Self-Healing Polymers and Composites. Nancy Sottos Department of Materials Science and Engineering University of Illinois Urbana-Champaign

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1 Self-Healing Polymers and Composites Nancy Sottos Department of Materials Science and Engineering University of Illinois Urbana-Champaign

2 Damage in Polymers and Composites Electronics Structural Composites Structural Plastic 5 mm Cracks are often deep in a structure where detection is costly and difficult Repair of cracks by external intervention is often impossible

3 Self-Healing Materials Autonomous Materials Systems: The ability to respond to environmental stimuli in an automatic and site specific fashion without manual intervention.

4 Three Strategies for Self-Healing Materials Embedded Microcapsules Microvascular Network Molecular Engineering Capsule-based Polymer add-in Once-and-done Vascular Delivery ConFnuous supply MulFple healing cycles Molecular Requires close contact External energy source (heat, UV, etc.) Very soc materials

5 Damage length scales 1 mm Laminated Composite Microvascular 100 µm Microcapsules Nanocapsules & molecular 1 µm

6 Microcapsule-Based Self-Healing

7 White et al., MRS Bulletin (2008) Microencapsulated Systems

8 Microcapsules

9 Scanning Electron Microscope Image of a Microcapsule shell wall shell interior matrix

10 Making Microcapsules Urea + Formaldehyde Water Control of capsule diameter Healing agent UF Oligomers Size limit ~ 10 micron diameter In situ polymerization of urea and formaldehyde

11 Healing Efficiency in Brittle Materials η = K Ic healed virgin K = 93% Ic 2.5 wt% Grubbs catalyst 5 wt% microcapsules Healing conditions: room temperature, 48 h Brown et al., Experimental Mechanics (2002)

12 Self-Healing Elastomers Pt catalyzed hydrosilylation of vinyl terminated PDMS Tear Test Protocol Keller et al., Adv. Func. Mat. (2007)

13 Healing Efficiency Healed 1 st Tear 10 mm 2 nd Tear path 13

14 Self-Sealing Laminates Model system for studying inflatables Puncture Damage Beiermann et al., Smart Mater. Struct. 18 (2009)

15 Sealing Evaluation

16 Healing Results Effect of Capsule Diameter Effect of Puncture Size Samples Healed (%) Samples Healed (%) Average Microcapsule Diameter (µm) Puncture Diameter (mm)

17 Healed Puncture Surfaces Fully Healed Partially Healed

18 Healing in Fiber Reinforced Composites Microcapsules mixed in epoxy resin with woven glass Successful self-sealing of microcrack damage in a woven glass composites Moll et al., Composites Science and Technology, 79, (2013).

19 Composite Self-Sealing Results 19

20 Healed Damage in Woven Composite Glass/epoxy composite containing 12 wt% capsules after damage and healing

21 Vascular Networks Vascular system functions: maintain homeostasis supply nutrients combat disease facilitate growth repair damage

22 3-D Printing of Complex Vascular Networks Direct-write method using Robotic Controlled Deposition (RCD) J.A. Lewis D.T. Therriault April 9, Background 2007 S-H coating Monomer delivery 2-part delivery 22/44 Conclusions

23 Fabrication of Microvascular Networks Deposition of ink Material Infiltration Curing of structural material Removal of fugitive ink

24 Vascular Composites

25 3D Vascular Composites 1. Catalyst treated polylactide (PLA) fibers woven into preform. Esser-Kahn et al. Adv. Mater. (2011) 2. Composite formed via Vacuum Assisted Resin Transfer Molding (VARTM). 3D microvascular structural composite 3. PLA evacuation by postcure at 200 C under vacuum.

26 Woven Composite Delamination Polymer 53 (2012) Compos. Struct. 79 (2007)

27 Laminate Self-Healing Cycle

28 In situ Healing Agent Delivery 15 mm 5 mm

29 Herringbone Self-Healing Results Three in situ healing cycles after 48 hrs at 30 C Virgin Heal q a = 30 mm Heal w a = 50 mm Heal e a = 70 mm Over 100% in situ recovery in G I achieved! Load - P (N) q w e Displacement - δ (mm) Patrick et al., Advanced Materials (2014)

30 Vascular Healing of Large Damage Volume Substrate polymer Microchannels White et al., Science, 2014, 344,

31 Summary Self-healing plastics can be achieved through three different strategies: embedded microcapsules, microvascular networks, and intrinsic molecular changes Microcapsules are made by creating an oil/water emulsion and in situ polymerization of the shell wall. Microcapsules are easily incorporated in coatings and adhesives and provide single shot healing. Complex microvascular networks can be created by 3-D printing and provide multiple healing cycles of large scale damage A variety of damage modes can be self-healed using these different strategies.

32 Acknowledgements Autonomous Materials Systems Group Beckman Institute for Advanced Science and Technology Jeff Moore Philippe Geubelle Scott White Paul Braun