Photonic crystals in biology - NanoTR-VI

PP scatteringPYusufPP CorrespondingPoster Session, Thursday, June 17Theme F686 - N1123Polymer-Nano-Particle Interaction Influence on The Rheology of Non-Newtonian Fluids11UBurcu ÖzelUP P* andP P Z. MenceloluP1PFaculty of Engineering and Natural Sciences, Sabanci University, Istanbul 34956, TurkeyAbstract-The aim of the present study is to systematical investigation of physicochemical parameter influence on the rheology of shearthickening/shear thinning behaviour of nano particles integrated polymeric fluids (also referred to as colloidal nanoparticle suspension, CNS) toshed a light on the mechanism behind the dilatant behaviour of CNS, which is an ongoing controversial issue in the relevant literature.Most of the chemical and allied processing industriesencountered non-newtonian flow behavior; namely shearthinning and shear thickening. Shear thinning is a decrease ofviscosity with increase shear rate, although less common, theopposite effect shear thickening occur in various kinds offluids. Shear thickening is often observed in highlyconcentrated colloidal dispersions, characterized by significantincrease in viscosity with increasing shear rate.There has been significant effort to understand the thestructural origin of the shear thickening and differentexplanations have been given; namely, the hydrodynamicclustering and order-to-disorder transition. According to orderdisorder transition (ODT), monodisperse particles hexagonallypacked within the layers but flow instability induce theparticle break out of their ordered layer cause increase inparticle interaction and induce rise in viscosity of the[1]suspension at the critical shear rate.PPThe second theory,hydrodynamic clustering, involves the hydrodynamic force[2-4]driven flocculation of particles.PPThese theories were[1-5]concluded from light/neutronPexperiments as[2,3]well as from Stokesian Dynamic simulationsP howeverODT theory investigated by these techniques can not explainthe shear thickening behavior of polydisperse and irregularparticle suspensions. All concentrated suspensions under rightconditions can exhibit the shear thickening behaviour,however, the exact conditions and the origin of shearthickening behaviour are not well understood.In this study, we studied the effect of constituent parameters;particle size, concentration, surface chemistry, continuousphases, molecular weight and polarity of polymeric phase onthe rheology of non-newtonian fluids.The most important parameter for the shear thickeningbehavior is the colloidal interactions between filler particlesand polymeric fluids. To be able to study the effect of thecolloidal interactions on the rheology of CNS, hydrophobic /hydrophilic fumed silica in the continuous liquid phase withdifferent degrees of polarity have also been studied.Viscoelastic characterization indicate that colloidalinteractions between particles and continuous phase andinteraction strenght can be tailored by modifying the surfacechemistry of silica particles or changing the polarity of thecontinuous phase (see figure). The relative strength of theinteractions between particle-liquid, liquid-liquid and particleparticledetermine whether dispersion is sol or gel. Sol showsshear thickening behavior under shear while gel shows shearthinning behavior.Although substantial number of researches have been studyon the rheology of non-newtonian flow, the nature of the shearthickening behavior of colloidal suspension are not clearlyunderstood until recently. Hydrodynamic clustering and orderdisorder transition theories are not reasonable model toexplain our results because most of the studies in literatureinvestigate the rheology of suspensions that are composed ofmonodisperse/nonagglomerated sphere particle. In our case,primary flow units are composed of flocs which arepolydisperse, irregular and anisotropic structures, flocstructure was observed in cryoscopic transmission electronmicrographs and observed hydrodynamic radius wassupported by dynamic light analysis. We designed anexperiment in order to support new theory about the origin ofshear thickening. Polyethylene glycol and hydrophilic fumedsilica is known to exhibit shear thickening behaviour. In thisHTpreliminaryTH study, lithyum chloride is dissolved inpolyethylene glycol to make it conductive hence mixture iscomposed of insulating particles and conductive continuousmedia. Conductivity of system was measured during viscosityanalysis and decrease in conductivity of system at criticalshear rate give a clue about the mechanism of this rheologicalbehaviour. Decrease in conductivity at critical shear rateindicate that effective volume fraction of insulating particleincrease therefore resistivity of system increase. As aconclusion, we believe that shear thickening is not driven bythese two theories that are suggested by publications. It is dueto shear driven reduction of cluster size, as a consequence,well disperse particles increase of the effective volumefraction of particles in dispersion.abFigure 1. Viscoelastic characterization of (a) shear thickening (b)shear thinning fluids*author: burcugenc@su.sabanciuniv.edu[1] R.L. Hoffmann, J.Colloid Interface Science 1972, 16, 155–173[2]G.Bossis, J.F.Brady, J.Chem.Phys. 1989, 91, 1866–1874[3] D.R.Foss, J.F.Brady, J. Fluid Mech. 2000, 407, 167-200[4] B.J.Maranzano, N.J.Wagner, J. Rheol. 2001, 45 , 1205–1222[5] H.M.Laun, R.Bung, S.Hess, W.Loose, O.Hess, K. Hahn,E.Hadicke, R. Hingmann, F.Schmidt and P.Lindner, J. Rheol. 1992,36, 743.6th Nanoscience and Nanotechnology Conference, zmir, 2010 736