{"71054":{"#nid":"71054","#data":{"type":"news","title":"Physicists Turn Liquid into Solid Using an Electric Field","body":[{"value":"\u003Cp\u003EPhysicists\nhave predicted that under the influence of sufficiently high electric fields,\nliquid droplets of certain materials will undergo solidification, forming\ncrystallites at temperature and pressure conditions that correspond to liquid\ndroplets at field-free conditions. This electric-field-induced phase\ntransformation is termed electrocrystallization.\nThe study, performed by scientists at the Georgia Institute of Technology,\nappears online and is scheduled as a feature and cover article in the 42\u003Csup\u003End\u003C\/sup\u003E\nissue of Volume 115 of the \u003Cem\u003EJournal of Physical Chemistry C\u003C\/em\u003E.\u003C\/p\u003E\n\n\u003Cp\u003E\u201cWe\nshow that with a strong electric field, you can induce a phase transition\nwithout altering the thermodynamic parameters,\u201d said Uzi Landman, Regents\u2019 and\nInstitute Professor in the School of Physics, F.E. Callaway Chair and director\nof the Center for Computational Materials Science (CCMS) at Georgia Tech.\u003C\/p\u003E\n\n\u003Cp\u003EIn\nthese simulations, Landman and Senior Research Scientists David Luedtke and\nJianping Gao at the CCMS set out first to explore a phenomenon described by Sir\nGeoffrey Ingram Taylor in 1964 in the course of his study of the effect of\nlightning on raindrops, expressed as changes in the shape of liquid drops when\npassing through an electric field.\u0026nbsp; While liquid drops under field-free\nconditions are spherical, they alter their shape in response to an applied\nelectric field to become needle-like liquid drops. Instead of the water\ndroplets used in the almost 50-year-old laboratory experiments of Taylor, the\nGeorgia Tech researchers focused their theoretical study on a 10 nanometer (nm)\ndiameter liquid droplet of formamide, which is a material made of small polar\nmolecules each characterized by a dipole moment that is more than twice as\nlarge as that of a water molecule.\u0026nbsp;\u0026nbsp; \u003C\/p\u003E\n\n\u003Cp\u003EWith\nthe use of molecular dynamics simulations developed at the CCMS, which allow\nscientists to track the evolution of materials systems with ultra-high\nresolution in space and time, the physicists explored the response of the\nformamide nano-droplet to an applied electric field of variable strength.\nInfluenced by a field of less than 0.5V\/nm, the spherical droplet elongated\nonly slightly. However, when the strength of the field was raised to a critical\nvalue close to 0.5 V\/nm, the simulated droplet was found to undergo a shape transition\nresulting in a needle-like liquid droplet with its long axis \u2013 oriented along\nthe direction of the applied field \u2013 measuring about 12 times larger than the\nperpendicular (cross-sectional) small axis of the needle-like droplet. The\nvalue of the critical field found in the simulations agrees well with the\nprediction obtained almost half a century ago by Taylor from general macroscopic\nconsiderations.\u003C\/p\u003E\n\n\u003Cp\u003EPast\nthe shape transition further increase of the applied electric field yielded a\nslow, gradual increase of the aspect ratio between the long and short axes of\nthe needle-like droplet, with the formamide molecules exhibiting liquid\ndiffusional motions.\u0026nbsp; \u003C\/p\u003E\n\n\u003Cp\u003E\u201cHere\ncame the Eureka moment,\u201d said Landman. \u201cWhen the field strength in the\nsimulations was ramped up even further, reaching a value close to 1.5V\/nm, the\nliquid needle underwent a solidification phase transition, exhibited by\nfreezing of the diffusional motion, and culminating in the formation of a\nformamide single crystal characterized by a structure that differs from that of\nthe x-ray crystallographic one determined years ago under zero-field\nconditions. Now, who ordered that?\u201d he added.\u0026nbsp; \u003C\/p\u003E\n\n\u003Cp\u003EFurther\nanalysis has shown that the crystallization transition involved arrangement of\nthe molecules into a particular spatial ordered lattice, which optimizes the\ninteractions between the positive and negative ends of the dipoles of\nneighboring molecules, resulting in minimization of the free energy of the\nresulting rigid crystalline needle.