# Rapid Synthesis of Silver Nanowires in the Polyol Process with Conventional and Microwave Heating
## 3 Results and Discussion
It was also observed that in the case of syntheses conducted for 15 min (in this case, the results have not been shown), the conversion for both the heating methods exceeded 99%, and the morphology of the final products did not exhibit considerable differences. On the other hand, using a solvent with a low dielectric constant value leads to forming a large number of nanoparticle monomers. This phenomenon accelerates the nucleation process and decreases the average size of the nuclei [35]. In the case under discussion, this causes a reduction in the average diameters of the product, which is corroborated by the results of synthesis with 1,3-propanediol (Figures 6b and 7b). Replacing the reductant with a polyol with a higher viscosity and a lower dielectric constant value (1,3-butanediol) led to further reduction in the diameter for both conventional and dielectric heating (Figures 6c and 7c). The tendency observed in the change in diameters confirms previous remarks on the effect of solvent polarity on the product size. In addition, an increase in viscosity hinders the diffusion-controlled transport of monomers. Consequently, the formation of a larger quantity of smaller nuclei is promoted, which influences a diminution of the final product diameters [46]. The peaks visible in UV-Vis spectrograms (Figures 6c and 7c) for radiation wave lengths of 354 nm and 390-403 nm may be attributed to the plasmon response of metallic silver and transverse plasmon mode of nanowires [47; 48; 49]. The use of 1,4-butanediol is a good illustration of the effect of the dielectric constant value upon the average diameter of nanowires, which in this case is slightly higher than when 1,3-propanediol (Table S1, Supplementary Materials) is used. Despite a higher viscosity value which promotes a reduction in diameters, an increase in the product diameter is observed (Figures 6d and 7d). Lower conversion values for conventional and dielectric heating equal, respectively, 97 and 83% and can indicate a stabilisation of precursor ions. As far as 1,5-pentanediol is concerned, despite its highest viscosity and lowest dielectric constant (Table S1, Supplementary Materials), nanowires are not the main product (Figures 6e and 7e). It may be caused by suppressing the growth of multiply twinned crystals in favour of single crystallite structures whose presence was observed by other authors in the synthesis using 1,5-pentanediol [29]. Many polyhedral objects and structures with a high aspect ratio value are observed in the case under analysis. The presence of objects with a low aspect ratio is confirmed by redshifted UV-Vis spectra (Figures 6e and 7e), whose peaks are recorded for the wavelength of 530 nm [47,50]. An obtuse-course spectrogram is observed for the 450-800 nm UV-Vis wavelength. The reason could be the presence of single crystallite nanoparticles for which the absorbance peaks lie precisely in the range of UV-Vis radiation [51]. Therefore, the observations of other authors are corroborated [32], according to which, in high-viscosity mediums the growth of higher-energy facets is privileged. As far as conventional heating is concerned, when 1,2-ethanediol and 1,5-pentanediol are used in the synthesis, this leads to obtaining structures with the highest diameters compared to the product generated when other reductants are used. An analogical tendency was observed in microwave-assisted syntheses. It implies the complex effect of the above-discussed factors influencing the size of the fabricated nanowires and the possibility of obtaining a final product with an optimal diameter and composition. It is worth noticing that the occurrence of an optimum diameter was combined with the reduction rate of the precursor of copper nanoparticles [36]. At this investigation stage, correlating the reducing power of polyols used in syntheses to the average AgNW size is difficult. The reason is that it is hard to separate the effects of other factors, viz., viscosity or polarity of the solvent, which simultaneously influence the final product size and morphology.