Ryan M. Deacon

Dipolar organization and magnetic actuation of flagella-like nanoparticle assemblies

Modeled after the design of eukaryotic protozoa, we fabricated artificial microscopic swimmers through the dipolar assembly of a bidisperse mixture of 250 nm superparamagnetic magnetite colloids and 24 nm ferromagnetic cobalt nanoparticles. The cobalt nanoparticles self-assemble into long, 1-D chains measuring approximately 24 nm × 5 µm. These chains then co-assemble with the magnetite beads to form “head” + “tail” structures. These types of asymmetric “flagella-like” colloidal assemblies were formed and maintained solely through dipolar interactions and is the first demonstration using randomly mixed dispersions of disparate magnetic colloids. When actuated by a pair of orthogonal static and sinusoidal magnetic fields, they undergo an asymmetric undulation that is the essential condition for locomotion at low Reynolds numbers. Based upon their shape, size, and articulation, these assemblies are potentially among the smallest structures capable of overcoming Brownian motion to perform useful locomotion. In addition to the head and tail structure, a variety of irregular structures formed that were incapable of swimming. A design of experiments (DOE) study was therefore implemented to optimize the production of artificial swimmers within a large parameter space that included concentration, the amount of sonication, and magnetic field strength. The artificial swimmers were most prevalent for intermediate concentrations of Co and magnetite particles. Statistical analysis suggested that the permanent dipole of the Co nanoparticles stimulated the assembly of the bidisperse mixture into complex, heterogeneous structures. Demonstration of in situ imaging of the magnetic actuation of these dipolar NP assemblies was conducted by optical microscopy.

Dipolar assembly of ferromagnetic nanoparticles into magnetically driven artificial cilia

Taking inspiration from eukaryotic cilia, we report a method for growing dense arrays of magnetically actuated microscopic filaments. Fabricated from the bottom-up assembly of polymer-coated cobalt nanoparticles, each segmented filament measures approximately 5–15 µm in length and 23.5 nm in diameter, which was commensurate with the width of a single nanoparticle. A custom microscope stage actuates the filaments through orthogonal permanent and alternating magnetic fields. We implemented design of experiments (DOE) to efficiently screen the effects of cobalt nanoparticle concentration, crosslinker concentration, and surface chemistry. The results indicated that the formation of dense, cilia-mimetic arrays could be explained by physical, non-covalent interactions (i.e. dipolar association forces) rather than chemistry. The experiments also determined an optimal Co nanoparticle concentration of approximately 500 µg ml−1 for forming dense arrays near the ends of the permanent magnets, and a critical concentration of approximately 0.3 µg ml−1, below which particle assembly into chains was not observed.

Liquid-Filled Metal Microcapsules

A moisture-sensitive diisocyanate liquid is microencapsulated within a metal shell measuring less than 2 μm thick and 50 μm in diameter. This mild synthesis takes place through a series aqueous processing steps that occur at or near room temperature. Through a combination of emulsification, interfacial polymerization, and electroless plating, one can microencapsulate moisture- or air-sensitive chemicals within a metal seal. The liquid-filled metal microcapsules promise a number of advantages compared to conventional polymeric microencapsulation, including improved mechanical properties and improved barrier properties to gases and organic molecules.

Surfactant sculpting of biologically inspired hierarchical surfaces

We describe a method for fabricating biologically inspired hierarchical surfaces in a single step through surfactant self-assembly at an oil/water interface. The key to this system is the use of polydimethylsiloxane-diacrylate for the oil phase, which makes it possible to solidify these delicate structures with UV photocuring. Scanning electron microscopy (SEM) and 3-D optical profilometry reveals morphologies that capture the randomness, fractal geometry, and hierarchical organization of natural materials. The morphology is controlled by surfactant type, surfactant concentration, viscosity, film thickness, and time. The experimental evidence is consistent with a spontaneous increase in surface area driven by a transiently negative surface tension. Spontaneous emulsification generates distinct morphologies for a given surfactant and surfactant concentration in a manner reminiscent of phase behavior in a ternary phase diagram. When emulsification cannot keep pace with the increase in surface area, buckles form. These perturbations are then amplified at increasing length scales by dewetting and the Rayleigh–Taylor instability.

