Order at Extreme Dilution

Abstract

9009wileyonlinelibrary.com to liquid crystals or materials generated under the influence of a strong external stimulus. [5][6][7] These techniques, amongst others, include photolithography [8,9] and soft lithography, [9,10] the applications of electric fields [11,12] and shear flow alignment. [13,14] An interesting approach to reduce the required fields strengths is liquid crystal templating, that allows to organize soft, self-assembling materials in (aqueous) liquid crystals and use external stimuli to exert spatial control. [15][16][17][18] In all these approaches, including liquid crystal templating, the molecular concentration and/or the susceptibility to external fields should be sufficient to establish longrange order. Looking at Nature, neither high concentrations, nor high susceptibilities are required. Here, we present a route toward macroscopically highly ordered materials at extremely high dilution (less than 0.3% in water). Following Onsager's hard rod model, [19] long range order at this concentration requires stiff rods of several micrometers long. Instead, we find that the order develops (slowly) through the interaction between a self-assembling chromophore and a semiflexible polymer; neither of the two components form structures in the micrometer range. In earlier work with DNA [20,21] or the chromonic liquid crystal DSCG [22,23] as the self-assembling material, the addition of polymers typically Control over the organization of assemblies from molecular dimensions up to the macroscopic length scale is an outstanding challenge in science, above all for materials in high dilution. Instead of inducing order by generating very long and stiff structures, an alternative approach is studied: a two-component assembly of a semiflexible polymer with a (self-assembling) chromonic liquid crystal. By following the structure formation in time using different techniques, a mechanistic model is proposed that explains how such unusually well-defined materials can be created from flexible components. It is concluded that at this very low concentration (>99.6% water), these macro scopically organized structures can only be formed when the energies between different assembly states and their interconversion rates are properly balanced. This may, however, be in reach for a wide range of materials, which makes this a generic route toward high definition at low concentration without the need for long and rigid building blocks. Figure 7. Schematic representation of the hierarchical assembly process to obtain macroscopic long-range order at high dilution without the use of highly rigid components. full paper 9016 wileyonlinelibrary.com