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Multiarm star polymers, consisting of a high number of linear homopolymer arms joined covalently to a central core, represent model soft 'hybrid' spheres encompassing both polymeric (arm) and colloidal (core) character. Due to this topology, the single star has a nonuniform monomer density distribution. In nondilute solutions, a liquid-like ordering occurs as a consequence of the enhanced osmotic pressure that outbalances the entropic stretching of the arms; this type of order persists in the melt as well, due to 'macromolecular excluded volume' effects. The resulting rich dynamic response, which is presented in this review, exhibits signatures of both polymeric and colloidal behaviour. In solution, concentration and number density fluctuations relax via cooperative diffusion, self-diffusion and structural relaxation. In the melt, the viscoelastic terminal relaxation involves arm relaxation (independent of arm number) and structural rearrangements of the stars (strongly dependent on arm number and size). The identification of the relaxation mechanisms in such complex soft spheres provides the necessary ingredients for the molecular design and control of novel composite materials combining properties of polymers and colloids.
Vlassopoulos et al. (Fri,) studied this question.