Quantitative Nanomechanical Mapping Mode Research Articles

Quantitative Elasticity Mapping of Submicron Silica Hollow Particles by PeakForce QNM AFM Mode.

Silica hollow spheres with a diameter of 100-300 nm and a shell thickness of 8±2 nm were synthesized using a self-templating amphiphilic polymeric precursor, i.e., poly(ethylene glycol)-substituted hyperbranched polyethoxysiloxane. Their elastic properties were addressed with a high-frequency AFM indentation method based on the PeakForce QNM (quantitative nanomechanical mapping) mode enabling simultaneous visualization of the surface morphology and high-resolution mapping of the mechanical properties. The factors affecting the accuracy of the mechanical measurements such as a local slope of the particle surface, deformation of the silica hollow particles by a solid substrate, shell thickness variation, and applied force range were analysed. The Young's modulus of the shell material was evaluated as E=26±7 GPa independent of the applied force in the elastic regime of deformations. Beyond the elastic regime, the buckling instability was observed revealing a non-linear force-deformation response with a hysteresis between the loading and unloading force-distance curves and irreversible deformation of the shell at high applied forces. Thus, it was demonstrated that PeakForce QNM mode can be used for quantitative measurements of the elastic properties of submicon-sized silica hollow particles with nano-size shell thickness, as well as for estimation of the buckling behaviour beyond the elastic regime of shell deformations.

Novel co-bonded thermoplastic elastomer-epoxy/glass hybrid composites: The effect of cure temperature on the interphase morphology

High adhesion strength in hybrid composites is a decisive factor for their widespread use in lightweight structures. The bond strength of co-bonded thermoplastic-thermoset composites is largely influenced by the interphase thickness and morphology, which are controlled by the cure and diffusion kinetics. Hence, this study aims to characterize the interphase of a hybrid composite comprised of thermoplastic elastomer (TPE) co-bonded to glass fiber reinforced epoxy (epoxy/glass) by correlating the cure temperature with the interphase thickness and morphology. The interphase thickness is analyzed with light microscopy, while the morphology is studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM) employing the PeakForce quantitative nanomechanical mapping mode (PF-QNM). The relationship between interphase thickness and cure temperature is investigated by assessing the diffusion and cure kinetics with a rheometer. It was observed that phase separation took place at the interphase, while the interphase thickness and morphology depended on cure temperature.

Heterogeneity of nanomechanical properties of the human umbilical vein endothelial cell surface

Endothelial cells, due to heterogeneity in the cell structure, can potentially form an inhomogeneous on structural and mechanical properties of the inner layer of the capillaries. Using quantitative nanomechanical mapping mode of atomic force microscopy, the parameters of the structural, elastic, and adhesive properties of the cell surface for living and glutaraldehyde-fixed human umbilical vein endothelial cells were studied. A significant difference in the studied parameters for three cell surface zones (peripheral, perinuclear, and nuclear zones) was established. The perinuclear zone appeared to be the softest zone of the endothelial cell surface. The heterogeneity of the endothelial cell mechanical properties at the nanoscale level can be an important mechanism in regulating the endothelium functions in blood vessels.

Water Molecule-Triggered Anisotropic Deformation of Carbon Nitride Nanoribbons Enabling Contactless Respiratory Inspection

The exploitation of the interaction between nanostructured matter and small molecules, such as H2O at interfaces via dynamic hydrogen bonding, is essentially the key for smart, responsive nanodevic...

Size-dependent elasticity of gold nanoparticle measured by atomic force microscope based nanoindentation

Elasticity is one of the key properties in gold nanoparticles (AuNPs) and plays an essential role in the process design and applications. In this work, we have proposed an Argon plasma based technique to obtain well dispersed and pure AuNPs without surface functional groups. Our investigation on the size-dependent elasticity focused on the AuNPs with the size ranging from 2 nm to 12 nm by using an atomic force microscope based nanoindentation technique under the peakforce quantitative nanomechanical mapping mode. The results show clearly that when the AuNPs are smaller than 6 nm, there is a significant increase in the elasticity as the smallest nanoparticles display a twofold higher elastic modulus of ∼140 GPa compared to bulk gold. Our result provides important experimental evidence that contributes to a better understanding of the size-property relations as well as process design in AuNPs, and it also can be applied to measure the mechanical properties in a wide range of nano-objects.

Size-Dependent Interaction of Amyloid β Oligomers with Brain Total Lipid Extract Bilayer-Fibrillation Versus Membrane Destruction.

