Atomic Force Microscopy in Analysis of Polymers

Abstract

Atomic force microscopy (AFM), in which a sharp probe is employed for profiling surfaces with unique resolution, has developed into an invaluable multidisciplinary technique for advanced characterization of polymer materials. In its basic function, AFM provides high‐resolution imaging of surface structures between the scales of a few nanometers to hundreds of micrometers. This capability is useful for quantitative analysis of surface microroughness of technological surfaces with high sensitivity and accuracy. The direct visualization of polymer structures, from single macromolecules to granular and lamellar nanostructures, to microphase separation and other morphologic patterns, makes AFM an important complementary tool for many of the techniques (light scattering, chromatography, optical and electron microscopy, X‐ray diffraction analysis, etc.) employed in polymer analysis. The advances in AFM of polymers are related to a better understanding of tip–sample force interactions and their use for examination of local sample properties. Different responses of the probing tip to surface locations with different mechanical and adhesive properties are the key for compositional imaging of heterogeneous polymer systems. Compositional mapping with AFM, which does not require any special sample treatment, substantially enhances its microscopic value. Visualization of individual components in block copolymers, polymer blends and semicrystalline materials can be performed with nanometer resolution. In addition to lateral compositional imaging, AFM probing of subsurface structures can be achieved for polymer samples with rubber‐like top layers. A further expansion of AFM applications is expected with the imaging of polymers at different temperatures. Monitoring of polymer structural changes at thermal phase transitions could help in the understanding of polymer melting, crystallization, recrystallization, glass transition and physical aging. In such applications, AFM will complement various thermal techniques. The review describes the basics of AFM, practical aspects of its applications to polymers and presents a broad range of examples illustrating the main trends in AFM of polymer materials.

Surface energetics, dispersion, and nanotribomechanical behavior of POSS/PP hybrid nanocomposites

“…The distance between the extending and retracting friction curves is a qualitative measure of the friction between the probe and the surface. 36 Surface friction measurements were conducted at a fixed scan rate of 1 Hz, consistent with methods commonly reported in the literature for polymer samples. 30,36 POSS nanocomposites exhibit reduced relative friction in comparison to the neat polymer, with friction decreasing as a function of increasing POSS concentration.…”

“…In same cantilever is employed to obtain the measurements. 30,36,38 The samples were imaged in tapping mode after LFM measurements to ensure that surfaces were not damaged during the friction studies, and no artifacts were observed on the images. Additionally, AFM probes were imaged via SEM after surface friction measurements to ensure that there were no visible changes to the geometry of the probe during scanning.…”

Bacillus atrophaeus Outer Spore Coat Assembly and Ultrastructure

“…Secondly, the AFM imaging parameters and tip sharpness are pivotal, interactions. 43 However, resolution was greatly enhanced during imaging of polymer samples by hard tapping applying a considerably decreased A sp /A o ratio. 43,47 Tip-sample force interactions are dependent on the sharpness and overall shape of the AFM probe.…”

“…43 However, resolution was greatly enhanced during imaging of polymer samples by hard tapping applying a considerably decreased A sp /A o ratio. 43,47 Tip-sample force interactions are dependent on the sharpness and overall shape of the AFM probe. Commercial AFM probes can be dull or can become dull during imaging due to wear or contamination with debris.…”

“…In tapping mode virtually no lateral forces are applied to the sample during imaging, 43 which makes it the preferred approach to probe biological structures at high resolution.…”