External and internal wetting of carbon nanotubes with organic liquids

Individual multiwalled carbon nanotubes were controllably wetted by polyethylene glycol, glycerol, and water. A Wilhelmy force balance approach was used to calculate contact angles at the nanotube-polyethylene glycol and nanotube-glycerol interfaces, allowing examination of the contact angle dependence on the nanotube diameter. Water, however, exhibited a significantly larger interaction with the nanotube, which could only be explained by allowing for internal wetting of the open carbon nanotube structure. This internal wetting angle is smaller than the external one.