doi:10.3850/978-981-08-6555-9_160

ABSTRACT

We study the total force F_tot between the working plate of a gripper and an object – cubical or spherical in shape, situated at a distance L of closest approach to each other and both immersed in a nonpolar fluid, which can be liquid or gas, with temperature T and chemical potential µ. For comparison, we also present results when the fluid is replaced by a vacuum. We consider the most general case when the materials of the working jaw of the gripper are made of different materials with both strongly preferring the liquid phase of the fluid. In our approach we take into account the direct particle-jaw van der Waals interaction ~ J^s, the van der Waals interactions between the molecules of the fluid with i) other molecules of the fluid ~ J^l; ii) with the constituent elements of the particle ~ J^l,p, and iii) the constituents of the plate ~ J^l,s. We consider both the contribution due to the standard van der Waals, as well as of the retarded van der Waals-Casimnir interactions. We conclude that tot F strongly depends on the contrast, at given fixed T and µ, between the physical properties of the fluid and the material of the arms of the gripper and the particle, and is proportional to J^l[ρ_pJ^l,p/J^l-ρ_l][ρ_sJ^l,s/J^l-ρ_l], where ρ_l(T,µ) is the density of the fluid, ρ_s is the density of the substrate, and ρ_p is that one of the particle. In addition, as expected, F_tot strongly depends on the shape of the object, its size, and the distance between it and the working jaw of the gripper. Our approach can be applied to any nonpolar fluid.

Keywords: Grippers, Micro parts, Thin fluid films, Nonpolar fluids, Van der Waals forces, Casimir effect.

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