Abstract
Due to the adhesion between the polymer melt and nickel (Ni) mold insert in the micro injection molding process, deformation defects frequently occur when the microstructures are demolded from the insert. In this study, self-assembled alkanethiols were applied to modify the surface of Ni mold insert to reduce its surface energy. Experimental trials were undertaken to explore the effect of alkanethiols coating on the replication quality. After that, molecular dynamics (MD) simulation was then used to investigate the adhesion behavior between the self-assembled coating and polypropylene (PP) by establishing three different types of alkanethiol material. The interaction energy, the potential energy change and radial distribution function were calculated to study the anti-adhesion mechanism. Experimental results show that all the three coatings can effectively decrease the adhesion and therefore promote the replication fidelity. It is demonstrated in MD simulation that the adhesion mainly comes from the van der Waals (vdW) force at the interface. The arrangement of sulfur atom on the Ni surface results in different absorbing behaviors. Compared with that of the PP–Ni interface, the interfacial energy and adhesion work after surface treatment is significantly reduced.
Highlights
Devices with micro/nano structures, which are widely used in adaptive optics [1], anti-counterfeiting coatings [2], bionic surface [3] and microfluidic chips [4] are playing an important role in the development of modern science and technology
The results showed that the surface coating improved the molding quality of microstructures in replication fidelity, aspect ratio and surface roughness
The molecular chains in the PP–DDT and PP–PFDT interfaces were close to the self-assembled surface, while such a phenomenon was not observed in PP–DT interface
Summary
Devices with micro/nano structures, which are widely used in adaptive optics [1], anti-counterfeiting coatings [2], bionic surface [3] and microfluidic chips [4] are playing an important role in the development of modern science and technology. Zhang et al [13] studied the effect of mold surface roughness on the cavity filling of polymer melt in micro injection molding. Nanomaterials 2021, 11, 1834 the demolding force of different materials and the surface roughness of the mold insert during the demolding process. Yoon et al [16] studied the effect of deposition of FOTS coating on the surface of Si mold insert on the microstructure array parts in an injection molding process. Kwon et al [17] studied the effect of thickness of self-assembled FOTS coating on the imprinting quality by a molecular dynamics method. Many studies on surface modification have been undertaken, the modification mechanism in micro/nano-scale, especially the interfacial interaction between the substrate and the coating layer, still needs much more investigation. The anti-adhesion mechanisms of the polymer-alkanethiols interface in different arrangements were explored by analyzing the morphological evolution, potential energy, interaction energy, adhesion work and the radial distribution function at the interface comprehensively
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