# Rapid Synthesis of Silver Nanowires in the Polyol Process with Conventional and Microwave Heating
## 1 Introduction  
Silver nanowires (AgNWs), defined as nanostructures with an average diameter of 10-200 nm and length of 5-100 \(\upmu\)m [1], are intensively investigated regarding their application and fabrication methods. This results from their unique electrical [2], optical [3] and bactericidal properties [4], which are applied in optoelectronics [5] and advanced microelectronic solutions [6], as well as separation processes [7]. The fabrication of the structures under discussion is based on hard and soft templates [8] or methods of direct chemical synthesis [9]. Silver nanowires are, in most cases, synthesised in the so-called polyol process, in which multi-hydroxyl alcohol plays the roles of both solvent and reductant of the nanomaterial precursor [10]. Other authors have adapted and developed the polyol process to fabricate silver nanowires in heterogeneous [11] or homogeneous nucleation conditions [12]. In most cases, the reductant is 1,2-ethanediol, whereas the data pertinent to using other polyols are limited to 1,2-propanediol [13, 14] or glycerol [15]. Because of their high values of loss tangent \(tg(\delta)\), polyols are characterised by an ability to absorb and transform microwave radiation into thermal energy. That is why they constitute an excellent environment for managing syntheses supported by microwave irradiation. One can notice a growing number of works related to the effective fabrication of AgNPs in processes in which dielectric heating is utilised [16]. The growth model of silver nanowires, reported in the open literature, results from the expansion of the \(\{111\}\) walls of five-fold-twinned decahedra seeds generated in the nucleation process [17]. The growth of opposite walls of twinned seeds leads to the creation of one-dimensional objects, such as nanowires or, more seldomly, V-shape nanorods [18]. Fabrication of the aforementioned seeds with the smallest possible sizes and preventing their lateral growth are believed to be the main factors determining the possibility of obtaining long nanowires with thin diameters [19]. This is possible by tuning down the reduction kinetics and using an appropriate stabilising agent. The anisotropic growth of the nanostructures under consideration is permitted by the use of polyvinylpyrrolidone (PVP) as a capping agent. Polyvinylpyrrolidone is adsorbed selectively on high surface energy planes of \(\{100\}\) due to an interaction between the oxygen from the PVP carboxyl group and silver. This effect promotes the extension of \(\{111\}\) walls with relatively lower surface energy [20]. The synthesis herein referred to is very often carried out with the presence of a mediating agent [21; 22], which, with the silver ions occurring in the reaction environment, forms sparsely soluble compounds, e.g., chlorides [23], bromides [24], sulphides [20] and carbonates [25]. The addition of mediating agents provides electrostatic stabilisation of the newly formed nuclei. It reduces the concentration of free silver ions due to buffer formation that controls the rate of Ag(I) ions release and enhances oxidative digestion of the nuclei [13]. The synthesis can be intensified by conducting the polyol process in the presence of metal ions with various degrees of oxidation, e.g., Cu(I)/Cu(II) [26] or Fe(II)/Fe(III) [27]. As a result of the oxidation-reduction reactions taking place with metal ions, atomic oxygen adsorbed on the walls of nanostructures is scavenged. The presence of oxygen hinders the access of silver monomers to the expanded walls of nanostructures, particularly to the planes of [111], whose expansion determines the growth of one-dimensional objects [22]. An effect of the viscosity of applied polyol on the shape, size and granulometric size distribution of the prepared nanoparticles is indicated in a few works [28; 29]. [PERSON] noticed a decrease in the average size of synthesised silver nanoparticles concerning the increased viscosity of the reaction environment [30].