Intermediate periodic "saddle-splay" nematic phase in the vicinity of a nematic-smectic-A transition.
Intermediate periodic "saddle-splay" nematic phase in the vicinity of a nematic-smectic-A transition.
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向列-近晶-A 转变附近的中间周期性“鞍状展开”向列相。
DOI：
10.1103/physreve.66.051706
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
V. Pergamenshchik
中科院分区：
文献类型：
--
作者：
G. Barbero;V. Pergamenshchik
当弹性常数K24的值不满足均匀基态的Ericksen稳定条件时，我们考虑了弹性鞍-展K24项引起的向列方向可能的自发调制。根据用扭转弹性常数K22表示K24的标准公式，这可以预期接近向列-拟合- a转变，其中K22变得非常大。据预测，在平面向列层中（或者，更一般地说，如果表面指向线足够接近平面指向线），具有可观察到的长波长周期的调制相位可能出现在比锚定外推长度相当厚的样品中。调制向列相可以持续到近晶相，因此其向近晶相转变的温度必须低于均匀向列相液晶的温度。对于任何厚度的低振幅短波调制，如果表面方向距纯同向取向足够远，则可以预测。以牺牲这种模式为代价，具有各向同性表面的平面晶胞中的向列-近晶- a跃迁的温度必须低于各向同性晶胞的温度，即使其周期结构无法直接观测。
We consider possible spontaneous modulations of the nematic director induced by the elastic saddle-splay K24 term when the value of the elastic constant K24 does not satisfy the Ericksen stability condition for the homogeneous ground state. According to the standard formula expressing K24 in terms of the twist elastic constant K22, this can be expected close to the nematic-smectic-A transition where K22 becomes very large. It is predicted that in a planar nematic layer (or, more generally, if the surface director alignment is sufficiently close to a planar one), a modulated phase with observable long wavelength period can occur in samples considerably thicker than the anchoring extrapolation length. The modulated nematic phase is expected to persist into the smectic phase so that its temperature of the transition to smectic phase has to be lower than that for the homogeneous nematic liquid crystal. Low amplitude short wavelength modulations are predicted for any thickness if the surface director is sufficiently far from a pure homeotropic alignment. At the expense of this mode the temperature of a nematic-smectic-A transition in a planar cell with isotropic surfaces has to be lower than that for a homeotropic cell even if the periodic structure is not accessible for the direct observation.