CONTROLLABLE SELF-ASSEMBLY BASED ON INTERACTION OF BORONIC ACIDS AND DIOLS

Abstract

<p>The interaction of boronic acid with diols is reversible and pH-dependent. Boronate groups are able to form complex with 1,2- diol or 1,3-diols at pH values above 9. Therefore, the unique property of boronic esters was employed to exploit controllable self-assembly by three independent mechanisms, each of which is independent of the other two. The three interaction mechanisms are 1) electrostatic attraction between positive polymers and negative surfaces. 2) Polyethylene glycol (PEG)—phenolic polymer complex formation, which is one type of hydrogen bonding. 3) Phenylboronate (PBA) binding to polyols.</p> <p>To exploit these interactions, families of water-soluble and bifunctional copolymers containing pairs of non-interacting groups were prepared and characterized. Characterization includes structure, molecular weight, composition, etc. These bifunctional polymers can specifically interact with two other types of polymers/surfaces. Therefore, it provides a possibility to prepare complex assemblies by using multiple polymer/polymer interactions in one step.</p> <p>The utility of multiple, independent interactions was demonstrated by formation of self-assembled multilayer thin films on both silicon wafers and polystyrene latex particles. Moreover, the formation of well-defined nanoparticle aggregates with three different sizes of polystyrene latex particles was studied to extend the application of controllable self-assembly by multiple interactions. The assembly structures of multilayers and latex aggregates were controllable by adjusting the pH and addition of competitive small molecules.</p> <p>In addition to the study of multilayer self-assembly, a new approach for controllable deposition of latex nanoparticles on surfaces was also exploited. Regenerated cellulose films were chemically modified to fabricate the cellulose films bearing surface phenylboronic acid groups (cellulose-PBA). The poly(glycerol monomethacrylate)- stabilized polystyrene (PGMA-PS) latex particles were used to have reversible, pH-dependent adsorption onto the cellulose-PBA by the interaction of boronic acids and diols. Specific adsorption of PGMA-PS onto cellulose-PBA was observed at pH 10.5, whereas the latex particles were removed at pH 4.</p>