tice (lattice spacing of 1.69σ ). Although ε LJ is larger for silicon, the larger lattice spacing means that the overall attraction of a single GB fluid particle to the substrate is weaker for silicon than graphene. An additional substrate with the same structure as graphene but with interactions that were twice as strong (ε LJ = 0.078ε, σ LJ = 1.11σ ) was also examined, which we will call the "strong" substrate. The structures of these substrates are shown in the ESI, Fig. . The mixing rules for combining GB parameters of two dissimilar particles, defined by eqns (S3)-(S8) of the ESI, were used to model the fluid-substrate interactions so as to maintain the correct shape dependence of the interactions. The interaction range σ in eqn (S2) of the ESI was replaced by the arithmetic mean, (σ + σ LJ )/2, of the fluid and substrate interaction ranges for the fluid-substrate interactions. The substrate parameters, and the influence of the type of substrate on the orientation at both interfaces are given in full in the ESI (Table , Fig. ).