Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, viale Risorgimento 4, 40136 Bologna, Italy.
J Chem Phys. 2011 Oct 7;135(13):134119. doi: 10.1063/1.3646310.
Classical molecular dynamics simulations have been used to explore the phase diagrams for a family of attractive-repulsive soft-core Gay-Berne models [R. Berardi, C. Zannoni, J. S. Lintuvuori, and M. R. Wilson, J. Chem. Phys. 131, 174107 (2009)] and determine the effect of particle softness, i.e., of a moderately repulsive short-range interaction, on the order parameters and phase behaviour of model systems of uniaxial and biaxial ellipsoidal particles. We have found that isotropic, uniaxial, and biaxial nematic and smectic phases are obtained for the model. Extensive calculations of the nematic region of the phase diagram show that endowing mesogenic particles with such soft repulsive interactions affect the stability range of the nematic phases, and in the case of phase biaxiality it also shifts it to lower temperatures. For colloidal particles, stabilised by surface functionalisation, (e.g., with polymer chains), we suggest that it should be possible to tune liquid crystal behaviour to increase the range of stability of uniaxial and biaxial phases (by varying solvent quality). We calculate second virial coefficients and show that they are a useful means of characterising the change in effective softness for such systems. For thermotropic liquid crystals, the introduction of softness in the interactions between mesogens with overall biaxial shape (e.g., through appropriate conformational flexibility) could provide a pathway for the actual chemical synthesis of stable room-temperature biaxial nematics.
经典分子动力学模拟已被用于探索一系列具有吸引力-排斥性软核 Gay-Berne 模型的相图[R. Berardi、C. Zannoni、J. S. Lintuvuori 和 M. R. Wilson，J. Chem. Phys. 131, 174107 (2009)]，并确定粒子柔软度（即适度排斥的短程相互作用）对单轴和双轴各向异性椭球粒子模型系统的有序参数和相行为的影响。我们发现，各向同性、单轴和双轴向列相和近晶相在模型中都得到了。对相图的向列区进行了广泛的计算，结果表明，赋予介晶粒子这种软排斥相互作用会影响向列相的稳定范围，而在相双轴性的情况下，它也会将其移至较低的温度。对于通过表面功能化（例如，用聚合物链）稳定的胶体粒子，我们建议应该可以调整液晶行为以增加单轴和双轴相的稳定范围（通过改变溶剂质量）。我们计算了第二维里系数，并表明它们是表征此类系统有效柔软度变化的有用手段。对于热致液晶，在具有整体双轴形状的介晶之间的相互作用中引入柔软度（例如，通过适当的构象灵活性）可能为实际合成稳定的室温双轴向列相提供途径。
