Prinsen Peter, van der Schoot Paul
Polymer Physics Group, Department of Applied Physics and Dutch Polymer Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Aug;68(2 Pt 1):021701. doi: 10.1103/PhysRevE.68.021701. Epub 2003 Aug 6.
Tactoids are droplets of a nematic phase that under suitable conditions form in dispersions of elongated colloidal particles. We theoretically study the shape and the director-field configuration of such droplets for the case where a planar anchoring of the director field to the interface is favored. A minimum of four regimes can be identified in which the droplets have a different structure. Large droplets tend to be nearly spherical with a director field that is bipolar if the surface tension is strongly anisotropic and homogeneous if this is not so. Small droplets can become very elongated and spindlelike if the surface tension is sufficiently anisotropic. Depending on the anchoring strength, the director field is then either homogeneous or bipolar. We find that the more elongated the tactoid, the more strongly it resists the crossing over from a homogeneous to a bipolar structure. This should have implications for the nucleation rate of the nematic phase. Our calculations qualitatively describe the size dependence of the aspect ratio of tactoids found in recent experiments.
类晶区是向列相的液滴，在合适的条件下，它们会在细长胶体颗粒的分散体中形成。对于指向矢场倾向于在界面处平面锚定的情况，我们从理论上研究了此类液滴的形状和指向矢场构型。至少可以识别出四种状态，其中液滴具有不同的结构。如果表面张力强烈各向异性，大液滴往往近乎球形，其指向矢场是双极的；如果表面张力并非如此，则是均匀的。如果表面张力足够各向异性，小液滴会变得非常细长且呈纺锤形。根据锚定强度，指向矢场随后要么是均匀的，要么是双极的。我们发现类晶区越细长，它从均匀结构转变为双极结构的阻力就越大。这应该对向列相的成核速率有影响。我们的计算定性地描述了最近实验中发现的类晶区纵横比的尺寸依赖性。
