Sorkin V, Pei Q X, Liu P, Thitsartarn W, He C B, Zhang Y W
Institute of High Performance Computing, A*STAR, Singapore, 138632, Singapore.
Institute of Materials Research and Engineering, A*STAR, Singapore, 138634, Singapore.
Sci Rep. 2021 Nov 29;11(1):23108. doi: 10.1038/s41598-021-02460-3.
Interfacial adhesion between polymer matrix and reinforcing silica nanoparticles plays an important role in strengthening polypropylene (PP) composite. To improve the adhesion strength, the surface of silica nanoparticles can be modified by grafted functional molecules. Using atomistic simulations, we examined the effect of functionalization of silica nanoparticles by hexamethyldisilazane (HMDS) and octyltriethoxysilane (OTES) molecules on the deformation and failure of silica-reinforced PP composite. We found that the ultimate tensile strength (UTS) of PP composite functionalized by OTES (28 MPa) is higher than that of HMDS (25 MPa), which is in turn higher than that passivated only by hydrogen (22 MPa). To understand the underlying mechanistic origin, we calculated the adhesive energy and interfacial strength of the interphase region, and found that both the adhesive energy and interfacial strength are the highest for the silica nanoparticles functionalized by OTES molecules, while both are the lowest by hydrogen. The ultimate failure of the polymer composite is initiated by the cavitation in the interphase region with the lowest mass density, and this cavitation failure mode is common for all the examined PP composites, but the cavitation position is dependent on the tail length of the functional molecules. The present work provides interesting insights into the deformation and cavitation failure mechanisms of the silica-reinforced PP composites, and the findings can be used as useful guidelines in selecting chemical agents for surface treatment of silica nanoparticles.
聚合物基体与增强二氧化硅纳米颗粒之间的界面粘附力在增强聚丙烯（PP）复合材料中起着重要作用。为了提高粘附强度，可以通过接枝功能分子来修饰二氧化硅纳米颗粒的表面。利用原子模拟，我们研究了用六甲基二硅氮烷（HMDS）和辛基三乙氧基硅烷（OTES）分子对二氧化硅纳米颗粒进行功能化处理对二氧化硅增强PP复合材料变形和破坏的影响。我们发现，经OTES功能化处理的PP复合材料的极限拉伸强度（UTS）（28MPa）高于经HMDS处理的（25MPa），而后者又高于仅用氢钝化的（22MPa）。为了理解其潜在的机理起源，我们计算了相间区域的粘附能和界面强度，发现对于经OTES分子功能化处理的二氧化硅纳米颗粒，粘附能和界面强度都是最高的，而仅用氢处理时两者都是最低的。聚合物复合材料的最终破坏是由质量密度最低的相间区域中的空化引发的，这种空化破坏模式在所有研究的PP复合材料中都很常见，但空化位置取决于功能分子的尾长。本工作为二氧化硅增强PP复合材料的变形和空化破坏机制提供了有趣的见解，这些发现可作为选择用于二氧化硅纳米颗粒表面处理的化学试剂的有用指导。
