{"529411":{"#nid":"529411","#data":{"type":"news","title":"It Takes More than Peer Pressure to Make Large Microgels Fit In","body":[{"value":"\u003Cp\u003EWhen an assembly of microgel particles includes one particle that\u0027s significantly larger than the rest, that oversized particle spontaneously shrinks to match the size of its smaller neighbors. This self-healing nature of the system allows the microparticles to form defect-free colloidal crystals, an unusual property not seen in systems made up of \u201chard\u201d particles.\u003C\/p\u003E\u003Cp\u003EIn 2009, Andrew Lyon, then a professor of chemistry at the Georgia Institute of Technology, observed this dynamic resizing in a microgel system he had created, but the mechanism behind the self-healing process remained uncertain. Now, researchers believe they\u0027ve finally solved the mystery, and what they\u0027ve learned could also have implications for biological systems made up of soft organic particles not unlike the polymer microgels.\u003C\/p\u003E\u003Cp\u003EUsing small-angle X-ray and neutron scattering techniques, the researchers carefully studied the structures formed by dense concentrations of the microparticles. They also used tiny piezoelectric pressure transducers to measure osmotic pressure changes in the system. Their conclusion: In dense assemblies of microparticles, counter ions bound to the microgels by electrostatic attraction come to be shared by multiple particles, increasing the osmotic pressure which then works to shrink the oversized particle.\u003C\/p\u003E\u003Cp\u003E\u201cWhen the particles are close enough together, there is a point at which the cloud of ions can no longer be associated with individual particles because they overlap other particles,\u201d said \u003Ca href=\u0022http:\/\/www.physics.gatech.edu\/user\/alberto-fernandez-nieves\u0022\u003EAlberto Fernandez-Nieves\u003C\/a\u003E, an associate professor in the \u003Ca href=\u0022http:\/\/www.physics.gatech.edu\/\u0022\u003ESchool of Physics\u003C\/a\u003E at the Georgia Institute of Technology. \u201cThe ions create an imbalance between osmotic pressure inside and outside the larger particles, pushing them to de-swell \u2013 expel solvent to change size \u2013 to match the pressure of the system given by these delocalized ions. This is only possible because the microgel particles are compressible.\u201d\u003C\/p\u003E\u003Cp\u003EThe research is reported April 25 in the early edition of the journal \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E. The work was supported by the Swiss National Science Foundation, and the research partnership between Georgia Tech and Children\u2019s Healthcare of Atlanta.\u003C\/p\u003E\u003Cp\u003EThe presence of non-uniform particles normally creates point defects in the crystals or prevents the formation of crystalline structures altogether. That\u2019s true for structures formed from atoms, but not those formed from the microgels, which are soft cross-linked polymer particles immersed in a solvent. The microgels, which range in size from about 100 nanometers up to several microns in diameter, can exist in either swollen or non-swollen states, depending on such external conditions as temperature.\u003C\/p\u003E\u003Cp\u003ELyon and his research group reported the self-healing nature of the colloidal crystals in the journal \u003Cem\u003EAngewandte Chemie International\u003C\/em\u003E in 2009. They initially believed that what they were seeing resulted from energetic issues associated with formation of the crystals.\u003C\/p\u003E\u003Cp\u003E\u201cWe interpreted the phenomenon in terms of the overall lattice energy \u2013 the propensity of the microgels to form an ordered array \u2013 perhaps being larger than the energy required to collapse the defect microgels,\u201d he said. \u201cIn other words, we believed there was an energetic penalty associated with disruption of the crystalline lattice that was greater than the energetic penalty associated with individual microgel de-swelling.\u201d\u003C\/p\u003E\u003Cp\u003EFernandez-Nieves initially supported that hypothesis, but later came believe there was more at work. For instance, the shrunken microgels, which are identifiable because of their higher optical density, freely move about just like the smaller ones, suggesting that the shrinkage doesn\u2019t result from being crowded by the smaller particles.\u003C\/p\u003E\u003Cp\u003EIn a collaboration with Researcher Urs Gasser and Ph.D. student Andrea Scotti at the Laboratory for Neutron Scattering and Imaging at the Paul Scherrer Institut in Switzerland, the researchers used X-ray and neutron scattering techniques to study the structure of the suspended microgels and the degree of swelling in the large microparticles of the colloidal crystals. The work confirmed that these larger particles had indeed de-swollen, even at concentrations far larger than those initially used by Lyon\u2019s research team.\u003C\/p\u003E\u003Cp\u003E\u201cThe system is able to make point defects disappear, and the mechanism we have proposed allows us to understand why this occurs,\u201d said Fernandez-Nieves. \u201cWhat we have proposed is a mechanism to explain what we see happening, and we think this is a general mechanism that could potentially apply to a wider range of soft particles.