Nature, 1999, 398, 137 letters to nature

Thorsten Goldacker*, Volker Abetz*, Reimund Stadler~t,Igor Erukhimovlch~ & Ludwik Leibler§

*Lehrstuhl Makromolekulare Chernie Il, Universitât Bayreuth, D-95440 Bayreuth, Germany

tPhysics Department, Moscow State University, RU-1 17234 Moscow, Russia

§Unité Mixte de Recherches CNRS - Elf Atochem (UMR 167), 95 rue Danton, BP 108, F-92303 Levallois-Perret Cedex, France

Materials with a macroscopic electric polarization display a variety of useful properties, such as piezo- and pyroelectricity and second-order nonlinear optical activityl. Macroscopic polarization results when dipolar molecules are orientated in the same direction, or when ions are organized in a non-centrosymmetric crystal structure2. Centrosymmetric molecules have no dipole moment and so cannot generate a macroscopic polarization. Non-centrosymmetry in amorphous materials can be engincered by depositing particular sequences of layers on top of each other, or by applying external fields (generally electric) to orientate the molecules'. Here we report the formation of a non-centrosymmetric: structure in an amorphous material through spontaneous selfassembly. Block copolymers are known to form ordered structures at the microscale owing to segregation of the diffèrent blocks'>'. We show that a mixture of a ternary triblock copolymer and a binary diblock copolymer will organize itself into a noncentrosymmetric layered structure in which the layers are occupied by different blocks. The structure is periodic with a length scale of around 60 nm

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