Student Project Abstracts 2005 - Pluto - University of Washington

BEHAVIORAL PROPERTIES OF COLLOIDAL CRYSTALS AT AND most AROUND crystalline THERMALLY INDUCED sample DEFECT so SITES thatclean trajectory images can bethe particles of the microgel that were out of phase. This out ofobtained. In addition, one could takephase transition occurred in the viewing of the microscope imagethat the camera took. So clear crystalline trajectories of thelonger movies so that the andefectobservationwere hard to obtain.of bothIn thethefuturemeltingit is suggestedandto use themost recrystalliation crystalline sample so process that clean trajectory could be images can beobtained. made. In In addition, this one experiment could take longer one movies could so that thean only observation look of at both fluid the melting to crystalline and recrystalliation processcould transition be made. In this with experiment the camera one could that only look at fluid tocrystalline was used. transition with the camera that was used.In addition, comparisons of the assemblies with goldnanoparticles were observed under heat cycling between 35°Cand room temperature to ensure no aggregation occurred. SeeFigure 2. This was done in a series of ten temperature cycling.If they were to aggregate then the spectra would look differentshifting closer to a wavelength around 560nm. It was found thatthe slopes all had similar trends having a distinct point at 520nmwhere the gold is visible. Thus no aggregation was observed.Phase BehaviorAnother test for these particles was done to ensure that therewas no perturbing of the phase behavior trend between the twocrystalline assemblies. It was observed that the assemblies dopedwith gold nanoparticles tended to start off in a glassy phase untilthey were heated. Yet the two assemblies followed the same trendof melting at the same temperature.Inducing the DefectAfter ensuring the assemblies were relatively the same theassemblies with the gold nanoparticles were tested with the microscopeand laser. The assembly was maintained at a set temperatureusing system. an objective The heater particles and temperature deswell stage, as and thenthe temperature increases to thethe laser was lower introduced critical to heat solution up a particular temperaturearea of the sample.of the polymer; allowing the systemIn addition, laser intensity was used to vary the amount of energyto act more as a fluid. 2added to the system. The energy ranged from barely exciting aExperimentparticular Assemblies spot to melting a of certain PNIPAm area of the (Poly-NisopropylAcrylamide)microgelsassembly. It wasseen that asdopedthe meltingwithtemperaturegold nanoparticleswas approached itwilltook lessintensity from have the a laser defect to melt or induced excite the sample. by The oppositepositioning a frequency doubled Nd:was also observed YAG (Yttrium that when the Aluminum sample was Garnet, far away from the=532nm) laser at a small sectionmelting temperature it took more energy from the laser to exciteof the crystal. As the laser hits athe sample. section of the crystalline the goldFigure 3. Left is trajectory of a microgel assembly obtained from IDL.Figure Right is image 3. obtained Left from is the trajectory camera on the microscope. of a Circledareas are the locations of the laser and the induce defect in the sample.microgel assembly obtained fromSpectrophotometry was run todetermine IDL. Right is how image many obtained gold fromnanoparticles ACKNOWLEDGEMENTSwere needed in theassemblies. the camera on Enough the microscope.goldnanoparticles were needed toabsorbCircledphotonsareas arefromthe locationsthe laser,ofbutnot too many nanoparticles so thatthe laser and the induce defect inthere were no perturbed phasebehaviors. the sample. At the first noticeablepeak of 520nm (this is where goldmost crystalline sample so particles that References of this size absorb) fromclean trajectory images can the be UV VIS 1. Torquato, read S,; out Truskett, determinedT.M.,Acknowledgementsobtained. In addition, one could how take much Debenedetti, gold was put into thelonger movies so that the an sample. It P.G. was Is random found close to packing be 500L.ofobservation of both the melting See and figure spheres 1. REFERENCESrecrystalliation process could bewell defined? Phys. Rev. Lett. 2000,nanoparticles will absorb the made. In this experiment 1. one Torquato, could S,; 84, Truskett, T.M., Debenedetti, P.G. Is random close1.6photons from the laser because only look at of fluid to crystalline2064.1.4their high extinction coefficient.transition with the camera packing that of spheres well defined? Phys. Rev. Lett. 2000, 84, 2064.Particles with noThe energy UV Vis graphs gained of 6.8 weight percent will of particles be released1.2gold nanoparticleswas used.in the form of heat. This released2. WU, J.; Zhou,2.B.;WU,Hu,J.; Zhou,Z. PhaseB.; Hu,behaviorZ. Phaseof thermally responsivemicrogel 0.8 colloids. of thermally Phys. Rev. responsive Lett. microgel 2003,1.61Particles withoutbehaviorParticles withheat 1.4 will warm up the gold crystal, and300MicroL of goldnanoparticles90, 0483041.2one can observe what Particles happens with 200 to1colloids.0.6Particles withMicroL of Goldthat part of the crystal as the500MicroL of gold0.8Particles with 300Phys. Rev. Lett. 2003, 90, 048304 nanoparticles0.4defect 0.6 is induced. Also MicroL one of Gold can0.4observe the crystal as it cools0.20.2Particles with 400down 0MicroL of Goldafter the laser is removed to0300 400 500 600 700 800 900 Particles with 500350 450 550 650 750 850see how the defect reordersMicroL of Goldinto aWavelength (nm)Wavelength (nmcrystal.AbsorbanceFigure 2. Annealing process of a microgel showing no aggregation Figure 1. Determination of theDifferential interference contrastafter microscopy 10 heat cycles between was 35°C used and room to temperature. look Figure at 3. the Left is trajectory amountof amicrogel particles. Afterwards microgel assembly the obtained of from gold nanoparticles needed toimages attained were analyzed IDL. Right is image obtained dope from the crystalline assemblies.CONCLUSIONS using IDL software. AND RECOMMENDATIONSIDL was the used camera on to the microscope.obtain particle trajectories Circled of areas the are the locationsIn addition,ofcomparisons of theassemblies Mallory Davidson with is currently gold studying nanoparticleschemical engineering at theIt wasimages.the laser and the induce defect inshown that a defect could be introduced from were observed under heat cyclingthe sample.University of Washington. Mallory Davidson Upon is graduation currently in June 2006 she plans tobetween 35 C and roomYAG laser. Results For defect and trajectory Discussions images see Figure 3. Howeveranalysis of the crystal assemblies proved to be inconclusivecompanies. However,get a full time job studying either doing chemical marketing engineering or consulting at for engineeringGold Incorporation In order Acknowledgementstemperature to ensure notothe UniversitygraduateofschoolWashington.is a consideredUponaggregation occurred. See Figure a future 2. optioninduce a defect the crystalgraduation in June 2006 she plansThis was done in a series of tenbecause asassembliesthe sample wouldneededbe heatedtoupbethedopedcrystal wouldwithbeto get a full time job either doingtemperature cycling. If they weregold nanoparticles. UV VISmarketing or consulting forexcited out of phase in the microscope image and the softwareengineering companies. However,graduate school is a considered anthat traces the particles could not produce accurate images offuture option30 CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005AbsorbanceRefer1. TorDebenP.Gspherwe84,202. WUbehavofcolloidPhyMallorstudythe Ungraduto getmarkeenginegradufuture