{"256751":{"#nid":"256751","#data":{"type":"news","title":"Sticky Business: Magnetic Pollen Replicas Offer Multimodal Adhesion","body":[{"value":"\u003Cp\u003EResearchers have created magnetic replicas of sunflower pollen grains using a wet chemical, layer-by-layer process that applies highly conformal iron oxide coatings. The replicas possess natural adhesion properties inherited from the spiky pollen particles while gaining magnetic behavior, allowing for tailored adhesion to surfaces.\u003C\/p\u003E\u003Cp\u003EBy taking advantage of the native pollen grain shape and a non-natural oxide chemistry, this work provides a unique demonstration of tunable, bio-enabled multimodal adhesion. The spikes inherited from the sunflower pollen provide short range adhesion \u2013 over nanoscale distances \u2013 while the oxide chemistry provides an adhesion mode that operates over much longer distances \u2013 up to one millimeter.\u003C\/p\u003E\u003Cp\u003EThe work was supported by the Air Force Office of Scientific Research, and has been accepted for publication in the journal \u003Cem\u003EChemistry of Materials\u003C\/em\u003E. A \u201cjust-accepted\u201d version of the manuscript has appeared online.\u003C\/p\u003E\u003Cp\u003E\u201cPollen grains are inexpensive and sustainable templates that are readily available in large quantities,\u201d said \u003Ca href=\u0022http:\/\/www.mse.gatech.edu\/faculty\/sandhage\u0022\u003EKen Sandhage\u003C\/a\u003E, a professor in the \u003Ca href=\u0022http:\/\/www.mse.gatech.edu\/\u0022\u003ESchool of Materials Science and Engineering\u003C\/a\u003E at the Georgia Institute of Technology. \u201cBecause pollen grains are already designed by nature for adhesion, we thought that it would be interesting to try to augment such natural behavior with an additional, non-natural mode of adhesion.\u201d\u003C\/p\u003E\u003Cp\u003ESandhage and graduate student Brandon Goodwin began by examining the microscopic shapes of several types of pollen \u2013 including ragweed, pecan and dandelion \u2013 before choosing particles from the sunflower (\u003Cem\u003EHelianthus annuus\u003C\/em\u003E). The sunflower pollen grains are nearly spherical, but covered with spikes that can entangle with the hairs on bees\u2019 legs, or adhere to surfaces via van der Waals forces at nanometer-scale distances, Sandhage explained.\u003C\/p\u003E\u003Cp\u003EThe researchers washed the burr-like pollen particles with chloroform, methanol, hydrochloric acid and water to clean the surfaces and expose hydroxyl groups for chemically attaching their coating. They then applied iron oxide using an automated, layer-by-layer surface sol-gel process they had developed earlier for coating diatom shells made of silica. Reaction of the iron oxide precursor with the hydroxyl groups on the surface of the pollen particles resulted in a highly-conformal coatings.\u003C\/p\u003E\u003Cp\u003EThe sol-gel process used alternating cycles of exposure to an iron (III) isopropoxide precursor solution and water to apply 30 thin layers of hematite (Fe\u003Csub\u003E2\u003C\/sub\u003EO\u003Csub\u003E3\u003C\/sub\u003E) onto the pollen. Heating the particles to 600 degrees Celsius then burned out the organic material from the original pollen grains and crystallized the iron oxide, leaving hollow 3D particles. The shells were then heated again in a controlled oxygen atmosphere to convert the hematite into magnetite (Fe\u003Csub\u003E3\u003C\/sub\u003EO\u003Csub\u003E4\u003C\/sub\u003E), which is more strongly magnetic.\u003C\/p\u003E\u003Cp\u003E\u201cWe examined individual pollen grains before and after firing, and we could see that the shape and surface features were well preserved,\u201d said Sandhage, who is the B. Mifflin Hood Professor in the School of Materials Science and Engineering. \u201cThe conformal nature of the coating process allowed us to generate ceramic replicas that retained even tiny surface features on the starting pollen grains.\u201d\u003C\/p\u003E\u003Cp\u003EThe adhesion properties of the magnetic pollen-shaped particles were then analyzed by graduate student Ismael Gomez and professor \u003Ca href=\u0022http:\/\/www.chbe.gatech.edu\/faculty\/meredith\u0022\u003ECarson Meredith\u003C\/a\u003E, both from Georgia Tech\u2019s \u003Ca href=\u0022http:\/\/www.chbe.gatech.edu\/\u0022\u003ESchool of Chemical and Biomolecular Engineering\u003C\/a\u003E. Gomez and Meredith used an atomic force microscope (AFM) tip to press the replicas onto a variety of surfaces, then measured the force required to remove them from the surfaces. They studied replica pollen adhesion to polyvinyl alcohol, polyvinyl acetate, polystyrene, silicon, nickel and neodymium-iron-boron \u2013 and compared the adhesion properties to those of the original sunflower pollen grains.