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Huixuan Zhang - One of the best experts on this subject based on the ideXlab platform.
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in situ Charge Neutralization controlled particle coagulation and its effects on the particle size distribution in the one step emulsion polymerization
European Polymer Journal, 2016Co-Authors: Wenting Meng, Mingyao Zhang, Huixuan Zhang, Ping WangAbstract:Abstract A novel approach to prepare sub-200 nm, narrowly dispersed polystyrene latex particles is proposed for the emulsion polymerization of a ca. 40 wt% solid-content solution. The presented method exploits the cationic comonomer methacryloxyethyltrimethyl ammonium chloride (MATMAC) or the initiator 2,2′-Azobis (2-methylpropionamidine) dihydrochloride (AIBA) to generate cationic oligomeric radicals shielded the negatively Charged surfactant molecules adsorbed on the particles surface, further induced particle coagulation by in situ Charge Neutralization. By adjusting the types and amounts of the comonomer, the extent of the in situ Charge Neutralization is controlled. In consequence, the extent of the particle coagulation is controlled, resulting in the production of large-size latex particles. The particle coagulation induced by in situ Charge Neutralization occurs at the particle nucleation stage, which extends the times of particle completive growth and reversible coagulation, and therefore, narrowed the width of the particle size distribution of the ultimate latex particles. The resulting colloidal latexes containing 40 wt% solid content are very stable by presenting the absolute value of zeta potentials larger than 40 mV. This approach is likely to be used for large-scale industrial productions of narrowly dispersed polymer particles.
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synthesis of large scale monodisperse latex particles via one step emulsion polymerization through in situ Charge Neutralization
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016Co-Authors: Baijun Liu, Mingyao Zhang, Huixuan ZhangAbstract:Abstract Monodisperse sub −200 nm polystyrene nanoparticles were synthesized by a facile one-step emulsion polymerization technology using sodium dodecyl sulfonate (SDS) and 2, 2′- azobis (2-methylpropionamide) dihydrochloride (AIBA) as the surfactant and initiator, respectively. The in situ Neutralization between negatively Charged surfactant SDS and positively Charged AIBA was used to control the primary particle (or swollen micelle) volume and the extent of the particle coagulation. As the oligomeric radicals with cationic AIBA chain ends were captured by anionic swollen micelles, the electrostatic stability of swollen micelles gradually reduced, further promoting the primary particle coagulation. As a result, the initial particle number decreased with the addition of AIBA. The earlier primary particle coagulation not only enlarged the particle size, but also narrowed the particle size distribution of final the latex particles.
Dongsheng Wang - One of the best experts on this subject based on the ideXlab platform.
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the influence of particle size and concentration combined with ph on coagulation mechanisms
Journal of Environmental Sciences-china, 2019Co-Authors: Hongyan Sun, Ruyuan Jiao, Dongsheng WangAbstract:Abstract In order to evaluate the influence of particle size and particle concentration on the coagulation process, two kinds of particle suspensions, nanoparticles and microparticles, were employed to investigate the effect of particle size on coagulation mechanisms with varying coagulation parameters. Results showed that it is easier for nanoparticles to cause self-aggregation because of Brownian motion, while interception and sedimentation are the mainly physical processes affecting particle transport for microparticles, so they are more stable and disperse more easily. The particle size distribution and particle concentration had distinct influence on the coagulation mechanisms. Under neutral conditions, as the amount of coagulant increased, the coagulation mechanism for nanoparticles changed from Charge Neutralization to sweep flocculation and the nanoparticles became destabilized, re-stabilized and again destabilized. For microparticles, although the coagulation mechanism was the same as that of nanoparticles, the increased rate of aluminum hydroxide precipitation exceeded the adsorption of incipiently formed soluble alum species, resulting in the disappearance of the re-stabilization zone. Under acidic conditions, Brownian motion dominates for nanoparticles at low particle concentrations, while sweep flocculation is predominant at high particle concentrations. As for microparticles, Charge Neutralization and sweep flocculation are the mechanisms for low and high particle concentrations respectively. Under alkaline condition, although the mechanisms for both nano- and microparticles are the same, the morphology of flocs and the kinetics of floc formation are different. At low particle concentrations, nanoparticles have larger growth rate and final size of flocs, while at high particle concentrations, nanoparticles have higher fractal dimension and recovery factors.