\u0026nbsp; When the electric field applied to the\ndroplet was subsequently decreased, the crystalline needle remelted and at\nzero-field the liquid droplet reverted to a spherical shape. The field reversal\nprocess was found to exhibit a hysteresis. \u003C\/p\u003E\n\n\u003Cp\u003EAnalysis\nof the microscopic structural changes that underlie the response of the droplet\nto the applied field revealed that accompanying the shape transition at 0.5\nV\/nm is a sharp increase in the degree of reorientation of the molecular\nelectric dipoles, which after the transition lie preferentially along the\ndirection of the applied electric field and coincide with the long axis of the\nneedle-\u0026shy;\u0026shy;like liquid droplet. The directional dipole reorientation, which is\nessentially complete subsequent to the higher field electrocrystallization\ntransition, breaks the symmetry and transforms the droplet into a field-induced\nferroelectric state where it possesses a large net electric dipole, in contrast\nto its unpolarized state at zero\u2013field conditions.\u0026nbsp; \u003C\/p\u003E\n\n\u003Cp\u003EAlong\nwith the large-scale atomistic computer simulations, researchers formulated and\nevaluated an analytical free-energy model, which describes the balance between\nthe polarization, interfacial tension and dielectric saturation contributions.\nThis model was shown to yield results in agreement with the computer simulation\nexperiments, thus providing a theoretical framework for understanding the\nresponse of dielectric droplets to applied fields. \u003C\/p\u003E\n\n\u003Cp\u003E\u201cThis\ninvestigation unveiled fascinating properties of a large group of materials\nunder the influence of applied fields,\u201d Landman said. \u201cHere the field-induced\nshape and crystallization transitions occurred because formamide, like water\nand many other materials, is characterized by a relatively large electric\ndipole moment. The study demonstrated the ability to employ external fields to\ndirect and control the shape, the aggregation phase (that is, solid or liquid)\nand the properties of certain materials.\u201d\u0026nbsp; \u003C\/p\u003E\n\n\u003Cp\u003EAlong\nwith the fundamental interest in understanding the microscopic origins of\nmaterials behavior, this may lead to development of applications of\nfield-induced materials control in diverse areas, ranging from targeted drug delivery,\nnanoencapsulation, printing of nanostructures and surface patterning, to\naerosol science, electrospray propulsion and environmental science.\u003C\/p\u003E\u003Cp\u003EThis research was supported by a grant from the U.S. Air Force Office of Scientific Research.\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EPhysicists\nhave predicted that under the influence of sufficiently high electric fields,\nliquid droplets of certain materials will undergo solidification, forming\ncrystallites at temperature and pressure conditions that correspond to liquid\ndroplets at field-free conditions. This electric-field-induced phase\ntransformation is termed electrocrystallization and was performed at the Georgia Institute of Technology,\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":"","uid":"27560","created_gmt":"2011-10-10 12:05:10","changed_gmt":"2016-10-08 03:10:26","author":"Jason Maderer","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2011-10-10T00:00:00-04:00","iso_date":"2011-10-10T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"40073":{"id":"40073","type":"image","title":"Uzi Landman","body":null,"created":"1449174146","gmt_created":"2015-12-03 20:22:26","changed":"1475894231","gmt_changed":"2016-10-08 02:37:11","alt":"Uzi Landman","file":{"fid":"189593","name":"tsm23821.jpg","image_path":"\/sites\/default\/files\/images\/tsm23821.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/tsm23821.jpg","mime":"image\/jpeg","size":1903110,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/tsm23821.jpg?itok=IcU_zvYC"}},"71061":{"id":"71061","type":"image","title":"Electrocrystallization","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894628","gmt_changed":"2016-10-08 02:43:48","alt":"Electrocrystallization","file":{"fid":"193487","name":"cover_elect_crys_joc_c_as_submitted_sept_01.jpg","image_path":"\/sites\/default\/files\/images\/cover_elect_crys_joc_c_as_submitted_sept_01_0.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/cover_elect_crys_joc_c_as_submitted_sept_01_0.jpg","mime":"image\/jpeg","size":1812239,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/cover_elect_crys_joc_c_as_submitted_sept_01_0.jpg?itok=UNGRiX8t"}}},"media_ids":["40073","71061"],"related_links":[{"url":"http:\/\/www.cos.gatech.edu\/","title":"College of Sciences"},{"url":"http:\/\/www.physics.gatech.edu\/","title":"Georgia Tech School of Physics"},{"url":"https:\/\/www.physics.gatech.edu\/user\/uzi-landman","title":"Uzi Landman"}],"groups":[{"id":"1214","name":"News Room"}],"categories":[{"id":"135","name":"Research"}],"keywords":[{"id":"4896","name":"College of Sciences"},{"id":"166937","name":"School of Physics"},{"id":"9180","name":"Uzi Landman"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJason Maderer, Media Relations\u003Cbr \/\u003E404-385-2966\u003C\/p\u003E","format":"limited_html"}],"email":["jason.maderer@comm.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}