Amyloid β, Aβ(1-42), is a component of senile plaques present in the brain of Alzheimer's disease patients and one of the main suspects responsible for pathological consequences of the disease. Herein, we directly visualize the Aβ activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aβ oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aβ oligomers, corresponding to high-molecular-weight Aβ oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aβ fibrillogenesis on the membrane surface. Importantly, the fibrillogenesis did not affect integrity of the membrane. In contrast, small-size (SS) Aβ oligomers, corresponding to low-molecular-weight Aβ oligomers, created pores and then disintegrated the BTLE membrane. Both forms of the Aβ oligomers changed nanomechanical properties of the membrane by decreasing its Young's modulus by ∼45%. Our results demonstrated that both forms of Aβ oligomers induce the neurotoxic effect on the brain cells but their action toward the membrane differs significantly.

High electrochemical stability of meso-Ni-salen based conducting polymer manifested by potential-driven reversible changes in viscoelastic and nanomechanical properties

The potential-driven counter ion ingress and egress effect on viscoelasticity and nanomechanics of the poly(meso-Ni-SaldMe) film was examined. This effect was characterized by a new approach using two complementary operando techniques, vis., electrochemical piezoelectric microgravimetry (EC-PM) at the electrochemical quartz crystal microbalance (EQCM) and atomic force microscopy in the PeakForce Quantitative Nanomechanical Mapping mode run under electrochemical conditions (EC-PFQNM AFM). The EC-PM and EC-PFQNM AFM experiments showed that changes in viscoelastic and nanomechanical behavior of the poly(meso-Ni-SaldMe) film, caused by counter ions doping and dedoping in the course of polymer charging and discharging, were repeatable. In that way, we demonstrated that the film high stability under these electrochemical conditions resulted from reversibility of processes occurring in both bulk and surface of the poly(meso-Ni-SaldMe) film. This is why the polymer is very much suitable for application as an electrode material for electrochemical devices.

Experimental observation of size-dependent behavior in surface energy of gold nanoparticles through atomic force microscope

Surface energy plays a key role in the physicochemical interactions of material surfaces, and it is closely related to the unique properties and numerous surface functionalization possibilities of gold nanoparticles. Herein, we have reported an atomic force microscopy based technique to measure the surface energies of different materials in the peakforce quantitative nanomechanical mapping mode. Our study on gold nanoparticles focuses on the particles with diameters ranging from 2 to 14 nm. The experimental results indicate a clear size-dependent behavior in the surface energy of gold nanoparticles when the size is smaller than 5 nm, and the smallest gold nanoparticle displays a threefold higher surface energy compared to bulk gold. Therefore, our experimental results provide essential evidence that can lead to a better understanding of the size-property relationships allowing for process design in gold nanoparticles.

Application of PeakForce tapping mode of atomic force microscope to characterize nanomechanical properties of organic matter of the Bakken Shale

Organic-rich shale, which is a heterogeneous material, has been studied extensively from various perspectives. Among all the components that constitute shale, organic matter is less known in regards to its mechanical properties. Since organic matter is relatively the softer part compared to inorganic minerals, high concentrations of it can have a significant impact on bulk mechanical properties of the rock, which can affect field operations such as hydraulic fracturing. In this study, four shale samples from the Bakken Formation in Williston Basin, North Dakota, were examined by a combination of experimental methods including X-ray diffraction (XRD), Rock-Eval pyrolysis, optical and scanning electron microscopy (SEM) along with atomic force microscope (AFM). PeakForce Quantitative Nano-mechanical Mapping mode in AFM was used particularly, to map the modulus of organic matter in nano-scale. XRD analysis showed that quartz and clays are the main constituent minerals in the shale samples. Geochemical results showed that all samples are extremely organic-rich, and the organic matter is mostly type II, varying from thermally immature to oil generation window. Elastic properties test results demonstrated that surface topographic features including pores, microfractures and grain boundaries would have a negative impact on AFM data, and a data filtering procedure was conducted on AFM data to get rid of wrong values. The elastic modulus of identified organic matter (bitumen and micrinite) was measured in the range of 7–23 GPa with a significant heterogeneity in a single studied organic particle and dependent upon the type of organic particle.

Adhesive force between graphene nanoscale flakes and living biological cells.

