The Mechanism and Feasibility of Self-Assembly with Capillary Force

This paper introduces a fluidic technique based on patterned shapes of hydrophobic self-assembly monolayers (SAMs) and capillary forces to self-assemble micro-parts onto substrates. Self-assembly is defined as a spontaneous process that occurs in a statistical, non-guided fashion. More specifically, the fluidic self-assembly with capillary force is driven by the gradient in interfacial free energy when a micro-part approaches a substrate binding site. In this paper, the mechanism of self-assembly with capillary forces is proposed. The hydrophobic-hydrophilic material system between the binding sites and micro-parts is then simulated. Finally, the surface energy of a self-assembling system in the liquid phase under different conditions is calculated. The results show that shift, twist, lift and tilts displacements are detected to be rather uncritical and the system turns out to be rather stiff with respect to such displacements. The theoretical result is supported by the experiments and gives quantitive explanations why and how the capillary force works in the self-assembly process.