Identifying Equipment Vendors in Scholarly Publications

When Metallography, Microstructure, and Analysis launched seven years ago, the founding editorial staff decided against having authors specify the vendors of equipment used in their work. The motivation for this decision was to avoid any appearance of partiality or endorsement of any specific instrument manufacturer. The author instructions for MMA state that vendor names are not to be listed in a manuscript, unless there is something unique about a certain vendor’s instrumentation. The editorial staff has recently begun to reconsider the initial decision to not provide instrument vendor names. A basic tenet of scholarly publishing is reproducibility of results—authors need to report sufficient detail of their work so that not only can readers properly interpret the results, but also so that someone practiced in the art could reproduce the work. Furthermore, considering that this journal is devoted to interpreting and analyzing microstructures, there is value in knowing which instrument has been used to prepare and image the microstructures. Identifying the equipment used to produce an image may also help the reviewers and editorial staff in identifying cases of image manipulation. Although I have not collected accurate numbers, I would estimate that 75% of the manuscripts submitted to MMA list the instrument vendors in the experimental section. This would seem to indicate that our authors consider this practice standard procedure, likely influenced by their interaction with other journals. A non-exhaustive survey of journals similar to MMA indicates that reporting the equipment vendor would seem to be the norm. Simply thumbing through the journals at my desk (my overflowing “to be read” pile), reveals the following journals permit, if not require, authors to list vendor names in their manuscripts: Journal of Materials Materials Characterization Metallurgical and Materials Transactions Microscopy and Microanalysis Microscopy Today Praktische Metallographie

Professor Guenter Petzow Named to MMA Honorary Advisory Board

Since its founding six years ago, Metallography, Microstructure, and Analysis has benefited greatly from the guidance and counsel of its editorial advisory board. This group of distinguished individuals has championed the journal’s growth, and helped MMA to find its place in the technical literature. One of the board members, Professor Guenter Petzow, has recently indicated his desire to step down from his position on the advisory committee, and reduce his active role in the International Metallographic Society. Professor Petzow has been a significant supporter of not only MMA, but also of the journal Materials Characterization, which was previously edited by MMA’s advisory editor, Dr. Chris Bagnall. Professor Petzow has also been a very active volunteer for the International Metallographic Society, serving on several committees, and lending his considerable energy and creativity to improving the society. In recognition of his significant contributions to both IMS and its journals, I am pleased to appoint Professor Petzow as the founding member of the Honorary Advisory Board for Metallography, Microstructure, and Analysis. It is my hope that the journal will continue to benefit from his advice and counsel as we continue to expand and improve. On behalf of the editorial staff of MMA and the Board of Directors of the International Metallographic Society, I offer my sincere gratitude for his service to our society and profession. Professor Guenter Petzow

Update on Special IMS 50th Anniversary Symposium at MS&T 2017

Recently, I shared the news that the International Metallographic Society would be celebrating its 50th anniversary this year, in part by having a special symposium at the MS&T conference in Pittsburgh, Pa., in October. This symposium will feature the previous recipients of the various honors that IMS bestows upon its members, including the Henry Clifton Sorby Award, the JacquetLucas Award, and the Buehler Best Paper Award. Abstract submissions for MS&T symposia closed just a few days ago, and I am happy to report that interest in the IMS symposium was quite high. We have received a number of abstracts from previous award recipients, in addition to some contributed talks from non-awardees. When the invitation to present a talk was sent to previous award winners, they were encouraged to select of topic of their own interest, be it an update on the work for which they were originally recognized by IMS, or something new entirely. Looking through the abstracts we have received, I see the speakers took this to heart; the topic areas for the proposed talks are quite diverse and will be of interest to a wide audience. The symposium coordinators are currently in the process of organizing the talks into sessions. In the next issue of MMA, I look forward to sharing some of the topics that our speakers will present. Additionally, MMA is planning to publish a special issue of manuscripts from this symposium; more details to follow. In the meantime, I hope that our readers will keep this special symposium in mind as you make plans for MS&T—it will be an excellent opportunity to see presentations from the luminaries in our field! I look forward to seeing you in Pittsburgh in October.

