Physico-Chemical Characterizations of Poly(vinylidene fluoride)/ Cu 3 (BTC) 2 Composite Membranes Prepared by In Situ Crystal Growth Nadhem Missaoui, 1 Gérald Chaplais , 2,3 Ludovic Josien, 2,3 Laure Michelin, 2,3 Gautier Schrodj, 2,3 Ayoub Haj Said 1,4 1 Laboratoire des Interfaces et des Matériaux Avancés (LIMA), Faculté des Sciences de Monastir, Université de Monastir, Monastir, Tunisia 2 Institut de Science des Matériaux de Mulhouse (IS2M), Université de Haute-Alsace, CNRS, Mulhouse, 68100, France 3 Université de Strasbourg, Strasbourg, 67000, France 4 Centre de Recherche en Microélectronique et Nanotechnologie, Technopole de Sousse, Sousse, 4054, Tunisia In this work, we present a simple and fast method for elab- orating hybrid membranes by growing metal–organic framework crystals inside a polymer solution. The solution thus obtained was casted then annealed at 90  C for 5 h. This method was tested with poly(vinylidene fluoride) (PVDF) as a piezoelectric polymer and the Cu 3 (BTC) 2 , BTC = 1,3,5-benzene tricarboxylate, as a filler. The charac- terization of the obtained membranes by attenuated total reflectance Fourier transform infrared spectroscopy and X- ray diffraction showed the presence of the characteristic signatures of Cu 3 (BTC) 2 and the β-phase of PVDF. More- over, scanning electron microscopy images reveal that the Cu 3 (BTC) 2 crystallites have grown along the PVDF mem- branes. The effect of the filler on both thermal and mechan- ical properties of the membranes was also studied. POLYM. ENG. SCI., 00:000–000, 2019. © 2019 Society of Plastics Engineers INTRODUCTION Recently, the elaboration of mixed matrix membranes (MMMs) has sparked increased attention [1]. MMMs consist of a dispersion of inorganic or inorganic–organic hybrid fillers inside organic polymers matrices, in such a way that they may combine the desirable properties of polymer matrices, mainly their excel- lent mechanical properties and processability, and those of the dis- persed fillers. Thus, a wide range of fillers have been studied, such as zeolites [2–5], inorganic oxides [6], fullerenes [7], meso- porous silicas [8], carbon nano-fibers [9], clays [10], as well as metal–organic frameworks (MOFs) [11–15] but in a lesser extent for this last type of materials. Indeed, MOFs, which can be described as a supramolecular assembly of metal cations (or oxo- metallic clusters) with organic linkers driven by coordination bonding, are hybrid porous material possessing very attractive properties and applications. Actually, MOFs have a relative high thermal stability, and especially high surface area with customized pore size and geometry. Moreover, they have extensive applica- tions including gas storage and separation, catalysis, sensors, and opto-electronics [16]. In general, solution blending, melt blending, and in situ polymerization are widely used to achieve the filler dispersion in the polymer matrix. For the elaboration of an MOF- based MMM, the MOF is synthesized separately and then dis- persed in the polymer matrix to form a composite solution and the MMM is obtained by casting this solution [13–15]. The major barrier for this method is the preparation of well dispersed fillers at different loading values. This barrier is governed by different factors such as the chemical composition of MOFs, their particle size distribution, the interface properties between the polymer chains and the MOFs particles as well as their loading ratio. In this paper, we present a simple and fast method for elaborating hybrid membranes. It consists in growing MOFs crystals inside a polymer solution. This method was applied with poly(vinylidene fluoride) (PVDF) as polymer matrix, and Cu 3 (BTC) 2 (also known as HKUST-1) as filler. The choice of PVDF was encouraged by its ability to form homogenous solution with metallic salts. In addition, thanks to the outstanding electro- active properties of its β-phase, PVDF and its membranes are important materials with extensively technological applications such as membrane distillation [17] sensors [18, 19], lithium-ion battery [20–24], energy harvesting [25, 26], and actuators [27, 28]. In fact, PVDF is a semi-crystalline fluoropolymer having differ- ent crystalline polymorphs namely the α, β, γ, and δ-phases. The α-phase is the most common form of PVDF. It is non-polar and non-piezoelectric due to its chain conformation TGTG’ (Trans- Left–Left-Trans). The phase α has a monoclinic unit cell (P2 1 /c) with dimensions a = 4.96 Å, b = 9.64 Å, c = 4.62 Å [29]. The β-phase is the most polar phase due to its conformation all Trans (TTTT), and it is principally responsible for piezo and pyro-electric properties of the polymer [30]. The unit cell of the β-phase is ortho- rhombic (Cm2m) with a = 8.58 Å, b = 4.91 Å, and c = 2.56 Å [31]. The γ-phase has a chain conformation which is approximately TTTGTTTG’, with the space group being C2cm [32]. The obtaining of the β-phase depends on the PVDF processing (mechanical stretching, solvent-casting, and electrospinning [33]) and the experimental conditions (solvent nature, casting support, addition of fillers, temperature, and time [34]). In this work, diverse characterization techniques such as atten- uated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, thermogravimetric anal- ysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used to characterize the obtained MMMs and to assess the effects of the used method of membrane elaboration. Additional Supporting Information may be found in the online version of this article. Correspondence to: H. S. Ayoub; e-mail: ayoub.hajsaid@fsm.rnu.tn Contract grant sponsor: Ministry of Higher Education and Scientific Research. DOI 10.1002/pen.25301 Published online in Wiley Online Library (wileyonlinelibrary.com). © 2019 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2019