• Macromolecular Research
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• v.17 no.10
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• pp.750-756
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• 2009

Stable, spherical, polystyrene particles were synthesized in ab initio dispersion polymerization by using the poly(methacrylic acid)[PMAA] macro-RAFT agent. The presence of the PMAA macro-RAFT agent on the polystyrene (PS) particles was confirmed by NMR and FTIR spectroscopy. The PS particle size was influenced by the concentration of the RAFT agent and monomer due to the initial nucleation. When the concentration of the PMAA macro-RAFT agent was increased from 2 to 10 wt% relative to the monomer, the average particle size decreased from 2.31 to 1.36 ${\mu}m$, the conversion decreased from 93.3 to 88.9%, the weight-average molecular weight increased from 46,300 to 150,200 g $mol^{-1}$ and the PDI decreased from 2.79 to 1.94, respectively. In particular, the incorporation of 10 wt% of PMAA macro-RAFT agent produced monodisperse PS spheres of 1.36 ${\mu}m$ with a coefficient of variation (CV) of 6.44%. Thus, the PMAA macro-RAFT agent worked as a reactive steric stabilizer providing monodisperse, micron-sized, PS particles.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.2
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• pp.54-60
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• 2000

Most droplet generators are based on the Rayleigh's theory of droplet breakup, and various kind of droplet generation devices have been designed in accordance with vibrating method of capillary liquid column. At present, VOAG(Vibrating Orifice Monodisperse Aerosol Generator) is used to generate primary aerosol standards. For the combustion experiments with isolated single droplet, it is found that dripping method or separating method of suspended drop at an end of filament are more effective. Single drops can be separated from continuous streams of droplets by controlling electric charge.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1066-1074
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• 2004

With a diode corona charger, which is a component of ELPI(Electrical Low Pressure Impactor), aerosol particles are charged to make electrical detection possible before they are collected by the impactor. We designed and evaluated two cylindrical corona chargers, each of which had a central corona needle electrode. For the performance evaluation of each corona charger the polydisperse dioctyl sebacate(DOS) particles, with diameters of 0.1∼0.8 $\mu$m and NaCl particles, smaller than 0.1$\mu$m, were used. The particles were then led through an electrostatic classifier (TSI model 3081) to classify monodisperse aerosol with minimal size deviation. After evaluating the wall loss of the particles in the corona charger, we measured the product of penetration and number of charges, Pㆍn, to evaluate the corona charger efficiency at high positive voltages of 4, 5, 6 kV.

• Macromolecular Research
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• v.10 no.5
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• pp.266-272
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• 2002

Although the reptational model of Doi and Edwards gives a successful description of viscoelasticity of flexible linear polymers, the success is restricted to the terminal region./sup 1/ There have been several attempts to modify the Doi-Edwards model to describe wider range of time or frequency./sup 2-6/ This paper suggests a simple phenomenological model which can describe wider range of molecular weight than such molecular models can. Although our model is a phenomenological one, it is practical and convenient to predict the effect of molecular weight distribution on linear viscoelastic data because of its simple mathematical form.

• Korea-Australia Rheology Journal
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• v.18 no.4
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• pp.199-207
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• 2006

Measurements by Luap et al. (2005) of elongational viscosity and birefringence of two nearly monodisperse polystyrene melts with molar masses $M_{w}$ of $206,000g{\cdot}mol^{-1}$ (PS206k) and $465,000g{\cdot}mol^{-1}$ (PS465k) respectively are reconsidered. At higher elongational stresses, the samples showed clearly deviations from the stress optical rule (SOR). The elongational viscosity data of both melts can be modeled quantitatively by the MSF model of Wagner et al. (2005), which is based on the assumption of a strain-dependent tube diameter and the interchain pressure term of Marrucci and Ianniruberto (2004). The only nonlinear parameter of the model, the tube diameter relaxation time, scales with $M_{w}^{2}$. In order to get agreement with the birefringence data, finite chain extensibility effects are taken into account by use of the $Pad\'{e}$ approximation of the inverse Langevin function, and the interchain pressure term is modified accordingly. Due to a selfregulating limitation of chain stretch by the FENE interchain pressure term, the transient elongational viscosity shows a small dependence on finite extensibility only, while the predicted steady-state elongational viscosity is not affected by non-Gaussian effects in agreement with experimental evidence. However, deviations from the SOR are described quantitatively by the MSF model by taking into account finite chain extensibility, and within the experimental window investigated, deviations from the SOR are predicted to be strain rate, temperature, and molar mass independent for the two nearly monodisperse polystyrene melts in good agreement with experimental data.