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distinct coagulation mechanism and model between alum and high al13 pacl
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Dongsheng Wang, Hongxiao TangAbstract:The conventional alum and polyaluminum chloride (PACl) with high content of Al13 were selected to study the interaction between coagulants and particles in suspension. Particulate silica microspheres were used for the investigation with emphasis on the surface adsorption behavior at a constant pH of 6.5. Residual turbidity (RT), zeta potential and fractional surface coverage (θ) were studied as functions of aluminum dosage (C). Differences in the coagulation behavior between alum and PACl were illustrated graphically as log C–RT and log C–θ, respectively. It was demonstrated that some distinct mechanisms existed between alum and PACl in their adsorption and coagulation with silica particles owing to their different speciation. The results suggested that, to accomplish destabilization and aggregation, alum interacted with silica particles mainly via monomers and Al(OH)3(am) flocs, while PACl interacted via the Al13 polycations. As a result, Charge-Neutralization, electrostatic patch coagulation and sweep-flocculation, bridge-aggregation may be included during the coagulation process. The main mechanisms for alum were Charge-Neutralization/sweep-flocculation while electrostatic patch coagulation and bridge-aggregation may be both involved for PACl besides Charge-Neutralization. Langmuir and Freundlich isotherm models were used to describe the adsorption process of PACl and alum on silica particles, respectively. Monolayer adsorption was observed for PACl with θ < 0.5 whereas multilayer adsorption occurred for alum with θ value reaching above 1. It was concluded that different adsorption mechanisms occurred for PACl and alum. The predominant driving force in the adsorption process of PACl was of electrostatic origin, whereas for alum was mainly through chemical precipitation.
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alkalinity effect of coagulation with polyaluminum chlorides role of electrostatic patch
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Dongsheng Wang, Marc Edwards, Aoyou Shi, Hongxiao TangAbstract:Abstract The coagulation behavior of polyaluminum chloride (PACl) with various basicities ( B = OH/Al values) was investigated under different alkalinities. It is aimed to get better insights into the coagulation mechanisms involving interactions between hydrolyzed Al(III) products and particles. Jar tests were used to evaluate the coagulation efficiencies, including zeta potentials, residual turbidities (RT) and pH values. An optical monitoring technique of photometric dispersion analyzer (PDA) was utilized to observe the coagulation dynamics. The experimental results show that the traditional coagulant such as alum evolves a rapid hydrolysis after dosing and the in situ formed hydrolysis products can destabilize the kaolin particles by precipitation Charge Neutralization (PCN). The preformed polymeric species in PACls exhibit a relatively high stability after dosing and can form “electrostatic patches” on clay particle surfaces. These patches play a crucial role in “electrostatic patch coagulation” (EPC). Increasing alkalinity extends both PCN and EPC zones. Under the low alkalinity, EPC with high Al b contained in PACls works better than PCN coagulation; increased alkalinity improves the efficiency of traditional coagulant due to sweep flocculation. Under the higher alkalinity, more coagulant is required to achieve complete Charge Neutralization. The stoichiometric relationships between the dosage and alkalinity are different depending on the B values of PACls.
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characterization of floc size strength and structure under various coagulation mechanisms
Powder Technology, 2006Co-Authors: Tao Li, Dongsheng Wang, Hongxiao TangAbstract:Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. Charge Neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent T was of the following hierarchy: Charge Neutralization (0.6107)> sweep (0.5618) > bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m(-2). An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated. (c) 2006 Elsevier B.V. All rights reserved.
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relative importance of Charge Neutralization and precipitation on coagulation of kaolin with pacl effect of sulfate ion
Environmental Science & Technology, 2002Co-Authors: Dongsheng Wang, Hongxiao Tang, John GregoryAbstract:The effect of the sulfate ion on coagulation with polyaluminum chloride (PACl) was investigated by using an optical monitoring technique together with the conventional jar test procedure and electrophoretic mobility (EM) measurements. The effect of the SO42-/Al ratio, dosage, and pH were examined in detail. The experimental results show that sulfate has a significantly different effect on PACl coagulation as a result of preformed hydrolysis products, where Charge Neutralization and precipitation play different parts in the coagulation process. The increased rate of coagulation with increasing SO42-/Al ratio can be partially explained by Charge Neutralization effects, through increased adsorption and complexation of sulfate, thus giving increased particle collision efficiency. Different PACl samples were prepared with different values of B ([OH]/[Al]). For B = 0 (i.e., AlCl3) with mainly monomers, hydroxide precipitation tends to be accelerated in the presence of sulfate, giving significant turbidity remov...
Hongxiao Tang - One of the best experts on this subject based on the ideXlab platform.
