Microcellular Plastic Manufacturing Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, Ontario M5S 3G8, Canada.
Smart and Adaptive Polymers & Composites Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, Ontario M5S 3G8, Canada.
J Colloid Interface Sci. 2017 Jan 1;485:65-74. doi: 10.1016/j.jcis.2016.09.030. Epub 2016 Sep 14.
A new high porosity resorcinol-formaldehyde (RF) aerogel with improved particle necking is presented in this work. This RF aerogel was developed under CO supercritical drying conditions without any structural shrinkage. The water content and the catalyst percentage were varied to modify the particles' nucleation and growth mechanisms and to control particle-particle connections. The nucleation mechanism solely dependent on the initial catalyst percentage; the number of nuclei increased with the catalyst percentage. However, the growth and connection of the particles dependent on both the water content and the catalyst percentage through their effect on the pH value. As the water content increased to have a larger void fraction, the pH value decreased. Consequently, the spherical growth of the particles became dominant and, thereby, the connection of the particles became more difficult. But as the catalyst percentage increased, the pH value increased, and the connection of the particles became facilitated with the formation of necks around the particles. As a result, the semi-fibril-like structure was developed with a high void fraction. A 30% increase in the structural elasticity and a very low thermal conductivity of 0.0249W/mK were obtained.
本工作提出了一种具有改进颗粒缩颈的新型高孔隙率的间苯二酚-甲醛（RF）气凝胶。该 RF 气凝胶是在 CO2 超临界干燥条件下开发的，没有任何结构收缩。通过改变水含量和催化剂百分比来改变颗粒的成核和生长机制，从而控制颗粒-颗粒的连接。成核机制仅取决于初始催化剂的百分比；核的数量随催化剂的百分比增加而增加。然而，颗粒的生长和连接取决于水含量和催化剂百分比，这是通过它们对 pH 值的影响来实现的。随着水含量的增加，以获得更大的空隙率，pH 值降低。因此，颗粒的球形生长变得占主导地位，从而使颗粒的连接变得更加困难。但是，随着催化剂百分比的增加，pH 值增加，颗粒之间的连接变得更加容易，因为在颗粒周围形成了颈。结果，形成了具有高空隙率的半纤维状结构。获得了结构弹性提高 30%和非常低的导热系数 0.0249W/mK。
