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Self‐assembled Dynamic 3D Fingerprints in Liquid‐Crystal Coatings Towards Controllable Friction and Adhesion
Author(s) -
Liu Danqing,
Broer Dirk J.
Publication year - 2014
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201400370
Subject(s) - coating , materials science , texture (cosmology) , azobenzene , polymer , perpendicular , adhesion , liquid crystal , substrate (aquarium) , fingerprint (computing) , surface forces apparatus , molecule , nanotechnology , composite material , crystallography , chemical physics , chemistry , optoelectronics , geometry , computer science , organic chemistry , oceanography , mathematics , computer security , artificial intelligence , geology , image (mathematics)
Abstract Chiral‐nematic polymer network coatings form a “fingerprint” texture through self‐assembly. For this purpose the molecular helix of the coating is oriented parallel to the substrate. The coating has a flat surface but when actuated by light in the presence of a copolymerized azobenzene compound, 3D fingerprint structures appear in the coating. The helix forms protrusions at the positions where the molecules are aligned parallel to the surface and withdraws at the positions where the orientation is perpendicular. This process proceeds rapidly and is reversible, that is, the fingerprint‐shaped protrusions disappear when the light is switched off. The texture in the on‐state resembles that of a human fingerprint and is used to manipulate the gripping friction of a robotic finger. The friction coefficient drops by a factor of four to five when the fingerprint switched on because of reduced surface contacts.