imaging the interphase in polymer composites
TRANSCRIPT
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
Polymers & Complex Fluids Group
Visualizing Polymer Composite Interfacial Deformation
Chelsea DavisJeremiah Woodcock, Ryan BeamsStephen Stranick, Jeffrey Gilman
Material Measurement LaboratoryNational Institute Standards and Technology
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
Why FRPCs?
3
0.5 mm
D. Hull and T.W. Clyne, Introduction to Composite Materials, 2nd ed., 1996.
Polymers & Complex Fluids Group
Composite Interfacial Strength Characterization
4
Adams, CompositeWorld, 2011.
Current techniques allow quantification of macroscalecomposites; what about nanoscopic reinforcement?
Polymers & Complex Fluids Group
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.
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
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.
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
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.
Polymers & Complex Fluids Group
Cellulose (DTAF channel)
10
(Dichlorotriazinyl) Aminofluorescein (DTAF)
DTAF100mm
J. Woodcock et al., In Preparation.
Polymers & Complex Fluids Group
Epoxy (Coumarin channel)
11
Epoxide-functionalized Coumarin
100mm
J. Woodcock et al., In Preparation.
Polymers & Complex Fluids Group
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
J. Woodcock et al., In Preparation.
Polymers & Complex Fluids Group
FRET Efficiency Map
13
100mm0% 100%50%
J. Woodcock et al., In Preparation.
Polymers & Complex Fluids Group
Interfacial Debonding Approach
14
J. Woodcock et al., In Preparation.
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
Polymers & Complex Fluids Group
Monitoring Debonding using FRET: Dried
16
50 µm
Before Thermal Shock
After Thermal Shock
Polymers & Complex Fluids Group
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
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Cellulose(DTAF)Epoxy
(Coumarin)100 µm
50 µm
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
Previous Mechanophore Work
19
Potisek, et al., JACS 2007.D. Davis, et al., Nature 2009.
Gossweiler, et al., ACS Mac. Let. 2014.
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
Mechanophore Attachment
21
Fiber Epoxy Matrix
Woodcock, Davis, Beams, et al., In Preparation.
Bisphenol A diglycidyl ether(DGEBA, monomer)
Polyetheramine(Jeffamine ED600)
Polymers & Complex Fluids Group
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.
Polymers & Complex Fluids Group
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)
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
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)
Polymers & Complex Fluids Group
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)
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
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
Polymers & Complex Fluids Group
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