Kiwing To

Electrorheological and dielectric characteristics of semiconductive polyaniline-silicone oil suspensions

We report experimental results of the electrorheological (ER) and dielectric characteristics of an ER fluid made of suspensions of semiconductive polymer (polyaniline) particles in silicone oil. We found that the shear stress of this ER fluid at different applied electric fields can be scaled into a universal curve by the dynamic yield stress which increases linearly with the square of the electric field strength. We also studied the effect of conductivity on the ER performance of these ER fluids. The results show that the ER performance can be improved by increasing the conductivity of the polyaniline particles. We also found that the difference in ER characteristics due to changing conductivity is consistent with the relaxation time obtained from the dielectric spectrum observed for these ER fluids.

Electrorheological characteristics of semiconducting poly(aniline-co-o-ethoxyaniline) suspension

Semiconducting poly(aniline-co-o-ethoxyaniline) was synthesized by chemical oxidation polymerization of aniline and o-ethoxyaniline with two different molar ratios in an acidic media. Its chemical structure and other physical properties, such as conductivity, thermal stability and density of the polymer particles, were examined. Electrorheological (ER) fluids were then prepared by dispersing the copolyaniline particles in silicone oil and their rheological properties under electric field were investigated. It was found that the ER fluids using copolyanilines show different ER behaviors than that of the homopolyaniline.

Period Extension and Randomness Enhancement Using High-Throughput Reseeding-Mixing PRNG

We present a new reseeding-mixing method to extend the system period length and to enhance the statistical properties of a chaos-based logistic map pseudo random number generator (PRNG). The reseeding method removes the short periods of the digitized logistic map and the mixing method extends the system period length to 2253 by “xoring” with a DX generator. When implemented in the TSMC 0.18- μm 1P6M CMOS process, the new reseeding-mixing PRNG (RM-PRNG) attains the best throughput rate of 6.4 Gb/s compared with other nonlinear PRNGs. In addition, the generated random sequences pass the NIST SP 800-22 statistical tests including ratio test and U-value test.

Decay dynamics of interchain excited states in luminescent conjugated polymer CN-PPV

Abstract We report the investigation of CN-PPV in poor solution. The fluorescence spectrum and the accompanying red-shifted absorption spectrum suggest that the polymer forms interchain state in poor solution. As the concentration increases, the intrachain emission becomes weaker, while the interchain species emission becomes stronger. The fluorescence of CN-PPV film exhibits similar behavior to that in concentrated poor solution. A two-state model is proposed to describe fluorescence dynamics of polymers in films and solution.

Flow and jam of granular particles in a two-dimensional hopper

The jamming phenomenon of granular flow of mono-disperse disks in a two-dimensional hopper is studied experimentally. When the opening of the hopper d is small, jamming occurs due to formation of an arch at the hopper opening. The jamming probability as a function of the hopper opening width is measured which show a sharp decrease at some range of d. By observing the disk configurations of the arch in the jamming events, the jamming probability can be explained quantitatively using a restricted random walker model. The average horizontal and vertical spans of the jamming arch are calculated from the restricted random walk model which compares favorably with experiments.

Scaling Behaviour in the Demixing of a Binary-Liquid Mixture under Gravity

Gravity-driven demixing experiments of mechanically mixed binary-liquid mixture are performed at various temperatures. A steady state is observed in which the demixing rate is nearly constant. We find that the droplet size in the demixing zone grows only for a short time. During most of the demixing process, the size of these droplets is stabilized by the flow itself. A relationship between the characteristic demixing time τ and the reduced temperature e is found, i.e. τ ~ e-θ with θ = 0.54 ± 0.03. A phenomenological model in which the demixing process is considered as a flow through a porous medium is proposed to explain the experimental results.

Packaging of granular bead chain

We find that a freely moving granular chain can be pushed, against the entropic force, into a confined cell if the passage to the cell is a channel of truncated-cone shape. In this setting, the granular chain, the cell and the channel can be considered as a mechanical analog of a DNA molecular, a bacteriophage and a portal motor, respectively. The force generated by the scaled-up analog of the mechanical motor and the packaging speed are found to be consistent with the real bacteriophage Φ29 portal motor. Pauses and slips found in single-molecule experiments of DNA packaging of the bacteriophage are also observed in the analog system.

Abnormal scattering of polymer in binary solvent

The behavior of a high molecular weight polymer (polyethylene-oxide, PEO) in a binary liquid mixture (nitroethane/3-methyl-pentane, NE/MP) is studied at the one-phase temperature of NE/MP by static and dynamic light scattering methods. We found that the scattering intensity increased abruptly near the critical composition of NE/MP although the sample was very far from the critical temperature of NE/MP. Explanations in terms of critical opalescence and wetting layer inversion are discussed.

Flow and clog in a silo with oscillating exit

When grains flow out of a silo, flow rate W increases with exit size D. If D is too small, an arch may form and the flow may be blocked at the exit. To recover from clogging, the arch has to be destroyed. Here we construct a two-dimensional silo with movable exit and study the effects of exit oscillation (with amplitude A and frequency f) on flow rate, clogging, and unclogging of grains through the exit. We find that, if exit oscillates, W remains finite even when D (measured in unit of grain diameter) is only slightly larger than one. Surprisingly, while W increases with oscillation strength Γ≡4π^{2}Af^{2} as expected at small D, W decreases with Γ when D≥5 due to induced random motion of the grains at the exit. When D is small and oscillation speed v≡2πAf is slow, temporary clogging events cause the grains to flow intermittently. In this regime, W depends only on v-a feature consistent to a simple arch breaking mechanism, and the phase boundary of intermittent flow in the D-v plane is consistent to either a power law: D∝v^{-7} or an exponential form: D∝e^{-D/0.55}. Furthermore, the flow time statistic is Poissonian whereas the recovery time statistic follows a power-law distribution.

Collapse kinetics of vibrated granular chains

The kinetics of the collapse of the coil state into condensed states is studied with vibrated granular chain composed of N metal beads partially immersed in water. The radius of gyration of the chain, R(g) is measured. For short chains (N < 140), disk-like condensed state is formed and R(g) decreases with time such that the function ΔR(g)(2) (≡ R(g)(2) - R(g)(2)(∞)) = A e(-t/τ), where the relaxation time τ follows a power-law dependence on the chain length N with an exponent γ = 1.9 ± 0.2. For the chains with length N ≥ 300, rod-like clusters are observed during the initial stage of collapse and R(g)(2) = R(g)(2)(0) - Bt(β), with β = 0.6 ± 0.1. In the coarsening stage, the exponential dependence of ΔR(g)(2) on time still holds, however, the relaxation time τ fluctuates and has no simple dependence on N. Furthermore, the time dependence of the averaged radius of gyration of the individual clusters, R(g,cl) can be described by the theory of Lifshitz and Slyozov. A peak in the structure function of long chains is observed in the initial stage of the collapse transition. The collapse transition in the bead chains is a first order phase transition. However, features of the spinodal decomposition are also observed.