| |
[摘要]：Amphiphilic molecules such as phospholipids, smectic liquid crystals or diblock copolymers are chemical dipoles which, under appropriate conditions, spontaneously line up side by side in a ferro-like arrangement to form stable monolayers. In three dimensions, these monolayers stack in a head-to-tail or antiferro-like arrangement, which favors monopolar contact between similar species. It results in a symmetric bilayered lamellar material. Here we show that dipolar chemical interactions can be extended in the direction normal to the lamellae by the use of triphilic rather than amphiphilic molecules, so that stable self-assembled smectic stacks may be designed with a fully polar, hence noncentrosymmetric, ordering. We describe in details a generic model of such materials. It is made of a mixture of three triblock copolymers aBc, bCa, and cAb with their end blocks twice sorter than the corresponding middle block. Because each constitutive molecule extends over three different chemical layers, all pairs of adjacent layers are linked and oriented via dipolar interactions. As a consequence, a polar structure with remarkable thermodynamic and mechanical stabilities is expected. We name these materials "ferrochemicals" because any given triblock molecule of the blend is oriented the same way through the whole sample due to chemical dipole interactions with all neighboring molecules. In the polymer case, the polar lamellar stacks can also be used as organic matrices hosting and orienting inorganic Janus particles in order to get a large variety of hybrid polar materials with interesting nonlinear optical, ferromagnetic, or ferroelectric properties. |
|
