1. Effect of Matrix Resin Properties on Activity of a Mechanochromic Fluorescent Probe for use in a novel Non-Destructive Inspection Technique for Aerospace Polymer Matrices Natalie M. Larson, Alex Jen, Ryan E. Toivola, Zhengwei Shi, Sei-Hum Jang, Gary Georgeson* and Brian D. Flinn University of Washington, *The Boeing Company 13 th International Symposium on Nondestructive Characterization of Materials Palais des Congrès et de la Culture du Mans, France May 20, 2013

2. 2 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪ Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Composite Impact Damage Composites Barely Visible Impact Damage (BVID): Subsurface damage produced by impact [2] Aluminum aircraft fuselage shows dents after impact [1] Research Goal: Improve Visual Inspection Techniques for Composites [1] Photo of the day: “Miracle on the Hudson” plane, on I-77, Available Online:http://davidsonnews.net/blog/tag/miracle- on-the-hudson/ [2] Iwahori, Y., JAXA Res. Rep. 14, www.apg.jaxa.jp/eng/publication

3. 3 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪ Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions NDI with Fluorescent Probes Fluorescence based inspection *Under UV Light Probe Block of Functionalized Epoxy Probe Block of Functionalized Epoxy

4. Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪ Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Research Question How do the mechanical properties of the matrix affect the fluorescent probe response? Motivations for Research Question: Polymeric materials used in aerospace fall within a large range of mechanical properties Research may reveal information about molecular mechanism of probe Research Approach: Reduce Elastic Modulus of Functionalized Epoxy with Diluent 4

5. 5 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Matrix Materials  Epoxy: Diglycidyl ether of bisphenol-A (DGEBA)  Curing Agent: Diethylenetriamine (DETA) Epoxide Functionalized Reactive Diluent: Diglycidyl ether (polypropylene glycol) (DGE(PPG)) Neat Epoxy System: (RT Cure, Optically Clear)

6. 6 Background Materials ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Mechanochromic Fluorescent Probe Donor Acceptor ON State-conjugated backbone OFF State-unconjugated backbone Force Rips Probe off of epoxy network Y X OFF State White LightUV Light ON State White LightUV Light ▪ Matrix

7. 7 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Mechanochromic Fluorescent Probe

8. 8 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Mixtures Fabricated Mixtures Fabricated: Ranged from 0-100wt% diluent DGE(PPG) Named by wt% DGE(PPG) ie. 40wt% DGE(PPG) + 60wt% DGEBA referred to as 40wt% DGE(PPG) Mixing Procedure Neat Epoxy (DGEBA) Diluent DGE(PPG) DETA + Probe Light pink solid Mix, vac, pour Cure 24h @ RT yellow liquid

9. 9 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Sample Characterization 1. Elastic Modulus Measurement Compression test Used Unloading Modulus 2. Glass Transition Temperature (Tg) PerkinElmer 7e DMA: Storage Modulus vs. Temp 3. UV-Vis Absorbance Spectra ThermoFisher UV-Vis 4. Fluorescence Spectra Stellarnet Blue-WAVE UVN spectrometer 390 nm excitation light

10. 10 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Probe Response Testing Fluorescence Before Compression Compress Specimens Fluorescence After Compression

11. 11 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Modulus and Tg Results-as cured RT

12. 12 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions UV-Vis Absorbance Spectra—as cured 0wt % DGE (PPG) 10wt % 20wt %30wt %40wt %50wt %75wt %100wt %

13. 13 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Fluorescence Spectra—as cured

14. 14 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Probe Response Testing: Typical Compression Behavior 1 2 3 456

15. 15 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Probe Response after Deformation* True Plastic Strain: Specimen 1: 0.39±0.02 Specimen 2: 0.41±0.02 Specimen 3: 0.35±0.02 Specimen 4: 0.26±0.02 Specimen 5: 0.15±0.02 Specimen 6: 0.06±0.02 Arrow indicates Increasing True Strain UNDEFORMED *Typical Response for 0-30wt% diluent samples

16. 16 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Probe Response after Deformation* True Plastic Strain: Specimen 1: 0.23±0.02 Specimen 2: 0.26±0.02 Specimen 3: 0.21±0.02 Specimen 4: 0.21±0.02 Specimen 5: 0.18±0.02 Specimen 6: 0.13±0.02 Specimen 7: 0.07±0.02 Specimen 8: 0.02±0.02 *Typical Response for 40-100wt% diluent samples UNDEFORMED

17. 17 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Probe Response Index (PRI) “OFF” Peak (505nm) “ON” Peak (~610nm) HIGH PRI LOW PRI

18. 18 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions PRI vs. Mechanical Deformation ΔPRI = slope of PRI vs. True Plastic Strain curve Linear Fit? PRI vs. strain energy PRI vs. maximum stress on sample PRI vs. true plastic strain

19. 19 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions ΔPRI vs. wt% DGE(PPG) and Elastic Modulus =Probe Responded to Compression =Probe did not respond to compression

20. 20 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Conclusion #2: ΔPRI does not vary monotonically with elastic modulus ΔPRI decreases monotonically as diluent wt% increases Effect of elastic modulus on the probe response was not isolated Diluent changed mechanical properties and local chemical environment (polarity, dielectric strength, free volume) – possible effect on probe integration into network ΔPRI is more significantly affected by the changes in the local chemical environment than the matrix mechanical properties Conclusion #1: Fluorescent probe responds to mechanical deformation for samples with 0-30wt% diluent PRI varies linearly with true plastic strain

21. 21 Background Materials ▪ Matrix ▪ Probe Methods ▪ Sample Characterization ▪Probe Response Testing Results ▪ Sample Characterization ▪ Probe Response Testing Conclusions Plans for Future Work 1.Determine how the local chemical environment affects the interactions between the probe and host polymers. 2.Separate the effects of matrix stiffness from the effects of the local chemical environment 3.Study effects of DGEBA derivatives with varying molecular weights as reactive diluents. 4.In General, a further understanding of Temporal stability Thermal stability Effect of fiber reinforcements

22. 22 Acknowledgements Flinn Group: Dr. Brian Flinn Dr. Ryan Toivola Students: Dana Rosenbladt, Ashley Tracey, Curtis Hickmott, Tucker Howie, Kevin Braun, Ali Dillon, Gary Weber, Jonathan Morasch, Dave Pate, David Sapiro Funding: The Boeing Company Project Code B8LDL Washington Research Foundation UW Office of Research, Mary Gates Endowment, Levinson Emerging Scholars Program, UW Undergraduate Research Program Special Thanks (The Boeing Company): Kelsi Hurley Grant Zenkner Mark Wilenski

23. 23 Backup Slides R 2 Values for Linear Fits to PRI vs: wt% DGE(PPG) True Plastic Strain Strain Energy Maximum Stress Applied 00.950.980.88 100.880.820.72 200.880.650.61 300.900.660.56 R 2 Values for Linear Fits of PRI vs. Mechanical Testing Values

24. 24 Backup Slides