{"71328":{"#nid":"71328","#data":{"type":"news","title":"AFM Shows Liquids Adjust Viscosity When Confined, Shaken","body":[{"value":"\u003Cp\u003EGetting ketchup out of the bottle isn\u0027t always easy. However, shaking the bottle before trying to pour allows the thick, gooey ketchup to flow more freely because it becomes more fluid when agitated. The opposite is not typically true - a liquid such as water does not become a gel when shaken.\u003C\/p\u003E\n\u003Cp\u003EHowever, new research published in the March 14 issue of the journal \u003Cem\u003EPhysical Review Letters \u003C\/em\u003E shows that when fluids like water and silicon oil are confined to a nanometer-sized space, they behave more like ketchup or toothpaste. Then, if these confined liquids are shaken, they become fluidic and exhibit the same structural and mechanical properties as those in thicker layers.\n\u003C\/p\u003E\n\u003Cp\u003EThe study - the first to use an atomic force microscope to measure the viscosity of confined fluids - revealed that these liquids can respond and modify their viscosity based on environmental changes. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022Knowing this could be very important,\u0022 said Elisa Riedo, an assistant professor in the Georgia Tech School of Physics. \u0022If a lubricant used in a piece of machinery becomes thick and gelatinous when squeezed between two solid surfaces, serious problems could occur. However, if the machine vibrated, the liquid could become fluidized.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EWith funding from the National Science Foundation and the U.S. Department of Energy, Riedo and graduate student Tai-De Li used atomic force microscopy (AFM) to measure the behavior of thin and thick layers of liquids while they were vibrated. A nanometer-size spherical silicon tip was used to approach a mica surface immersed in water or silicon oil, while small lateral oscillations were applied to the cantilever support.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Some researchers have measured the force it takes to squeeze out a fluid, but we took a different approach,\u0022 explained Riedo. \u0022We are the first group to use AFM to study the viscosity of confined fluids from direct high-resolution lateral force measurements.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe normal and lateral forces acting on the tip were measured directly and simultaneously as a function of the liquid film thickness. The ratio of stress to strain under vibratory conditions, called the viscoelastic modulus, was also measured at different frequencies and strains.\n\u003C\/p\u003E\n\u003Cp\u003ERiedo and Li measured the relaxation times of two wetting liquids: water and silicone oil (octamethylcylotetrasiloxane), which is primarily used as a lubricant or hydraulic fluid, and is the main ingredient in Silly Putty.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The relaxation time describes how active the molecules are. A longer relaxation time means it takes longer for the molecules to rearrange themselves back into their original shape after shaking them,\u0022 said Li. \u0022Liquids have very short relaxation times - as soon as one stops shaking a bottle of water, it reverts to its original configuration.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EExperimental results showed that the relaxation time became orders of magnitude longer in water and silicone oil when they were confined, meaning they behaved more like gels or glass. The researchers also showed that the relaxation times depended on the shaking speed when the liquids were confined. However, in thick layers that were not confined, the molecules showed no dependence on the shaking speed and always relaxed very quickly, meaning they behaved like a \u0027normal\u0027 liquid.\n\u003C\/p\u003E\n\u003Cp\u003ELonger relaxation times were observed when the water film was less than one nanometer thick, composed of about three molecules of water stacked on top of each other. Otherwise, its properties were the same as in a bottle of water. For silicone oil, a thickness of four nanometers was required before the properties were like those of a glassy material.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022We observed a nonlinear viscoelastic behavior remarkably similar to that widely observed in metastable complex fluids, such as gels or supercooled liquids,\u0022 noted Riedo. \u0022Because we observed these phenomena in both water and silicone oil, we believe they are very general phenomena and may apply to all wetting liquids.\u0022\n\u003C\/p\u003E\n\u003Cp\u003ESince the behavior of confined water observed in these experiments is similar to the behavior of supercooled water at -98.15 degrees Celsius, the researchers are currently examining whether confinement defines a lower effective temperature in the confined liquid.\n\u003C\/p\u003E\n\u003Cp\u003EThe views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\n\u003C\/strong\u003E\u003C\/p\u003E\n\u003Cp\u003EMedia Relations Contacts: Abby Vogel (404-385-3364); E-mail: (\u003Ca href=\u0022mailto:avogel@gatech.edu\u0022\u003Eavogel@gatech.edu\u003C\/a\u003E) or John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter:\u003C\/strong\u003E Abby Vogel\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"A new study - the first to use an atomic force microscope to measure the viscosity of confined fluids - shows that liquids can respond and modify their viscosity based on environmental changes.","format":"limited_html"}],"field_summary_sentence":[{"value":"Liquids can modify their viscosity based on environmental"}],"uid":"27206","created_gmt":"2008-04-29 00:00:00","changed_gmt":"2016-10-08 03:03:24","author":"Abby Vogel Robinson","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2008-04-29T00:00:00-04:00","iso_date":"2008-04-29T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"71329":{"id":"71329","type":"image","title":"Elisa Riedo 1","body":null,"created":"1449177367","gmt_created":"2015-12-03 21:16:07","changed":"1475894634","gmt_changed":"2016-10-08 02:43:54"},"71330":{"id":"71330","type":"image","title":"Tai-De AFM scanner","body":null,"created":"1449177367","gmt_created":"2015-12-03 21:16:07","changed":"1475894634","gmt_changed":"2016-10-08 02:43:54"},"71331":{"id":"71331","type":"image","title":"AFM liquid cell","body":null,"created":"1449177367","gmt_created":"2015-12-03 21:16:07","changed":"1475894634","gmt_changed":"2016-10-08 02:43:54"}},"media_ids":["71329","71330","71331"],"related_links":[{"url":"http:\/\/dx.doi.org\/10.1103\/PhysRevLett.100.106102","title":"Physical Review Letters article"},{"url":"http:\/\/www.physics.gatech.edu\/","title":"Georgia Tech School of Physics"},{"url":"http:\/\/www.physics.gatech.edu\/people\/faculty\/eriedo.html","title":"Elisa Riedo"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"3105","name":"atomic"},{"id":"7420","name":"confined"},{"id":"2402","name":"film"},{"id":"2473","name":"fluid"},{"id":"7419","name":"force"},{"id":"3132","name":"liquid"},{"id":"2834","name":"mechanical"},{"id":"7392","name":"microscopy"},{"id":"5926","name":"Molecules"},{"id":"7425","name":"nanometer"},{"id":"7427","name":"oscillate"},{"id":"6773","name":"relaxation"},{"id":"170875","name":"shake"},{"id":"170876","name":"silicon oil"},{"id":"170877","name":"structural"},{"id":"170878","name":"supercool"},{"id":"7423","name":"vibrate"},{"id":"7424","name":"viscosity"},{"id":"788","name":"Water"},{"id":"7428","name":"wetting"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EAbby Robinson\u003C\/strong\u003E\u003Cbr \/\u003EResearch News and Publications\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=avogel6\u0022\u003EContact Abby Robinson\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-385-3364\u003C\/strong\u003E","format":"limited_html"}],"email":["abby@innovate.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}