Invitation to a seminar by Prof. Jan Genzer, Elected Fellow of the American Physical Society and co-director of the NSF Research Triangle Materials Research Science & Engineering Center (NC State, Duke and UNC)

Topic of the seminar is: Spontaneous vs. on-demand degrafting of polymer brushes and organosilane monolayers from silica surfaces

Abstract:

We discuss spontaneous degrafting of polyelectrolyte brushes and on-demand degrafting of polymer grafts and organosilane monolayers from silica surfaces.  We show that spontaneous degrafting occurs in strong and weak polyelectrolyte brushes via hydrolysis of ester or amide linkers in the initiator molecule due to mechanical tension in the grafted chains.  Sources of tension include high grafting density of polymer brushes on the surface (σ) as well as swelling and electrostatic repulsion associated with increasing degree of deprotonation (α) of repeat units in weakly charged polyelectrolyte brushes.  We also present a method for on-demand degrafting of polymer grafts and small molecules by using tetrabutyl ammonium fluoride (TBAF).  We employ this technique to determine the molecular weight distribution of polymer grafts prepared by surface-initiated controlled radical polymerization on flat silica supports.  We also demonstrate the application of TBAF for creating spatial degrafting patterns of polymers and organosilane modifiers on silica substrates.  Desired in-plane patterns in polymer brush layers in millimeter scale are created by using a microcontact printing TBAF with a stamp made of agarose gel.  Position-dependent gradients of the degrafted areas are formed by dipping substrates featuring homogeneous coatings into TBAF solution.  The use of TBAF for degrafting is appealing because it cleaves selectively Si-O bonds, does not alter chemically the structure of the degrafted moieties, and activates hydroxyl groups on silicon surfaces to enable deposition of organosilane-based initiators for growth of fresh polymer brush layers and organosilane monolayers.  The reusability of the substrate allows us to create a diblock copolymer brushes on selected portions of the substrate not exposed to TBAF while decorating the TBAF-treated sections of the substrate with homopolymer brushes.