Advanced Structured Materials Alexander L. Yarin Min Wook Lee Seongpil An Sam S. Yoon Self-Healing Nanotextured Vascular Engineering Materials Advanced Structured Materials Volume 105 Series editors Andreas Öchsner, Faculty of Mechanical Engineering, Esslingen University of Applied Sciences, Esslingen, Germany Lucas F. M. da Silva, Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Porto, Portugal Holm Altenbach, Faculty of Mechanical Engineering, Otto-von-Guericke-UniversitätMagdeburg,Magdeburg,Sachsen-Anhalt,Germany Common engineering materials reach in many applications their limits and new developments are required to fulfil increasing demands on engineering materials. The performance ofmaterials can beincreasedby combiningdifferent materials to achieve better properties than a single constituent or by shaping the material or constituents in a specific structure. The interaction between material and structure mayariseondifferentlengthscales,suchasmicro-,meso-ormacroscale,andoffers possible applications in quite diverse fields. Thisbookseriesaddressesthefundamentalrelationshipbetweenmaterialsandtheir structure on the overall properties (e.g. mechanical, thermal, chemical or magnetic etc) and applications. The topics of Advanced Structured Materials include but are not limited to (cid:129) classical fibre-reinforced composites (e.g. glass, carbon or Aramid reinforced plastics) (cid:129) metal matrix composites (MMCs) (cid:129) micro porous composites (cid:129) micro channel materials (cid:129) multilayered materials (cid:129) cellular materials (e.g., metallic or polymer foams, sponges, hollow sphere structures) (cid:129) porous materials (cid:129) truss structures (cid:129) nanocomposite materials (cid:129) biomaterials (cid:129) nanoporous metals (cid:129) concrete (cid:129) coated materials (cid:129) smart materials Advanced Structured Materials is indexed in Google Scholar and Scopus. More information about this series at http://www.springer.com/series/8611 Alexander L. Yarin Min Wook Lee (cid:129) (cid:129) Seongpil An Sam S. Yoon (cid:129) Self-Healing Nanotextured Vascular Engineering Materials 123 Alexander L. Yarin Min WookLee Department ofMechanical andIndustrial Institute of AdvancedComposite Materials Engineering Korea Institute of Science andTechnology University of Illinois at Chicago Jeollabuk-do, Korea(Republic of) Chicago, IL, USA SamS. Yoon SeongpilAn Schoolof MechanicalEngineering Department ofMechanical andIndustrial Korea University Engineering Seoul, Korea (Republicof) University of Illinois at Chicago Chicago, IL, USA ISSN 1869-8433 ISSN 1869-8441 (electronic) AdvancedStructured Materials ISBN978-3-030-05266-9 ISBN978-3-030-05267-6 (eBook) https://doi.org/10.1007/978-3-030-05267-6 LibraryofCongressControlNumber:2018966402 ©SpringerNatureSwitzerlandAG2019 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. 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ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Preface Nature-inspired self-healing strategies have been explored in biomimetic engi- neeringdesignswiththegoalofrepairingstructuraldamageorfacilitatingcorrosion protection by the systematic transport of healing agents, which can be cured and polymerized at damage sites. Microscopic capsules filled with healing agents, the proposedstrategy,arecertainlyviableandrequirenoexternalenergytotriggerthe healing process. However, a material layer with such capsules is inherently thick because of the bulky microcapsules. Moreover, the capsule-based approach is inappropriate for repeatable healing, since capsules can be used only once. Accordingly, a different approach with much smaller confined containers for healingagentsandthecapacityformultiplehealingwasdesired.Recentyearshave included success inthe development and characterization of nanotextured vascular self-healingmaterials,whicharethefocusofthepresentbook.Here,wediscussthe state of the art in the field of such materials, which emerged to mimic multiple natural materials, for example, those characteristics of the human body (e.g., skin and bones healed by the vascular system). The book describes relevant healing agents and the basic physicochemical phenomena characteristic of the self-healing materials and composites based on them. The book also details fabrication methods used for the key elements of vascular systems in modern nanotextured engineering self-healing materials, such as electrospinning (including co-electrospinning and emulsion spinning) and solution blowing (including coaxial solution blowing and emulsion blowing). It also outlines other approaches based on hollow fibers, tubes, etc. Self-healing materials should be capable of self-restoring their mechanical properties,e.g.,stiffness,toughness,adhesion,andcohesion.Itisnecessarytoheal the invisible and practically undetectable fatigue cracks, which endanger airplanes and multiple other