Nanomechanical Characterization Research Articles

Nanoscale Investigations of α- and γ-Crystal Phases in PVDF-Based Nanocomposites.

The impact of carbon nanotube (CNT) incorporation into semicrystalline poly(vinylidene fluoride), PVDF, was investigated at both the macro and nanoscales. A special effort was devoted to probe the local morphology and the mechanical, ferroelectric, piezoelectric, and electrical conductivity response by means of atomic force microscopy. Incorporation of CNTs mainly induces the development of the polar γ-phase, and as a consequence, the coexistence of the γ-phase with the most stable nonpolar α-phase is observed. A maximum γ-phase content is reached at 0.7 wt % CNT loading. The spherulitic morphology of the PVDF α-phase is assessed, in conjunction with the lack of any ferroelectric response, while the presence of the polar γ-phase is confirmed, owing to clear piezoresponse signals. Local piezoelectric measurements on γ-phase domains yield a maximum effective coefficient | d33| ≈ 13 pm/V, thus underlining the potential for applications of such functional PVDF-based nanocomposites in advanced piezoelectric devices. An increase in macroscopic conductivity with CNT content is observed, with a percolation threshold achieved for a composition close to 0.7 wt %. Nanoscale investigation of the electrical conductivity confirms the presence of some infinite CNT cluster homogeneously distributed over the surface. The macroscopic viscoelastic behavior of the composite reflects the reinforcing effect of CNTs, while the nanomechanical characterization yields a local contact modulus of the γ-phase domains larger than that of its α-phase counterpart, in agreement with the fact that the CNTs act as γ-phase promoters and subsequently reinforce the γ-domains.

Assessment of titanium metallization thin film deposited on alumina substrate: Microstructure and nano-indentation.

Surface titanium (Ti) metallization was conducted on alumina (Al2O3) through chemical vapor deposition (CVD) method derived from non-contact pack cementation. The effects of different deposition temperature (1000 °C, 1050 °C, and 1100 °C) were examined in this scenario. The morphology, phase composition, and interfacial defects of the resulting films were systematically investigated through scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The nanomechanical characterization of the proposed thin films was evaluated by conducting nano-indentation tests at different depths. The results revealed that uniform Ti films were coated on the Al2O3 substrate. During coating, the atoms on the matrix surface were driven to form different structure due to different deposition temperature, leading to disparate morphologies of the surface and the interface, which consequently influenced the binding force between the film and the substrate. Moreover, the nanomechanical properties were found to be related to the internal and interface structure. Decreased modulus and hardness were obtained for metallization films treated at 1050 °C, and plastic deformation was the main deformation pattern.

A close-up view of the wood cell wall ultrastructure and its mechanics at different cutting angles by atomic force microscopy.

AFM measurements on spruce sample cross-sections reveal that the structural appearance of the S2 layer changes from a network structure to a concentric lamellar texture depending on the cutting angle. The structural assembly of wood constituents within the secondary cell wall has been subject of numerous studies over the last decades, which has resulted in contradicting models on the spatial arrangement and orientation of the wood macromolecules. Here, we use multichannel atomic force microscopy by means of quantitative imaging, to gain new insights into the macromolecular assembly. Cross-sections of spruce wood, which had been cut at different angles ranging from 0° to 30° were investigated. Strikingly, depending on the cutting angle, the structural appearance of the S2 layer changed from a network-like structure to a distinct concentric lamellar texture. This makes us conclude that the often visualized lamellar organization of the secondary cell wall is not the consequence of a continuous inherent ring pattern, but rather a result of the specific surface cross-section appearance of cellulose aggregates at larger cutting angles. By analyzing the recorded force distance curves in every pixel, a nano-mechanical characterization of the secondary cell wall was conducted. Substantially lower indentation modulus values were obtained compared to nanoindentation values reported in the literature. This is potentially due to a smaller interaction volume of the probe with a by far less deep indentation.

