Imaging the interphase in polymer composites

Engineering Conferences InternationalECI Digital Archives

Composites at Lake Louise (CALL 2015) Proceedings

Fall 11-9-2015

Imaging the interphase in polymer compositesJeffrey GilmanNIST

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Recommended CitationJeffrey Gilman, "Imaging the interphase in polymer composites" in "Composites at Lake Louise (CALL 2015)", Dr. Jim Smay,Oklahoma State University, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/composites_all/30

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Polymers & Complex Fluids Group

Visualizing Polymer Composite Interfacial Deformation

Chelsea DavisJeremiah Woodcock, Ryan BeamsStephen Stranick, Jeffrey Gilman

Material Measurement LaboratoryNational Institute Standards and Technology


Interfacial Visualization Project Overview

Fiber-reinforced composite interfacial damage sensing with mechanophores

• Silk fibers in epoxy• Semi-quantitative measurement of

stress transfer across interface in single fiber tensile experiments

2

20 µm

100 µm

Debonding of interface via Förster Resonance Energy Transfer (FRET)

• Cellulose nanofibrils in epoxy• Qualitative observation of interfacial

separation in macroscopic composite


Why FRPCs?

3

0.5 mm

D. Hull and T.W. Clyne, Introduction to Composite Materials, 2nd ed., 1996.


Composite Interfacial Strength Characterization

4

Adams, CompositeWorld, 2011.

Current techniques allow quantification of macroscalecomposites; what about nanoscopic reinforcement?


Visualizing Interfacial Debonding

Goal• Develop and validate method

to characterize interfacial debonding in a cellulose/epoxy nanocomposite

Approach• Functionalize reinforcement and matrix phases with

interacting FRET dye pair

• Prepare well defined interface (bilayer sample)

• Apply thermal treatment to damage interface

5Zammarano M. et al., ACS Nano. 2011.


Förster Resonance Energy Transfer (FRET)

Ground State

Absorbed

(excitation)

Emitted

(fluorescent)

Excited State Levels

En

erg

y

Fluorescence

lifetime (ns)

Förster, Annalen der Physik, 1948.Clegg, Methods in Enzymology 1992.

6


Förster Resonance Energy Transfer (FRET)

Ground State

Absorbed

(excitation)

Emitted

(fluorescent)

Excited State Levels

En

erg

y

Fluorescence

lifetime (ns)

Relaxation (ps)

7

Wavelength (nm)

Inte

nsity (

a.u

.)

Förster, Annalen der Physik, 1948.Clegg, Methods in Enzymology 1992.


Wavelength (nm)

Inte

nsity (

a.u

.)

FRET at a Composite Interface

Zammarano M. et al., ACS Nano. 2011.

8

Cellulose(DTAF)

Polyethylene (Coumarin)

Acceptor Donor


Bilayer Composite Interface Preparation

9

Epoxy (DGEBA/Jeffamine D230)

with 0.1 mass% Coumarin

Pressed DTAF-modified cellulose

Cellulose

Teflon

Wedge

Epoxy

Molding of nanofibrillated cellulose

onto partially-cured epoxy

Freeze-fracture and surface

preparation of interface

Fluorescent imaging

of cross-section

J. Woodcock et al., In Preparation.


Cellulose (DTAF channel)

10

(Dichlorotriazinyl) Aminofluorescein (DTAF)

DTAF100mm



Epoxy (Coumarin channel)

11

Epoxide-functionalized Coumarin

100mm



Dual Channel Image of Interface

12

2 channel composite image of Coumarin (l=475 nm) and DTAF (l=515 nm) emission

Cellulose(DTAF)Epoxy

(Coumarin)100mm



FRET Efficiency Map

13

100mm0% 100%50%



Interfacial Debonding Approach

14


Bilayer composite sample

conditioned (T=40°C and

controlled humidity)

Epoxy

Cellulose

Thermal Conditioning Cycle

Sample

submerged in

liquid nitrogen for

5 min

Sample replaced in

conditioning chamber for

12 h (same conditions)

Epoxy

Cellulose

Polymers & Complex Fluids Group 15

Monitoring Debonding using FRET: Humidified

50 µm

Before Thermal Shock

After Thermal Shock


Monitoring Debonding using FRET: Dried

16

50 µm

Before Thermal Shock

After Thermal Shock


Cellulose Debonding Summary

• Developed materials system to monitor interface in cellulose/epoxy composite system utilizing fluorescence microscopy

• Presented first results demonstrating optical imaging of sub-micron interfacial debonding

17

Cellulose(DTAF)Epoxy

(Coumarin)100 µm

50 µm


Interfacial Visualization Project Overview

Fiber-reinforced composite interfacial damage sensing with mechanophores

• Silk fibers in epoxy• Semi-quantitative measurement of

stress transfer across interface in single fiber tensile experiments

18

20 µm

100 µm

Debonding of interface via Förster Resonance Energy Transfer (FRET)

• Cellulose nanofibrils in epoxy• Qualitative observation of interfacial

separation in macroscopic composite


Previous Mechanophore Work

19

Potisek, et al., JACS 2007.D. Davis, et al., Nature 2009.