\u201d\u003C\/p\u003E\u003Cp\u003EAs a next step, the research group expects to determine the ionic structure to confirm what the existing research has suggested. Fernandez-Nieves believes the work will generate more research with soft particle suspensions, for both experimentalists and theoreticians.\u003C\/p\u003E\u003Cp\u003E\u201cThere is indeed much more theory and simulation work needed to confirm what we propose and to fully understand how this self-healing process occurs,\u201d he said. \u201cThis principle could be at play in a large number of contexts, including biological systems, in which there is a subtle balance between rigidity, osmotic pressure and ionic balance. This is a mechanism that doesn\u2019t really involve the other particles in the assembly. It involves the ions.\u201d\u003C\/p\u003E\u003Cp\u003ELyon, now dean of the Schmid College of Science and Technology at Chapman University, believes the findings might go beyond creating better colloidal systems to provide insights into how living cells operate.\u003C\/p\u003E\u003Cp\u003E\u201cBy obtaining a deeper insight into microgel assemblies, we may be able to take advantage of the subtle energetic balances that determine the overall structures to create more complex, defect-tolerant assemblies,\u201d he said. \u201cThe physics we uncovered here could be relevant for other crowded, soft-materials systems, such as the interior of the eukaryotic cells. Perhaps an extension of this knowledge will provide a better understanding of how the interior of a cell is organized, and how material is transported through this complex and crowded environment.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: A. Scotti, et al., \u201cSelf-healing colloidal crystals: Why soft particles feel the squeeze,\u201d \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E, 2016).\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 30332-0181 USA\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: John Toon (404-894-6986) (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) or Ben Brumfield (404-385-1933) (\u003Ca href=\u0022mailto:ben.brumfield@comm.gatech.edu\u0022\u003Eben.brumfield@comm.gatech.edu\u003C\/a\u003E).\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\u003EWhen an assembly of microgel particles includes one particle that\u0027s significantly larger than the rest, that oversized particle spontaneously shrinks to match the size of its smaller neighbors. This self-healing nature of the system allows the microparticles to form defect-free colloidal crystals, an unusual property not seen in systems made up of \u201chard\u201d particles.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers believe they now understand why oversized microgels shrink to fit in with colloidal crystals."}],"uid":"27303","created_gmt":"2016-04-26 09:47:35","changed_gmt":"2016-10-08 03:21:28","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2016-04-26T00:00:00-04:00","iso_date":"2016-04-26T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"529361":{"id":"529361","type":"image","title":"Alberto Fernandez-Nieves in Lab","body":null,"created":"1461895200","gmt_created":"2016-04-29 02:00:00","changed":"1475895307","gmt_changed":"2016-10-08 02:55:07","alt":"Alberto Fernandez-Nieves in Lab","file":{"fid":"206202","name":"colloidal-crystals_3235.jpg","image_path":"\/sites\/default\/files\/images\/colloidal-crystals_3235.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/colloidal-crystals_3235.jpg","mime":"image\/jpeg","size":1593124,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/colloidal-crystals_3235.jpg?itok=ghApFQy0"}},"529381":{"id":"529381","type":"image","title":"Colloidal crystals","body":null,"created":"1461895200","gmt_created":"2016-04-29 02:00:00","changed":"1475895307","gmt_changed":"2016-10-08 02:55:07","alt":"Colloidal crystals","file":{"fid":"206204","name":"colloidal-crystals_3231.jpg","image_path":"\/sites\/default\/files\/images\/colloidal-crystals_3231.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/colloidal-crystals_3231.jpg","mime":"image\/jpeg","size":1129743,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/colloidal-crystals_3231.jpg?itok=43JzgPLM"}},"529401":{"id":"529401","type":"image","title":"Colloidal crystals2","body":null,"created":"1461895200","gmt_created":"2016-04-29 02:00:00","changed":"1475895307","gmt_changed":"2016-10-08 02:55:07","alt":"Colloidal crystals2","file":{"fid":"206206","name":"colloidal-crystals-figure.jpg","image_path":"\/sites\/default\/files\/images\/colloidal-crystals-figure.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/colloidal-crystals-figure.jpg","mime":"image\/jpeg","size":162461,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/colloidal-crystals-figure.jpg?itok=6Fwrn1d7"}}},"media_ids":["529361","529381","529401"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"135","name":"Research"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"66681","name":"Alberto Fernandez-Nieves"},{"id":"4912","name":"Andrew Lyon"},{"id":"89","name":"chemistry"},{"id":"170174","name":"colloidal"},{"id":"170175","name":"colloidal crystals"},{"id":"171973","name":"migrogel"},{"id":"960","name":"physics"},{"id":"170178","name":"self-healing"}],"core_research_areas":[{"id":"39441","name":"Bioengineering and Bioscience"},{"id":"39471","name":"Materials"}],"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":""}}}