Combined effect of oxidative treatment and residual alcohol on the mechanics of a multiwalled carbon nanotube laden interface

Single and multiwalled carbon nanotubes (SWCNT & MWCNT) have been investigated over the past three decades because of their excellent properties, including their mechanical strength and large electrical and thermal conductivities. Incorporating CNTs into consumer and industrial products is challenging because of strong attractive interactions, heterogeneity, and lack of separation techniques for these nanomaterials. Further challenges include those associated with CNT interaction and adsorption to interfaces. In the present work, the properties of an air/water interface laden with industrial grade MWCNTs with systematically varied oxidative treatment in nitric acid were measured. The duration of treatment was varied and the surface pressure of the nanotube laden interfaces was measured. Results suggested that film stiffness increased with treatment duration in the presence of residual isopropyl alcohol. However, these measurements revealed that stiffness increased with compression number, suggesting that treatment duration had an indirect effect and compressive history was primarily responsible for changes in interfacial mechanics. Additionally, optical micrographs showed evidence of buckling in the films at low modification times. Relaxation of a compressed interface showed that MWCNTs with longer oxidative treatments induced longer relaxation times. These data suggest MWCNT films densify particle-particle contacts at higher modification times, with relaxation occurring through diffusive microstructural changes. One potential physical mechanism for such behavior is that MWCNT aggregate due to capillary interactions brought on by stronger adsorption to the interface in the presence of residual alcohol and longer oxidative treatment.