Comparative studies on the surface chemical modification of silica aerogels based on various organosilane compounds of the type RnSiX4−n
Comparative studies on the surface chemical modification of silica aerogels based on various organosilane compounds of the type RnSiX4−n
复制标题
DOI：
10.1016/j.jnoncrysol.2004.06.034
复制
发表时间：
2004-12
影响因子：
3.5
通讯作者：
A. Rao;G. Pajonk;S. Bhagat;P. Barboux
中科院分区：
文献类型：
--
作者：
A. Rao;G. Pajonk;S. Bhagat;P. Barboux
我们报道了基于RnSiX4−n(其中R=烷基或芳基，X=氯或烷氧基，n=0-4)的单、双、三和四官能有机硅烷化合物的各种前驱体和共前驱体对二氧化硅气凝胶进行表面化学修饰的实验结果。前驱体具有四官能团或三官能团的化学功能，而共前驱体具有1-3个官能团。基于甲基三甲氧基硅烷(MTMS)的有机硅烷既可以作为前驱体，也可以作为共前驱体。化学改性气凝胶是通过(I)共前体和(Ii)衍生化方法制备的。共前驱体法制备的气凝胶具有较高的接触角(θ≈136°)，但气凝胶是不透明的，而用衍生化方法得到了接触角较低(θ≈120°)的透明(可见光透过率为80%)气凝胶。苯基改性气凝胶的疏水性在520℃以下是热稳定的，使用MTMS前驱体可以得到接触角高达175°的气凝胶，但气凝胶是不透明的。使用TEOS前驱体和三甲基乙氧基硅烷(TMES)共前驱体获得的气凝胶，体积收缩可以忽略不计。压力-体积曲线显示，当压力大于拉普拉斯压力时，水侵入MTMS改性气凝胶表现出滞后现象。在倾角为8°的超疏水气凝胶粉末包覆的表面上，水滴的速度高达0.4ms−1。
We report the experimental results dealing with the surface chemical modification of silica aerogels using various precursors and co-precursors based on mono-, di-, tri- and tetrafunctional organosilane compounds of the type RnSiX4−n(where R=alkyl or aryl groups, X=Cl or alkoxy groups, n=0–4). The precursors exhibit either tetrafunctional or trifunctional chemical functions while the co-precursors have a number of functional groups varying from 1 to 3. The organosilane based on the methyltrimethoxysilane (MTMS) can be used as a precursor as well as co-precursor. The chemically modified aerogels have been produced by (i) co-precursor, and (ii) derivatization methods. The co-precursor method results in aerogels with higher contact angle (θ≈136°) but the aerogels are opaque, whereas transparent (>80% optical transmission in the visible range) aerogels with lower contact angle (θ≈120°) are obtained using the derivatization method. The hydrophobicity of the phenyl-modified aerogels has been found to be thermally stable up to a temperature of 520°C. Using the MTMS precursor, aerogels with contact angles as high as 175° have been obtained, but the aerogels are opaque. The aerogels obtained using TEOS precursor along with the trimethylethoxysilane (TMES) co-precursor, show negligible volume shrinkage. Water intrusion into the MTMS-modified aerogels at pressures greater than the Laplace pressure exhibits hysteresis, as shown in the pressure-volume curves. Water droplets placed on surfaces coated with superhydrophobic aerogel powder with 8° of inclination showed velocities as high as 0.4ms−1. The results are discussed with respect to the ratios of organic and inorganic components of the organosilane compounds.