Nanomechanical characterization of recalcitrant foulants and hollow fiber membranes in ultrafiltration systems

Long-term nanomechanical changes of polymeric ultrafiltration (UF) membranes caused by fouling/cleaning agents in water treatment are not well established in the literature. The goal of this study was to investigate the nanomechanical properties of polymeric UF hollow fiber membranes operating at a pilot-scale for 449 d and subjected to a low-quality feed (i.e., high turbidity/TOC content). Quantitative nanomechanical mapping technique was used to measure the deformation, dissipation, modulus, adhesion, and roughness of the polymeric structures of commercial Aquaflex virgin membranes, harvested membranes, and foulant layers. Results indicated that the recalcitrant and heterogeneous nature of the foulants absorbed on harvested membranes showed low elastic properties, and high modulus, adhesion, and roughness. The strong affinity of these foulants towards membrane surface would alter membrane characteristics and influence subsequent fouling behaviour. The cleaning process and extended operation did not significantly affect the nanomechanical properties of membranes. Despite the low-quality feed, the three modules were only subjected to 37 chemi-cal-enhanced backwashes and filtered a total volume of 2.155 m3. These results indicate the importance of operating conditions (i.e., frequency of backwash/cleaning/disinfection steps) and feed quality on the long-term changes of UF membranes and would assist in identifying research directions that are necessary to minimize membrane fouling/ageing. (Less)

Nano-mechanical Characterization of Mg-Zn-Mn-Si Alloy Fabricated by Spark Plasma Sintering for Biomedical Applications

Here in, a bio-inspired biodegradable Mg-Zn-Mn-Si Alloy was synthesised by mechanical alloying and spark plasma technique. The effect milling time, sintering temperature, and sintering pressure has been studied on the elastic modulus and hardness of the as-synthesized alloy. The microstructure, surface topography, and element composition as-synthesized alloy was investigated using optical microscope, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The elastic modulus and hardness of as-synthesized alloy was measured by nano-indentation technique. The microstructure examination of the compact reveled that Si not only refined the gain structure but also formed Mg2Si in the structure. XRD pattern analysis confirmed the formation of Mg2Si, Mg-Zn, Mn-Si, SiO2, and ZnO2 due to heat developed during the process, which enhanced the mechanical properties and corrosion characteristics

The Role of Nanomechanics in Healthcare.

Nanomechanics has played a vital role in pushing our capability to detect, probe, and manipulate the biological species, such as proteins, cells, and tissues, paving way to a deeper knowledge and superior strategies for healthcare. Nanomechanical characterization techniques, such as atomic force microscopy, nanoindentation, nanotribology, optical tweezers, and other hybrid techniques have been utilized to understand the mechanics and kinetics of biospecies. Investigation of the mechanics of cells and tissues has provided critical information about mechanical characteristics of host body environments. This information has been utilized for developing biomimetic materials and structures for tissue engineering and artificial implants. This review summarizes nanomechanical characterization techniques and their potential applications in healthcare research. The principles and examples of label-free detection of cancers and myocardial infarction by nanomechanical cantilevers are discussed. The vital importance of nanomechanics in regenerative medicine is highlighted from the perspective of material selection and design for developing biocompatible scaffolds. This review interconnects the advancements made in fundamental materials science research and biomedical technology, and therefore provides scientific insight that is of common interest to the researchers working in different disciplines of healthcare science and technology.

