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

Abstract

Polymer encapsulation of clay platelets through (mini)emulsion polymerization can be a versatile method to obtain hybrid nanoparticles with several important applications. However, to achieve actual encapsulation of the single clay platelets inside latex particles is relatively difficult. For single clay platelet encapsulation, complete exfoliation and colloidal stability needs to be achieved as well as kinetic and/or thermodynamic control mechanisms to locate and maintain the position of the single clay platelet on the inside of the latex particle. An overview of these mechanisms will be given and an overview of the most relevant attempts in this area will be discussed in retrospect in the context of a systematic mechanistic understanding.

Tailoring the Morphology of Polymer/Montmorillonite Hybrid Latexes by Surfactant-Free Emulsion Polymerization Mediated by Amphipathic MacroRAFT Agents

“…In the literature, comonomer compositions corresponding to copolymers with T g above the polymerization temperature have been preferably used as they favor the encapsulation of the inorganic nanoparticles by decreasing chain mobility, thereby preventing possible migration of the clay platelets to the polymer/water interface in a thermodynamically driven process. 8 Thus, the encapsulated morphology is aided by kinetics control as the inorganic nanoparticles are trapped inside a hard copolymer shell. With the intent to prepare film-forming latexes and verify the impact of the comonomer composition on the morphology of the hybrid particles, R13 and R14 with a MMA/BA ratio of 1/1 (wt/wt), were prepared with MR7 and MR8 respectively (Table 2).…”

Polymer/Laponite Nanocomposite Films Produced from Surfactant-Free Latexes using Cationic Macromolecular Reversible Addition-Fragmentation Chain Transfer Copolymers

“…The encapsulation of inorganic particles within a layer of binder polymer yielding core-shell hybrid particles has shown to be of great interest in the last few years as it is an ultimate solution to avoid agglomeration of the inorganic objects and guarantee that they remain isolated during the film-formation process, in addition to offering the possibility to control their arrangement in the nanocomposite film . Since the invention of this strategy by Hawkett’s research group, a variety of inorganic nanoparticles has been encapsulated, mostly spherical. − Although the encapsulation of high aspect ratio inorganic particles by emulsion polymerization approaches is known to be more challenging because of the high surface energy of these systems, there are also examples in the literature of the encapsulation by REEP of nonspherical particles such as Gibbsite platelets, carbon nanotubes, , graphene oxide nanosheets, layered double hydroxides (LDHs) , and Montmorillonite (MMT) platelets…”

“…25 Since the invention of this strategy by Hawkett's research group, 26 a variety of inorganic nanoparticles has been encapsulated, mostly spherical. 27−33 Although the encapsulation of high aspect ratio inorganic particles by emulsion polymerization approaches is known to be more challenging because of the high surface energy of these systems, 34 there are also examples in the literature of the encapsulation by REEP of nonspherical particles such as Gibbsite platelets, 35 carbon nanotubes, 36,37 graphene oxide nanosheets, 38 layered double hydroxides (LDHs) 39,40 and Montmorillonite (MMT) platelets. 41 Nanocomposite particles with morphologies other than core-shell have also been prepared by means of the REEP process.…”

A Roadmap towards Successful Nanocapsule Synthesis via Vesicle Templated RAFT-Based Emulsion Polymerization

“…Surprisingly it was shown that not only did the RAFT approach work for successful encapsulation, but also that conventional free radical polymerization could work under certain circumstances [7]. The interplay of kinetics and thermodynamics is paramount in determining the resulting morphology [8]. This was also shown in a parallel approach, utilizing Atom Transfer Radical Polymerization (ATRP) instead of RAFT, which was investigated for Gibbsite encapsulation [9,10,11].…”

“…The reason is that in ATRP and RAFT, the initial molecular weight is low and building up slowly whereas in free radical polymerization the initial molecular weight is already high from the start. As a result, forming high molecular weight polymer initially, in combination with a low monomer concentration in the growing particles restricts mobility of the molecules and particles and can capture non-equilibrium morphologies [7,8,10]. Alternatively, crosslinking can also capture non-equilibrium morphologies [11].…”