Gossweiler, et al., ACS Mac. Let. 2014.


Interfacial Mechanophore in Silk Fiber System

20

Goal• Detect interfacial separation in a

fiber-reinforced composite using fluorescent activation

Approach

20

Black Light

White Light

Collaborators:Silk provided by F. Volrath (Oxford Silk Group)Silk functionalization by J. Woodcock (MML)FLIM imaging with R. Beams (MML) and S. Stranick (MML)

DegummedSilk

Mechanophore Control

ε

Silk Fiber

MP

MPMPMP

MP

ε

Epoxy

ε


Mechanophore Attachment

21

Fiber Epoxy Matrix

Woodcock, Davis, Beams, et al., In Preparation.

Bisphenol A diglycidyl ether(DGEBA, monomer)

Polyetheramine(Jeffamine ED600)


Fluorescence Lifetime Imaging Microscopy (FLIM)

22

< 442nm

> 594nm

442-538nm

538-594nm

NIST FLIM SystemExcitation: Pulsed, two photon IR laser

Detector: Four channel, time correlated

single photon counting (TCSPC)

FLIM image of fluorescent Si

particles (D=200nm)

Photon Counts vs. Lifetime

Beams, Stranick, et al., In Preparation.


Attachment of Dye to Silk Fiber (Bombyx Mori)

Woodcock, Davis, Beams, et al., In Preparation.

23

τ1 = 0.7 nsτ2 = 1.7 ns

τ1 = 2.4 ns

Physically Adsorbed Dye

Covalently

Attached Dye

20µm

0-4000 ps

0-4000 ps

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Physically AdsorbedCovalently Attached

No

rma

lize

d In

ten

sity (

a.u

.)

Fluorescence Lifetime (ns)


0.0

0.2

0.4

0.6

0.8

1.0

400 450 500 550 600 650 700

UnreactedPartially ReactedFully ReactedControl Dye

Norm

aliz

ed I

nte

nsity (

a.u

.)

Wavelength (nm)

24

Control

Matrix Attachment: Spectral Effects of Curing

MP

Fiber

MP

Fiber

MP

Fiber

MP

Fiber

As mechanophore is reacted more strongly with epoxy

matrix, emission wavelength shifts towards that of control

(monofunctional) dye.

Unreacted 1 Attachment 3 Attachments


Hyperspectral Imaging to Monitor Reaction

25

10µm

Silk Fiber Cross-SectionMechanophore (T = 80 °C cure)

Partially reacted with matrix

Lifetime and wavelength varies by location,

highlighting areas where mechanophore is fully

reacted across composite interface.

0.0

0.2

0.4

0.6

0.8

1.0

400 450 500 550 600 650 700

UnreactedPartially ReactedFully ReactedControl Dye

Norm

aliz

ed I

nte

nsity (

a.u

.)

Wavelength (nm)


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

(

MP

a)

Mechanophore at Interface of Silk/Epoxy Composite

Davis, Woodcock, Beams, et al., In Preparation.

Ex situ tensile strain of single silk fiber in rubbery

matrix by fluorescence lifetime imaging (FLIM)

εc ≈ 0.63

E ≈ 7.7 MPa

ε = 0

ε = εc

20µm τ1 = 2.4 ns

26

1000 2500 4000

Inte

nsity (

a.u

.)

Lifetime (ps)

1000 2500 4000

Inte

nsity (

a.u

.)

Lifetime (ps)


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

=64%=20%

(

MP

a)

MP Silk in ED600lo=22 mm, A

x = 8 mm

Mechanophore Intensity Response

27

ε = εc

ε ≈ 20%

τ = 2.5 ns

1000-4000 ps

20µm

442-538nm ε ≈ 0


Discussion and Future Work

28

In situ Strain StageDual motion crossheads keep region of interest centered

over the microscope objective.

Motor

Encoder(displacement sensor)

Tensile Grips(dual actuation)

Load Cell

Sample

Viewing window for inverted microscope

objective

Load Cell

Objective

Load Cell

Fixed Posts

Epoxy

MovingStage

SideView

TopView

FOV

MP Labeled

Silk

FOV


Acknowledgements

• Team

– Aaron Forster, NIST

– Ning Chen, NIST

– Jae Hyun Kim, NIST

– Fritz Volrath, Oxford Silk Group

– Darshil Shah, Oxford Silk Group

• Funding

– National Research Council Postdoctoral Fellowship

– NIST Nano EH&S Initiative

– Air Force Office of Scientific Research, Hugh DeLong

– Army Research Office, Robert Mantz

Postdoctoral positions open immediately

29

Imaging the interphase in polymer composites

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