Effect of composition and structure of gold/copper bimetallic nanoparticles on dispersion in polymer thin films

The effect of composition on the dispersion of AuxCu1-x bimetallic nanoparticles into a nylon 11 matrix has been investigated. TEM, UV-VIS, EDX, and XPS depth profiling were used for characterizing the changes in the composition of the bimetallic particles and the depth distribution of the particles in the nylon 11 layer caused by annealing in an N-2 atmosphere. TEM observation and EDX analysis revealed that island-like bimetallic particles were formed on the nylon 11 surface before annealing, the composition of which was systematically controlled. Upon annealing in an N-2 atmosphere, the AuxCu1-x bimetallic particles with x less than or equal to 0.55 were not dispersed into the nylon 11 layer while those with x greater than or equal to 0.70 were homogeneously dispersed in the films, indicating the existence of a critical composition for penetration of the bimetallic particles. By comparing the composition and structure of the bimetallic particles, the cause of these finding is discussed in terms of the surface free energy of the particles, which can be varied with their composition by the effect of alloying.