Presentations for Special IMS Symposium at MS&T’17 Have Been Accepted

As this issue ofMMA goes to print, we are only a fewmonths away from the 2017 MS&T conference, and the special symposium honoring the 50th anniversary of the founding of the International Metallographic Society. This symposium was created to recognize previous IMS award recipients, and the final lineup of presenters is truly impressive. This year’s Henry Clifton Sorby Award recipient, Professor Sir Colin Humphreys, will lead off the first session with a talk entitled ‘‘How Microscopy Can Help to Save Energy, Save Lives, Create Jobs, and Improve Our Health.’’ Throughout the course of this symposium, there will be presentations from seven previous Henry Clifton Sorby Award recipients, with topics including the following:

Announcing the MMA 2015 Editor’s Choice Awards

I am pleased to announce the manuscripts that have been selected for the 2015 Metallography, Microstructure, and Analysis Editor’s Choice award. The authors of these manuscripts are recognized for both the novelty of their research, and for the high quality of their respective manuscripts. These papers exhibit the characteristics that are considered especially important for this journal: clarity of presentation, a proper interpretation and thorough discussion of microstructure, and high-quality micrographs. These five papers are available ‘‘Free Access’’ through the Editor’s Choice link on the MMA website at http:// www.springer.com/materials/special?types/journal/13632, as well as through the journal’s page on SpringerLink. Normally, there is a charge for free access, but for papers selected by the editor for this award, the benefit is free. Study of Coarsening in c0 Precipitates by Diffusion Couples C.G. Garay-Reyes, S.E. Hernandez-Martinez, J.L. Hernandez-Rivera, I. Estrada-Guel, H.J. DorantesRosales, J.J. Cruz-Rivera, R. Martinez-Sanchez Metallogr. Microstruct. Anal. 4(6), 467–474 (2015)

Metallography, Microstructure, and Analysis: Birth of a New Journal

We are very pleased to be offering materials scientists a new forum for dissemination of technical advances as recorded with the aid of a microscope. ASM International perceived a need for a new publication to add to its current coverage of the materials world, and to give one of its affiliate societies, the International Metallographic Society, a journal to call its own. Metallography, Microstructure, and Analysis (MMA) was conceived to fill this need. After two years of planning and collaboration with our publisher, Springer, we are pleased to present our first issue. The appropriate preparation and analysis of a microstructure is a critical component of many materials characterization efforts, whether the ultimate goal is to develop new materials, to advance our understanding of an existing material, or to determine why a failure has occurred. More than any other attribute, microstructure exerts a controlling influence over the final properties and performance of a material. With clear interpretation and a sound understanding, microstructure can be exploited to provide outstanding mechanical, electrical, magnetic, or chemical properties. Conversely, insufficient attention to control of microstructure can lead to unpredictable properties, inconsistent behavior, and material failure. MMA is dedicated to the presentation, illustration, and recognition of microstructure and the important implications that can be realized from it. Accordingly, the journal focuses on methods for revealing microstructure, instruments used for its interpretation, and analysis of its influence on material properties. The objective of a technical journal in any field is to foster the dissemination of acquired knowledge to a broader audience, so that other researchers may use and build upon the work of their colleagues. This sharing of knowledge is especially critical in the fields of metallurgy and materials science, where the preparation of a mounted sample to reveal microstructure is oftentimes equal parts science and art. The myriad lessons learned in the laboratory by metallographers, technicians, and scientists constitute an important body of knowledge that can be of significant benefit to others in this field. One important goal of MMA is to promote the sharing of this information. It is an especially fitting time to be launching a new technical journal in this field, in light of the recent growth and development of analytical techniques that can be applied to the study of microstructures. These tools, such as electron backscattered diffraction, X-ray microtomography, and high resolution electron microscopy, are providing new levels of information about the structure of materials. In addition, continued development in new fields of materials production and design, such as additive manufacturing and integrated computational materials engineering, will require enhanced understanding of the role of R. M. Deacon (&) Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA e-mail: ryan.deacon@jhuapl.edu