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distinct coagulation mechanism and model between alum and high al13 pacl
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Dongsheng Wang, Hongxiao TangAbstract:The conventional alum and polyaluminum chloride (PACl) with high content of Al13 were selected to study the interaction between coagulants and particles in suspension. Particulate silica microspheres were used for the investigation with emphasis on the surface adsorption behavior at a constant pH of 6.5. Residual turbidity (RT), zeta potential and fractional surface coverage (θ) were studied as functions of aluminum dosage (C). Differences in the coagulation behavior between alum and PACl were illustrated graphically as log C–RT and log C–θ, respectively. It was demonstrated that some distinct mechanisms existed between alum and PACl in their adsorption and coagulation with silica particles owing to their different speciation. The results suggested that, to accomplish destabilization and aggregation, alum interacted with silica particles mainly via monomers and Al(OH)3(am) flocs, while PACl interacted via the Al13 polycations. As a result, Charge-Neutralization, electrostatic patch coagulation and sweep-flocculation, bridge-aggregation may be included during the coagulation process. The main mechanisms for alum were Charge-Neutralization/sweep-flocculation while electrostatic patch coagulation and bridge-aggregation may be both involved for PACl besides Charge-Neutralization. Langmuir and Freundlich isotherm models were used to describe the adsorption process of PACl and alum on silica particles, respectively. Monolayer adsorption was observed for PACl with θ < 0.5 whereas multilayer adsorption occurred for alum with θ value reaching above 1. It was concluded that different adsorption mechanisms occurred for PACl and alum. The predominant driving force in the adsorption process of PACl was of electrostatic origin, whereas for alum was mainly through chemical precipitation.
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alkalinity effect of coagulation with polyaluminum chlorides role of electrostatic patch
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Dongsheng Wang, Marc Edwards, Aoyou Shi, Hongxiao TangAbstract:Abstract The coagulation behavior of polyaluminum chloride (PACl) with various basicities ( B = OH/Al values) was investigated under different alkalinities. It is aimed to get better insights into the coagulation mechanisms involving interactions between hydrolyzed Al(III) products and particles. Jar tests were used to evaluate the coagulation efficiencies, including zeta potentials, residual turbidities (RT) and pH values. An optical monitoring technique of photometric dispersion analyzer (PDA) was utilized to observe the coagulation dynamics. The experimental results show that the traditional coagulant such as alum evolves a rapid hydrolysis after dosing and the in situ formed hydrolysis products can destabilize the kaolin particles by precipitation Charge Neutralization (PCN). The preformed polymeric species in PACls exhibit a relatively high stability after dosing and can form “electrostatic patches” on clay particle surfaces. These patches play a crucial role in “electrostatic patch coagulation” (EPC). Increasing alkalinity extends both PCN and EPC zones. Under the low alkalinity, EPC with high Al b contained in PACls works better than PCN coagulation; increased alkalinity improves the efficiency of traditional coagulant due to sweep flocculation. Under the higher alkalinity, more coagulant is required to achieve complete Charge Neutralization. The stoichiometric relationships between the dosage and alkalinity are different depending on the B values of PACls.
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characterization of floc size strength and structure under various coagulation mechanisms
Powder Technology, 2006Co-Authors: Tao Li, Dongsheng Wang, Hongxiao TangAbstract:Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. Charge Neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent T was of the following hierarchy: Charge Neutralization (0.6107)> sweep (0.5618) > bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m(-2). An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated. (c) 2006 Elsevier B.V. All rights reserved.
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relative importance of Charge Neutralization and precipitation on coagulation of kaolin with pacl effect of sulfate ion
Environmental Science & Technology, 2002Co-Authors: Dongsheng Wang, Hongxiao Tang, John GregoryAbstract:The effect of the sulfate ion on coagulation with polyaluminum chloride (PACl) was investigated by using an optical monitoring technique together with the conventional jar test procedure and electrophoretic mobility (EM) measurements. The effect of the SO42-/Al ratio, dosage, and pH were examined in detail. The experimental results show that sulfate has a significantly different effect on PACl coagulation as a result of preformed hydrolysis products, where Charge Neutralization and precipitation play different parts in the coagulation process. The increased rate of coagulation with increasing SO42-/Al ratio can be partially explained by Charge Neutralization effects, through increased adsorption and complexation of sulfate, thus giving increased particle collision efficiency. Different PACl samples were prepared with different values of B ([OH]/[Al]). For B = 0 (i.e., AlCl3) with mainly monomers, hydroxide precipitation tends to be accelerated in the presence of sulfate, giving significant turbidity remov...
Yasuhisa Adachi - One of the best experts on this subject based on the ideXlab platform.
