Water Droplets as Template for Next-Generation Self-Assembled Poly-(etheretherketone) with Cardo Membranes Annarosa Gugliuzza,* ,† Marianna Carmela Aceto, †,‡ Francesca Macedonio, †,‡ and Enrico Drioli †,‡ Research Institute on Membrane Technology-National Research Council (ITM-CNR), Via P. Bucci, Cubo 17C, I-87030 Rende (CS), Italy, and Department of Chemical Engineering and Materials, UniVersity of Calabria, Via Pietro Bucci 45A, I-87030 Rende, Italy ReceiVed: March 11, 2008; ReVised Manuscript ReceiVed: July 1, 2008 Next generation PEEK-WC membranes have been fabricated by using an innovative self-assembly technique. Patterned architectures have been achieved via a solvent-reduced and water-assisted process, resulting in honeycomb packed geometry. The membranes exhibit monodisperse pores with size and shape comparable to those left by templating water droplets. Influencing factors for the formation of self-assembled poly- (etheretherketone) with Cardo [PEEK-WC] membranes have been evaluated, identifying the critical parameters for nucleation, growth, and propagation of the droplet-mobile arrays through the overall films. Structure-transport relationships have been discussed according to the results achieved from the implementation of membrane distillation processes, yielding indication about the suitability of self-assembled PEEK-WC films to work as interfaces in contactor operations. Introduction Regular and ordered patterns represent an attractive topic of research, especially for advanced branches of the membrane technology that include membrane contactors. 1,2 Usually, the contactor technology utilizes devices equipped by microporous hydrophobic membranes, working as nonselective interfaces between two different phases through which mass transfer is promoted. Specifically, the membrane keeps in contact two different phases at the entrance of the pores, preventing the media from mixing and promoting transport by diffusion through the open channels of the interface. Well-sized and well-shaped pore density and narrow distribution influence positively the trans-membrane flux, because of the uniformity of the process through the overall membrane surface. Unfortunately, the fabrication of well-structured membranes working as interfaces for contactor applications still represents an important challenge. Despite many attempts, well-sized and well-shaped membranes remain an ambitious target. Recently, the breath figures (BFs) approach has been redis- covered as a powerful tool for the fabrication of well-defined 2D and 3D micro- and nanostructures. 3-7 The technique strategically exploits the templating action of the moist air, resulting in self-assembled and well-structured architectures. 8 The driving force of this water-assisted process is a gradient of temperature generated between the casting solution and humid atmosphere, caused by the solvent evaporation. The difference of temperature induces the water droplets to condense and arrange at the air-polymer dope interface, behaving as templates for porous layers. The growth and propagation of the water droplets through the liquid films usually lead to hexagonally packed regular arrays. During the formation of BFs, the water droplets are prevented from coalescing by the precipitation of the polymer at the water-solution interface. Finally, the complete evaporation of both the solvent and water leaves air- bubble arrays orderly sequenced. This simple method seems undeniably to offer an attractive opportunity to tailor smart membranes having suitable structural characteristics for equipping contactor devices. Drawbacks concerned with size, shape, and uniformity of the membrane pores could be successfully overcome at lower costs and in shorter time than traditional techniques. 9,10 In addition, solvent reduced, large availability of a nontoxic template, fast removal, and feasible recovery of the solvents make the manufacturing process more environmentally friendly. The accomplishment of membrane contactor processes can be seriously affected by the membrane operated; thus, a well- controlled structure together with adequate physicochemical interfacial properties of the film represent crucial issues for the implementation of this advanced membrane technology. The membrane has to be accomplished by well-defined pores uniformly distributed on the surface, since high surface porosity combined with high bulk porosity can productively result in a high interfacial area per unit of volume and high volumetric mass transfer rate. Furthermore, mutual membrane-liquid in- teractions must be considered in order to prevent the liquid from wetting the pores. Indeed, the penetration of liquid inside of the pores should cause a drastic increase in the resistance to the transport, resulting in reduced productivity of the process. Thus, well-defined morphology and surface properties must be necessarily combined in the membranes equipping contactor devices. This target could be achieved by mimicking what is daily occurring in nature: the spontaneous tendency of the water droplets to condense on cold surfaces and their self-assembly in ordered lattices. This approach can lead to a new class of next-generation porous polymeric architectures where the polymer generates the network of the matrix and the air bubbles array the membrane pores. * To whom correspondence should be addressed: E-mail: a.gugliuzza@ itm.cnr.it. Address: Research Institute on Membrane Technology-Research National Council, ITM-CNR, Via Pietro Bucci 17/C, c/o University of Calabria, I-87030 Rende (CS), Italy. † ITM-CNR. ‡ University of Calabria. J. Phys. Chem. B 2008, 112, 10483–10496 10483 10.1021/jp802130u CCC: $40.75  2008 American Chemical Society Published on Web 08/05/2008