs’ catalyst: high metathesis activity, tolerant of a wide range of functional groups

Mechanism of ROMP

Initiation by a carbene transition metal (Ru, W, Mo)

NMR studies in an epoxy matrix

Rubbs’ catalyst

Solid state 31P-NMR and 1H-NMR of self-assembling composite:

y

Solid state P NMR and H NMR of self assembling composite: characteristic signals of PCy3 and of liquid DCPD monomer, respectively

Stability of Rubbs’ Catalyst and DCPD monomer within the polymer matrix

Rupture & release of the microencapsulated agents

A time sequence of video (optical) images describing a rupture of a filled microcapsule with a red dye and release of healing agent.The elapsed time from the left to right image is 1/15 s

Fracture plane of a self-healing material with a ruptured ureaformaldehyde microcapsule in a thermosetting matrix by SEM

ESEM and IR: evidence of polymerization induced by damage

Neat DCPDNeat DCPD

Authentic Poly(DCPD)

Poly(DCPD) film formed at the

healed interface

ESEM micrograph and IR analyses

Highlighted peak at 965cm-1: Trans double bonds of ring-opened poly (DCPD)

Limitations…

Crack-healing kinetics

Instability of the catalyst to environmental conditions

P di i f G bb ’ t l t i t iPoor dispersion of Grubbs’ catalyst in epoxy matrix

Attack of epoxy’s curing agent (DETA) on Grubbs’ catalyst: reduction of catalyst amount

Encapsulation of Grubbs’ catalyst needed

Encapsulation:wax-protected catalyst microspheres for efficient Self healing Materialsfor efficient Self-healing Materials

S. R. White and al., Adv. Mater. 2005, 17, 205-208

Results:

•Much lower destruction of catalyst by DETA

•Much lower overall catalyst loading

•Much better dispersion of catalyst particles

Healing efficiency

O l 0 75 t % t l t l di h li ffi i i 93 % Only 0.75 wt % catalyst loading, healing efficiency is 93 %

Much better healing efficiency compared to the cas of unprotected catalystcatalyst

Limitations:Limitations:

The self-healing system based on poly(DCPD):Ai d t hi h t t t bl- Air and water, high temperature unstable

- High cost of catalyst

An other self-healing composite neededg p

Self-healing by monomer phase separation:

P. V. Braun,S. R. White, Adv. Mater. 2006, 18, 997-1000

PDMS-based self-healing materials

Polydimethylsiloxane: PDMS

Advantages over the previous methodologies

Chemically stable in humid or wet environments

Stable in the air and high temperature (>100°C)

Wid l il bl d ti l l i tWidely available and comparatively low in cost

Simplicity of procedure

Organotin catalyst: limit side reaction

Schematic of self-healing process

a. Self-healing composite consisting of:

Mi l t d t l t-Microencapsulated catalyst- Phase-separated healing-agent droplets- Green matrix

b. Crack propagating into the matrix l i t l t i t th k lreleasing catalyst into the crack plane

c. Crack healed by polymerization of healing agent PDMS

d E t i l f f t f d h t d h li t d. Empty microcapsule of a fracture surface and phase-separated healing agent

Polycondensation of HOPDMS with PDMSy

DBTL, 50°C,

Air or water media

DBTL = Di-n-butyltin dilaurate

Self-healing efficiency under real-world conditions

RH: relative humidityHigh RH: >90 % Low RH: <10 %Low RH: <10 %

The fracture load of the sample healed under water decrease only 25 % with respect to the other samples

Aim

Obtain a self-healing polymer, effective for both model and industrially important coating systems

Respond to rigorous demands: chemical stability, p g y,passivating ability and any external stimuli excluded

Choice of self-healing systemChoice of self healing system

Catalyst: •Rubbs’ catalyst: costly, air and water unstable •Organotin catalyst: cheap, widely available, air, water and temperature stableHealing agent: •DCPD: catalyzed by Rubbs’ catalyst, good mechanical properties of crosslinking materials•Mixture HOPDMS + PDES: catalyzed by Organotin catalyst, performance of chemicalstability and passivating ability but not exceptional mechanical t th f th h l d t istrength of the healed matrix

Siloxane-based materials system:best choice

Two Strategies

Two self healing coating approaches:Two self-healing coating approaches:

1.Microencapsulation of the catalyst and phase-separatedd l t f h li t ithi i l t t idroplets of healing agents within an epoxy vinyl ester matrix

2. Encapsulation of both catalyst and healing agents

Encapsulation of both phases is advantageous in cases capsu at o o bot p ases s ad a tageous caseswhere the matrix can react with the healing agent

Optimal percentages of components in the self-healing matrixin the self healing matrix

The maximum efficiency of healing for samples containing 12 wt % PDMS, 4wt % adhesion promoter and 3.6 wt % microcapsules

First strategy:only catalyst encapsulated

This model system consists of:

• Epoxy vinyl ester matrix

This model system consists of:

• 12 wt % phase-separated healing agent: mixture HOPDMS + PDES

• 3 wt % catalyst DMDNT in microencapsule polyurethane (PU))

• 3 wt% adhesion promoter (methylacryloxy propyl triethoxy silane)

DMDNT/ chlorobenzene-filled PU Capsules

Size histogramOptical microscopy

Average 90 µm in diameter

DMDNT: dimethyldineodecanoate tin (catalyst)

Microcapsule Synthesis

DBTL containing microcapsule

Interfacial Polymerization: chlorobenzene/H2O

70 °C, 2 h70 C, 2 h

Stirring: 1000 rpm

Thermogravimetric Analysis (TGA)

•Primary weight loss: 131 °C near the boiling point of chorobenzene•Primary weight loss: 131 C, near the boiling point of chorobenzene•Secondary weight loss : 225°C, decomposition of PU shell

