Electrospraying (electrohydrodynamic spraying) is a method of liquid atomization by electrical forces. Spraying solutions or suspensions allow production of fine particles, down to nanometer size. These particles are interesting for a wide variety of applications, thanks to their unprecedented chemical and physical behaviour in comparison to their bulk form. Knowledge of the particle size in powders is important in many studies employing nanoparticles. In this paper, the effect of some process parameters on the size of electrosprayed polyacrylonitrile particles is presented in the form of response surface model. The model is achieved by employing a factorial design to evaluate the influence of parameters on the polyacrylonitrile nanoparticle size and response surface methodology. Four electrospraying parameters, namely, applied voltage, electrospraying solution concentration, flow rate, and syringe needle diameter were considered. 1. Introduction Nanoparticles are defined as particulate dispersions or solid particles with a size in the submicron range of 10–1000？nm [1]. Nanoparticles can be prepared from a variety of materials such as proteins, polysaccharides, and synthetic polymers. Particles in nanosize range are being investigated for a number of applications such as catalysts, cosmetics, pharmaceutics, medical, and compound materials [2–5]. The properties of materials with nanometer dimensions are significantly different from the same materials in bulk form. This is mainly due to the nanometer size of the materials leading to large fraction of surface atoms, high surface energy, spatial confinement, and reduced imperfections, which are much less pronounced in the corresponding bulk materials. Large fraction of surface atoms result in much more pronounced surface dependent properties of materials. Many of the mechanical properties of nanomaterials, including hardness, elastic modulus, and yield strength, are very different when compared with the bulk form [6–8]. With dimensions going down to nanoscale, the size of the nanomaterials is comparable to the light wavelength and the mean free path of the photons. This means that the photon transport within the materials is changed significantly because of photon confinement and quantization of photon transport, which leads to modified thermal properties [6, 9–11]. The most important property of nanoparticles, that is, inherent large surface to volume ratio, can potentially improve catalytic processes and interfacial driven phenomena such as wetting and adhesion. The estimation of the dependence of
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