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dynamics of polyelectrolyte adsorption and colloidal flocculation upon mixing studied using mono dispersed polystyrene latex particles
Advances in Colloid and Interface Science, 2015Co-Authors: Lili Feng, Martien Cohen A Stuart, Yasuhisa AdachiAbstract:The dynamic behavior of polyelectrolytes just after their encounter with the surface of bare colloidal particles is analyzed, using the flocculation properties of mono-dispersed polystyrene latex (PSL) particles. Applying a Standardized Colloid Mixing (SCM) approach, effects of ionic strength and Charge density of polymer chain on the rate of flocculation, the electrophoretic mobility of particle coated with polyelectrolyte, and the thickness of adsorbed polymer layer were analyzed, focusing on distinguishing features of two modes of flocculation, namely bridging formation and Charge Neutralization. In the case of excess polymer dosage, the bridging flocculation clearly highlights the transient behavior of polymer conformation from random-coil-like in bulk solution to increasingly flatten on the surface. The adsorption of polymer chains leads to a stagnant layer of solvent near the solid wall, which is confirmed by electrokinetic data. In the regime near optimum dosage two cases emerge. For high Charge density polymer, Charge Neutralization is dominant and advantageous for the continuous progress of flocculation by heterogeneous double layer interaction. As a function of elapsed time after the onset of mixing, crossover from bridging to Charge Neutralization is found. In the case of low Charge density polymer, bridging flocculation is the mechanism. Fluid mixing is concluded to have an essential role in the formation of bridges.
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coagulation and charging of latex particles in the presence of imogolite
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2013Co-Authors: Motoyoshi Kobayashi, Miki Nitanai, Naoya Satta, Yasuhisa AdachiAbstract:Abstract Imogolite, an aluminum silicate clay mineral obtained from volcanic ash soil, has several unique properties: a nano-tubular structure, having positive Charge below pH 9, and coagulation beyond pH 6–7. Thus, imogolites can play an important role when volcanic ash soil-based coagulants are used for coagulation. To understand the mechanism of imogolite-induced coagulation and subsequent sedimentation, we studied the coagulation and charging of three types of latex spheres in the presence of purified imogolites, obtained from natural soil in Kitakami, Iwate, Japan. Coagulation and dispersion were analyzed by observing latex–imogolite mixed suspensions with the unaided eye and by measuring the supernatant absorbance. The charging property was studied by electrophoretic mobility. These experiments were carried out as a function of the ratio of the concentration of imogolites (CI) to that of latex particles (CL) at three different pH values (pH 4, 6.5, and 10). The experimental results clarified that the mechanisms of imogolite-induced coagulation depend on the charging and coagulation properties of the imogolites. That is, when the latex and the imogolites are oppositely Charged and the imogolites are dispersed, coagulation occurs only around the isoelectric point. Here, the main coagulation mechanism is Charge Neutralization. If the latex and the imogolites are oppositely Charged and the imogolites are coagulated, coagulation occurs not only around the isoelectric point but also at higher CI/CL ratios. This result indicates that the particles coagulate due to both Charge Neutralization and sweep coagulation, in which the latex particles are enmeshed by the flocs of the imogolites. When the latex and the imogolites are similarly Charged and the imogolites are coagulated, the particles aggregate at higher CI/CL ratios through sweep coagulation only. We also found that the efficiency of sweep coagulation depends on the electrokinetic potential of the imogolites and that the Charge Neutralization is determined by the imogolite dosage per total particles surface area.
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study of colloidal stability of allophane dispersion by dynamic light scattering
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005Co-Authors: Yasuhisa Adachi, Motoyoshi Kobayashi, S Koga, M InadaAbstract:Abstract The aggregation kinetics of the aqueous dispersion of allophane was measured by dynamic light scattering as functions of pH and ionic strength. The sample was purified from natural Kanuma soil (Tochigi, Japan). A notable feature is that the dispersion is composed of aggregated flocs of allophane particles. The experiments were performed adjusting the initial floc diameter by centrifugation. The aggregation was induced by Charge Neutralization or compression of the electrical double layers, by merely mixing the suspension with an electrolyte solution of controlled pH and ionic strength. After the initial mixing operation, the suspension was placed in a static condition and the temporal variation of the average hydrodynamic diameter was monitored in situ . In the initial stage, the diameter dramatically increased reflecting the aggregation induced by the hydrodynamic mixing. Due to the Brownian aggregation, this initial enhancement was followed by a moderate increase. Under the Brownian aggregation, the aggregation rates were found to take a certain limiting value denoting fast coagulation irrespective of Charge Neutralization or compression of the electric double layers. When the salt concentration is not sufficiently high, the rate of aggregation against pH gradually increases and approaches the fast-coagulation domain; however, the rate decreases rather rapidly as the pH increases. This behavior was interpreted considering pH-dependent Charge distribution generated on the surface of allophane particles with peculiar morphology. This interpretation was supported by electrophoretic mobility data. In contrast with the Brownian aggregation, the rate of orthokinetic aggregation induced by Charge Neutralization was detected to be slightly faster than that induced by compression of the electric double layers.
