Sewring Tor, Trulsson Martin
Theoretical Chemistry, Lund University, 221 00Lund, Sweden.
ACS Omega. 2023 Feb 6;8(6):6040-6051. doi: 10.1021/acsomega.2c08060. eCollection 2023 Feb 14.
This computational study investigates the energy minimum, that is, ground state, of suspensions of monodisperse (single-component) charged linear rods at various densities and screening lengths. We find that closed-packed unidirectional configurations have the lowest energies for all studied cases. We further specify the lattice parameters for these crystalline structures. In addition, we identify a few metastable phases, including heliconical structures. These metastable heliconical phases are composed of hexagonal smectic C layers with particle orientations forming a conical helicoid with a short pitch of three layers. We evidence this by zero-temperature Monte Carlo simulations starting from an energy-minimized hexagonal cholesteric configuration, which rapidly transforms to a heliconical phase. Furthermore, this heliconical phase is remarkably stable even at finite temperatures and melts to a disordered phase at high temperatures. Finally, we conduct simulations at room temperature and conditions typical for cellulose nanocrystal suspensions to study the onset of nematic order and compare our results to available experimental data. Our findings suggest that electrostatics play an important role in the isotropic/anisotropic transition for dense suspensions of charged rods.
这项计算研究考察了单分散（单组分）带电线性棒状粒子悬浮液在不同密度和屏蔽长度下的能量最小值，即基态。我们发现，在所有研究的情况下，密堆积单向构型具有最低能量。我们进一步确定了这些晶体结构的晶格参数。此外，我们还识别出了一些亚稳相，包括螺旋结构相。这些亚稳螺旋结构相由六方近晶C层组成，粒子取向形成一个短螺距为三层的锥形螺旋面。我们通过从能量最小化的六方胆甾相构型开始的零温度蒙特卡罗模拟证明了这一点，该构型会迅速转变为螺旋结构相。此外，这种螺旋结构相即使在有限温度下也非常稳定，在高温下会熔化为无序相。最后，我们在室温以及纤维素纳米晶体悬浮液的典型条件下进行模拟，以研究向列相序的起始，并将我们的结果与现有的实验数据进行比较。我们的研究结果表明，静电作用在带电棒状粒子浓悬浮液的各向同性/各向异性转变中起着重要作用。
