- Nano Express
- Open Access
Dispersion Polymerization of Polystyrene Particles Using Alcohol as Reaction Medium
© Cho et al. 2016
- Received: 26 August 2015
- Accepted: 15 January 2016
- Published: 1 February 2016
In this study, monodisperse polystyrene nanospheres were prepared by dispersion polymerization using alcohol as reaction medium to prepare colloidal clusters of the latex beads. Polyvinylpyrrolidone (PVP) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTC) were used as dispersion stabilizer and comonomer, respectively. The particle size could be controlled by adjusting the reactant compositions such as the amount of stabilizer, comonomer, and water in the reactant mixture. The size and monodispersity of the polymeric particles could be also controlled by changing the reaction medium with different alcohols other than ethanol or adjusting the polymerization temperature. The synthesized particles could be self-organized inside water-in-oil emulsion droplets by evaporation-driven self-assembly to produce colloidal clusters of the polymeric nanospheres.
- Dispersion polymerization
- Polystyrene nanospheres
- Colloidal clusters
Over the past decades, the synthetic routes of polymeric latex beads have been developed by various researchers for the applications of biosensors, templates for porous materials, and colloidal crystals [1–3]. Since latex particles have been used in rubber industry during World War II, the synthesis of polymeric particles has attracted much attention in the field of fine chemistry such as ink materials and adhesives [4–7]. In addition, various researches have been conducted for the applications of the polymeric colloids including fiber industry, calibration of electron microscopes, protein recovery, cancer cell removal, cell isolation, and contrast agent for MRI [8–12]. Packing and organization of the particles have been also studied applying self-assembly in the field of colloid science .
The fabrication routes of the latex colloids have been developed as various polymerization methods such as emulsion, suspension, or precipitation polymerization schemes. For the control of the size and size distribution of the latex beads, it is necessary to establish suitable synthesis conditions. For this purpose, special techniques have been developed including successive polymerization from seed particles as multi-step polymerization scheme . In addition, morphologies of the polymeric particles could be also controlled by swelling and polymerization of the seeds . Since most researches are focused on emulsion polymerization, robust recipes for the particle synthesis are still necessary to prepare polymeric beads dispersed in organic solvent by proper synthesis method such as dispersion polymerization .
In this study, dispersion polymerization of polystyrene nanospheres was performed to control the diameter of the particles by adjusting the reaction parameters such as the amount of stabilizer. The polymerization was carried out at 70 °C using batch-type reactor. As reactants, styrene, AIBN, and PVP were used as monomer, initiator, and stabilizer, respectively, in the reaction medium such as ethanol. The synthesized polystyrene nanospheres were used as building block particles for the self-organization inside emulsion droplets to induce capillary pressure for evaporation-driven self-assembly.
For the synthesis of polystyrene beads, styrene monomer (99 %), and initiator such as α,α’-azobis(isobutyronitrile) (AIBN: 99 %) were purchased from Daejung Chemicals and Sigma-Aldrich, respectively. 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTC: 72 % aq) was used as cationic comonomer and bought from Aldrich Chemicals. Polyvinylpyrrolidone (PVP K30, Mw = 40,000) was used as stabilizer and purchased from Junsei Chemicals. Ethanol (99.9 %, HPLC grade, Daejung Chemicals) was used as reaction medium.
For the synthesis of colloidal clusters of polystyrene nanospheres, Abil EM 90 (modified polyether-polysiloxane/dimethicone copolyol) was used as emulsifier and purchased from Cosnet. Hexadecane (anhydrous, 99 %) was used as continuous oil phase and bought from Sigma-Aldrich.
Synthesis of Polystyrene Nanospheres
Dispersion polymerization was performed to synthesize monodisperse polystyrene nanospheres with narrow size distribution. Ethanol as reaction medium containing polyvinylpyrrolidone (PVP) was poured into batch-type reactor where the temperature was maintained as 70 °C. At room temperature, the monomer is not miscible with reaction medium to form turbid mixture, whereas they can be mixed at elevated temperature such as 70 °C to become transparent solution.
Then, suitable amount of styrene and aqueous solution of comonomer (MTC) were added to the reactor during gentle stirring at around 170 to 200 rpm. Before the addition of initiator, nitrogen purging was conducted to remove oxygen from the reaction vessel for 1.5 h. Then, AIBN initiator was added to the reactor and the synthesis continued for 19 h.
Fabrication of Colloidal Clusters of Polymeric Nanospheres
The polystyrene nanosphere suspension synthesized by dispersion polymerization was washed by centrifugation and redispersion in fresh ethanol to prepare dispersed phase. The emulsion stabilizer, Abil EM90 was dissolved in hexadecane with 3 wt.% as continuous phase. These dispersed and continuous phases were mixed with the volume ratio of 1:3 and emulsified using mechanical homogenizer for 1 min. The resultant emulsion droplets were evaporated by heating at 90 °C for 1 h to induce the capillary pressure for the self-organization of the PS nanospheres. After heating, the clusters of the polystyrene nanospheres were washed with hexane to remove oil phase such as hexadecane, followed by drying for the observation using electron microscope.
Instruments for Characterizations
The morphologies of the polystyrene particles were observed using field emission scanning electron microscope (FE-SEM; Hitachi-S4700).
Here, H and a stand for the separation distance between the particles and the particle radius, respectively. Ψ 0 and 1/κ denote the surface electric potential and the electric double layer thickness, respectively. Since the 1/κ is proportional to the square root of the dielectric constant, the maximum range of electrostatic force increases with decreasing value of dielectric constant. However, the particle size was increased with decreasing value of the dielectric constant of solvent, indicating that steric force has more strong contribution of the particle diameter. In Eq. (2), the steric force V s due to PVP molecules adsorbed on the particle surface also plays an important role for the stabilization of the polymeric particles and the diameter of the particles. The solution state of PVP can be changed in heavy alcohols since the steric force of the stabilizing agent may be decreased in such alcohols due to the change of the radius of gyration. Thus, the particle growth could be observed by adopting the alcohols with high molecular weight, as shown in the graph of Fig. 5.
Monodisperse polystyrene nanospheres were synthesized by dispersion polymerization in alcohol as reaction medium, and the particle size was controlled by adjusting the reaction parameters such as polymerization temperature and reactant compositions. The effect of the amount of the stabilizer such as PVP, comonomer, and water were studied systemically to control the average diameter of the polymeric particles. The size range of the polystyrene latex could be adjusted from 200 nm to 1 μm. Besides the particle diameter, monodispersity was also affected when different types of reaction medium or stabilizing agent were used during dispersion polymerization. The synthesized particles were adopted as building blocks for the fabrication of clusters or supraparticles by evaporation-driven self-assembly using water-in-hexadecane emulsions as confining geometries.
This research was financially supported by a grant by Ministry of Land, Infrastructure and Transport (MOLIT) of Korea Government and Korea Agency for Infrastructure Technology Advancement (KAIA, 14CTAP-C078865-2).
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