H. J. Choi

Intercalated polypyrrole/Na+-montmorillonite nanocomposite via an inverted emulsion pathway method

An inverted emulsion pathway polymerization method was introduced to synthesize conducting polypyrrole (PPy) into the layer of inorganic clay within a nanolevel, using dodecylbenzenesulfonic acid (DBSA) as both an emulsifier and a dopant. The synthesized PPy/Na þ montmorillonite (MMT) nanocomposite was confirmed to have a layered structure with a folded or penetrated PPy from X-ray diffraction, and it was further characterized via FT-IR spectroscopy. Four probes method was adopted to examine electrical DC conductivity. Electrorheological (ER) behavior of the nanocomposite dispersed in silicone oil was also investigated using a rotational rheometer equipped with a high voltage generator. q 2002 Published by Elsevier Science Ltd.

Synthesis and electrorheological characteristics of microencapsulated polyaniline particles with melamine–formaldehyde resins

Abstract Polyaniline particles with low pH cannot be directly used in the electrorheological (ER) systems, since their emerald base form has a conductivity that is too high. Therefore, the pH of the polyaniline has been controlled to yield a lower conductivity. To improve the particle preparation method for polyaniline, which generates ER fluids with its semi-conducting characteristics, we synthesized microencapsulated polyaniline particles with melamine–formaldehyde (MF) resins. Microcapsules, containing polyaniline with a low pH as the core material, were prepared by polymerization of MF resin, which play the role of an insulator between the polyaniline particles. From rheological measurements, the yield stress of the ER fluid decreased with the increase of MF resin, and this effect enhanced as the applied electric field strength increased.

Electrorheological characterization of polyaniline dispersions

Suspensions of polyaniline in silicone oil have been investigated as potential candidates for dry-base electrorheological (ER) fluid systems. Polyaniline was synthesized by a chemical oxidation of aniline in an acidic media. Its optimum conductivity (in the semiconductive range) for ER purposes was achieved by adjusting the pH of an aqueous solution containing polyaniline particles. ER experiments were conducted with a Haake rheometer for steady shear experiments to investigate the effects of imposed electric fields, the polymerization temperature (molecular weight), and the dispersing oil on ER performance. ER properties of polyaniline suspensions were found to be improved by increasing both the imposed electric field and the polymerization temperature of the used polymer. Suspensions using kerosene also show greater ER effect than that using silicone oil because of the smaller dielectric constant of kerosene than that of silicone oil. A scaling law is introduced to analyse the ER data.

Role of organic coating on carbonyl iron suspended particles in magnetorheological fluids

Carbonyl iron (CI) has been widely used as a suspended particle in magnetorheological (MR) fluids. However, pristine CI-based MR fluids have several drawbacks, including severe sedimentation of the CI particles due to the large density difference with the carrier liquid, difficulties in redispersion after caking, abrasion of device surfaces during long-term operation, and rust of iron by oxidation. To overcome these shortcomings, we coated the CI particles with a poly(vinyl butyral) (PVB) shell. CI and CI-PVB particles were suspended in mineral oil and their MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. Yield stress and flow response (shear stress and shear viscosity) were investigated at magnetic field strengths ranging from 0to343kA∕m. Although the MR properties, such as yield stress and shear viscosity of CI-PVB based MR fluids, changed slightly compared with those of the pristine CI based MR fluid, the dispersion quali...

Synthesis and electrorheology of emulsion intercalated PANI-clay nanocomposite

Polymer-clay nanocomposite particles with polyaniline (PANI) and Na + -montmorillonite (MMT) were synthesized using an emulsion intercalation method and then adopted for electrorheological (ER) fluids by dispersing the synthesized nanocomposite particles in silicone oil. Insertion of the PANI into the layer of clay was examined by X-ray diffraction, which confirmed that the conducting PANI polymer chain was aligned with the layers of clay. Dodecyl benzenesulfonic acid (DBSA) adopted as both an emulsifier and a dopant was found to play an important role for PANI-clay nanocomposite, affecting conductivity of the nanocomposite particles and their ER properties. Furthermore, ER fluids composed of PANI-clay composite were observed to exhibit typical ER behavior with higher static yield stresses under an applied electric field.

Viscoelasticity of biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(ethylene oxide)

The viscoelastic properties, measured via both steady shear and oscillatory experiments, for blends of biodegradable poly(3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) were examined. We observed that PHB/PEO blends are miscible. The first normal stress difference, the shear stress, and the shear viscosity (obtained from the steady shear experiment) were correlated with the storage modulus, the loss modulus, and the complex viscosity (obtained from the oscillatory experiment) via either the Cox and Merz rule or other empirical equations. For biodegradable PHB/PEO blend systems, we found that both the viscous and the elastic behavior from the steady shear experiment are qualitatively related to those from the oscillatory experiment.

