frechettelab.johnshopkins.edu 1

Preetika Karnal1, Paul Roberts1, Georgia Pilkington1, Carlos Barrios2, and Joelle Frechette1

1. Chemical and Biomolecular Engineering Department, Johns Hopkins University, Baltimore MD 21218

2 3M Corporate Research Materials laboratory, 3M Center, 201-4-N-01, St. Paul, MN, 55144-1000

Adhesion and debonding of pressure sensitive adhesives under extreme conditions

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Part 1. Tests for debonding of PSA

• Characterization techniques:Peeling experiment Probe tack experiment

• Steady state peel tests are conducted (generally at 90° or 180° peel angle) to measure work of debonding.

• Measures response to mixed-mode shear and tensile forces.

• Shape of the force curve can be used to characterize PSA.

• Measures response to tensile deformation.

Villey et al., Soft Matter, 11, 3480-3491, 2015

Creton and Cicotti, Rep. Prog. Phys. 79, 046601 , 2016

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Small angle peel test

• Unsteady → Crack initiation and propagation• Mechanical properties and interactions in

contact set the adhesion• Important contribution in understanding

interfacial mechanics for soft materials

Sharma, Langmuir, 2012, Majumder et al., Science 318, 258, 2007

Ghatak, Proc. R. Soc. Lond. A, 460, 2004

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Motor Motion and PeelerMotorized Z-StageVelocity Range: .15-1000 µm/sStep Resolution: .1 µmForce: .01 - 5N @ > 1000 readings/sec

Compliant bending-beam load cell

In-line or Side imaging AVT Stingray Camera Resolution: 644 x 592 pixels @ 70 FPSPixel Size: 3.4 µm

See: (1) Dhong and Frechette, Soft matter 2015 (2) Dhong & Frechette J. App. Phys. 2017

Custom low-angle peeling apparatus with imaging

initiation

Type of Measurements• Approach and detachment• Unsteady & Dynamic• Adhesion and peeling in fluids and on

rough/porous/dirty/wet surfaces• Pressure sensitive adhesives• Viscous forces and dissipation• Dewetting

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Prior work with low angle peeling

Interplay between fluid viscosity, compliance (extensional and bending)

Backing microstructure vs loading and viscosity

All effects (vdW, compliance, microstructure) combined

(1) Dhong and Frechette, Soft matter 2015 (2) J. App. Phys. 2017, (3) Dhong and Frechette, in prep.

Extend to PSA under extreme conditions?

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Multi-Mode Force Microscope (MMFM)

Bright field/ fluorescencelight source

High speed CMOS camera

Vertical and lateral micro-translation stage

Inverted microscope

Fiber-optic sensors

Cantilever*

Vibration Isolation Table

Piezo stage

Liquid bath

Modular design: Different translation stages canbe used based on experiments needsXZ microtranslation stages Travel range: 25 mmResolution: 5-50 nmVelocity: max. 1.5 mm/sMax. force: 10 NForce feedback loop: ± 0.05 mN from setpoint

Travel range: 102 mmResolution: 500 nmVelocity: max. 20 mm/sMax. force: 100 NForce feedback loop: ± 0.5 mN from setpoint

Piezo Z stage Travel range: 100 µmResolution: 0.1 nmVelocity: max. 10 m/sMax. frequency: ~ 0.1 100 HzMax. force: ~ 8 N

Micrometer stage

*Different tip and cantilever geometries possible.

Roberts, Pilkington, Karnal, and Frechette, in prep.

See Paul’s poster

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Part 2: PSAs in extreme environments

Surgical procedures

Underwater construction

PSAs in extreme conditions Temperature change Low/high humidity Exposure to water

Office supplies

Electronic displays

See Preetika’s poster

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Pressure sensitive adhesive under investigation

• 88 mol%• Tg= -70°C

• 12 mol%• Tg= +106°C

Poly (2-ethylhexyl acrylate-co-acrylic acid)

- Synthesized by solution polymerization method.- Benzophenone derivative used as photocrosslinker.- Transfer PSA coated on paper or PET release liners.- Thickness of PSA film is 25 µm.

Random copolymer of:

2-Ethylhexyl acrylate

Acrylic acid

OO

*

CH3

CH3

O

OH*

400 mJ/cm2

Increase in cohesion by inter-chain bonding.

Increase in cohesion by polymer entanglement.

UV crosslinking

Mol

ecul

ar w

eigh

t Low MW, Uncrosslinked

Low MW , Crosslinked

High MW, Uncrosslinked

High MW , Crosslinked

Molecular weight and crosslinking density matrix:

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Peeling measurements

PSA (10 X 50 mm)

Substrate(Glass)

t=0 t=Dwell time

Peeler

v

Backing sheet (PMMA)

peel velocity (50 µm/s)

Dwell time is the time of contact of substrate with PSA.

Fraction of the substrate indirect contact with PSA

10x

Uncrosslinked

PSA surface on glass

10x

Crosslinked

Image contact area after transfer (Peeling)

Contact area image after rolling the PMMA-PSA-Glass sandwich with (2kg) loaded roller

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Effect of water exposure on peel adhesionHydrophobic substrate

0

40

80

120

160

0 5 60

WL/

2 (m

J)

Exposure to water (min)

Low MwHigh Mw

0

5

10

15

20

25

0 5 60

WL/

2 (m

J)

Exposure to water (min)

Uncrosslinked

Crosslinked

(OTS coated glass)

0

40

80

120

160

0 5 60

WL/

2 (m

J)

Exposure to water (min)

0

5

10

15

20

25

0 5 60

WL/

2 (m

J)

Exposure to water (min)

Uncrosslinked

Crosslinked

Hydrophilic substrate(oxygen plasma treated glass)

Reduction in WL/2

Increase in WL/2

Competing phenomena causing increase in WL/2 with water exposure.

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Conclusions• Developed instruments to study pressure sensitive adhesive under normal and

extreme conditions- Small angle peel test- MMFM probe tack test

• Studied the effect of molecular architecture in terms of crosslinking and molecular weight on peel adhesion and tack of acrylate PSA.

• Adhesion after exposure to water seems to be influenced by two competing phenomena:– Short term

- Decreases adhesion- Interfacial

– Long term- Increases adhesion- Possibly bulk phenomena

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Acknowledgements

3M Corporate ResearchCarlos Barrios (co-advise PhD student)Stefan Gryska (3M-CRML) with help with synthesis of model systems

Group:

Rohini Gupta (now at Intel)Christian Pick (now at JHMI)Xiaoqing HuaCharles Dhong (now at UCSD)Yumo WangGeorgia Pilkington (now at KTH Sweden)Denise NeibloomPreetika KarnalXue Li (now at IFP)Tianyu Yang (now at Penn State)Kelley HeatleyPaul RobertsLeo FengMatthew TanBrian Ryu Funding:

NSF-CMMI 1538003Hopkins Extreme Materials Institute (HEMI)

Thank you!