Mingyao Zhang - One of the best experts on this subject based on the ideXlab platform.
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in situ Charge Neutralization controlled particle coagulation and its effects on the particle size distribution in the one step emulsion polymerization
European Polymer Journal, 2016Co-Authors: Wenting Meng, Mingyao Zhang, Huixuan Zhang, Ping WangAbstract:Abstract A novel approach to prepare sub-200 nm, narrowly dispersed polystyrene latex particles is proposed for the emulsion polymerization of a ca. 40 wt% solid-content solution. The presented method exploits the cationic comonomer methacryloxyethyltrimethyl ammonium chloride (MATMAC) or the initiator 2,2′-Azobis (2-methylpropionamidine) dihydrochloride (AIBA) to generate cationic oligomeric radicals shielded the negatively Charged surfactant molecules adsorbed on the particles surface, further induced particle coagulation by in situ Charge Neutralization. By adjusting the types and amounts of the comonomer, the extent of the in situ Charge Neutralization is controlled. In consequence, the extent of the particle coagulation is controlled, resulting in the production of large-size latex particles. The particle coagulation induced by in situ Charge Neutralization occurs at the particle nucleation stage, which extends the times of particle completive growth and reversible coagulation, and therefore, narrowed the width of the particle size distribution of the ultimate latex particles. The resulting colloidal latexes containing 40 wt% solid content are very stable by presenting the absolute value of zeta potentials larger than 40 mV. This approach is likely to be used for large-scale industrial productions of narrowly dispersed polymer particles.
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in situ Charge Neutralization on governing particle coagulation nucleation and size distribution in macroemulsion polymerization
RSC Advances, 2016Co-Authors: Baijun Liu, Mingyao Zhang, Wenting Meng, H X ZhangAbstract:Fabricating monodispersed polymer latex particles with ∼300 nm size at high monomer concentrations by batch macroemulsion polymerization remains significantly challenging because of latex stability. In this study, we developed a novel approach based on in situ Charge Neutralization to prepare 40 wt% solid content latex containing monodispersed sub-300 nm latex particles. The cationic initiator 2,2′-azobis(2-methylpropionamidine)dihydrochloride (AIBA) was used to induce in situ Charge Neutralization in the particle nucleation period and shield the negative Charges of surfactant sodium dodecyl sulfate molecules to further reduce the electrostatic repulsion between primary particles, resulting in primary particle coagulation nucleation. The primary particle coagulation promoted particle number decreased to ∼1016 L−1, and the average particle size increased to ∼100 nm at a very low monomer conversion (<0.12). With increasing AIBA concentrations from 0.6 and 0.8 to 1.0 wt% (the molar ratio of AIBA/SDS is 0.64, 0.85 and 1.06, respective), the average particle size of the latex ultimately attained from 170.6 and 221.7 to 288.0 nm, respectively. Moreover, the addition of an electrolyte and copolymerization composition also governed the particle coagulation extent and affected the particle size distribution of the ultimate latex particles. To the best of our knowledge, this is the simplest, most efficient, and inexpensive approach to prepare large sized, monodispersed latex particles.
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synthesis of large scale monodisperse latex particles via one step emulsion polymerization through in situ Charge Neutralization
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016Co-Authors: Baijun Liu, Mingyao Zhang, Huixuan ZhangAbstract:Abstract Monodisperse sub −200 nm polystyrene nanoparticles were synthesized by a facile one-step emulsion polymerization technology using sodium dodecyl sulfonate (SDS) and 2, 2′- azobis (2-methylpropionamide) dihydrochloride (AIBA) as the surfactant and initiator, respectively. The in situ Neutralization between negatively Charged surfactant SDS and positively Charged AIBA was used to control the primary particle (or swollen micelle) volume and the extent of the particle coagulation. As the oligomeric radicals with cationic AIBA chain ends were captured by anionic swollen micelles, the electrostatic stability of swollen micelles gradually reduced, further promoting the primary particle coagulation. As a result, the initial particle number decreased with the addition of AIBA. The earlier primary particle coagulation not only enlarged the particle size, but also narrowed the particle size distribution of final the latex particles.