Mechanistic Investigation of Surfactant-Free Emulsion Polymerization Using Magnetite Nanoparticles Modified by Citric Acid as Stabilizers

Fe₃O₄-armored latexes were successfully synthesized by using modified Fe₃O₄ (IO) nanoparticles as stabilizers without a surfactant. The particle size, conversion, and particle number density of latex particles during the formation process were studied in detail. The surface charge density and the particle size evolutions of latexes were studied by dynamic light scattering. The use of scanning electron microscopy confirmed that IO nanoparticles were adsorbed on the polymer particle surface. Furthermore, the efficiency of iron oxide incorporation (IE) was evaluated by thermogravimetric analysis. The effect of pH, solid content, and zeta potential of IO nanoparticles on the results of polymerization was also discussed in detail. Attempts were made to explain the change of latex particle surface charge density by using Guy-Chapman-Stern's electric double layer theory. In addition, the effect of ionic strength of ammonium sulfate on particle number density of latex particles was described using P. John Feeney's equation. Finally, the mechanistic insights were discussed by studying polymerization kinetics.

Surfactant-free synthesis of layered double hydroxide-armored latex particles

MgAl-layered double hydroxide (LDH)-armored latexes were produced by Pickering emulsion polymerization of styrene using 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) as auxiliary comonomers.

Effect of the addition of salt to Pickering emulsion polymerizations using polymeric nanogels as stabilizers

Nanogels made from crosslinked block copolymer micelles are used as stabilizers in the Pickering emulsion polymerization of styrene.

Synthesis of clay-armored poly(vinylidene chloride-co-methyl acrylate) latexes by Pickering emulsion polymerization and their film-forming properties

Use of LAPONITE® clay platelets as Pickering stabilizers of vinylidene chloride-based latexes.

A mechanistic investigation of Pickering emulsion polymerization

Unravelling the mechanism of Pickering emulsion polymerization using silica nanoparticles as the stabilizer.

Investigation of Four Different Laponite Clays as Stabilizers in Pickering Emulsion Polymerization

Clay-armored polymer particles were prepared by emulsion polymerization in the presence of Laponite platelets that adsorb at the surface of latex particles and act as stabilizers during the course of the polymerization. While Laponite RDS clay platelets are most often used, the choice of the type of clay still remains an open issue that is addressed in the present article. Four different grades of Laponite were investigated as stabilizers in the emulsion polymerization of styrene. First, the adsorption isotherms of the clays, on preformed polystyrene particles, were determined by ICP-AES analysis of the residual clay in the aqueous phase. Adsorption of clay depended on the type of clay at low concentrations corresponding to adsorption as a monolayer. Adsorption of clay particles as multilayers was observed for all the grades above a certain concentration under the considered ionic strength (mainly due to the initiator ionic species). The stabilization efficiency of these clays was investigated during the polymerization reaction (free of any other stabilizer). The clays did not have the same effect on stabilization, which was related to differences in their compositions and in their adsorption isotherms. The different grades led to different polymer particles sizes and therefore to different polymerization reaction rates. Laponite RDS and S482 gave similar results, ensuring the best stabilization efficiency and the fastest reaction rate; the number of particles increased as the clay concentration increased. Stabilization with Laponite XLS gave the same particles size and number as the latter two clays at low clay concentrations, but it reached an upper limit in the number of nucleated polymer particles at higher concentrations indicating a decrease of stabilization efficiency at high concentrations. Laponite JS did not ensure a sufficient stability of the polymer particles, as the polymerization results were comparable to a stabilizer-free polymerization system.

Partitioning of Laponite Clay Platelets in Pickering Emulsion Polymerization

Partitioning of laponite disklike clay platelets between polymer particles and bulk aqueous phase was investigated in Pickering surfactant-free emulsion polymerization of styrene. Adsorption of laponite clay platelets plays an important role in the stabilization of this system, influencing the particle size and the number of particles, and, hence, the reaction rate. Adsorption isotherms show that, while the laponite clay platelets are almost fully exfoliated in water, they form multilayers on the surface of the polymer particles by the end of polymerization, as confirmed by transmission electron microscopy (TEM). This observation is supported by quartz crystal microbalance, conductivity, and TEM measurements, which reveal interactions between the clay and polystyrene, as a function of the ionic strength. The strong adsorption of clay platelets leaves a low residual concentration in the aqueous phase that cannot cause further nucleation of polymer particles, as demonstrated during seeded emulsion polymerization experiments in the presence of a high excess of clay. A Brunauer-Emmett-Teller (BET)-type model for laponite adsorption on polystyrene particles matches the adsorption isotherms.

Nanoclay stabilized Pickering miniemulsion of fluorinated copolymer with improved hydrophobicity via RAFT polymerization

Fluoropolymer/clay nanocomposite with improved polymer–clay interaction via electrostatic attraction was prepared by Pickering miniemulsion polymerization.

Tailor-Made Fluorinated Copolymer/Clay Nanocomposite by Cationic RAFT Assisted Pickering Miniemulsion Polymerization

Fluorinated polymers in emulsion find enormous applications in hydrophobic surface coating. Currently, lots of efforts are being made to develop specialty polymer emulsions which are free from surfactants. This investigation reports the preparation of a fluorinated copolymer via Pickering miniemulsion polymerization. In this case, 2,2,3,3,3-pentafluoropropyl acrylate (PFPA), methyl methacrylate (MMA), and n-butyl acrylate (nBA) were copolymerized in miniemulsion using Laponite-RDS as the stabilizer. The copolymerization was carried out via reversible addition-fragmentation chain transfer (RAFT) process. Here, a cationic RAFT agent, S-1-dodecyl-S'-(methylbenzyltriethylammonium bromide) trithiocarbonate (DMTTC), was used to promote polymer-Laponite interaction by means of ionic attraction. The polymerization was much faster when Laponite content was 30 wt % or above with 1.2 wt % RAFT agent. The stability of the miniemulsion in terms of zeta potential was found to be dependent on the amount of both Laponite and RAFT agent. The miniemulsion had particle sizes in the range of 200-300 nm. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses showed the formation of Laponite armored spherical copolymer particles. The fluorinated copolymer films had improved surface properties because of polymer-Laponite interaction.

Synthesis of multi-hollow clay-armored latexes by surfactant-free emulsion polymerization of styrene mediated by poly(ethylene oxide)-based macroRAFT/Laponite complexes

We report the RAFT-mediated synthesis of Laponite-armored latexes by surfactant-free emulsion polymerization.