## 3 Results and Discussion
### Influence of Centrifugation on Particle Size Distributions  
As-obtained suspensions were opaque and non-transparent at any significant layer thickness (>1 mm). Transparent electrically conductive suspensions are a prerequisite for  
Figure 2: Electron microscopy data for nanoparticles used in the present work: (**a**,**b**) AgNPs, (**c**) polyhedral AgNPs, (**d**) FLG, (**e**,**f**) typical hybrid particles. successful TCE manufacturing; therefore, it is of the utmost importance to reduce optical absorption while retaining most of the electrical conductivity (>100 uS/cm is usually a desired level for suspensions for printing technologies [63]). Particle-size distribution management is another major factor for electrically conductive suspensions intended for either inkjet printing or spray coating as agglomerates, and large particles may cause clogging of the nozzle; they may also have higher sintering temperatures, which may limit their applications for polymer substrates. Centrifugation proved to be effective for separation of large particles and agglomerates [54; 64; 65] from FLG. In addition, it is also effective for increasing the average morphological homogeneity of particles in fugates [66], such as for separating FLG by the number of layers [67]. As can be readily seen from data in Figure 3a,b, centrifugation allows a two- to threefold reduction of mean particle size in AgNP suspensions. Symmetry of particle size distribution remain almost intact. As for FLG suspensions, the initial distribution is non-symmetrical, mean particle size being around 3-4 um with a significant amount of small particles and a broad distribution of larger particles and agglomerates present (Figure 3c). After only mild centrifugation, particle size distribution becomes quite narrow and highly symmetrical with mean particle size reducing to ca. 0.5 um (Figure 3d) (it generally varied in the range 0.5-1.5 um from sample to sample). As for hybrid (mixed) FLG/AgNP suspensions, in an un-centrifuged state (see representative distribution in Figure 3e) they generally followed the distribution for FLG, as the particles are larger in size, and a relative decrease in size should be expected to be slower, since flakes have an increased coefficient of friction compared to rods and spheres [68]. After centrifugation, however, particle-size distribution does not resemble the sum of both components (see Figure 3f); while the primary maximum is that of FLG, no peak at ca. 0.3 um attributed to AgNPs is observed. This fact is consistent with TEM observations (see Figure 2e,f), and one could state that AgNPs primarily decorate the surface of FLG with only excess smaller particles remaining freely suspended. The overall particle size distributions were clearly bimodal for all of the studied FLG/ AgNPs ratios; therefore, in any case, although the peak attributed to FLG dominates the distribution, some AgNPs are not linked to the FLG surface (through non-covalent interactions, apparently [69]). This excess of AgNPs may lead to the increase in system connectivity in both suspensions and films. It should also be noted that the initial FLG suspension concentration was 6.0 mg/mL, whereas for AgNPs it was 3.2 mg/mL. The average yield of the solid phase in centrifuged suspensions was 7.8 wt.% for FLG and ca. 15 wt.% for AgNPs, leaving centrifuged suspensions with bulk weight concentrations of 0.47 and 0.48 mg/mL, respectively (taking into account a not obvious assumption that centrifugation of particles in hybrid suspensions occurs independently). Nevertheless, as concentrations of the suspensions were relatively close, we took relative FLG content (wt.%), calculated as simply proportional to the initial FLG suspension weight in the mixture, to be the simple parameter to estimate the influence of the suspension composition on its properties.