Imaging the interphase in polymer composites

Transcription

1 Engineering Conferences International ECI Digital Archives Composites at Lake Louise (CALL 2015) Proceedings Fall Imaging the interphase in polymer composites Jeffrey Gilman NIST Follow this and additional works at: Part of the Materials Science and Engineering Commons Recommended Citation Jeffrey 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). This Conference Proceeding is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion in Composites at Lake Louise (CALL 2015) by an authorized administrator of ECI Digital Archives. For more information, please contact

2 Visualizing Polymer Composite Interfacial Deformation Chelsea Davis Jeremiah Woodcock, Ryan Beams Stephen Stranick, Jeffrey Gilman Material Measurement Laboratory National Institute Standards and Technology

3 Interfacial Visualization Project Overview 100 µm Debonding of interface via Förster Resonance Energy Transfer (FRET) Cellulose nanofibrils in epoxy Qualitative observation of interfacial separation in macroscopic composite 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 20 µm 2

4 Why FRPCs? 0.5 mm D. Hull and T.W. Clyne, Introduction to Composite Materials, 2nd ed.,

5 Composite Interfacial Strength Characterization Current techniques allow quantification of macroscale composites; what about nanoscopic reinforcement? Adams, CompositeWorld,

6 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 Zammarano M. et al., ACS Nano

7 Energy Förster Resonance Energy Transfer (FRET) Excited State Levels Absorbed (excitation) Emitted (fluorescent) Fluorescence lifetime (ns) Ground State Förster, Annalen der Physik, Clegg, Methods in Enzymology

8 Energy Intensity (a.u.) Förster Resonance Energy Transfer (FRET) Excited State Levels Relaxation (ps) Absorbed (excitation) Emitted (fluorescent) Fluorescence lifetime (ns) Wavelength (nm) Ground State Förster, Annalen der Physik, Clegg, Methods in Enzymology

9 Intensity (a.u.) FRET at a Composite Interface Acceptor Cellulose (DTAF) Donor Polyethylene (Coumarin) Wavelength (nm) Zammarano M. et al., ACS Nano

10 Bilayer Composite Interface Preparation Molding of nanofibrillated cellulose onto partially-cured epoxy Cellulose Teflon Wedge Epoxy Epoxy (DGEBA/Jeffamine D230) with 0.1 mass% Coumarin Pressed DTAF-modified cellulose Freeze-fracture and surface preparation of interface Fluorescent imaging of cross-section J. Woodcock et al., In Preparation. 9

11 Cellulose (DTAF channel) DTAF 100mm (Dichlorotriazinyl) Aminofluorescein (DTAF) J. Woodcock et al., In Preparation. 10

12 Epoxy (Coumarin channel) 100mm Epoxide-functionalized Coumarin J. Woodcock et al., In Preparation. 11

13 Dual Channel Image of Interface Epoxy (Coumarin) Cellulose (DTAF) 100mm 2 channel composite image of Coumarin (l=475 nm) and DTAF (l=515 nm) emission J. Woodcock et al., In Preparation. 12

14 FRET Efficiency Map 0% 50% 100% 100mm J. Woodcock et al., In Preparation. 13

15 Interfacial Debonding Approach Thermal Conditioning Cycle Cellulose Cellulose Epoxy Epoxy Bilayer composite sample conditioned (T=40 C and controlled humidity) Sample submerged in liquid nitrogen for 5 min Sample replaced in conditioning chamber for 12 h (same conditions) J. Woodcock et al., In Preparation. 14

16 Monitoring Debonding using FRET: Humidified Before Thermal Shock After Thermal Shock 50 µm 15

17 Monitoring Debonding using FRET: Dried Before Thermal Shock After Thermal Shock 50 µm 16

18 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 Epoxy (Coumarin) Cellulose (DTAF) 100 µm 50 µm 17

19 Interfacial Visualization Project Overview 100 µm Debonding of interface via Förster Resonance Energy Transfer (FRET) Cellulose nanofibrils in epoxy Qualitative observation of interfacial separation in macroscopic composite 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 20 µm 18

20 Previous Mechanophore Work Potisek, et al., JACS D. Davis, et al., Nature Gossweiler, et al., ACS Mac. Let

21 Interfacial Mechanophore in Silk Fiber System Goal Detect interfacial separation in a fiber-reinforced composite using fluorescent activation Approach ε White Light Degummed Silk Mechanophore Control MP MP Black Light ε MP Silk Fiber MP MP ε Epoxy 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) 20 20

22 Mechanophore Attachment Fiber Epoxy Matrix Polyetheramine (Jeffamine ED600) Bisphenol A diglycidyl ether (DGEBA, monomer) Woodcock, Davis, Beams, et al., In Preparation. 21

23 Fluorescence Lifetime Imaging Microscopy (FLIM) NIST FLIM System Excitation: Pulsed, two photon IR laser Detector: Four channel, time correlated single photon counting (TCSPC) < 442nm nm nm > 594nm Photon Counts vs. Lifetime FLIM image of fluorescent Si particles (D=200nm) Beams, Stranick, et al., In Preparation. 22

24 Attachment of Dye to Silk Fiber (Bombyx Mori) Physically Adsorbed Dye τ 1 = 0.7 ns τ 2 = 1.7 ns ps τ 1 = 2.4 ns Covalently Attached Dye 20µm Normalized Intensity (a.u.) Physically Adsorbed Covalently Attached Fluorescence Lifetime (ns) ps Woodcock, Davis, Beams, et al., In Preparation. 23

25 Matrix Attachment: Spectral Effects of Curing As mechanophore is reacted more strongly with epoxy matrix, emission wavelength shifts towards that of control (monofunctional) dye. Normalized Intensity (a.u.) Unreacted Partially Reacted Fully Reacted Control Dye Wavelength (nm) Fiber Fiber Fiber Fiber MP MP MP MP Unreacted 1 Attachment 3 Attachments Control 24

26 Hyperspectral Imaging to Monitor Reaction Silk Fiber Cross-Section Mechanophore (T = 80 C cure) Partially reacted with matrix Lifetime and wavelength varies by location, highlighting areas where mechanophore is fully reacted across composite interface. 10µm Normalized Intensity (a.u.) Unreacted Partially Reacted Fully Reacted Control Dye Wavelength (nm) 25

27 Mechanophore at Interface of Silk/Epoxy Composite ε = (MPa) Intensity (a.u.) Ex situ tensile strain of single silk fiber in rubbery matrix by fluorescence lifetime imaging (FLIM) 20µm τ 1 = 2.4 ns Lifetime (ps) ε = ε c ε c 0.63 E 7.7 MPa Intensity (a.u.) Lifetime (ps) Davis, Woodcock, Beams, et al., In Preparation. 26

28 Mechanophore Intensity Response ε 20% MP Silk in ED600 l o =22 mm, A x = 8 mm (MPa) nm ε 0 τ = 2.5 ns =64% =20% ε = ε c ps 20µm

29 Discussion and Future Work In situ Strain Stage Dual motion crossheads keep region of interest centered over the microscope objective. Load Cell Epoxy FOV Side View Sample Motor Moving Stage Objective Fixed Posts Tensile Grips (dual actuation) Load Cell Load Cell MP Labeled Silk FOV Viewing window for inverted microscope objective Encoder (displacement sensor) Top View 28

30 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