vehicles and structures using composite components. Nanotextured vascular self-healing can also prevent or delay delamination in composites on ply surfaces. Therefore, the book details certain fundamental mechanicaltests(e.g.,tensile,fatigue,blister,andimpacttests)andtheperformance of nanotextured vascular self-healing materials in these tests. It demonstrates the v vi Preface degreetowhichsuchmaterialscanrestoretheirstiffness,toughness,adhesion,and cohesion. Another field where nanotextured vascular self-healing materials are extremely desirable is in corrosion protection. The corrosion of metals is recognized as one of the major problems in various metal-framed structures. As an introduction to corrosion phenomena, the book discusses the electrochemical fundamentals of corrosion crack growth. Numerous corrosion protection approaches have been suggested, including the cathodic protection method, the anti-corrosion paint coating method, and others. However, the toxicity of the chemical paints used and other problems relating to the cost and to the environment remain as serious con- cernswiththesemethods.Accordingly,thebookdescribesthebio-inspiredvascular self-healing techniques recently explored as alternative approaches for corrosion prevention. In particular, it discusses in detail the extrinsic self-healing based on nanotextured vascular nanofiber networks and demonstrates the successful perfor- manceofsuchmaterialsincrackhealingincorrosionprotectionlayers.Theresults revealthatthisapproachtoanti-corrosionprotectionholdsgreatpromisebecauseof its economic and industrial feasibility. Our personalresearch experience inthis fieldcovers and spans nearly all topics covered in this book. This monograph is based significantly on our own results published in peer-reviewed journals over the last 8 years. The book begins with the Introduction, which provides an overview of the existingself-healingapproachesandtracesthembacktonaturallyhealingtissuesof humantissueandbone.Thus,theideaofbiomimeticapproachforthedevelopment ofself-healingengineeringmaterialsisintroduced.Thefirstbiomimeticallyderived approach to composite engineering materials was based on microcapsules that contained healing agents, which were released by propagating cracks, thus healing the cracks. The benefits and drawbacks of the microcapsule-based approach are discussed, namely, the relatively large scale of such microcapsules and the diffi- culties in their manufacturing, which drove the development of nanotextured vas- cular composites. These composites are based on core-shell nanofiber networks filled with healing agents, which can be released by the propagation of cracks to heal these cracks. These nanotextured vascular self-healing materials are the main focus of the present book. The Introduction is followed by four parts, each comprising several chapters. Part I begins with a description of the healing agents used in engineering self-healingmaterials(Chap.2).ThischapterofPartIismostlychemicalinnature. Chapter 3 is devoted to the fundamental physicochemical phenomena accompa- nying self-healing, namely, the spreading of the released drops of healing agents, their mixing, and the stitching of the cracks. This chapter involves some theory regarding drop spreading and imbibition in porous nanofiber mats, as well as experimental observations employing macroscopic models of self-healing materials. Part II of the book addresses the fabrication methods used to form core-shell nanofiber mats, with the cores containing healing agents. These methods are, namely, electrospinning and co-electrospinning, emulsion spinning, solution Preface vii blowing,etc.(Chap.4).InChap.5,thecharacterizationmethodsusedtodetectthe presence, release, polymerization, and solidification of the encaged healing agents on the nanometer scale are described. The following Part III begins with Chap. 6, where the fundamental theoretical aspectsoffracturemechanicsareoutlined.Namely,abrieftheoreticaldescriptionof cracks in brittle elastic materials is given and the fundamentals of the Griffith approach based on the surface energy are introduced. The fracture toughness of Mode I, II, and III cracks is described, including viscoelastic effects. Critical (catastrophic) and subcritical (fatigue) cracks and their growth are also described theoretically. The adhesion and cohesion energies are introduced as well, and the theory of the blister test for the two limiting cases of stiff and soft materials is developed. In addition, the effect of non-self-healing nanofiber mats on the tougheningofplysurfacesincompositesisdiscussed.Then,inChap.7inPartIII, theexperimentaldataacquiredwithself-healingnanotexturedvascularmaterialsin tensile tests are discussed. Blister and impact tests, as well as the results on the interfacial toughening associated with nanofibers are the focus of Chap. 8. The interpretation of the results of blister