Clustering in binary mixtures of axial multipoles confined to a two-dimensional plane

Structures in the binary mixtures of model charged colloidal particles resembling axial multipoles confined to a two-dimensional plane have been studied with special attention to clustering, using hypernetted chain integral equation theory. The multipolar symmetric axes of the particles are assumed to be directed along the normal to the plane of confinement. Particles in the mixtures interact via purely repulsive potential proportional to the (2l+1)-th power of the inverse interparticle separation. Corresponding to the values of l being equal to 1,2 and 3, we have three different binary mixtures comprising dipoles, quadrupoles, and octupoles respectively. We observe that the structural features of the three systems are distinct from each other and changes significantly with the variation in the characterizing parameters of the mixture. Smaller particles of the mixture are found to form clusters marked by the emergence of a prepeak preceding the principal peak of their partial structure factors of all the three systems. Size of the clusters is found to be largest for the dipoles, and decreases successively for the quadrupoles and octupoles. Simultaneously we notice that the clusters are most diffused for the dipolar system but become sharp with well defined boundaries as we move to the mixtures of higher order multipoles. Cluster size and its sharpness are found to depend on the interaction strength, particle asymmetry and the composition of the mixtures. Fluid phase of the mixtures remains macroscopically homogeneous and no phase separation is observed.