To further clarify the entropy effect on the distribution of particles, we eliminated the particle-particle attractive forces, in addition to the particle-wall interaction that was imposed in the previous step, by designing a binary mixture of hard spheres in a box with reflective walls. As described in Methods, for hard spheres, we used a strongly repulsive potential for spheres at contact and approximately zero potential when they are not in contact. In this system, the energy effect that is responsible for the aggregation of particles, owing to particle-particle attractive forces, and accumulation of particles adjacent to the wall, owing to wall-particle attractive forces, are eliminated from the system. In this set of simulations, we systematically increased the radius of larger particles to further understand the relationship between the entropic force and the volume of particles. Fig. and Supporting Information, Figs. S7 confirm the higher tendency of larger particles in laying next to the wall for hard-sphere with approximately zero attractive forces between particles. Fig. indicates that the entropy effect owing to depletion force attract larger particles to the wall -as if there is gravity that pulling particles toward the wall -as it creates larger residual space for smaller particles to gain a higher configurational entropy through the exclusion of excluded volume.