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Morphological similarity of a tri-block copolymer processed at ambient and elevated temperatures
Inceoglu, Sebnem,Aytun, Taner,Menceloglu, Yusuf Z.,Ozen, Ilhan,Acar, Metin H. 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.4
We investigated the effect of temperature on the morphology of a tri-block copolymer (BCP) processed in a capillary rheometer. The material used was a polystyrene-b-poly(2-ethylhexyl acrylate)-b-polystyrene (PS-b-PEHA-b-PS) tri-block copolymer, which was synthesized by ATRP with a molecular weight of 38.5 K consisting of 49 molar % PEHA. According to the rheological data obtained with dynamic viscoelastic oscillatory measurements, order-disorder temperature (ODT) of the BCP was measured at around $110^{\circ}C$. Considering this observation, the samples were studied under different temperatures and pressures (from $110^{\circ}C$ to $28^{\circ}C$ and from 48 to 75 bar) in capillary rheometer. All processed materials were characterized by using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). It was found that all samples processed by aid of either temperature or pressure showed similar mixed morphologies (a mixture of the ordered and disordered structures i.e., the reduction of microphase separation due to processing).
Experimental study on the rheology of anisotropic, flocculated and low volume fraction colloids
Ozel, Burcu Genc,Orum, Aslihan,Yildiz, Mehmet,Menceloglu, Yusuf Z. 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.1
In this work, we have investigated rheological behavior of colloids with a low particle volume fraction, and anisotropic and flocculated microstructures through measuring their viscosity and electrical resistance under varying shear rates together with utilizing several relevant characterization methods (i.e., Dynamic Light Scattering, Transmission Electron Microscopy, Atomic Force Microscopy, and Capacitance and Electrical resistance measurements). The colloids are formed through the suspension of hydrophilic/phobic fumed silica particle with attractive/repulsive interaction in polyethylene glycol and/or ethylene oxide-propylene oxide copolymer. It is observed that studied suspensions display shear thickening/thinning flow behavior depending on their microstructure (the spatial distribution and arrangements of particles in continuous media) and associated changes in cluster sizes, which are controlled by the break down of densified clusters (due to the shear induced mechanical and hydrodynamical forces) and the interaction forces among particle-particle and particles-polymers (owing to physicochemical effects). The detailed evaluation of the experimental results indicates that the shear thickening phenomena in low volume fraction, anisotropic and flocculated systems can be mainly attributed to the increase in the effective volume fraction of particles due to both hydrodynamic and physicochemical forces.