All simulations were conducted at constant volume and temperature with the positions of the substrate particles fixed. Each system consisted of 6000 fluid particles and 4680 (graphene) or 800 (silicon) substrate particles. The simulation timestep was 0.012 τ, which corresponds to 5 fs if the unit of mass m 0 is taken to be the molecular mass of perylene. Temperature was controlled with a Nosé-Hoover thermostat and set to values of 0.56, 0.62, 0.73, or 0.84ε/k B . Most systems were constrained to a constant overall volume fraction φ av (that is, the volume fraction calculated from the number density of all particles between z = σ sub /2, the surface of the substrate, and z = z w , the position of the harmonic wall) of 0.39, corresponding to a real density on the order of 1.1 g/cm 3 if ε = 1.8 kcal/mol and σ = 3.2 Å. The z coordinate of the harmonic wall, chosen to achieve the desired overall volume fraction for the different values of κ, are given in the ESI Table . Additional systems were examined at lower (0.28) and higher (0.49) φ av values to determine the dependence (if any) of interfacial orientation on the system density. The pressure in each system was measured as the normal force per unit area acting on the solid substrate. The average pressure at equilibrium was generally < 200ε/σ 3 , but was up to 1200ε/σ 3 for φ av = 0.49.