## 3 Results and Discussion
### Effects of the Grafting Degrees on the Physicochemical Properties of EWP
#### 3.2.3 The Porous Properties of EWP Aerogels Changed with Grafting Degrees  
The adsorption-desorption isotherms of the samples were finally plotted by first determining the adsorption efficiency of the samples exposed to the inert gas stream, and subsequently measuring the amount of gas desorbed due to heating the samples. As shown in Figure 4a, all of the isotherms belonged to type IV, following the categorization of the International Union of Pure and Applied Chemistry (IUPAC). These materials were inherently mesoporous and the hysteresis loops were a feature of the isotherms, which did correlate with the presence of capillary condensation in the mesopores [33; 57].  
The pore parameters of all samples are listed in Table 2. The BET specific surface areas (S\({}_{\text{BET}}\)) of EWP, EC\({}_{0}\), EC\({}_{12}\), EC\({}_{24}\), EC\({}_{36}\), and EC\({}_{48}\) were 0.54, 1.87, 2.59, 1.96, 1.75, and 2.43 m\({}^{2}\)/g, respectively, as determined by the adsorption-desorption isotherms. In general, the fine-structured network contains a large number of smaller pores, which implies a higher specific surface area [23]. The graft-modified EWP aerogels network became more porous and fine, which resulted in a general trend of increasing and then decreasing the S\({}_{\text{BET}}\) of EWP aerogels with increasing grafting degree. This is also reflected in the column of D\({}_{\text{A}}\) in Table 2. Notably, the EC\({}_{48}\) aerogel was second to the EC\({}_{12}\) aerogel in S\({}_{\text{BET}}\), which may be because the higher grafting degree could significantly improve the hydrophilic performance of the molecular surface of EWP and inhibit the heating aggregation behavior of EWP, which reduces the generation of water-insoluble aggregates [58]. Meanwhile, we found that the values of BET specific surface area (S\({}_{\text{BET}}\)) were significantly correlated with the values of average pore diameters (D\({}_{\text{A}}\)); in other words, the lower the D\({}_{\text{A}}\) values, the higher the S\({}_{\text{BET}}\) values, which was also reflected in the study by [PERSON] et al. [19]. As is well known, in a porous material, a lower pore size distribution means higher porosity and, in general, a higher pore volume. However, in our research, there was no evident relationship between the values of S\({}_{\text{BET}}\) and the pore volumes (V\({}_{\text{P}}\)). As reported by [PERSON] et al. [23], the only possible explanation would be the existence of micropores or macropores, which could not be detected in the nitrogen adsorption measurement technique used here. The corresponding distribution of pore sizes obtained by the BJH method is shown in Figure 4b. Although all samples showed a fairly broad distribution of pore sizes in the range of 2-100 nm, their peaks were concentrated between 2 and 10 nm. Moreover, we found that the microporosity of the graft-treated aerogel samples seemed to have a tendency to increase, which may be due to the increased grafting degree of the aerogel, contributing further to the cross-linking interaction [59]. The average mesopore diameter was calculated according to the simple formula 4 Vm/S\({}_{\text{BET}}\), which led to values within the range of 12-36 nm.  
Figure 4: Nitrogen adsorption–desorption isotherms (**a**) and BJH plot (**b**) for the aerogels with different grafting degrees.