## 1 Introduction
An amphiphilic additive was used, thereby increasing the number of interaction sites without substantially affecting the hydrophobic character of the membrane surface. The result was an increasingly lower free energy of interfacial interaction, which is an expression of affinity between protein and membrane immersed in water. Consequently, a reduction of the crystallization induction time was achieved with formation of nanosized crystals in a range of 3-7 h [11]. The understanding of crystal nucleation is far from complete [12; 13]. This is because the molecular details of the process appear in a very small length scale of the order of nanometers, and they are, by definition, unstable and therefore form only transiently, so they are quite challenging to probe even in real time. However, today, with state-of-the-art measurements, nucleation has also been observed at the molecular scale [12; 14; 15; 16]. The rapid advance of experimental techniques such as in situ atomic force microscopy [17], liquid-cell transmission electron microscopy [18], and cryo-TEM [15] will deliver novel results in order to refine the understanding of crystal nucleation and growth [19]. Computational modelling and in particular molecular dynamics (MD), where the temporal evolution of the liquid into the crystal is studied, complementary experiments provide exciting insights into the mechanisms of such phenomena and enable kinetic and thermodynamic quantities to be estimated. Surely, the rapid progress in computational methodology has unraveled crucial aspects of crystal nucleation in liquids. Several studies have been performed to depict the mechanism of heterogeneous crystal nucleation by simulation [13; 20; 21; 22; 23], such as atomic simulation [24; 25; 26] and phase field theory [27], while there are limited publications for heterogeneous salt crystal nucleation from an aqueous solution [28; 25; 29]. Moreover, the mechanics of the earliest stages of the crystallization assisted by membranes still remain an important fundamental issue. However, there have been a series of papers discussing crystal nucleation in aqueous solutions [30; 31; 32; 33; 34], focusing on available force fields and models. Here, we present the results from molecular dynamics simulations of the crystal nucleation and growth of a sodium chloride solution in contact with hydrophobic polymer surfaces of polyvinylidene fluoride (PVDF) and polypropylene (PP) at a supersaturated concentration of salt. The crystallization of NaCl from aqueous solutions was chosen because it is a typical example of most inorganic crystallizing systems. First, crystal nucleation and growth were simulated in a slightly supersaturated aqueous bulk solution as performed by [PERSON] [33]. Then, PVDF and PP membrane surfaces interfacing an NaCl solution were studied and the results were compared with that of bulk solutions and with experimental data. In parallel, membrane crystallization experiments were performed utilizing the same kind of polymeric membranes in order to compare the experimental findings with the computational data. Moreover, the comparison in terms of nucleation time between the crystallization of sodium chloride using the traditional evaporation process and the membrane-assisted crystallization process was performed. By means of molecular dynamics simulations, we demonstrate that the PVDF and PP membranes assist the crystal growth of NaCl, speeding up crystal nucleation in comparison to the bulk solution and leading to smaller and regularly structured face-centered cubic lattice NaCl crystals. A mutual validation between theoretical data and experimental findings was found. These preliminary simulations shed light on their application capability to predict crystallization with different complex polymeric matrices.