Chemistry Department and CICECO, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal.
J Phys Chem B. 2010 Mar 25;114(11):4047-55. doi: 10.1021/jp911270y.
The hydration of cellulose/silica hybrids (CSH) containing 13, 35, and 46% (w/w) silica synthesized in situ by a mild sol-gel aqueous process was studied employing sorption isotherms and surface energy measurements. Water sorption is governed by two simultaneous equilibria at the silica-vapor and cellulose-vapor interfaces due to the presence of cellulose regions covered and uncovered with silica as confirmed by X-ray scattering analysis. The important contribution of a water impermeable cellulose-silica interface to the surface properties of CSH is highlighted. CSH exhibit type II isotherms in the temperature range 15-40 degrees C, more appropriately described by the Guggenheim-Anderson-de Boer (GAB) model than by the Brunauer-Emmett-Teller (BET) model. Specific surface areas calculated using both models (S(BET) and S(GAB)) increase linearly with the amount of silica influencing the higher moisture content of CSH for the same water activity. However, the presence of silica reduces the strength of interaction between monolayer water molecules and the CSH surface as revealed by the net isosteric heat of sorption (35 kJ/mol for cellulosic pulp and 26 kJ/mol for CSH with 35% silica). Silica confers a higher surface energy to CSH contributing to its polar component and surface wettability (contact angle with water) when compared to cellulosic pulp. The average diameter of cellulose microfibrils and the interfacial cellulose-silica areas are assessed on the basis of the analysis of sorption isotherms.
采用吸附等温线和表面能测量法研究了通过温和的溶胶-凝胶水相过程原位合成的纤维素/二氧化硅杂化材料（CSH）的水合作用，其二氧化硅含量分别为 13%、35%和 46%（w/w）。由于纤维素区域被二氧化硅覆盖和未覆盖，在二氧化硅-蒸汽和纤维素-蒸汽界面存在两个同时的平衡，因此水分吸附受两个同时平衡的控制，这一点通过 X 射线散射分析得到证实。纤维素-二氧化硅界面对 CSH 表面性能的重要贡献是不可渗透水的。CSH 在 15-40°C 的温度范围内表现出 II 型等温线，更恰当地说是由 Guggenheim-Anderson-de Boer (GAB) 模型而不是 Brunauer-Emmett-Teller (BET) 模型描述的。使用两种模型（BET 和 GAB）计算的比表面积（S(BET)和 S(GAB)) 随二氧化硅量线性增加，这影响了相同水活度下 CSH 的更高水分含量。然而，正如吸附等温线分析所揭示的那样，二氧化硅的存在降低了单层水分子与 CSH 表面之间的相互作用强度，其净等吸附热为 35 kJ/mol（对于纤维素纸浆）和 26 kJ/mol（对于 35%二氧化硅的 CSH）。与纤维素纸浆相比，二氧化硅赋予 CSH 更高的表面能，这有助于其极性组分和表面润湿性（与水的接触角）。根据吸附等温线的分析，评估了纤维素微纤维的平均直径和界面纤维素-二氧化硅区域。
