Atomic force microscopy (AFM) studies of liquid crystalline polymer (LCP) surfaces

Abstract

An atomic force microscope (AFM) operating in tapping or contact mode was used to study the surface topography and the molecular organization of Vectra-A and Vectra-B films. Large-scale (15 3 15 mm) AFM images revealed that ribbonlike fibrils with a width/height @ 1.0 are the dominant surface features of these liquid crystalline polymers (LCPs). The region of local disorder, surface debris, and interfi- brillar debris as well as possible amorphous regions were observed in both LCP samples. Large fibrils, 5.0 -10.0 mm in width, can be thought of as formed by smaller microfibrils capable of forming ordered structures. Microfibrils can bend upward, form- ing raised surface features; bend inward, originating cracks 1-2 mm wide on the film surface; or divide and subdivide into smaller units. Longitudinal and lateral stresses are believed responsible for the variation in fibril size, shape, and orientation. AFM images containing molecular-scale details showed that microfibrils consists of chains of molecules coiled around a central axis and that they can be only about 2.0 nm wide. These submicron surfaces consist of white spots (representing molecules) that can form ordered structures or that can cluster to form agglomerates distributed in a random manner. Submicron fibrils are believed to represent the LCP basic structural unit. AFM results indicate that the surface topography of Vecta-B is more ordered and uniform than is the one observed for Vectra-A. Seemingly, amorphous particles form debris on Vectra-A surfaces. Short rods oriented crosswise on the fibril surface are instead what increases the Vectra-B roughness. These LCPs can have a surface topography similar to the one observed in AFM images of a spiderweb. However, the spiderweb fibrils are formed by more uniform microfibrils that are oriented parallel to each other. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2243-2254, 1999