• Korea-Australia Rheology Journal
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• v.19 no.1
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• pp.35-42
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• 2007

The effects of particle size distribution on the magnetorheological response of inverse ferrofluids was investigated using controlled mixtures of two monodisperse non-magnetisable powders of sizes $4.6\;{\mu}m\;and\;80{\mu}m$ at constant volume fraction of 30%, subjected to large amplitude oscillatory shear flow. In the linear viscoelastic regime (pre-yield region), it was found that the storage and loss moduli were dependent on the particle size as well as the proportion of small particles, with the highest storage modulus occurring for the monodisperse small particles. In the nonlinear regime (post yield region), Fourier analysis was used to compare the behaviour of the $1^{st}\;and\;3^{rd}$ harmonics ($I_{1}\;and\;I_{3}\;respectively$) as well as the fundamental phase angle as functions of the applied strain amplitude. The ratio of $I_{3}/I_{1}$ was found to become more pronounced with decreasing particle size as well as with increasing proportion of small particles in the bidisperse mixtures. Furthermore, the phase angle was able to clearly show the transition from solid-like to viscous behaviour. The results suggested that the nonlinear response of a bidisperse IFF is dependent on particle size as well as the proportion of small particles in the system.

• Journal of Powder Materials
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• v.23 no.6
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• pp.442-446
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• 2016

The sol-gel method is the simplest method for synthesizing monodispersed silica particles. The purpose of this study is to synthesize uniform, monodisperse spherical silica nanoparticles using tetraethylorthosilicate (TEOS) as the silica precursor, ethanol, and deionized water in the presence of ammonia as a catalyst. The reaction time and temperature and the concentration of the reactants are controlled to investigate the effect of the reaction parameters on the size of the synthesized particles. The size and morphology of the obtained silica particles are investigated using transmission electron microscopy and particle size analysis. The results show that monodispersed silica particles over a size range of 54-504 nm are successfully synthesized by the sol-gel method without using any additional process. The nanosized silica particles can be synthesized at higher TEOS/$H_2O$ ratios, lower ammonia concentrations, and especially, higher reaction temperatures.

• Polymer(Korea)
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• v.34 no.1
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• pp.25-31
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• 2010

Polymer core and metal shell composite particles have been prepared by the electroless nickel plating on the surface of monodisperse polystyrene microspheres. Various sizes of polystyrene particles with highly monodisperse state could be synthesized by controlling the dispersion medium in dispersion polymerization. Electroless nickel plating was performed on the polystyrene particle with diameter of $3.4\;{\mu}m$. The morphology of polystyrene/nickel composite particles was investigated to see the effect of the plating conditions, such as the $PdCl_2$ and glycine concentrations and the dropping rate of nickel plating solution, on nickel deposition. With $PdCl_2$ and glycine concentrations at more than 0.4 g/L and 1 M, respectively, more uniform nickel layer and less precipitated nickel aggregates were formed. At the given plating time of 2 h, the same amount of plating solution was introduced by varying the dropping rate. Though the effect of dropping rate on particle morphology was not noticeable, the dropping rate of 0.15 mL/min for 60 min showed rather uniform plating.

• Polymer(Korea)
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• v.36 no.2
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• pp.177-181
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• 2012

This study presents the preparation of double emulsions in a poly(dimethylsiloxane) (PDMS)-based microfluidic device. To improve the wettability of hydrophilic continuous phase onto a hydrophobic PDMS microchannel, the surface was modified with 3-(trimethoxysilyl) propyl methacrylate (TPM) and then sequentially reacted with acrylic acid monomer solution, which produced selective covalent bonding between acrylic acids and methacrylate groups. For the proof of selective surface modification, tolonium chloride solution was used to identify the modified region and we confirmed that the approach was successfully performed. When water containing 0.5% w/w sodium dodecyl sulfate and 1% w/w Span80 with hexadecane were loaded into the selectively modified microfluidic channels, we can produce stable double emulsion. Based on the spreading coefficients, we predict the morphology of double emulsions. Our proposed method efficiently produces monodisperse double emulsions having 48.5 ${\mu}m$(CV:1.6%) core and 65.1 ${\mu}m$ (CV:1.6%) shell. Furthermore, the multiple emulsions having different numbers of core were easily prepared by simple control of flow rates.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.2
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• pp.39-44
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• 2004

The present paper gives a review of the recent development of a differential mobility analyzer (DMA) available for both particle size measurements and production of monodisperse particles in the nanometer range. Operating principles of a general DMA are introduced as well as characteristics of highly functional DMAs such as those capable of classifying particles in a measurement range as broad as 1-1000nm at low pressures. Some examples of DMA applications are also described.