Membranes with tailored wettability properties for the generation of uniform emulsion droplets with high efﬁciency Emma Piacentini a,n , Alessandra Imbrogno a,b , Enrico Drioli a , Lidietta Giorno a,nn a Institute on Membrane Technology, National Research Council, ITM-CNR, Via P. Bucci 17/C at University of Calabria, 87036 Rende (CS), Italy b Dipartimento di Ingegneria per l'Ambiente e il Territorio e Ingegneria Chimica, University of Calabria, Via P. Bucci 42/A, 87036 Rende (CS), Italy article info Article history: Received 4 December 2013 Received in revised form 29 January 2014 Accepted 31 January 2014 Available online 18 February 2014 Keywords: Membrane emulsiﬁcation Membrane wettability Protein adsorption Productivity Controlled droplet size abstract Membrane emulsiﬁcation is a promising technology for the production of micro–nano particles, which is able to compete with the conventional mechanical emulsiﬁcation processes. The production of emulsions with narrow droplet size distribution at dispersed phase ﬂuxes (productivity) sufﬁciently high to make the process suitable for industrial application is still a considerable challenge. The interfacial tension between the dispersed phase and the membrane pore wall is a crucial parameter to maintain droplets shape while enhancing productivity. In the present paper, a membrane thickness with asymmetric properties in terms of wettability between external and internal sides has been tested in the preparation of W/O emulsions. The membrane surface wettability modiﬁcation was obtained by adsorption of hydrophobic macromolecules on the lumen side of hydrophilic membrane. Lipase was used as a model macromolecule. W/O emulsion droplets with smaller droplets size have been produced with lipase- loaded membrane compared with the unmodiﬁed hydrophilic membrane. High dispersed phase ﬂux of 30 L h 1 m 2 was also obtained with a signiﬁcant increase of process productivity compared to the use of hydrophobic membranes. These results show that membrane–protein interaction can be used to functionalize opportunely the membrane for membrane emulsiﬁcation application reducing emulsiﬁca- tion time and increasing dispersed phase ﬂux without modifying the control on droplets properties in terms of size and size distribution. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Emulsion-based products are widely used in food, pharmaceuti- cal, chemical and cosmetics industries. Emulsions with tailored microstructure in terms of droplet size and droplet size distribution are required for the high quality of the product respect to the stability and functionality. Repeatable manufacturing processes able to make products with high productivity are also required for proﬁtability of food, pharmaceutical, chemical and cosmetics companies. Emulsions are usually prepared using homogenizers by generation of turbulent droplet break-up. Some limitations associated with these existing methods of production include (i) the droplet size and droplet size distribution cannot easily be controlled, (ii) high energy consump- tion, and (iii) poor reproducibility of the product properties. Mem- brane emulsiﬁcation has attracted academic and industrial interests as alternative method to produce emulsion-based products in mild conditions by a drop-by-drop mechanism [1–3]. The technology is characterized by size and size distribution control, high energy efﬁciency and environment-friendly production. All these properties are suitable for efﬁcient operations in emulsions production to develop new emulsion-based products or improve those existing. However, the production of emulsions with narrow droplet size distribution at high productivity is still a challenge in membrane emulsiﬁcation. The interaction between the dispersed phase and the membrane pore wall is a signiﬁcant factor for the productivity enhancement. The membrane pore wall with good wettability to the disperse phase allows a quick permeation of the phase in the pores, and hence results in signiﬁcant higher productivity. However, membranes with high interfacial tension compared to the dispersed phase are necessary to avoid the wetting of the membrane by the phase to be dispersed and as a consequence to obtain emulsion with controlled size and size distribution. Therefore, hydrophilic mem- branes are usually used for the preparation of oil-in-water (O/W) emulsions and on the contrary, hydrophobic membranes are used for the preparation of water-in-oil (W/O) emulsions. This means that low dispersed phase ﬂux values are usually obtained resulting in low productivity. Kawakatsu et al. [4] demonstrated that when the contact angle of water droplet on microchannel plate in an oil phase was greater than 1201, monodispersed droplets were produced whereas Kobayashi et al. [5] obtained monodispersed O/W emulsions when the contact angle of oil droplet on microchannel plate in water Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science http://dx.doi.org/10.1016/j.memsci.2014.01.075 0376-7388 & 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ39 0984 492051; fax: þ39 0984 402103. nn Corresponding author. Tel.: þ39 0984 492050; fax: þ39 0984 402103. E-mail addresses: e.piacentini@itm.cnr.it (E. Piacentini), l.giorno@itm.cnr.it (L. Giorno). Journal of Membrane Science 459 (2014) 96–103