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New Nano‐ and Microparticles with a Liquid‐Crystal‐Like Interior

We report the formation of well-defined and uniformly sized nano- and microparticles in aqueous solutions of oppositely charged polyelectrolytes and surfactants. Such mixed aqueous solutions are currently the focus of much attention because of the large number of applications in which they are involved. [1,2] The particles that we have obtained are spherical and possess an internal liquid-crystal-like structure. The radius of the particles is independent of the polymer concentration but increases exponentially with the surfactant concentration. The particle size can therefore be varied over a broad range, from 10 nm up to several micrometers. Here, we discuss the conditions used to synthesize these particles. Upon mixing the polyelectrolytes and surfactants, two distinct behaviors are observed. First, precipitation occurs above a critical concentration for both the polymer and the surfactant when the two species are oppositely charged (Fig. 1). In contrast to the usual precipitation of salts, or even mixtures of two surfactants, this precipitation does not occur at a point where the ionic concentrations of the two species are close. In the following discussion we denote the surfactant and polymer ion concentrations by Cs and Cp, respectively. The phase separation has an “associative” character: at large Cp, the surfactant concentration threshold Cs* is roughly independent of