Phase Behavior of Mixtures of Hard and Soft Penetrable Particles

The effective interactions between a pair of amphiphilic dendrimers is found to be approximately expressed within a generic model called as Generalized Exponential Model (GEM-n) U(r) = ε exp[-(r/σ)]n with n≈3. These potentials represent bounded and purely repulsive interactions. The absence of divergence at origin in the interaction potentials between these macromolecules, allows them to penetrate each other, and their centers of mass can overlap. At high enough densities, these systems form cluster crystals.

We have studied mixtures of soft and hard particles at different densities and with different fraction of hard particles in the system. Both hard and soft particles are well dispersed at low densities for all compositions. When the mixture has a high fraction of hard or soft particles, it macrophase separates into a hard-rich and soft-rich region. The system undergoes microphase separation for intermediate fraction of hard particles, in which there are alternating soft-rich, and hard-rich domains. We find that this self-assembled state is disordered and bicontinuous. Within the hard-rich domains, the hard particles are ordered into FCC crystal structure. The soft particles form clusters in both micro and macro phase separated domains.