Jabbarzadeh Ahmad, Halfina Beny
Faculty of Engineering, School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney NSW 2006 Australia
Sydney Nano Institute, The University of Sydney NSW 2006 Australia.
Nanoscale Adv. 2019 Oct 17;1(12):4704-4721. doi: 10.1039/c9na00525k. eCollection 2019 Dec 3.
We conducted large scale molecular dynamics simulations to understand the effects of size, shape and volume fraction of additive nanoparticles on the crystallization of nanocomposite polymers. We used spherical and cubic gold nanoparticles of various sizes ranging from 2 to 8 nm to create hexacontane (CH)-gold nanocomposites at various volume fractions of 0.84-19.27%. We show that, regardless of the shape, decreasing the size of particles at the same volume fraction results in decreased final crystallinity. Similarly, for the same particle size, increasing the volume fraction causes a decrease in the crystal growth rate and final crystallinity. We demonstrate that this is a confinement induced phenomenon, and the free interparticle space captures the combined effects of particle size and volume fraction. If this free space is smaller than the extended length of the molecule or the characteristic size of the crystal lamella thickness of the polymer, significant slow-down in crystallinity will emerge. In this confinement limit, the interparticle free space controls the crystal growth rate and final crystallinity. We have developed the equations that predict the critical volume fraction ( ) for a given size or critical size ( ) for a given volume fraction. For > or < , one would expect confinement induced retardation of crystallization. We also show that cubic particles result in a higher growth rate and crystallinity in comparison to spherical particles, purely due to their shape. Furthermore, cubic particles due to flat surfaces lead to distinct two-tier crystallisation kinetics manifested by enhanced crystallization at the early stage of crystallization, followed by slow crystallization due to confinement effects. This two-tier crystallization is more distinct at higher volume fractions. For spherical particles, however, this two-tier crystallization is almost absent and molecular crystallization near the particle is frustrated by the curved shape of the nanoparticle.
我们进行了大规模分子动力学模拟，以了解添加剂纳米颗粒的尺寸、形状和体积分数对纳米复合聚合物结晶的影响。我们使用了尺寸范围从2到8纳米的球形和立方体形金纳米颗粒，以不同的体积分数（0.84 - 19.27%）制备了正十六烷（CH）-金纳米复合材料。我们发现，在相同体积分数下，无论颗粒形状如何，减小颗粒尺寸都会导致最终结晶度降低。同样，对于相同的颗粒尺寸，增加体积分数会导致晶体生长速率和最终结晶度降低。我们证明这是一种受限诱导现象，颗粒间的自由空间综合了颗粒尺寸和体积分数的影响。如果这个自由空间小于聚合物分子的伸展长度或晶体片层厚度的特征尺寸，结晶度将显著降低。在这个受限极限下，颗粒间的自由空间控制着晶体生长速率和最终结晶度。我们已经推导出了预测给定尺寸下的临界体积分数（ ）或给定体积分数下的临界尺寸（ ）的方程。对于 > 或 < ，预计会出现受限诱导的结晶延迟。我们还表明，与球形颗粒相比，立方体形颗粒由于其形状导致更高的生长速率和结晶度。此外，由于立方体形颗粒具有平坦表面，导致明显的两级结晶动力学，表现为结晶早期结晶增强，随后由于受限效应结晶缓慢。这种两级结晶在较高体积分数下更为明显。然而，对于球形颗粒，几乎不存在这种两级结晶，并且颗粒附近的分子结晶受到纳米颗粒弯曲形状的阻碍。