We report on a measurement technique that quantifies the adhesive force between multi-layers of graphene flakes and the cell wall of live Escherichia coli cells using atomic force microscopy (AFM) in-fluid Peak Force- Quantitative Nanomechanical Mapping mode. To measure the adhesive force, we made use of the negative charge of E. coli cells to allow them to stick to positively charged surfaces, such as glass or silicon, that were covered by poly-L-Lysine. With this approach, cells were held in place for AFM characterization. Both pristine graphene (PG) flakes and functionalized graphene (FG) flakes were put on the E. coli cells and measurements of lateral size, flake thickness, and adhesion were made. Using this approach, the measured values of the adhesive force between multi-layers of graphene flakes (total thickness of 50 nm) and E. coli was determined to be equal or greater than 431 ± 65pN for (PG) and 694 ± 98pN for the (FG). More interestingly, the adhesive force of a graphene flake (thickness 1.3 nm) with the cell is determined to be equal or greater than 38.2 ± 16.4pN for the (PG) and 34.8 ± 15.3pN for the (FG). These interaction values can play an important role in determining and understanding the possible toxicity of graphene flakes. Copyright © 2017 John Wiley & Sons, Ltd.

The effect of cellulose nanofibers on the crystallinity and nanostructure of poly(lactic acid) composites

Poly(lactic acid) (PLA) is a semi-crystalline polymer with good transparency, mechanical strength, and melt processability. However, the use of PLA in applications like food packaging is limited by its low heat resistance and slow crystallization rate. The addition of cellulose nanofibers can be an efficient solution to enhance PLA crystallinity and stiffness, maintaining the transparency and biodegradability, which are mandatory for packaging applications. The combined effect of annealing and cellulose nanofibers (surface treated—SCN or untreated—CN) on the crystalline structure of PLA was thoroughly studied at both micro- and nano-scales by differential scanning calorimetry (DSC), mechanical tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM), Peak Force QNM (Quantitative Nanomechanical Mapping) mode. The ability of CN to act as nucleating agents was highlighted by DSC and XRD, both methods pointing out similar trends of crystallinity variation. Higher crystallinity was observed after annealing, 59 % instead of 40 % for PLA, 67 % instead of 48 % for PLA-CN and 57 % instead of 39 % for PLA-SCN, respectively. A mixture of α and α′ crystals was detected in all the samples after annealing but the concentration of the more disordered α′ form was higher in PLA-CN than in PLA-SCN. The transformation of the grained structure specific to amorphous PLA into a crystalline lamellar structure (average lamellar thickness of about 22 nm) after annealing was detected by Peak Force QNM. Nanoindentation tests showed an improvement of the surface modulus and hardness for the composites compared to PLA, after annealing. Thus, modulus increased from 5.9 GPa for PLA to 6.2 GPa for PLA-CN and 6.6 GPa for PLA-SCN. The understanding of PLA nanostructure modification by annealing and CN addition may contribute to adjust post-processing treatments, thus making PLA more suitable for packaging and other applications.

AFM PeakForce QNM mode: Evidencing nanometre-scale mechanical properties of chitin-silica hybrid nanocomposites

PeakForce Quantitative Nanomechanical Mapping (QNM) AFM mode was used to explore the mechanical properties of textured chitin-silica hybrid films at the nanoscale. The influence of the force applied by the tip on the sample surface was studied for standard homogeneous samples, for chitin nanorods and for chitin-silica hybrid nanocomposites. Thick films of superimposed chitin nanorods showed a monotonous increase of DMT modulus (based on the Derjaguin-Muller-Toporov model) owing to an increase in modulus at the interface between nanorods due to geometrical constraints of the AFM acquisition. A similar variation of DMT modulus was obtained for chitin-silica hybrid thick films related to mechanical strengthening induced by the presence of silica. This work revealed the role of the organic-inorganic interface, at the nanoscale, in the mechanical behaviour of textured materials using PeakForce QNM mode, with optimized analysis conditions.

Scrutinizing the Nanostructural and Nanomechanical Features of Regenerated Cellulose Ultrafiltration Membranes

Ultrafiltration (UF) membranes have been widely used for many separation processes in which high performance is required. Commercial regenerated cellulose UF membranes with variable molecular weight cut-offs were characterized by high performance atomic force microscopy (AFM) using the novel quantitative nanomechanical mapping mode and the versatility of its signal channels towards nanoscale features elucidation of the materials surface. In addition, Raman spectroscopy was applied in order to investigate some possible chemical behavior changes associated with the UF membranes’ cut-offs. Overall, the results showed that the proposed AFM method was reliable to gain qualitative and quantitative data at unprecedented nanoscale resolution and such information can be used to distinguish UF membranes according to their specific molecular weight cut-offs and properties even on situations in which the molecular behavior were not influenced by the UF membrane’ cut-off. This approach can be useful on quality control procedures of researchers and manufacturers producing or modifying these polymeric materials.