Self-Healing Materials Hager, Martin D.; Greil, Peter; Leyens, Christoph ...
Advanced materials (Weinheim),
December 14, 2010, Volume:
22, Issue:
47
Journal Article
Peer reviewed
Self‐healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality can be restored. This article covers ...the design and generic principles of self‐healing materials through a wide range of different material classes including metals, ceramics, concrete, and polymers. Recent key developments and future challenges in the field of self‐healing materials are summarised, and generic, fundamental material‐independent principles and mechanism are discussed and evaluated.
Self‐healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality of self‐healed materials can be restored. This behavior can be applied across a wide range of different material classes including metals, ceramics, concrete, and polymers.
Inspired by naturally occurring species that allow for self-healing of nonfatal harm, self-healing polymeric materials have been prepared and represent a component of the intelligent materials ...family. These materials possess the inherent ability to rehabilitate damage produced during manufacturing and/or usage. The self-healing methodologies developed to date can be classified as intrinsic or extrinsic according to the method used to deliver the healing components to the target site in the material. Intrinsic self-healing operates through inter- or intra-macromolecular interactions, whereas extrinsic self-healing makes use of a pre-embedded healing agent. Extrinsic self-healing can be more easily realized in commercially available polymers because no structural modification of the matrix molecules is required. In recent years, extrinsic self-healing based on microencapsulated healing agents has attracted growing interest. Extrinsic self-healing in a variety of materials (including thermosets, thermoplastics, rigid, and elastomeric materials) has been demonstrated and offers recovery of both mechanical and non-structural functional properties. Self-healing based on microcapsules can deliver further results if combined with intrinsic self-healing. Using a bottom-up perspective, the current article presents a comprehensive review of recent progress in this field from the viewpoint of material design and preparation. The topics presented include (i) a basic overview of self-healing systems, (ii) microencapsulation techniques (e.g., in situ polymerization, interfacial polymerization, Pickering emulsion templating, miniemulsion polymerization, solvent evaporation/solvent extraction, sol–gel reaction, etc.), (iii) crack response of microcapsules, and (iv) healing chemistries (e.g., ring-opening metathesis polymerization, polycondensation, anionic ring opening polymerization, cationic polymerization, free radical polymerization, addition reaction, etc.). The strengths and weaknesses of each microencapsulation technique and type of healing chemistry are analyzed and compared. Additionally, formulation optimization (including species of healing agent and wall substance of capsules), processing, structure and property relationship, healing mechanisms, and stability are discussed. Trends and challenges are summarized at the end of the review. The scope of this review is to provide the reader with an overview of achievements to date and insight into future development for engineering applications.
"If the Saint calls you, if you have an open road, then you don't feel the fire as if it were your enemy," says one of the participants in the Anastenaria. This compelling work evokes and contrasts ...two forms of firewalking and religious healing: first, the Anastenaria, a northern Greek ritual in which people who are possessed by Saint Constantine dance dramatically over red-hot coals, and, second, American firewalking, one of the more spectacular activities of New Age psychology. Loring Danforth not only analyzes these rituals in light of the most recent work in medical and symbolic anthropology but also describes in detail the lives of individual firewalkers, involving the reader personally in their experiences: he views ritual therapy as a process of transformation and empowerment through which people are metaphorically moved from a state of illness to a state of health. Danforth shows that the Anastenaria and the songs accompanying it allow people to express and resolve conflict-laden family relationships that may lead to certain kinds of illnesses. He also demonstrates how women use the ritual to gain a sense of power and control over their lives without actually challenging the ideology of male dominance that pervades Greek culture. Comparing the Anastenaria with American firewalking, Danforth includes a gripping account of his own participation in a firewalk in rural Maine. Finally he examines the place of anthropology in a postmodern world in which the boundaries between cultures are becoming increasingly blurred.
In the second half of the twentieth century, Reiki went from an
obscure therapy practiced by a few thousand Japanese and Japanese
Americans to a global phenomenon. By the early twenty-first
century, ...people in nearly every corner of the world have undergone
the initiations that authorize them to channel a cosmic
energy-known as Reiki-to heal body, mind, and spirit. They lay
hands on themselves and others, use secret symbols and incantations
to send Reiki to distant recipients, and strive to follow five
precepts to cultivate their spiritual growth. Reiki's international
rise and development is due to the work of Hawayo Takata
(1900-1980), a Hawai'i-born Japanese American woman who brought
Reiki out of Japan and adapted it for thousands of students in
Hawai'i and North America, shaping interconnections across the
North Pacific region as well as cultural transformations over the
transwar period spanning World War II. Alternate Currents: Reiki's
Circulation in the Twentieth-Century North Pacific analyzes how,
from her training in Japan in the mid-1930s to her death in Iowa in
1980, Takata built a vast trans-Pacific network that connected
Japanese American laborers on plantations in Hawai'i to social
elites in Tokyo, Hollywood, and New York; middle-class housewives
in American suburbs; and off-the-grid tree planters in the
mountains of British Columbia. Using recently uncovered archival
materials and original oral histories, Justin B. Stein examines how
these relationships between healer and patient, master and
disciple, became deeply infused with values of their time and place
and how they interplayed with Reiki's circulation, performance, and
meanings along with broader cultural shifts in the
twentieth-century North Pacific. Highly readable and informative,
each chapter is structured around a period in the life of Takata,
the charismatic, rags-to-riches architect of the network in which
Reiki spread for decades. Alternate Currents explores Reiki as an
exemplary transnational spiritual therapy, demonstrating how lived
practices transcend artificial distinctions between religion and
medicine, and circulate in global systems while maintaining strong
connections with the practices' homeland.
An extrinsic self‐healing coating system containing tetraphenylethylene (TPE) in microcapsules was monitored by measuring aggregation‐induced emission (AIE). The core healing agent comprised of ...methacryloxypropyl‐terminated polydimethylsiloxane, styrene, benzoin isobutyl ether, and TPE was encapsulated in a urea‐formaldehyde shell. The photoluminescence of the healing agent in the microcapsules was measured that the blue emission intensity dramatically increased and the storage modulus also increased up to 105 Pa after the photocuring. These results suggested that this formulation might be useful as a self‐healing material and as an indicator of the self‐healing process due to the dramatic change in fluorescence during photocuring. To examine the ability of the healing agent to repair damage to a coating, a self‐healing coating containing embedded microcapsules was scribed with a razor. As the healing process proceeded, blue light fluorescence emission was observed at the scribed regions. This observation suggested that self‐healing could be monitored using the AIE fluorescence.
An extrinsic self‐healing coating containing tetraphenylethylene in microcapsules is monitored by aggregation‐induced emission (AIE). As the healing process proceeds, blue fluorescence is observed at scribed region. Self‐healing can be monitored using the AIE.
Self-healing polymer composites possess the inherent ability to heal the damage event autonomically or non-autonomically with external intervention. These advanced materials can be commercialized if ...the challenges and limitations of different self-healing mechanisms are well known and considered. These include capsule-based healing systems, vascular healing systems, and intrinsic healing systems. To date, most of the reviews have studied and reported on different self-healing mechanisms including their response to impact, fatigue, and corrosion tests. This review focuses mostly on extrinsic and intrinsic self-healing polymer composites which have been reported during the past five years by comparing their healing efficiency, advantages, and challenges in the prospect of their future development as well as their possible applications across various industries such as aerospace, automobile, coating, electronics, energy, etc.
