Research Article A Novel Low-Pressure Device for Production of Nanoemulsions A novel device is applied to produce emulsions of methyl methacrylate in water with a controllable size in the range of 30–100 nm. The process is based on the reciprocating flow of the material through an abrupt contraction which generates a strong elongational flow. This results in highly efficient dispersive mixing even at moderate pressures, thus reducing viscous dissipation and improving tempera- ture control. The original design of the device also allows easy feeding and sam- pling, easy adjusting of the total volume of the emulsion, and processing volatile components owing to the liquid- and gas-tightness of the device. The influence of process parameters (like pressure drop and mixing time) and composition of the system (volume ratio of the dispersed and continuous phases, surfactant and hydrophobic agent weight percentages) on the droplet size and stability of the emulsions is investigated and discussed. Keywords: Elongational flow, Emulsification, Miniemulsion, Nanoemulsion Received: December 14, 2011; revised: January 26, 2012; accepted: February 10, 2012 DOI: 10.1002/ceat.201100676 1 Introduction There has been growing interest in miniemulsion polymeriza- tion in the last two decades because of specific advantages of this heterogeneous polymerization process. Several general ar- ticles review the main mechanistic features and advantages of miniemulsion polymerization [1–3]. Monomers are emulsified in droplets, small enough to become the main loci of particle nucleation [4]. Several kinds of polymerization reactions be- come possible in heterogeneous media, not only all chain poly- merizations but also polycondensations and polyadditions [3]. On the other hand, miniemulsion polymerization is particu- larly well-suited for the synthesis of organic-inorganic hybrid particles [5], for encapsulation of various materials [6], and for functionalization of particle surfaces [7]. Monomer emulsification is a key step in the process of mini- emulsion polymerization. Ideally, emulsification should lead to predecided, well-controlled average droplet sizes and distri- butions in a time as short as possible, with minimal energy in- put and temperature increase. Several emulsification devices are available [8], none of them being ideal. They are generally classified in high- or low-energy approaches [9], with the ener- gy input, besides processing time, being a major practical issue. In the field of miniemulsion polymerization, the most often used devices are ultrasound generators, rotor-stator mixers, high-pressure homogenizers, and static mixers. Ultrasound generators [10] and rotor-stator mixers [11] can generate na- nodroplets but with a rather broad distribution which leads to emulsions that are not very stable in time. They are classically used at laboratory scale but are not convenient for scale-up to commercial volumes. On the other hand, high-pressure homo- genizers [12] are used in industry, but since they are working under high pressures (in the order of 1000 bar), they induce high specific energy, which results in significant temperature rise due to viscous dissipation. Alternatively, it has been shown that miniemulsions can also be created with a static mixer placed in the flow. McKenna et al. [13,14] demonstrated that the use of such mixers can be more efficient for the production of miniemulsions because of their low energy consumption and the relatively low shear rate that they impose on the dis- persed phase. A static mixer and a high-pressure homogenizer have also been associated in series [15], allowing the produc- tion, at high rates, of miniemulsions with high solids content. In this context, it was tried to develop a new dispersion device to generate monomer emulsions, based on elongational flow and involving moderate pressures in order to limit vis- cous dissipation [16]. The idea of promoting elongational flow for mixing came up a long time ago [17] and specific devices were developed for high-viscosity polymer melts or for disper- sion of fillers in viscous liquids. The idea of successive conver- gent/divergent elements [18, 19] proved its efficiency in this re- spect, however, its practical use was limited due to the high total pressure drop which arises when associating several con- vergent/divergent units in series. Son[20] recently developed a Chem. Eng. Technol. 2012, 35, No. 00, 1–8 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Inès Souilem 1 René Muller 1 Yves Holl 2 Michel Bouquey 1 Christophe A. Serra 1 Thierry Vandamme 3 Nicolas Anton 3 1 Université de Strasbourg, École de Chimie Polymères et Matériaux, Strasbourg, France. 2 Institut Charles Sadron, Strasbourg, France. 3 Université de Strasbourg, Faculté de Pharmacie, Strasbourg, France. – Correspondence: Prof. R. Muller (rene.muller@unistra.fr)), Université de Strasbourg, École de Chimie Polymères et Matériaux, LIPHT – Eac(CNRS 4379, équipe G2IP, 25 rue Becquerel, F-67087 Strasbourg, France. Miniemulsion 1