Control of the anisotropic morphology of latex nanocomposites containing single montmorillonite clay particles prepared by conventional and reversible addition‐fragmentation chain transfer based emulsion polymerization

Abstract

Single montmorillonite platelets have been successfully encapsulated by polymer through both a conventional and a reversible addition-fragmentation chain transfer (RAFT) based emulsion polymerization. For both synthetic methods, the encapsulation process basically consisted of three steps: (i) adsorption of cationic RAFT copolymers (RAFT approach) or surfactant (conventional approach); (ii) high shear dispersion of the stabilized clay in aqueous solutions; (iii) starved-feed addition of monomers starting the polymerization. In the conventional approach, the morphology of the latex/clay nanocomposites was close to the dumbbell shapes previously reported and did not depend on the presence of organic modifier as evidenced by cryotransmission electron microscopy and scanning electron microscopy. In the RAFT approach a completely different morphology was obtained which has been coined the cornflake morphology. With these two new approaches we can control the orientation of the clay platelets inside the latex particles which in turn can control the orientation of the clay platelets in a film. A perspective on possible applications of these different morphologies is given, e.g. their use in high barrier coatings.

Polymer Encapsulation of Single Clay Platelets by Emulsion Polymerization Approaches, Thermodynamic, and Kinetic Factors

“…We would like to categorize the different morphologies obtained in both emulsion and miniemulsion clay encapsulation. First of all, it is noticed that the size and size distribution of the clay platelets are important parameters in the obtained morphologies, it is clearly observed that in encapsulation of a polydisperse clay different sizes of the clay are associated with different morphologies …”

“…Initially most of the work was focused on hydrophobized clay and in some cases clay with reactive groups like monomer functionalities. In the work of Voorn, it seemed that edge modification worked best to fully encapsulate the clay, later also unmodified clay was successfully encapsulated …”

“…An interesting example is given by Chakrabary and Singha where the use of neutral functional monomer, in combination with a fluorinated acrylate in miniemulsion polymerization, led to encapsulated Cloisite hybrid latex particles (multiple clay platelets per particle) whereas the use of a positively charged functional monomer led to armored morphology. In emulsion polymerization, one would like to create an affinity of the monomer for the clay particle surface, this is typically done by creating a hemimicelle around the clay, using surfactant absorption on a more or less hydrophobized clay surface . Unfortunately, complete hydrophobization will lead to stacking of the clay platelets again because of the loss of favorable interactions between the clay surface and water that have led to the spontaneous exfoliation in the first place.…”

“…[19] Initially most of the work was focused on hydrophobized clay and in some cases clay with reactive groups like monomer functionalities. In the work of Voorn, it seemed that edge modification worked best to fully encapsulate the clay, [20] later also unmodified clay was successfully encapsulated. [21] The modification of the clays was either ion replacement on the faces of the clay or edge modification through reaction with the hydroxyl groups.…”

Self‐assembly of block copolymers with an alkoxysilane‐based core‐forming block: A comparison of synthetic approaches

“…These hybrid materials are typically pursued for their attractive properties; some examples include the enhancement of mechanical strength of a matrix relative to the neat polymer, response to an applied magnetic field, incorporation of nanomaterials with catalytic function as well as optical properties for diagnostic imaging . The range of materials used to prepare such nanocomposites is extensive, with published examples including natural and synthetic clays, (semi‐)metal oxide nanoparticles, graphene‐derived nanosheets, carbon nanotubes, layered double hydroxides, and quantum dots . Aside from the layer‐by‐layer deposition approach, the most common method of creating such composite materials is heterophase polymerization, which encompasses emulsion, miniemulsion and dispersion polymerization .…”