Dynamic atomic force microscopy methods

We investigated the influence of the relative humidity on amplitude and phase of the cantilever oscillation while operating an atomic force microscope (AFM) in the tapping mode. If the free oscillation amplitude A0 exceeds a certain critical amplitude Ac, the amplitude- and phase-distance curves show a transition from a regime with a net attractive force between tip and sample to a net repulsive regime. For hydrophilic tip and sample this critical amplitude Ac is found to increase with increasing relative humidity. In contrast, no such dependence was found for hydrophobic samples. Numerical simulations show that this behavior can be explained by assuming the intermittent formation and rupture of a capillary neck in each oscillation cycle of the AFM cantilever.

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Capillary forces in tapping mode atomic force microscopy

An outstanding aspect of pharmaceutical nanotechnology lies in the characterization of nanocarriers for targeting of drugs and other bioactive agents. The development of microscopic techniques has made the study of the surface and systems architecture more attractive. In the field of pharmaceutical nanosystems, researchers have collected vital information on size, stability, and bilayer organization through the microscopic characterization of liposomes. This paper aims to compare the results obtained by atomic force microscopy, environmental scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy to point out the limits and advantages of these applications in the evaluation of vesicular systems. Besides this comparative aim, our work proposes a simple confocal laser scanning microscopy procedure to rapidly and easily detect the liposomal membrane.

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AFM, ESEM, TEM, and CLSM in liposomal characterization: a comparative study.

Supramolecular organization in block copolymers containing a conjugated segment: a joint AFM/molecular modeling study

Biodegradable nanocomposites were successfully fabricated from cellulose acetate (CA) plasticized with triethyl citrate (TEC), and combined with Cloisite 30B organoclay, using maleic anhydride grafted cellulose acetate butyrate (CAB-g-MA) as the compatibilizer. The nanostructure of the nanocomposites was investigated by AFM, TEM, and XRD. AFM analysis clearly showed the presence of exfoliated clay platelets in the nanocomposite. Nanocomposites with 5 wt % compatibilizer contents showed better-exfoliated structure than the counterpart without compatibilizer hybrid. The clay platelet polygonal shape was observable by AFM. The exfoliated platelets were characterized to be ∼1.3 nm in thickness, ∼500 nm in width, and ∼800 nm in length. These results correspond to the XRD and TEM analysis. It was showed that the mechanical properties were improved due to good exfoliation and dispersion of clay in the plasticized CA matrix. The 5 wt % compatibilizer loading is optimum for mechanical improvement.

Effect of Compatibilizer on Nanostructure of the Biodegradable Cellulose Acetate/Organoclay Nanocomposites

In atomic force microscopy, tapping-mode (also called intermittent contact mode) operation is known for its ability to image soft materials without inducing severe damage. For soft materials, the determination of the relative contributions of the topography and the local mechanical properties to the recorded image is of primary importance. In this paper, we report a systematic comparison between images and approach−retract curve data. We show that this experimental comparison allows the origin of the contrast that produces the image to be straightforwardly evaluated. The method provides an unambiguous quantitative measurement of the contribution of the local mechanical response to the image. To achieve this goal, experimental results are recorded on a model system, a triblock copolymer, with a nanophase separation between elastomer and glassy domains. In this particular case, we show that most of the contrast in the height and phase images is due to variations of the local mechanical properties.

Quantitative Measurement of the Mechanical Contribution to Tapping-Mode Atomic Force Microscopy Images of Soft Materials

This work is an attempt to investigate viscosities at the nanometer scale To do so, the tapping mode atomic force microscopy is used on a triblock copolymer exhibiting a well-defined periodic structure at the nanometer scale Variations of the oscillator amplitude and phase delay as a function of the tip-sample distance are recorded on the glassy and rubbery domains of the copolymer The experimental data are compared to analytical expressions derived from Stokes law In the present study, among the different possible expressions of the viscous forces depending on the tip shape and on the experimental length scale, only a force proportional to the indentation depth is able to describe the experimental data In this particular case, quantitative measurements are possible Finally, the oscillator is shown to be sensitive to local variations of the viscosity within few nanometers

S. Kopp-Marsaudon

Papers

Quantitative Measurement of the Mechanical Contribution to Tapping-Mode Atomic Force Microscopy Images of Soft Materials

Experimental determination of the viscosity at the nanometer scale on a block copolymer with an oscillating nanotip

Dynamic force microscopy analysis of block copolymers: beyond imaging the morphology