Production and characterization of piezo-electric membranes H.G.L. Coster ⁎, T. Darestani Farahani, T.C. Chilcott School of Chemical and Biomolecular Engineering, University of Sydney, Sydney, NSW 2006, Australia abstract article info Article history: Received 15 December 2010 Received in revised form 8 April 2011 Accepted 30 April 2011 Available online 23 May 2011 Keywords: Fouling Piezoelectric Membrane Electrical effects Vibration PVDF It is shown that it is possible to impart piezo-electric properties to polyvinylidene fluoride (PVDF) membranes. This was achieved by “poling” the membranes in an intense electric field. Out of the plane surface displacements were produced when AC signals were applied to the membrane. Flux and separation performance measurements performed in a cross flow membrane module demonstrated that piezoelectric induced vibrations out of the plane of the membrane (i.e. in the direction of the flux) increased the flux by an order of magnitude and delayed membrane fouling. The relative antifouling effect of piezoelectric induced vibration was enhanced with increasing cross flow velocity. © 2011 Published by Elsevier B.V. 1. Introduction Accumulation of unwanted materials onto membrane surfaces and into membrane pores results in a decline in the permeate flux during filtration. Attachment of the accumulated material may make it difficult to remove even with severe chemical treatments. Such fouling of membranes, resulting also in increased power consumption and a reduction in membrane lifespan is recognized as a major operational and economic factor in determining the viability of membrane separation plants [1]. Approaches commonly used to combat fouling include pretreatment of the feed [2], modification of membrane bulk or surface properties [3], modification of the operating parameters and various cleaning procedures [4]. The latter include procedures to destabilize the fluids in contact with the membranes [5], using, for example, magnetic [6], or ultrasonic fields [7] and turbulence promoters [8]. During membrane separation processes, concentration polarization at the membrane surface occurs and this plays a major role not only in modulating the driving forces but also in the development of fouling of the membrane. In turn, the fouling can exacerbate the concentration polarization; the so called cake enhanced polarization [9]. It has been suggested that fluid instability might ameliorate concentration polarization and mem- brane fouling [5]. Ultrasonic agitation produced by piezoelectric transducers to overcome fouling during filtration has been described [10] but this technique has not been implemented in industrial plants. Here we describe the construction of piezo-electric membranes that can be made to undergo internal vibrational deformations normal to the plane so that itself becomes the source of agitation [11]. For this study PVDF membranes were chosen, because of the potential piezoelectric properties of PVDF. PVDF is used in the fabrication of actuators and sensors [12]. It is also used to manufacture membranes because it lends itself to commonly used methods of membrane manufacture that involve phase-inversion techniques as well as its superior chemical resistance [13]. 1.1. Piezo-electric properties of PVDF PVDF is a semicrystalline polymer that has at least four known crystalline structures (α, β, γ and δ) but the all-trans (β) phase is mainly responsible for its piezoelectric properties [12]. Common melt or solution processing techniques do not yield the β-phase due to thermodynamic limitations [14]. One method of converting the other crystalline structures into the β form is by electrical “poling”. This involves the application of an intense electric field whilst the sample is held at an elevated temperature (just below the melting temperature) and then cooled whilst still in the intense electric field. This, in the case of PVDF, converts the other forms into the β form with permanent electric dipoles aligned with the field and imparts piezo-electric properties to the material [15,16]. Poling in an intense electric field for changing the crystalline configuration of PVDF and fabrication of piezoelectric films is a common technique [15–17]. However, to the best of our knowledge this technique has not been applied to PVDF membranes or other porous structures of this polymer such as foams. This may be related to the fact that the presence of pores, voids or defects tends to Desalination 283 (2011) 52–57 ⁎ Corresponding author. Fax: + 61 293512854. E-mail address: hans.coster@sydney.edu.au (H.G.L. Coster). 0011-9164/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.desal.2011.04.071 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal