No abstract

The force on a polydisperse polymer brush with chains of increasing persistence length, L P , is obtained by numerical simulations. Unexpectedly, the force needed to compress a stiff brush is smaller than that for a soft brush. This is due to the ordering of the largest polymer chains in bundles, which buckle when L P grows releasing pressure, thus reducing the force. Stiffer brushes lose translational entropy, increasing the entropy of the solvent. Our predictions agree with optical tweezer force spectroscopy and ellipsometry measurements on polymer brushes. Clues for the interpretation of experiments on human cervical epithelial cells that are covered with polymer-like brushes are offered, which find that cancer cells are softer than normal ones.