Use of hydrogen bonded layer-by-layer assemblies for particle manipulation

With the constant progress in miniaturization of systems and devices, the manipulation of µ-objects is becoming increasingly important. Chemical functionalization is a promising way to improve this manipulation, in particular multilayer polymer films based on hydrogen bonds can allow to achieve reversible adhesion of µ-objects. To prepare such hydrogen-bonded Layer-by-Layer (LbL) films, poly(ethylene glycol) (PEG), poly(acrylic acid) (PAA), Tannic acid (TA) and Poly(N-isopropylacrylamide) carboxylic acid-terminated (PNIPAM) were selected due to their hydrogen donor or acceptor properties. The growth of these films was originally confirmed by in situ optical reflectometry. Their erasability was also investigated by exposure to an aqueous solution with a pH gradient. Depending on the polymer couple, the pH of disintegration was adjusted from an acidic to a basic medium. The surface roughness was also affected by the building block of the LbL architecture since a rougher surface was recorded for PEG/TA than for PEG/PAA. To mimic the manipulation of an object, adsorption and desorption of a model object (silica particles) was carried out onto a LbL film. Two approaches were employed: optical reflectometry as an indirect method and optical microscopy for direct visualization. For both analyses, particles of different sizes could be adsorbed onto a PEG/PAA or PAA/PNIPAM film. Finally, a complete desorption of the particles was recorded due to the disintegration of the LbL film when the pH was increased. [Display omitted]