## 3 Results and Discussion
### Size Distribution  
Three types of frequency distributions were observed among the 81 samples, namely normal, positively skewed and bimodal distributions (see Figure 4a-c). The probability for a sample picked at random from the 81 to have a particular type of distribution is almost equal, 35% of the samples exhibited a normal distribution, 33% of the samples exhibited a positively skewed distribution (right skewed) and 32% of the samples exhibited a bimodal distribution (the frequency size distribution for each of the 81 samples can be found in the Supplementary Information Table S1). The main cause of differences in distribution types can be attributed to laser processing parameters. All samples synthesised at 2 min ablation time produced a bimodal distribution and bimodal distributions were only observed for 2 min ablation times. At short ablation times, the number of primary nanoparticles (large slightly fragmented particles) and secondary nanoparticles (smaller nanoparticles with multiple fragmentations) are almost equal since there has not been enough time for multiple nanoparticle fragmentation to occur, hence the bimodal distribution (both large and smaller particles exist in large numbers). An increase in ablation time from 2 to 5\(\backslash\)25 min shifts the distribution from being bimodal to being normal/skewed as shown in Figure 4d. An increase in ablation time from 2 to 5 min changes the distribution from being bimodal (100% of the samples) to mostly skewed (66% of the samples) and some normally distributed (46%). A further increase in ablation time from 5 to 25 min changes the distribution from being mostly skewed (66% of the samples) to being mostly normal (56% of the samples). This can be explained by the fact that at the beginning of the ablation process, the laser breaks the powder particles into smaller particles. Further ablation will enable nanoparticle fragmentation, causing the distribution to be skewed towards smaller sizes, and additional ablation time will enable the distribution to become normal. It can be concluded that at each ablation time, a most probable nanoparticle size distribution type (normal, skewed or bimodal) exists; this is in agreement with the statistical data mentioned earlier stating that about a third of the samples exhibited a normal distribution, about another third of the samples exhibited a skewed distribution and about another third of the samples exhibited a bimodal distribution. Hence, one can control the size distribution type by simply varying the ablation time. The size distribution is an important factor in the development of nano/micro flexible sensors based on nanomaterials [30]. A bimodal distribution may provide a wide spread of nanoparticles whereby the larger nanoparticles cover larger surface areas while the smaller nanoparticles fill in the gaps for good conductivity. On the other hand, a positively skewed distribution may be ideal when mostly small nanoparticles are required, such as during surface coating for solar cells. A narrow normally distributed sample could be good for inkjet printing as the nanoparticles must be of a certain narrow size range to avoid clogging the printer (a major problem faced with inkjet printing of nanoinks at the moment). It is worth noting that one can produce a normally/uniformly distributed colloid from a bimodal/skewed sample by using a filter of certain size; however, one always runs the risk of losing nanoparticles during the filtering and transferring of colloids from one vessel to another, which is why no filtering was conducted in this study. Similarly, one can produce a skewed/bimodaldistributed colloid from normally distributed colloids by mixing or sonicating colloids of different mean nanoparticle diameters.