AFM enables direct visualization of membrane pore size, pore distribution, and surface roughness. These measurements are critical for optimizing membranes used in vital processes such as safe drinking and waste water filtration, desalination, the manufacture of high-performance batteries, and biomedical devices.

An example of this is shown in figure 3, which shows two membranes, both made from polycaprolactone but in which the inclusion of nanoparticles in the polymer membrane leads to a radical change in pore shape and size, and a roughening of membrane surface. Indeed, membrane roughness has been measured using AFM in a number of different systems. ^(9,10,11,12)

Figure 3. Images of two polymeric membranes showing the difference in structure when nanoparticles are included (right), compared to the simple membrane (left). In the left image, the pores are reproducible in format, compared to the highly variable shape in the membrane on the right. Quantitatively, the nanoparticle - containing membrane was also shown by the AFM to be significantly rougher. Images provided compliments of the author. Original work published in: M.H. Mruthunjayappa et al.⁽¹²⁾

AFM is particularly well suited for characterizing electrically insulating polymer membranes, which can be difficult to analyze using electron microscopy. By providing quantitative three-dimensional measurements of surface roughness, pore morphology, and membrane structure with minimal sample preparation, AFM enables researchers to optimize membrane performance across a wide range of applications. AFMWorkshop systems have been used to characterize polymeric membranes for lithium-ion batteries ^{(13, 14)}. AFM is also useful to characterize polymeric membranes under development for desalination ⁽⁹⁾ and distillation ⁽¹⁵⁾, as well as for general filtration, especially nanofiltration ⁽¹⁶⁾, where the ultrahigh resolution of AFM makes it an indispensable tool.

AFM provides a quantitative method for monitoring polymer degradation by measuring changes in surface roughness and morphology over time. Unlike many imaging techniques, AFM produces numerical roughness values that can be directly correlated with weathering, abrasion, or chemical exposure. ^(14,17,18)

Figure 4 shows the effect of exposure to sand abrasion over several days on two different polymers. Displaying the images on the same scale makes the effect of weathering very clear. Roughness values can also be used to quantify the effect. In this case, roughness initially increased upon weathering and then decreased with more weathering due to a filling-in effect. In a similar way degradation of polymeric dental materials has been analyzed with AFM, after exposure to acidic drinks ⁽¹⁸⁾.

Figure 4. AFM height images showing the effect of abrasion by sand on a PET plastic surface. Images adapted from Aghilinasrollahabadi et al. ⁽¹⁹⁾

AFM phase imaging enables researchers to distinguish and measure individual polymer domains in polymer blends by detecting differences in stiffness and viscoelastic behavior, providing quantitative information about blend morphology, domain size, and distribution.

Phase imaging is particularly useful for characterizing polymer blends because differences in the mechanical and viscoelastic properties of the constituent polymers produce measurable phase contrast. This contrast allows researchers to visualize the distribution and morphology of individual polymer phases at the nanoscale.

Polypropylene (PP) and polyethylene (PE) blends illustrate this application. Because PP and PE have significantly different elastic moduli and viscoelastic properties, the AFM probe experiences distinct phase shifts as it interacts with each polymer, producing contrast between the two phases.

• 75% PP / 25% PE Blend -In a 75% PP / 25% PE blend, phase imaging typically reveals a continuous matrix of the stiffer polypropylene containing discrete, circular domains of softer polyethylene. AFM phase imaging provides clear contrast between the two polymers, allowing researchers to characterize domain size, shape, and distribution—properties that can influence the blend’s mechanical performance, including impact resistance.
• 50/50 PP / PE Blend - As the composition approaches a 50/50 ratio, the morphology can transition from a “sea-island” structure to a co-continuous network. Phase imaging enables researchers to visualize the complex interpenetrating structures of the two polymers and evaluate how mixing conditions and thermal history influence the final morphology and structural integrity.

Figure 5. Circular phase domains in a 75% PP / 25% PE blend showing many features in the phase image not visible in the height data.

A: topography, 20x20 μm scan, height scale 177 nm and

B: corresponding phase image.

C: topography, 8x8 μm scan, height scale 232 nm and

D: corresponding phase image.

Optimizing Polymer Blend Performance

AFM phase imaging can help researchers evaluate compatibilizers and optimize polymer-processing parameters by directly visualizing changes in nanoscale blend morphology. This information can be used to develop polymer blends with targeted mechanical properties and improved performance.

The HR AFM includes the AFM Stage, control electronics, and software for high resolution scanning.
AFMWorkshop offers several vibration solutions, and installation packages.