Pickering Emulsion Polymerization Using Laponite Clay as Stabilizer To Prepare Armored “Soft” Polymer Latexes

Abstract

The fabrication of “soft” nanocomposite clay armored polymer latexes is described. Laponite clay XLS is used as stabilizer in the Pickering emulsion polymerization of a variety of monomer mixtures, that is, methyl methacrylate and n-butyl acrylate, styrene and n-butyl acrylate, and styrene and 2-ethylhexyl acrylate. Overall solids contents of the hybrid latexes in complete absence of coagulation of up to 24 wt % are reported under batch conditions. Key mechanistic aspects of the Pickering emulsion polymerization process are discussed. The use of monomers that have high water solubility and are prone to hydrolyze under basic conditions, for example methyl methacrylate, should be restricted. The use of small amounts of methacrylic acid as auxiliary monomer promotes clay adhesion to the surface of the particles in the Pickering emulsion (co)polymerization of hydrophobic monomers. Detailed kinetic studies at both 60 and 80 °C of the Pickering emulsion copolymerization of styrene and n-butyl acrylate (Sty:BA = 0.67 w/w) are reported, with varying amounts of Pickering stabilizer. The Laponite clay discs play a crucial role in the particle formation (nucleation) stage of the Pickering emulsion polymerization process. Use of increasing amounts leads to smaller average particle sizes but inflicts longer nucleation periods, thereby broadening the particle size distributions. We report the occurrence of a catastrophic coagulation phenomenon for Pickering emulsion polymerizations carried out at a low initiator (ammonium persulfate) flux at 60 °C, for a small window of concentrations of Laponite clay discs.

A mechanistic investigation of Pickering emulsion polymerization

“…Further additions of silica progressively played a smaller role in the reduction of the overall polymerization time until its influence became almost negligible. Similar results were reported by Teixeira et al 23 and by Bourgeat-Lami et al 27 using Laponite clay in the polymerization of styrene/n-butyl acrylate and styrene, respectively. When we take a closer look at Figures 6a and 6b, higher rates of polymerization are observed at low to intermediate monomer conversion when larger amounts of silica are used.…”

“…Methacrylic acid (MAA) is hydrophilic and can promote interaction with silica through Hbonding. 23 However, under reaction conditions, pH ca. 5, the carboxylic acid groups are partially dissociated and the charge repulsion between the negatively charged carboxylic groups and the silica surface seemed to be the predominant effect.…”

“…15 In their work, the authors used talc, barium sulphate, kaolin clay and aluminium oxide in the suspension polymerization of a variety of monomers. Since then Pickering hetero-phase polymerization has been developed further and now includes mini-emulsion, [16][17][18] dispersion 19,20 and emulsion polymerization processes, [21][22][23][24][25][26][27] using a variety of monomers and with a range of fillers, such as silica, laponite clay, magnetite, titanium dioxide, graphene oxide. 28 One driver for the development of heterogeneous Pickering polymerization processes is that they do not require molecular surfactants, offering a big advantage to the paint industry as surfactant migration often deteriorates the performance of coatings.…”

New evidence for hybrid acrylic/TiO2 films inducing bacterial inactivation under low intensity simulated sunlight

“…Among all the polymer/inorganic NPs hybrid morphologies that can be obtained by this method, Pickering stabilization allows obtaining a layer of NPs at the surface of the film after film formation. Pickering latexes are usually stabilized by inorganic fillers such as silica NPs and clays [27][28][29][30]. Nevertheless, in the last decade titanium dioxide NPs have also been employed as polymer particle's stabilizers [31][32][33].…”

Methacrylic block copolymers by sulfur free RAFT (SF RAFT) free radical emulsion polymerisation

“…Firstly, the reactor contents remain under oxygen-free conditions and at an appropriate temperature to carry out the copolymerisation immediately after the macromonomer production. Secondly, the deoxygenation of latexes compromises their colloidal stability, since polymer nanoparticles can cover nitrogen bubbles, [64][65][66][67] in essence inducing coagulation. Unless stated otherwise, we utilised the one-pot approach to fabricate a variety of block copolymers, producing a macromonomer and subsequently extending it with a second monomer, Table 2, Figures S6-S13.…”