{"83481":{"#nid":"83481","#data":{"type":"news","title":"Technique Creates Patterns in Unique Crystals Formed from Hydrogel Nanoparticles","body":[{"value":"\u003Cp\u003EThe development could make possible the fabrication of waveguides, three-dimensional microlenses and other photonic structures from the unusual crystals.\n\u003C\/p\u003E\n\u003Cp\u003EIn related work, the Georgia Institute of Technology researchers have also learned to use weak attractive forces between the soft spheres to produce uniform crystalline structures with particle concentrations much lower than possible with hard spheres.  The developments were described September 10th at the 226th national meeting of the American Chemical Society in New York.\n\u003C\/p\u003E\n\u003Cp\u003EIn April 2002, a research team led by Andrew Lyon, a professor in Georgia Tech\u0027s School of Chemistry and Biochemistry, announced it had developed a family of hydrogel-based nanoparticles that could be used to create photonic crystals whose optical properties could be tuned by thermally adjusting the water content of the particles.\n\u003C\/p\u003E\n\u003Cp\u003EThe soft, conformable spherical particles provided a unique system for producing self-assembled periodic structures that could be tuned to transmit specific wavelengths of light.  Applications were expected in optical switching and optical limiting.\n\u003C\/p\u003E\n\u003Cp\u003EThe work discussed at the ACS meeting moves the nanoparticles closer to practical application by providing a way to form complex patterns in the crystalline structures.  The patterns could be useful as optical waveguides or lenses.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This represents a fundamentally new method for patterning self-assembled photonic materials,\u0022 Lyon said.  \u0022By combining a photo-patterning method with a self-assembly technique, we can rapidly make large volumes of very nice optical materials.  This provides the best of both worlds - a good optical material that is easy to prepare, combined with a process that allows us to tell the material what kind of overall structure it should have.\u0022\n\u003C\/p\u003E\n\u003Cp\u003ELyon\u0027s group creates the pattern with a frequency-doubled Nd:YAG laser whose beam applies specific amounts of heat to the poly-N-isopropylacrylamide nanoparticles, which average 224 nanometer in diameter.  To produce the smallest possible features, the researchers include tiny gold nanoparticles with the hydrogels; the gold converts the laser light to heat, allowing precise thermal control.  \n\u003C\/p\u003E\n\u003Cp\u003EThe heat prompts phase transitions, causing the particles to shrink or swell depending on the temperature.  That changes the crystalline structure.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The gold particles allow us to use a very narrowly-focused laser beam to locally heat the material,\u0022 Lyon said.  \u0022We can have a very sharp temperature gradient between the center of the laser spot and the surroundings.  Everything outside of the laser spot experiences mostly ambient conditions and stays crystallized.  Everything inside the laser spot goes through a melting phase.  Then, the effective cooling rate is very rapid as the laser moves away, trapping the material as an optically transparent, non-diffractive glassy material.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe patterning could be used to create optical waveguides or microlenses.\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"Researchers have developed a laser-based technique for creating patterns in self-assembled colloidal crystals produced from hydrogel nanoparticles - soft spheres that respond to heat by changing size.","format":"limited_html"}],"field_summary_sentence":"","uid":"27304","created_gmt":"2003-09-10 00:00:00","changed_gmt":"2016-10-08 03:03:41","author":"Matthew Nagel","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2003-09-10T00:00:00-04:00","iso_date":"2003-09-10T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"related_links":[{"url":"http:\/\/gtresearchnews.gatech.edu\/newsrelease\/patterning.htm","title":"Possible applications"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[],"keywords":[],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003E \u003C\/strong\u003E\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=\u0022\u003EContact  \u003C\/a\u003E","format":"limited_html"}],"email":[],"slides":[],"orientation":[],"userdata":""}}}