Entropic death of polyelectrolyte brushes: chain stretching, bond scission and surfactant complexation. Oberflächenchemie und -physik von Mikrosystemen Bd. 16 # Pb., 186 S. Großformat, 81 Abb., 14 Tab.
Chemically modified surfaces are present in our daily life, from low friction coatings to more sophisticated surfaces with specific biological properties. These tailor-made surfaces can be generated with organic coatings like polymer brushes, where polymer chains are bound to the surface at high grafting densities. In this situation, where the conformational entropy per chain decreases and a high elastic energy is stored in the system, small amounts of additional energy supplied to the polymer chains can lead to a homolytic cleavage of main chain covalent bonds. This results in a degrafting/reduction of the molecular weight of the brush chains, after which, the cleaved off chains recoil, regain their entropy and thus reduce their energy; which represent the "entropic death" of polymer brushes. This work shows how this phenomenon of polymer brushes can be controlled by their intrinsic parameters such as graft density, molecular weight and degree of charging, as well as by the solution properties like temperature and polymer-solvent interactions. This last parameter is studied in detail through the formation of polyelectrolyte brushes-surfactant complexes. Based on this, hydrophobic microstructures are generated on top of a hydrophilic layer.
Kimberly Simancas studied polymer engineering at the University Simón Bolívar in Caracas (Venezuela), where she obtained her Engineering degree in 2005. After finishing a Master in Biomaterials at the University Paris-Nord Paris XIII (France) in 2006, she joint the laboratory of Prof. Jürgen Rühe at the Institut of Microsystems Engineering of the University of Freiburg (Germany), for her Ph.D. thesis on the stability of polyelectrolyte brushes.