Microencapsulated polyaniline particles for electrorheological materials

Electrorheological (ER) fluids are a class of materials whose rheological characteristics are controllable through the application of an electric field. ER fluids are usually made of particle suspensions with a large dielectric constant mismatch between the particles and the fluid [1]. Upon application of an electric field, the suspended dielectric particles in an ER fluid align themselves into chains and columns parallel to the field, thereby inducing yield phenomenon, viscoelasticity, and a drastic increase in viscosity. Because of their controllable viscosity and fast response, ER fluids are regarded as a smart material for active devices, which can transform electric energy to mechanical energy [2]. Recently, much attention has been put on dry-base, nearly anhydrous ER fluids. Examples include carboneous particle [3], zeolite [4] and various polymer semi-conductors, such as acene quinone radical polymers [5, 6], poly (p-phenylene) [7], polyaniline [8, 9], and copolyaniline [10, 11]. Among these ER fluids, polyaniline in its emeraldine base form has advantages with respect to density, conductivity control and thermal stability. Polyaniline is also easy to polymerize by oxidation polymerization at relatively low temperatures [12]. Despite these merits, only the semi-conducting emeraldine base form of polyaniline can be used due to the high conductivity of the hydrochloride form and the resulting high current density causing breakdown in the structure of the fluid. In this note, we microencapsulated homopolyaniline particles with melamine-formaldehyde resin and then investigated their ER characteristics. Because microencapsulation entraps core liquid materials by circulating them with certain polymeric materials, we used this method to modify the polyaniline particles. Based on the finding that melamine-formaldehyde resin is better than urea-formaldehyde resin in hardness and resistance to heat and moisture [13], we adopted the melamine-formaldehyde resin for our microencapsulation process of homopolyaniline particles. At first, the polyaniline particles were polymerized by oxidation polymerization [14]. 1.2 mol of aniline monomer was added to 800 ml of 1 M HCl, and was chilled and stirred for 2 h. A pre-chilled solution of ammonium peroxysulfate (0.72 mol in 400 ml of

SYNTHESIS AND ELECTRORHEOLOGICAL CHARACTERIZATION OF POLYANILINE AND NA+-MONTMORILLONITE CLAY NANOCOMPOSITE

Polyaniline-Na+-montmorillonite nanocomposite particles were synthesized using an emulsion intercalation method, and electrorheological (ER) fluids were produced by dispersing the synthesized nanocomposite particles in an electrically-insulating silicone oil. The emulsion of an aniline monomer with dodecyl benzenesulfonic acid was inserted into the layers of clay, and polymerization was processed by adding the oxidant initiator solution. DBSA as a emulsifier and a dopant took a important role for polyaniline clay nanocomposite. This insertion of polyaniline was confirmed by X-ray diffraction. To observe its ER properties, we measured the shear viscosity and the shear stress by controlling shear rate. Furthermore, we conducted dynamic tests to investigate the viscoelastic properties of the ER fluid under an electric field in the linear viscoelastic region.

Drag-reduction effectiveness of xanthan gum in a rotating disk apparatus

Drag reduction, achieved by introducing a minute amount of a homologous series of polysaccharide xanthan gum in an aqueous solution, is investigated using a rotating disk apparatus. In this paper, the ultrasonic degradation method is adopted to obtain different fractions of molecular weights of xanthan gum. The dependence of drag reduction on various factors, including polymer molecular weight, polymer concentration, rotational disk speed, ionic strength of solution, and temperature, is investigated. Drag reduction induced by the xanthan gum is found to increase with polymer concentration, reaching a maximum at its critical concentration, while the concentration required for maximum drag reduction decreases with increasing molecular weight. Polymer degradation due to the high shear forces, which occur during drag-reduction experimentation, is also found to increase with turbulence intensity. Furthermore, tests show that xanthan gum is a suitable drag reducer even at relatively high temperatures.

Electrorheological characterization of zeolite suspensions

The rheological properties of the electrorheological (ER) fluids prepared from commercial zeolites 3A, 5A and 13X suspended in silicone oil were investigated through steady shear and oscillatory shear experiments. Dielectric spectra of the fluids were also measured to examine their possible correlation with the flow behavior of the ER fluids. Among the zeolite ER fluids investigated, the ER fluid using 13X showed the best performance and had the shortest relaxation time of an interfacial polarization. Viscoelastic behavior was observed in the dynamic test under the applied electric field. The elasticity increased with the strength of the electric fields under linear viscoelastic conditions.