Mechanical response of a surface of increasing hardness covered with a nonuniform polymer brush: a numerical simulation model

Abstract

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

Polymer Chains of a Large Persistence Length in a Polymer Brush Require a Lower Force to Be Compressed Than Chains with a Short Persistence Length

“…Experiments − and numerical simulations , show that the thickness of the brush ( L ) determines the shape of the force profile. To obtain L , the average thickness of the brush made up of chains of three lengths is obtained from the first moment of the density profiles of all the chains’ beads along the direction of the compression, ρ­( h ), defined as follows …”

“…If the brush is made up of chains of different chemical compositions, as is the case in stimuli-responsive polymers or “smart polymers”, , the solubility of the chains in the solvent will play a role on the force applied by the tip of the AFM probe. The influence of the substrate’s stiffness on the compression force has been studied before, and it is found that if the properties of the brush are kept constant, a stiffer substrate requires a larger compression force. This effect, which is in agreement with intuition and experiments, shows that a polydisperse brush does not absorb or diffuse the stiffness of the substrate, which propagates through the fluid to the AFM tip .…”

“…The influence of the substrate’s stiffness on the compression force has been studied before, and it is found that if the properties of the brush are kept constant, a stiffer substrate requires a larger compression force. This effect, which is in agreement with intuition and experiments, shows that a polydisperse brush does not absorb or diffuse the stiffness of the substrate, which propagates through the fluid to the AFM tip . However, in this work, we kept the substrate’s stiffness fixed so that the effect of the varying persistence length could be borne out clearly.…”

“…Regarding the AFM experiments on cancerous and healthy human cervical epithelial cells that inspired this work, − our conclusions suggest that the reported softener nature of cancerous epithelial cells compared with that of normal epithelial cells may also be a response of the brush stiffness. It has been shown , that if the properties of the brush are not modified, increasing the stiffness of the grafting surface only increases the force required to compress the brush. Therefore, it is possible that in cancerous cells covered by polymer-like protrusions, their softener nature compared with that of normal cells under compression may be due to the stiffening of the brush, rather than a stiffening of the surface.…”