Torsional Noise of a Colloidal Probe in Contact with Surface-Grafted PEG Layers

Surface coatings modify the interaction between microparticles and surfaces. To analyze the effect of a PLL-g-PEG surface coating on the sticktion of a microparticle, we analyzed the torsional Brownian fluctuations of a colloidal probe attached to an atomic force microscope (AFM) cantilever. Results obtained with uncoated surfaces indicate that the torsional oscillation due to noise was only weakly affected by hydrodynamic effects. Upon mechanical contact, however, the uncoated probe stuck to the uncoated surface. Coating probe or surface with a PLL-g-PEG brush polymer reduced the lateral interaction (sticktion and friction) of the colloidal probe. For such a combination, the torsional fluctuations persisted during mechanical compression of the brush layer. The results demonstrate that a PLL-g-PEG coating can effectively reduce the lateral interaction of a microparticle with a surface and prevent sticktion.