Influence of the Surfactant Concentration on Miniemulsion Polymerization for the Preparation of Hybrid Nanoparticles

Abstract

The surfactant concentration in miniemulsion polymerization is a very important parameter. At surfactant concentrations lower than a critical value, coalescence of monomer droplets changes their size, whereas concentrations too high lead to the formation of micelles and micellar nucleation in the polymerization step. Inorganic particles dispersed in the monomer phase, with the goal to produce hybrid particles, infl uence the surfactant concentration needed as shown in this contribution. Values for the ideal surfactant concentration have been determined for different combinations of particles and surfactant. Underlying mechanisms for the required adjustment of surfactant concentration are discussed.

Continuous Preparation of Polymer/Inorganic Composite Nanoparticles via Miniemulsion Polymerization

“…In [19] it was shown that the mechanisms for the increase in A surf,min are: (1) The inorganic particles leave the droplet completely and falsify the measurement results. (2) The inorganic particles are localized in the interface, replacing the surfactant molecules there and forcing the latter to reside in the continuous phase.…”

“…To overcome this problem, the interaction of polymer and silica has to be enhanced by using a polar co-monomer such as 4-vinylpyridin (4-VP) [19]. The increased interaction between polymer and silica results in an improved encapsulation of the silica [20].…”

“…2). Mechanism 2 and 3 cannot be avoided when using a physical modification agent (see [19] for details), therefore a chemical modification of the particle surface is recommended. In order to achieve a chemical modification, particles were hydrophobized with MPS (see Sect.…”

“…In a system consisting of poly(methyl methacrylate) (PMMA) and silica particles hydrophobized with cetyltrimethylammonium chloride (CTMA-Cl), desorption of the surfactant leads to a decrease of surface hydrophobicity, which prohibits the integration of the silica particles into the polymer matrix [19]. To overcome this problem, the interaction of polymer and silica has to be enhanced by using a polar co-monomer such as 4-vinylpyridin (4-VP) [19].…”

“…Although this adsorption process offers a very simple and cheap route to hydrophobize inorganic nanoparticles, hydrophobization by surfactants has a significant disadvantage in the preparation of hybrid nanoparticles: the surfactant molecules are still able to desorb from the surface of the inorganic material, as ionic interaction is reversible. With regard to the application in focus, this reversibility leads to two effects critical for morphology control: the surface properties of the inorganic particles are no longer well-defined and the total amount of free surfactant in the system is not constant [19].…”