| Polymer brushes, in particular, are formed when long-chain polymer molecules are attached at one end to an interface. When the spacing between attachment points is less than the polymer chain's radius of gyration, Rg, the chains overlap and are forced to stretch away from their attachment points to decrease crowding. This stretching along the direction normal to the grafting surface is different from the typical behaviors of flexible polymer chains in a solution and with wide application potential for modifying interfacial properties such as wetting, adhesion and lubrication. The stability or durability of the polymer brush layer was directly influenced by the surface coverage which will constrain the practical application. In standard grafting-to methods, the polymers were grafted on the surfaces by physical adsorption or covalent bonding of end-tailed functional group and the coverage is limited by the steric obstacle of the polymer itself during the process. In this work the force profiles of a series of moderate to high grafting density diblock copolymer brushes prepared by the spin-coating method are reported. Instead of accessing different grafting density regimes by changing the molecular weight (MW) of the blocks, a single diblock was used. Two distinct compression regimes were observed. The measured force profiles demonstrate scaling behavior and discrepancies between the experimental data and theory are discussed. To further explore the interactions between more highly-stretched brushes, the neutral Polystyrene (PS) films prepared by grafting-from method was also studied using surface force apparatus (SFA). Both the normal and shear force behaviors of the opposing ATRP-formed brushes are presented. Excellent lubricant performance was also observed. |