\u003C\/p\u003E\u003Cp\u003E\u201cWe found that we achieved multimodal adhesion by retaining short-range van der Waals attraction, as exhibited by the native pollen, and gaining magnetic adhesion,\u201d Sandhage said.\u003C\/p\u003E\u003Cp\u003EThe layer-by-layer nature of the coating process allowed for control of the amount of magnetic material, and the magnetic properties of the pollen replicas. The researchers chose to apply 30 layers to achieve sufficient long-range magnetic behavior while retaining high-aspect-ratio, sharp spikes that provide for short-range van der Waals forces.\u003C\/p\u003E\u003Cp\u003E\u201cReproducibly generating large quantities of such cheap microparticles possessing high-aspect surface features over their entire particle surfaces would be quite challenging using synthetic top-down methods,\u201d Sandhage said.\u003C\/p\u003E\u003Cp\u003EThe Air Force Multidisciplinary University Research Initiative (MURI) that funded the work is aimed at both understanding adhesion in natural systems and controllably tailoring such adhesion.\u0026nbsp; In future research supported by the MURI, Sandhage and Meredith plan to study other oxide materials and explore the variety of shapes available in pollen particles.\u003C\/p\u003E\u003Cp\u003E\u201cNow that we know how to generate such particle replicas, there is certainly more chemical tailoring that we can explore for adhesion,\u201d said Sandhage, who also holds an adjunct position in Georgia Tech\u2019s School of Chemistry and Biochemistry.\u0026nbsp; \u201cThrough the proper combination of pollen shape, synthetic chemistry and thermal treatments, we can significantly expand the range of properties of these pollen replicas.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by the U.S. Air Force Office of Scientific Research through award number FA9550-10-1-0555. Any conclusions are those of the authors and do not necessarily represent the official views of the U.S. Air Force.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: William Brandon Goodwin, Ismael J. Gomez, Carson Meredith and Kenneth H. Sandhage, \u201cConversion of Pollen Particles into Three-Dimensional Ceramic Replicas Tailored for Multimodal Adhesion.\u201d (Chemistry of Materials, 2013): \u003Ca href=\u0022http:\/\/%20dx.doi.org\/10.1021\/cm402226w\u0022\u003Ehttp:\/\/ dx.doi.org\/10.1021\/cm402226w\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia\u0026nbsp; 30332\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: John Toon (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E)(404-894-6986) or Brett Israel (\u003Ca href=\u0022mailto:brett.israel@comm.gatech.edu\u0022\u003Ebrett.israel@comm.gatech.edu\u003C\/a\u003E)(404-385-1933).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EResearchers have created magnetic replicas of sunflower pollen grains using a wet chemical, layer-by-layer process that applies highly conformal iron oxide coatings. The replicas possess natural adhesion properties inherited from the spiky pollen particles while gaining magnetic behavior, allowing for tailored adhesion to surfaces.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have created magnetic replicas of pollen grains using a wet chemical process that preserves the particles\u0027 shape."}],"uid":"27303","created_gmt":"2013-11-22 10:49:22","changed_gmt":"2016-10-08 03:15:25","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2013-11-22T00:00:00-05:00","iso_date":"2013-11-22T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"256731":{"id":"256731","type":"image","title":"Magnetic Pollen Particles","body":null,"created":"1449243846","gmt_created":"2015-12-04 15:44:06","changed":"1475894936","gmt_changed":"2016-10-08 02:48:56","alt":"Magnetic Pollen Particles","file":{"fid":"198233","name":"pollen_image.jpg","image_path":"\/sites\/default\/files\/images\/pollen_image_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/pollen_image_0.jpg","mime":"image\/jpeg","size":261770,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/pollen_image_0.jpg?itok=1HR4ZFjC"}}},"media_ids":["256731"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"7437","name":"adhesion"},{"id":"9563","name":"Ken Sandhage"},{"id":"2053","name":"magnetic"},{"id":"7663","name":"magnetic particles"},{"id":"4497","name":"Materials Science and Engineering"},{"id":"80651","name":"pollen"},{"id":"169747","name":"sol-gel"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39471","name":"Materials"},{"id":"39481","name":"National Security"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJohn Toon\u003C\/p\u003E\u003Cp\u003EResearch News\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E(404) 894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}