(209g) Surface Pressure and Microstructure of Carbon Nanotubes Adsorbed at an Air-Water Interface
Particles of appropriate size and wettability adsorb strongly at fluid-fluid liquid interfaces, lowering the interfacial energy and thereby stabilizing emulsions and foams. In this presentation, we will report the surface pressure and microstructure of two different types of carbon nanotubes (CNTs) at an air-water interface; namely as-produced CNTs (nf-CNTs) and CNTs functionalized with carboxyl groups (f-CNTs)1. Both types of CNTs formed 3D aggregates at the interface upon compression. However, f-CNTs showed less degree of aggregation compared with nf-CNTs. This is attributed to the deprotonation of the carboxyl groups within the water subphase, leading to additional electrostatic repulsion between f-CNTs. At high compression, f-CNTs formed aligned CNT domains at the interface. These 2D domains resembled 3D liquid-crystalline structures formed by excluded volume interactions. The denser packing and orientational ordering of f-CNTs also contributed to a compressional modulus higher than that of nf-CNTs. The actual coverage of CNTs during compression was back calculated from the Volmer equation of state and was in agreement with the value obtained independently from optical micrographs. The findings of this work may have a broader impact on understanding the assembly and collective behavior of rod-like particles with a high aspect ratio at an air-water interface. This work is supported by NSF CAREER award #1253613.
(1) Vora, S. R.; Bognet, B.; Patanwala, H. S.; Chinesta, F.; Ma, A. W. K. Surface Pressure and Microstructure of Carbon Nanotubes at an Air–Water Interface. Langmuir 2015.