Density gradient aerogel is a kind of porous material with non-uniform density change in a specific direction. It has some unique properties and can be used in some extreme conditions. The resorcinol–formaldehyde (RF) gradient aerogels were prepared by the method based on double diffusion convection. We studied the influences of injection velocity and diffusion before gelation on the distribution of gel density gradient, and obtained an optimized injection velocity scheme. The RF density gradient aerogels were characterized by x-ray transmission imaging, scanning electron microscopy (SEM), and nitrogen adsorption–desorption isotherm. The density distribution and microstructure of the RF density gradient aerogels were obtained. The solution obtained by the optimized multi-velocities injection method presents a gradient change in the low-density part that is greater than the high-density part. This uneven change can offset the diffusion caused by the long gel time of the low-density part, and finally form a gel whose density changes uniformly with the thickness. The aerogel obtained by the optimized method ranges from 100 to 400 mg cm⁻³, and the density of the sample varies linearly. The results indicate that this is an efficient and direct method for preparing density gradient aerogels, and aerogels with specific density trends can be obtained by adjusting the injection velocities.

密度梯度气凝胶是一种在特定方向上密度变化不均匀的多孔材料。它具有一些独特的特性，可以在一些极端条件下使用。采用基于双扩散对流的方法制备了间苯二酚-甲醛（RF）梯度气凝胶。研究了凝胶化前注射速度和扩散对凝胶密度梯度分布的影响，得到了优化的注射速度方案。RF 密度梯度气凝胶通过 X 射线透射成像、扫描电子显微镜 (SEM) 和氮吸附-解吸等温线进行表征。获得了射频密度梯度气凝胶的密度分布和微观结构。优化后的多速注射法得到的解在低密度部分呈现梯度变化大于高密度部分。这种不均匀的变化可以抵消低密度部分凝胶时间长造成的扩散，最终形成密度随厚度变化均匀的凝胶。优化方法获得的气凝胶范围为100至400 mg cm⁻³，样品的密度呈线性变化。结果表明，这是制备密度梯度气凝胶的一种有效且直接的方法，通过调节注射速度可以获得具有特定密度趋势的气凝胶。