Stick−Slip Phenomenon in Measurements of Dynamic Contact Angles and Surface Viscoelasticity of Poly(styrene-b-isoprene-bstyrene) Triblock Copolymers

摘要

In this paper, a series of poly(styrene-bisoprene-nb-styrene) triblock copolymers (SIS), with differentnchemical components, was synthesized by anionic polymerization.nThe relationships between surface structures of thesenblock copolymers and their stick−slip phenomena wereninvestigated. There is a transition from stick−slip to a closelynsmooth motion for the SIS films with increasing PS content;nthe patterns almost vanish and the three-phase line appears tonmove overall smoothly on the film surface. The results shownthat the observed stick−slip pattern is strongly dependent onnsurface viscoelasticity. The jumping angle Δθ, which is definednas θ1 − θ2 (when a higher limit to θ1 is obtained, the triple linen“jumps” from θ1 to θ2 with increases in drop volume), was employed to scale the stick−slip behavior on various SIS film surfaces.nScanning force microscopy/atomic force microscopy (AFM) and sum frequency generation methods were used to investigate thensurface structures of the films and the contributions of various possible factors to the observed stick−slip behavior. It was foundnthat there is a linear relationship between jumping angle Δθ and the slope of the approach curve obtained from AFM forcenmeasurement. This means that the stick−slip behavior may be attributed mainly to surface viscoelasticity for SIS blockncopolymers. The measurement of jumping angle Δθ may be a valuable method for studying surface structure relaxation ofnpolymer films.