## 1 Introduction  
The shortage of water is one of the biggest concerns for future society as the human population is increasing steadily. Desalination, a good option for coastal areas short of fresh water, has been becoming the major approach for potable water as the supply of seawater can be considered unlimited. Presently, reverse osmosis (RO) has reached the state of the art and has become the dominant technology because of its higher energy efficiency and stability compared to conventional thermal-based processes [1]. However, there are two main issues in RO: high energy consumption and brine treatment, which are becoming great challenges for future human society [2]. Hence, continuous efforts for finding new technologies that can provide lower energy consumption while still obtaining high process and production efficiencies are being sought out [3]. Among them, membrane distillation (MD) is one of the most promising emerging technologies [4]. One of the major advantages for MD is the potential usage of low-grade waste heat as its feed temperature requirement is much lower than that of the conventional distillation process. If sufficient waste heat is available, much less energy will be required for operation. Fundamentally, the membranes in MD serve as Contactors, and are not involved in the separation process themselves. The mass transport starts from the evaporation of water at the boundary between the vapor and liquid phase at the membrane pores. Then the vapor is driven by the partial pressure, caused by a partial vapor pressure difference which is triggered by the temperature difference between the hot feed and cold permeate [5; 6]. Although MD has these unique advantages, major challenges must still be addressed for its wide acceptance in the industry, which include a lack of specifically designed MD membranes and modules, difficulty in up-scaling the laboratory setup, and a shortage of techno-economic data [6]. Membrane fabrication has gained a great deal of interest, as researchers are using membranes designed for other processes. However, the characteristics of a decent MD membrane are different, as much higher hydrophobicity and liquid entry pressure (LEP) with high porosity are needed for a high flux performance with minimal wetting issues [7]. Polymers with relatively lower surface energies, such as polystyrene, polyvinylidene and polytetrafluoroethylene, have been used to fabricate membranes in the laboratory [8; 9; 10; 11]. Phase inversion is one of the most used techniques due to its simplicity [12; 13]. However, its products usually have low flux in MD due to its relatively low porosity and pore size [14; 15]. Currently, electrospinning is gaining popularity in membrane fabrication [8; 9; 10; 13; 16]. Electrospun membranes have many advantages including a high contact angle, very high porosity, and simplicity for modification, making them very suitable for MD [17; 18]. However, they have a large maximum pore size and, hence, a low LEP, making them susceptible to wetting [6; 18]. Much effort has been invested into finding solutions to improve their LEP. For example, [PERSON] fabricated a modified electrospun membrane by adding lab-made macromolecules into the solution, and later made a composite membrane consisting of both electrospun and phase inversion membranes, improving its LEP enormously [13; 19]. [PERSON] improved the LEP by adding surface-modified silica nanoparticles into the solution [16]. [PERSON] added fluorosilane-coated TiO\({}_{2}\) into the solution and obtained an electrospun membrane with an increased LEP [20]. Other hydrophobic nanoparticles used as additives, including graphene and carbon nanotubes, were also extensively studied [12; 21]. The other method is to incorporate a secondary polymer with very low surface tension into the polymer solution. Polydimethylsiloxane (PDMS) was found to be able to improve the hydrophobicity and LEP when mixed with the carrier polymer in the solution [22; 23].