Procedure of corrosion test

Healed coated steel or control sample

Hand scribing 100 µm

by razor blade

1. Healing, 50 oC, 24 h

2. Immersed in 5 wt % yNaCl solution, 24 h

•Rapidily corrosion •Extensive rust formation within the groove of the scribed and extending across the substrate surface surface

Control simpleSelf-healing simple

No is el e idence of co osion e en 120 h afte e pos eNo visuel evidence of corrosion, even 120 h after exposure

Necessary presence of both healing agents and catalyst

Coating without catalyst

Coating without PDMS

Removal of either phase: rapid corrosion of coating

SEM images of the scribed region

Self healing sampleControl simple Self-healing sample

In the self-healing coating:40 % of damage filled

In the control simple: scribe with 15 µm of extension into the metal substrate

Profilometry and EDS

.Good agreement with SEM mesurements

Further evidence by electrochemical testing

•An electrochemical cell: coated metal

System consists of:

Current versus timesubstrate•A platinum electrode held 3 V•An aqueous electrolyte (1M NaCl)

Current versus time

Before scribing, current passing:-Nearly identical: ~ 0.34 µA cm-2 through both control and self-healing coatingfAfter scribing and healing, current passing :

- 26.6-58.6 mA cm-2 through control simple and 12.9 µA cm-2 -1.4 mA cm-2

through self-healing samples

Dramatically reduced current for the self-healing coating

Limitation & solution

Systems consisting of phase-separated PDMS healing agent:

PDMS healing agent in direct contact with the coating matrix, susceptible to matrix –initiated reactions

Strategy: Protect also healing agent PDMS by encapsulationgy g g y p

Dual capsule self-healing coating systemp g g y

Second strategy: Dual capsule coating system

PDMS Microcapsules

Optical microscopy image

TGAPDMS Microcapsules

•Slow Weight loss at 150 °C

Average diameter of PDMS capsules is 60 µm

S o e g t oss at 50 C•Overall small weight loss at 500°C

High thermal stability of PDMSPDMS capsules is 60 µm High thermal stability of PDMS

Dual capsule self-healing coating systemPreliminary corrosion Testing

Inadequate adhesion of this epoxy-based coating and the substate

Application of 50 µm thick epoxy-based primer layer to the substrateand cured prior to coating application

Corrosion-test for 100 µm thick control and dual capsule self-healing coating simples

•All control simples: extensive corrosion after only 24 h of salt water exposureexposure•Self-healed simples (healed 24 h at 50°C), no evidence of rust formation, even after 120 of exposure

Dual capsule self-healing coating systemControl experiments

All images 75 mm x 150 mm.

a, Matrix + adhesion promoter. b, Matrix + adhesion promoter + PDMS healing agent.c, Matrix + adhesion promoter + catalyst containing microcapsules. d dh l l h ld, Matrix + adhesion promoter + catalyst containing microcapsules + PDMS healing agent (self-healing sample)

Removal catalyst and/or healing agent resulted in rapid corrosionNo evidence of rust formation for self-healed samples

Summary of corrosion testing of control and self-healing simples

a, Matrix + adhesion promoter promoter. b, Matrix + adhesionpromoter + PDMS healing agent agent. c, Matrix + adhesion promoter + catalyst containingmicrocapsules microcapsules. d, Matrix + adhesion promoter + catalyst containing microcapsules + PDMSc ocapsu es Shealing agent (self-healing sample). All images 75 mm x 150 mm.g

Dual capsule self-healing coating systemEfficient at RT

True self healing: no external intervention including DMDNT: reduced True self-healing: no external intervention, including heating to temperatures greater than ambient

DMDNT: reduced catalytic activity at RT

TKAS: a highly effective catalyst for curing PDMS, not require moisture for activation

Successful for preparing a true self-healing coating (at RT) C4H9

C4H9C4H9 C4H9

Potential self-healing coating for SiO

O

Sn

OCOCH3Sn

C4H9

H3COCO

C4H9

moisture-free environments: aerospace applications; buries interfaces

OOSn

SnH3COCO

C4H9C4H9

C4H9

C4H9

H3CCOO

TKAS: Si [OSn(n-C4H9)2OOCCH3] J. Appl. Polym. Sci. 1998, 70, 2235Macromol. Chem. 1980, 181, 2541

Synthesis of TKAS

C4H9 C4H9

Sn

C4H9C4H9C4H9 C4H9

Sn

4 9

H3CCOO

4 9

OOCCH3

SiO

O

Sn

OCOCH3Sn

4 9

H3COCO

H3CCOO 3

150°C, anhydrousDi-n-butyltin diacetate

Si

OOSn

SnH3COCO

C4H9C4H9

C4H9

C4H9EtO OEt- AcOEt

C4H9 H3CCOOSi

EtO OEt Si[OSn(n-C4H9)2OOCCH3]

US t t 4 137 249 1979

TKASTetraethylsilicate

US patent 4, 137, 249, 1979

Corrosion performance in real-world condition

Control and self-healing samples of general epoxy-based coating system

a, b,

c, dc, d

Control and self-healing samples of a commercial marine (epoxy) coating systemsystem

Efficacy of the RT activity for both systems

Conclusion & perspectives

Conclusion:

D l l PDMS h li t h i l tibilit d t bilit•Dual-capsule PDMS healing system: chemical compatibility and stability•TKAS catalyst: autonomic corrosion protection under ambient environmental conditions

Perspective:

•Formulation of multilayer coating to provide self-healing functionality while maintaining extreme tolerances on surface finish, specific requirements for engineered primers, or unique

f h ( lf l )surface chemistries (self-cleaning)

•Microcapsule motif: a delivery mechanism for multifunctional h i l t ti i bi l t chemical agent, antimicrobial agent…