## 3 Results and Discussion
### Characterization of Fiber-Cement Nanohybrids  
#### 3.2.1 Flexural Strength  
The standard deviation was computed for all specimens and is presented in Figure 7. For the reference paste, F.PC6 LS40 PVA3 SP2, and for the nC2 modified pastes, it ranged from 1 to 1.4. The addition of nC3 reduced the variation between 1.0 to 1.2 MPa, whereas the standard deviation of nC4 was approximately equal to 1.1 MPa. Hence, as in the case of nMt modified pastes without _PVA_[32], the standard deviation was improved with nC3. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **0–100 \({}^{\circ}\)C** & **100–250 \({}^{\circ}\)C** & **250–400 \({}^{\circ}\)C** & **400–500 \({}^{\circ}\)C** & **500–700 \({}^{\circ}\)C** \\ \hline
**nC4** & 1.33 & 0.31 & 13.63 & 8.00 & 2.86 \\ \hline \hline \end{tabular}  
Respectively, analyses for nC2 and nC3 can be found in literature [19].  
\end{table} 
Table 4: Mass loss (%) of nC4. Figure 6: Comparison of Differential mass loss (dTG) of the organomodified montmorillonite (MMT) dispersion (nC2), inorganic MMT dispersion (nC3) [19], and organomodified MMT powder (nC4). As shown in Figure 7, given more curing time, the nMt modified pastes outperformed the reference paste, in contrast to [21] who suggested that the nMt particles (just like nanosilica particles) are more effective in the first seven days and their effectiveness reduces at middle ages (28 and 90 days). nC3 showed the highest flexural strength of all three. In fact, at day 28 the nC3 reinforced nanohybrids showed a 7.2% increase compared to the reference paste, at day 56 a 28% increase, and at day 90 a 9% increase in flexural strength compared to the reference formulation. nC2 showed a lower strength at day 56, which could be attributed to bad compaction. If this was the case, then all three types of nMt would not manage to maintain the strength gain after day 56, showing a relative reduction in flexural strength at day 90. It is of particular interest to note that the powder nMt did not offer any major strength improvements, neither did nC2. It should also be noted that PVA fibers are highly hydrophobic; therefore, the hydrophobic nature of nC2 and nC4 was possibly responsible for an inferior combination compared to nC3. For this it is postulated that nMt performs best when dispersed in water before being added to any cementitious formulation. It is possible that with longer mixing time and less amount of fibers, the nMt modified specimens can be better compacted and, consequently, deliver even higher strengths. Potential re-agglomeration of nanoparticles when added to cementitious matrices is expected to influence rheological properties of pastes, pore structure, and density, and induce weak zones in compression. It has been postulated in previous studies that the use of a sonicator or any other advanced technique, such as generation of nanofluidic droplets, could help (i) eliminate discrepancies (mixing limitations), and (ii) minimize possible agglomeration of the nMt particles in the pastes produced [31]. In the present study the first step for better mixing, compaction, and avoidance of re-agglomeration of nanoparticles or clustering of fibers was the addition of 2% superplasticizers, magnetic stirring of the nMt dispersion, and mechanical mixing of the fiber-cement nanohybrids. Results, show; however, that there is room for improvement in the techniques employed, particularly for applications that necessitate the use of fibers. In addition to this, recently a number of papers have been presented on digital or droplet based microfluidics systems, which are particularly important for biological applications [48], or for the generation and manipulation of discrete droplets inside  
Figure 7: Flexural strength of 1% nC2, nC3 [28], and nC4 fiber–cement nanohybrids based on F.PC60 LS40 PVA3 SP2. micro-devices [49].