tests is based on the previously introduced theoryandallowstheelucidationoftheextenttowhichsuchmechanicalproperties as stiffness and the adhesion/cohesion energy are restored in self-healing nan- otextured vascular materials. Double-cantilever beam and bending tests are also discussed in this chapter. Part IV begins with Chap. 9, which contains a brief description of the electro- chemical theory of corrosion crack growth. Then, the discussion turns to repre- sentative extrinsic self-healing techniques developed in the last decade, with the capsule-based (Chap. 9) and nanofiber-based self-healing approaches (Chap. 10) being in focus. Such physicochemical approaches are expected to effectively replace or supplement existing corrosion protection methods. An overview of the corrosionprotectionintheself-healingextrinsicnanotexturedvascularengineering materials formed using the capsule-based and nanofiber-based self-healing approaches is given. ThefinalChap.11ofthebookisdevotedtofutureperspectives,withthecurrent limitationsbeinghighlightedandattractivedirectionsforfutureresearchdiscussed. These directions hold great promise for the further improvement of extrinsic self-healing techniques for the recovery of mechanical properties and corrosion protection, and their industrial scalability. Each chapter in the book can be read by itself. A wide range of relevant ref- erences toexistingliterature are included at theend of each chapter. Thisdoesnot preclude the discussion of all topics in the book in a sufficiently self-contained, detailed, and in-depth manner. This book is intended as a comprehensive guide in the field of self-healing nanotextured vascular materials for senior-year undergraduate students, graduate students, researchers, engineers, and practitioners in industry. The reader can benefit from previous exposure to the fundamentals of chemistry, fluid and solid mechanics,andelectrochemistry.However,ifthereaderhasnotbeenintroducedto these topics, all necessary concepts are briefly but thoroughly introduced in the viii Preface appropriatechapters.Investigatorsfromthefollowingdifferentfieldsareaddressed: materials science, aerospace engineering, automotive and chemical engineering, production, as well as polymer science, and fluid and solid mechanics. The book may be of special importance to researchers and engineers interested in the development of novel self-healing engineering materials, because they can benefit from its in-depth and comprehensive exposition of physicochemical and mechan- ical fundamentals relevant to materials development. We areindebtedto our parents andfamilies whose permanent supporthas been tremendously beneficial to our research. We are thankful to our students and col- leagueswhodirectlyorindirectly,viafruitfuldiscussionscontributedtotheresults explained in this book. Many of their names are listed as our coauthors in the referencesincludedineachchapter.ALYisextremelygratefultoEmmanuelY,for his special contribution to this work. In addition, we acknowledge the generous supportofourjointworkbytheAgencyforDefenseDevelopmentoftheRepublic of Korea through its International Collaboration Program. Chicago, USA Alexander L. Yarin Jeollabuk-do, Korea (Republic of) Min Wook Lee Chicago, USA Seongpil An Seoul, Korea (Republic of) Sam S. Yoon Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Nature-Inspired Biomimetic Self-Healing for Self-sustained Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Self-Healing: Extension to Corrosion Protection . . . . . . . . . . . . 4 1.3 Capsule-Based Approach to Self-Healing . . . . . . . . . . . . . . . . . 5 1.3.1 Microcapsules Filled with Healing Agents . . . . . . . . . . 6 1.3.2 Nanoscale Capsules Filled with Healing Agents. . . . . . 8 1.4 Tube and Channel Networks and Microfibers . . . . . . . . . . . . . . 9 1.5 Sacrificial Materials and Shape-Memory Polymers . . . . . . . . . . 16 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Part I Materials and Fundamental Physicochemical Phenomena 2 Healing Agents Used for Mechanical Recovery in Nanotextured Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.1 Dicyclopentadiene (DCPD) and Grubbs’ Catalyst . . . . . . . . . . . 25 2.2 Poly(Dimethyl Siloxane) (PDMS) . . . . . . . . . . . . . . . . . . . . . . 26 2.3 Other Elastomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.4 Bisphenol-A-Based Epoxy and Other Types of Epoxy . . . . . . . 31 2.5 Gels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3 Macroscopic Observations of Physicochemical Aspects of Self-Healing Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1 Spreading of Released Drops of Healing Agents on Horizontal Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.1 Experimental Observations . . . . . . . . . . . . . . . . . . . . . 38 3.1.2 Wetting of Self-Healing Agents on Porous Electrospun NFs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 ix