Interaction forces and lubrication of dendronized surfaces

Dendron brushes provide excellent opportunities to tune mechanical properties of interfacial layers. Compared to linear brushes the dendronic version is more compact and thus gives more steep repulsive barriers upon brush overlap. Provided that the range is sufficient to overcome the Van der Waals forces, the many free ends may be used to functionalize the colloidal particles for 'smart' delivery applications. Brushes show little interpenetration upon lateral compression and therefore brushed surfaces feature low friction coefficients. Dendron brushes have comparatively lower interpenetration lengths and hence are expected to protect surfaces even better against wear. We argue that one can still improve on this: when the free ends of star-like or dendronic molecules are (chemically) linked to each other to form a brush with a peripheral layer of macrocycles, the interpenetration length is even less. The latter is shown to be the case in recent computer simulations and is reproduced here using the numerical self-consistent field method. We conclude that the role of branching of molecules, possibly in combination with charges in the brush, should be further investigated to come to a deeper understanding of lubrication and wear protection in aqueous media. The recent progress that is reviewed below has a small bias to theoretical developments. It contains solid stepping stones for more systematic experimental verifications and detailed computer simulations. (C) 2016 Elsevier Ltd. All rights reserved.