## 3 Results and Discussion
### Performance Evaluation Results  
Figure 8 shows a scanning electron microscopy (SEM) image of the PMS xerogel. Preparation of a high-porosity structure using only a PMS network with varied material properties of the ligaments and joints is difficult. Therefore, we developed a composite of PMS xerogel and CNFs. Figure 8: Scanning electron microscopy image of poly(methylsiloxane) (PMS) xerogel. The CNF-PMS xerogel composite was synthesized using the raw material formulation in Table 3 as follows: A CNF dispersion was mixed with a 5 mmol/L aqueous acetic acid solution, and the mixture was stirred using a stirrer at 1150 rpm for 15 min at room temperature. Urea and \(n\)-hexadecylammonium bromide (CTAB) were then dissolved in the mixture, and dimethyldimethoxysilane (DMDMS) and methyltrimethoxysilane (MTMS) were added to the mixture for hydrolysis. The samples were allowed to gel and age at 80 \({}^{\circ}\)C, washed, solvent-exchanged, and dried to obtain dried samples. Finally, the samples were dried at 120 \({}^{\circ}\)C for 1 h. The CNF dispersions used were Rheocrysta (2 wt% aqueous dispersions of CNFs oxidized using 2,2,6,6-tetramethylpiperidine-1-oxyl; DKS Co., Ltd., Kyoto, Japan) and hydrophobic CNF dispersions prototyped by DKS Co., Ltd. The appearance of the produced PMS xerogels is shown in Figure 9. The original PMS xerogel (Figure 9a) was synthesized as a homogeneous dry gel. Its porosity, calculated using the bulk and skeletal densities, was 89.5%. The aged and diluted PMS xerogel (Figure 9b), in which the amount of alkoxysilane precursors was decreased to half its volume to increase its porosity, did not form a gel structure after aging; it remained in solution form. The CNF-PMS xerogel composite (Figure 9c), in which the amount of alkoxysilane precursors was also decreased to half its volume, was synthesized as a dry gel. However, it was mechanically weak, and its surface was damaged when something came in contact with the specimen. Its porosity was 94.2%. The hydrophobic CNF-PMS xerogel composite (Figure 9d) was a tougher dry gel than the CNF-PMS xerogel composite. Its porosity was 93.2%. A moderate interaction or inter-dispersion was observed between the sol framework and CNFs, and the toughness of the gel depended on the balance between them. SEM images of the original PMS xerogel and the hydrophobic CNF-PMS xerogel composite are shown in Figure 10. In the original PMS xerogel, gel particles with diameters of several micrometers are strung together to form the three-dimensional porous structure. The hydrophobic CNF-PMS xerogel composite comprises gel particles with a broad size distribution (diameters ranging from several hundred nanometers to several micrometers). No fibrous structures are observed. The CNF is the substance that adheres to the periphery of the gel particles to the extent that it covers the particle shape of the gel particles (Figure 10d). The hydrophobic CNF-PMS xerogel composite has a higher porosity than the original PMS xerogel, suggesting that the CNFs also function as binders. The CNFs are sparsely distributed, indicating that gel particles are exposed in places. As shown in [PERSON] et al. (2017), it can be inferred that gel particles coated with C-C bond-dominated CNFs exhibit a higher modulus than the exposed gel particles. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Original** & **Diluted** & **CNF** & **Hydrophobic CNF** \\  & **PMS Xerogel** & **PMS Xerogel** & **PMS Xerogel** \\ \hline CTAB/g & 0.4 & 0.2 & 0.2 & 0.2 \\ Urea/g & 3.0 & 3.0 & 3.0 & 3.0 \\ Acetic acid/mL & 10 & 10 & 10 & 10 \\ CNF dispersion/g & 0 & 0 & 1.0 & 0.2 \\ MTMS/mL & 3.0 & 1.5 & 1.5 & 1.5 \\ DMDMS/mL & 2.0 & 1.0 & 1.0 & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Raw material formulation of composite cellulose nanofibers (CNFs) and PMS xerogel. CTAB—\(n\)-hexadecylammonium bromide; MTMS—methyltrimethoxysilane; DMDMS—dimethyldimethoxysilane.