Strain-driven self-rolling of hybrid organic–inorganic microrolls: interfaces with self-assembled particles

Strain driven micro and nanoroll fabrication is generally restricted to multilayer and multiprocessing systems, limiting the ability to exploit self-organization at different length scales. We have designed a hybrid organic–inorganic single-layered film with a surface that responds selectively to external stimuli, resulting in mechanical strain and self-rolling in one-step fabrication. The scrolling is initiated by water and any aqueous solution of molecules or colloidal particles. During scrolling, the different species in solution remain entrapped in the rolls; the constrained environment at the interface of the roll walls pushes the particles to organize into ordered structures. We used this rolling process to create self-assembled hybrid films with well-ordered layers of gold nanoparticles and opals of polystyrene nanospheres. These films also respond selectively to solvents, allowing the easy release of molecules/particles entrapped at the interface. Researchers from Japan and Italy have devised a one-step strategy to roll single-layer films into microtubes. Films of materials ranging from metals to semiconductors to polymers have previously been rolled up. They typically consist of two or more mismatched layers, so that the scrolling process relies on the strain between layers. The researchers have now prepared a self-rolling single-layer film by ‘sol–gel’ synthesis of a glycidoxy-organosilane derivative in basic conditions, spin-coating of the product obtained on a silica substrate and subsequent drying. The bottom part of the film formed, less condensed than its upper counterpart, takes up water preferentially. Simply dipping it in water creates a strain that is sufficient to provoke scrolling. Species such as molecules or particles can be trapped within the resulting microtubes, whose diameters are controlled by adjusting the processing conditions. This simple and convenient method may facilitate preparation of rolls for functional materials. Strain-driven micro- and nanorolls fabrication is generally restricted to multilayer and multiprocessing systems, which limit the possibility of exploiting the self-organization at different length scales. We have designed a hybrid organic–inorganic film whose surface shows a selective response to external stimuli, which induces mechanical strain and self-rolling in one-step–one-layer fabrication. The scrolling is initiated by water and any aqueous solution that also contains molecules or colloidal particles. During scrolling, the different species in solution remain entrapped in the rolls, giving rise to functional microrolls.