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Title:Novel encapsulation technologies for small size-scale self-healing applications
Author(s):Jackson, Aaron C.
Director of Research:Braun, Paul V.
Doctoral Committee Chair(s):Braun, Paul V.
Doctoral Committee Member(s):Sottos, Nancy R.; Moore, Jeffrey S.; Dillon, Shen J.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Optical Polymers
Abstract:Self-healing technology offers an autonomic route to repairing damage in advanced polymers to extend their lifetime. A variety of self-healing systems have been developed for mechanical self-healing, protective coatings, and electronic self-healing. These self-healing systems rely on functional groups within the polymer, microvascular networks, or compartmentalization in capsules and particles. The healing agents become active in the crack plane upon damage, forming new bonds that heal the material. Of these systems, compartmentalization offers a simple and inexpensive means to apply self-healing to current advanced polymer applications. In this research, the primary motivation is to address challenges associated with small size-scale self-healing in compartmentalized systems. The term “small size-scale” in self-healing technology is applied to technologies where components are between 100 and 2000 nm. As the size of the capsules and particles decreases, current encapsulation methods do not ensure that self-healing components disperse well in a polymer matrix and that the components retain their contents during processing. The ring-opening metathesis polymerization reaction between dicyclopentadiene and Grubb’s catalyst is especially important to self-healing applications and provides a model system that uses both encapsulated liquid and solid healing agents. DCPD is encapsulated in polyureaformaldehyde (PUF) capsules while catalyst is protected in wax particles. Silica coatings, applied using a variety of silica condensation chemistries, help to improve the functionality of liquid-filled capsules. Fluoride-catalyzed silica condensation offers the best route to coating PUF capsules with a variety of sizes and contents. Coated capsules, 1.5 μm in diameter, can be dried to a powder without aggregates, something that cannot be achieved without the coating. Although a silica shell adds an additional diffusion barrier to the capsules, the stability of PUF capsules relies more on the washing conditions and capsule contents than on the addition of a silica shell. Polymer protection of Grubbs’ catalyst allows the catalyst to be incorporated into an epoxy matrix at smaller size scales without deactivation. The final particles contain catalyst encapsulated in particles made of polystyrene (PS) and polymethylmethacrylate (PMMA) and coated with silica. At larger size-scales, the polystyrene is sufficient to protect the particles and helps to improve the thermal stability of the particles compared to as-received Grubbs’ catalyst or catalyst encapsulated with wax. One important application requiring small size-scale self-healing components is in fiber-rich regions of epoxy composites where the spacing between fibers is limits the size of the components that can be used for self-healing. The small size scale self-healing components, DCPD capsules and Grubbs’ catalyst particles, are successfully incorporated into epoxy without aggregation or deactivation and demonstrate nominal healing. The size of the capsules limits the amount of healing agent delivered to the crack plane so pressure is applied across the crack plane, decreasing the crack volume and improving healing. PS in the catalyst particles also contributes to healing as it is dissolved by the DCPD and redeposits in the crack plane. The full system provides a healing efficiency of approximately 25%. Another important application requiring small size-scale self-healing components is in optical self-healing. 10 μm thick PMMA coatings containing 1.5 μm in diameter dibutyl phthalate (DBP) capsules scatter minimal light as a result of index matching. The capsules are capable of partially healing sub-micron damage in 100 μm PMMA films that have been mechanically damaged. The healed material scatters minimal light and retains the protective capabilities of the original PMMA coating. Larger capsules, 80 μm in diameter, containing DBP provide more healing allowing full healing at 6 wt.% capsules in polymer. They scatter more light than the 10 μm coatings containing 1.5 μm in diameter capsules but are still more optically clear than systems with poor index matching.
Issue Date:2012-02-06
Rights Information:Copyright 2011 Aaron C. Jackson
Date Available in IDEALS:2012-02-06
Date Deposited:2011-12

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