Deformation and capillary self-repair of carbon nanotube brushes

Brushes with nanoscale bristles, such as nanotube arrays held together by van der Waals forces, have applications as compliant electrical switches, probes and micro-scale cleaning tools. Repeated use exposes the brushes to contact and impact at high strains resulting in the bristles undergoing exfoliation, deformation and damage. We show that the damages incurred can be nearly recovered by capillary evaporation of solvents from the free standing aligned nanotube brushes. 2012 Elsevier Ltd. All rights reserved. Brushes are simple inhomogeneous, anisotropic structures that are indispensable to our everyday chores that include brushing, grooming, polishing, and cleaning of teeth, hair, shoes, vessels, floors and sidewalks. Their ubiquity in these applications derives from their functional ability to smoothly interpolate between the behavior of an individual bristle to clean a crevice and the collective behavior of a brush to sweep a surface. Indeed, as a function of their geometry and loading, they can maintain a large range of intermittent contact with surfaces, which gives wide and easy tenability of electrical, thermal and mechanical transport/contact properties [1]. For example, in cleaning and grooming applications, the individual behavior of the bristles prevent the brush from jamming or clogging easily, while in conducting applications such as in electric motor armatures, brushes are the best way to maintain low-resistance and low-friction contact between moving parts [2,3]. Since it is the geometry of the assembled brush structure that leads to its unique properties, an obvious question is if similar advantages might accrue with brushes at much smaller scales. A natural direction 0008-6223/$ see front matter 2012 Elsevier Ltd. All rights reserved http://dx.doi.org/10.1016/j.carbon.2012.06.025 * Corresponding author. E-mail address: [email protected] (V. Pushparaj). towards this is afforded by self-assembled carbon nanotube structures consisting of tens of thousands of nanotubes oriented in parallel that can be synthesized quite readily over areas of square millimeters with length reaching millimeters [4]. Since the structure of these aligned arrays of nanotubes resembles that of macroscopic brushes that we use in daily life; we will use the terminology of nanobrushes from now on to characterize these structures. The differences between macroscale brushes and the nanotube brushes are in the dimensions of individual bristles and how they are held together. Macroscale brushes have macroscale bristles that are held together or embedded in a common support. In nanobrushes, the individual nanotubes are weakly entangled physically along their entire length and the intermittent contact if any, rises from the presence of short range van der Waals forces holds them together (Fig. 1a), hence nanobrushes are free standing structures. In the structure we describe here, the bristles are made of multiwalled nanotubes that have a distribution of diameters depending on the conditions used during growth. The