This work presents the preparation of cross-linking Au nanoparticle (NP) monolayer membranes by the thiol exchange reaction and their enhanced mechanical properties. Dithiol molecules were used as a cross-linking mediator to connect the adjacent nanoparticles by replacing the original alkanethiol ligand in the monolayer. After cross-linking, the membrane integrity was maintained and no significant fracture was observed, which is crucial for the membrane serving as a nanodevice. TEM (Transmission Electron Microscopy), UV-Vis absorption spectrum, and GISAXS (grazing incidence small angle X-ray scattering) were performed to characterize the nanostructure before and after cross-linking. All results proved that the interparticle distance in the monolayer was controllably changed by using dithiols of different lengths as the cross-linking agent. Moreover, the modulus of the cross-linking monolayer was measured by atomic force microscopy (AFM) and the result showed that the membrane with a longer dithiol molecule had a larger modulus, which might derive from the unbroken and intact structure of the cross-linking monolayer due to the selected appropriately lengthed dithiol. This study provides a new way of producing a nanoparticle monolayer membrane with enhanced mechanical properties.
Keywords: cross-linking; gold; monolayer; nanoparticles; self-assembly.