Functional Polymeric Complex Fluids under External Fields: Materials and Rheology
Hyoung Jin Choi
Department of Polymer Science and Engineering, Inha University, Korea

We have been studying various polymeric complex fluids with interesting functionalities under external fields, in which the external fields imply typical flow fields of laminar flow with most cases of rheological aspects and turbulent flow, electrical and magnetic fields. They include non-Newtonian fluid mechanics with flow fields of rod-climbing, turbulent drag reduction, suspension rheology of Boger fluid and magnetic particles, polymer nanocomposites with clay and carbon nanotube (CNT), DNA dynamics under turbulent flow, rheology of PFPE lubricant and biodegradable polymers, in addition to conducting polymer based electrorheological (ER) fluids, electronic paper, and electrospinning under an electric field, while magnetorheological (MR) suspensions have been characterized under applied magnetic field. Among these, polymer induced turbulent drag reduction along with DNA dynamics, electronic paper, PFPE lubricant rheology and ER & MR fluids will be covered, and specific focus will be put on the ER and MR fluids. Various electroresponsive ER materials include conducting polymers such as polyaniline, polypyrrole and their derivatives, biopolymers, inorganics, and their modifications such as core-shell structure, polymer/clay nanocomposite, polymer/mesoporous composite and carbon nanotube associated systems from material rheological viewpoint. Interesting characteristics of their ER suspensions such as yield stress analysis using universal scaled yield stress concept, flow curve behavior and dielectric analysis will be reviewed. Its analogy under applied magnetic fields using magnetoresponsive MR materials will also be delivered, in which our efforts include improving MR characteristics of various magnetic particles. Coating the surface of carbonyl iron particles producing favourable core-shell structure along with apparently decreased density for synthesized composite particles with several polymers will be covered in addition to CNT coating and double wrapping process with polymeric shell (PMMA, PANI, and PS) and CNT layers. Polymeric systems of PVB, PS, PMMA, and conducting polymers such as polyaniline and polypyrrole have been also employed to fabricate Fe3O4/polymer composites via various polymerization methods. 

Bio:
Professor Hyoung Jin Choi obtained his B.Sc. degree in Chemical Technology in 1980 from the Seoul National University and his Ph.D in Chemical Engineering in 1987 from Carnegie Mellon University, Pittsburgh. He joined Dept. of Polymer Science and Engineering of Inha University in 1988 as an Assistant Professor and has become a full professor since 1997. He was a Research Professor of University of Pittsburgh and visiting professor of Institute of Physics, Academia Sinica in Taiwan; Carnegie Mellon University in USA; and RMIT University in Australia. His research interests are Electrorheology and Magnetorheology, Polymer Nanocomposites (with clay or carbon nanotube), Magnetic Particles, Polymer and Suspension Rheology, Conducting Polymers, Turbulent Drag Reduction, Electronic-Pape and Sonochemistry.

Fabrication and Physical Characteristics of Polymer/Carbon Nanotube Nanocomposites
Ke Zhang
Department of Polymer Science and Engineering, Inha University, Korea

Since its first discovery, carbon nanotube has been widely investigated by researchers due to its unique properties such as excellent conductivity, low density, chemical stability, low-dimensionality and superior mechanical property. In our study, multi-walled carbon nanotube (MWNT) as an excellent electroresponsive candidate was successfully incorporated onto monodispersed polymeric microspheres surface via either physical adsorption or covalent bonding to form core-shell structure, showing typical electrorheological (ER) characteristics of fibril structure under an applied electric field. Moreover, nanocomposites of MWNT as a potential filler into polymer matrix were prepared via in-situ bulk polymerization or solvent casting method. Based on the results of the scanning electron microscopy, it is found that MWNTs were sufficiently wetted into the polymer matrix. Thermal stability and conductivity of the polymer/MWNTs nanocomposites were found to be increased due to incorporation of MWNTs. In addition, rheological properties of the polymer/MWNTs nanocomposites were also examined using a rotational rheometer, showing the increase of both storage and loss moduli for all frequency range as the MWNT content increases. Functionalization of the MWNT for its better affinity to the polymer matrix will be also covered.

Giant Electrorheological Fluid: Liquid Phase Effect and Surface Modification
Shuyu Chen
Department of Physics, The Hong Kong University of Science and Technology

In this talk, I will briefly review our recent works on the Giant Electrorheological (GER) effect, based on the urea-coated barium titanyl-oxalate nanoparticles [NH2CONH2@BaTiO(C2O4)2] (BTRU) dispersed in silicone oil. We investigated the effect of liquid phase on the behavior of GER fluid experimentally. The interaction between different kinds of silicone oils and solid nanoparticles was shown to significantly influence the GER effect. Recently, we fabricated suspensions exhibiting the GER effect comprising urea-coated nanoparticles—multiwall carbon nanotubes composite (MCNT-BTRU) particles dispersed in silicone oil. This type of GER fluids display dramatically enhanced anti-sedimentation characteristic without sacrificing the yield stress. In the best cases, stabilized suspensions with MCNT-BTRU particles dispersed in silicone oil have been maintained for several months without any appreciable sedimentation being observed. Both the sedimentary and rheological properties of the MCNT-BTRU suspension were systematically studied and compared with their urea-coated barium titanyl-oxalate (BTRU) counterparts. Yield stress as high as 190 kPa was obtained in the MCNT-BTRU suspensions. Theoretically we have obtained a microscopic picture of the GER effect by using molecular dynamics to simulate the urea-silicone oil mixture trapped in a nano contact between two polarizable particles. It is found that the urea molecules, which normally reside at the oil-particle interface, can form aligned dipolar filaments that penetrate the oil film to bridge the two boundaries of the nanoscale confinement. The resulting electrical energy density is shown to give an excellent account of the observed yield stress variation as a function of the electric field.