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.

The interfacial tension between immiscible liquids is studied as a function of a model linear surfactant length and concentration using coarse-grained, dissipative particle dynamics numerical simulations. The adsorption isotherms obtained from the simulations are found to be in agreement with Langmuir's model. The reduction of the interfacial tension with increasing surfactant concentration is found to display some common characteristics for all the values of chain length modeled, with our predictions being in agreement with Szyszkowski's equation. Lastly, the critical micelle concentration is predicted for all surfactant lengths, finding exponentially decaying behavior, in agreement with Kleven's model. It is argued that these findings can be helpful guiding tools in the interpretation of available experiments and in the design of new ones with new surfactants and polymers.

The contributions to the force on a deformable surface covered with polymer brushes can be accounted for separately.