Cinacchi Giorgio, De Gaetani Luca
Dipartimento di Chimica, Università di Pisa,Via Risorgimento 35, I-56126 Pisa, Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 May;77(5 Pt 1):051705. doi: 10.1103/PhysRevE.77.051705. Epub 2008 May 27.
By employing molecular dynamics computer simulations, the phase behavior of systems of rodlike particles with varying degree of internal flexibility has been traced from the perfectly rigid rod limit till very flexible particles, and from the high density region till the isotropic phase. From the perfectly rigid rod limit and enhancing the internal flexibility, the range of the smectic- A phase is squeezed out by the concomitant action of the scarcely affected crystalline phase at higher density and the nematic phase at lower density, until it disappears. These results confirm the supposition, drawn from previous theoretical, simulational and experimental studies, that the smectic- A phase is destabilized by introducing and enhancing the degree of particle internal flexibility. However, no significant changes in the order of nematic-to-smectic- A phase transition, which appears always first order, nor in the value of the layer spacing, are observed upon varying the degree of particle internal flexibility. Moreover, no evidence of a columnar phase, which was thought of as a possible superseder of the smectic- A phase in flexible rods, has been obtained.
通过运用分子动力学计算机模拟，研究了具有不同内部柔韧性程度的棒状颗粒体系的相行为，其范围从完全刚性的棒极限情况到非常柔性的颗粒，以及从高密度区域到各向同性相。从完全刚性的棒极限情况开始并增强内部柔韧性，在较高密度下几乎不受影响的晶相和较低密度下的向列相的共同作用挤压了近晶A相的范围，直至其消失。这些结果证实了先前理论、模拟和实验研究所得到的推测，即引入并增强颗粒内部柔韧性程度会使近晶A相失稳。然而，在改变颗粒内部柔韧性程度时，未观察到总是呈现一级相变的向列相到近晶A相转变的顺序有显著变化，也未观察到层间距值有显著变化。此外，未获得柱状相的证据，而柱状相曾被认为是柔性棒中近晶A相可能的替代相。
