Crystal-Orientation Control for Improving Adhesion and Wettability at PEEK-Resin/Al<sub>2</sub>O<sub>3</sub> Interface

The adhesion strength and wettability at the interfaces between a polyetheretherketone (PEEK) resin and aluminum oxide (Al2O3), which have become more and more important for direct joining of PEEK resin and aluminum (Al), is investigated by using molecular simulations. Especially, the dependence of the adhesion strength and wettability on crystal orientations of sapphire Al2O3 were focused on to realize strong joint between the PEEK resin and Al2O3. By placing a PEEK-resin sphere on a sapphire Al2O3 surface and by heating the system to 650 K, the contact angles at the interfaces were calculated to evaluate the wettability. After the system is cooled to 300 K from 650 K, the adhesive fracture energy is calculated to evaluate the adhesion strength. The results of the contact angles showed that PEEK resin on the Al2O3 (10-10) and that on the Al2O3 (11-20) surface have low wettability with large contact angles. On the other hand, PEEK resin on the Al2O3 (0001) surface has high wettability with a small contact angle. The results of the adhesive fracture energies showed that the adhesion at the PEEK-resin/ Al2O3 (10-10) and PEEK-resin/ Al2O3 (11-20) interfaces are weak. On the other hand, the adhesion at the PEEK-resin/ Al2O3 (0001) interface is extraordinarily strong. To clarify the reason that the higher wettability and higher adhesion strength are obtained at the PEEK/Al2O3 (0001) interface, atomic configurations were visualized. The atomic configuration showed that the lattice-matched coherent interface and high surface atomic density is realized only at the PEEK/Al2O3 (0001) interface. Therefore, the lattice matching and the high surface atomic density at the PEEK/ Al2O3 (0001) interface are considered to be dominant factors in the high wettability and strong adhesion. The experimental results show that the wettability and critical load of scratch tests increase in the order: PEEK/Al2O3(10-10)< PEEK/Al2O3(11-20)<< PEEK/Al2O3 (0001).