Compressed collagen constructs with optimized mechanical properties and cell interactions for tissue engineering applications

In this study, we are introducing a simple, fast and reliable add-in to the technique of plastic compression to obtain collagen sheets with decreased fibrillar densities, representing improved cell-interactions and mechanical properties. Collagen hydrogels with different initial concentrations (1.64mg/mL–0.41mg/mL) were compressed around an electrospun sheet of PLGA. The scaffolds were then studied as non-seeded, or seeded with 3T3 fibroblast cells and cultured for 7days. Confocal microscopy and TEM imaging of non-seeded scaffolds showed that by decreasing the share of collagen in the hydrogel formula, collagen sheets with similar thickness but lower fibrous densities were achieved. Nanomechanical characterization of compressed collagen sheets by AFM showed that Young’s modulus was inversely proportional to the final concentration of collagen. Similarly, according to SEM, MTS, and cell nuclei counting, all the scaffolds supported cell adhesion and proliferation, whilst the highest metabolic activities and proliferation were seen in the scaffolds with lowest collagen content in hydrogel formula. We conclude that by decreasing the collagen content in the formula of collagen hydrogel for plastic compression, not only a better cell environment and optimum mechanical properties are achieved, but also the application costs of this biopolymer is reduced.

The use of advanced atomic force microscopy for the quantitative nanomechanical characterization of Co-doped ZnO thin films

Cobalt-doped zinc oxide (CZO) thin films were deposited on glass substrates by dip-coating method. The correlation between the X-ray diffractometer (XRD) and the new atomic force microscopy operated in peak force tapping mode (PF-QNM (™)) has been performed to study the microstructural and nanomechanical properties of CZO thin films. The XRD results indicated that all samples possess the hexagonal wurtzite structure with two predominant growth directions (002) and (103). The PF-QNM results show that the mechanical properties of ZnO films enhance significantly with increasing Co concentrations. The Young's modulus maps show that a large part of CZO films have a high elasticity, which ranged between 367 ± 66 and 391 ± 44 GPa. In addition, deformation maps show that the grain boundaries were softer than the grain centers. The adhesion force has improved considerably from 25.87 ± 15 to 85.98 ± 49 nN, which means an additional adhesion strength was acquired due to the Cobalt doping effect. The results were also compared with relevant literature. Our excellent mechanical properties indicate that CZO films can be used in the spintronic devices.

Nanostructure in the trabecular bone of postmenopausal women: Mechanical and chemical analysis

The possibility of diagnosis and prediction of multiple disorders in trabecular bone through nano-biomechanics and chemical analysis are summarized. Improvements to the understating of the compositional contributors of bone mineral and organic components to mechanical competence are crucial. Viscoelastic properties and Raman characterization have been used to evaluate possible alterations of the trabecular bone associated with aging, disease, or injury. In this study, the trabecular bone of postmenopausal women has been analyzed throughout. (a) Nanomechanical characterization, by using nano-DMA: complex modulus, tan δ, loss modulus (E′), and storage modulus (E′); and (b) Raman analysis: relative presence of minerals, carbonate-to-phosphate ratio (both from the mineral components), the crosslinking and nature/secondary structure of collagen (both from the organic components). Complementary nano-morphological studies were done assessing roughness (SRa) and collagen fibrils width, on this trabecular bone. A general idea of the behavior of the viscoelastic performance can be obtained by the Tan δ (E″/E′), that achieved 0.98GPa of damping. 249nm and 0.898μm of SRa roughness and fibrils width were obtained, respectively. The relative presence of minerals, the carbonate-to-phosphate ratio, the crosslinking and the nature/secondary structure of collagen, between 700 and 1700cm−1, were also obtained, in order to propose a study protocol for trabecular bone characterization.

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode.

Tapping mode atomic force microscopy (AFM), also known as amplitude modulated (AM) or AC mode, is a proven, reliable, and gentle imaging mode with widespread applications. Over the several decades that tapping mode has been in use, quantification of tip-sample mechanical properties such as stiffness has remained elusive. Bimodal tapping mode keeps the advantages of single-frequency tapping mode while extending the technique by driving and measuring an additional resonant mode of the cantilever. The simultaneously measured observables of this additional resonance provide the additional information necessary to extract quantitative nanomechanical information about the tip-sample mechanics. Specifically, driving the higher cantilever resonance in a frequency modulated (FM) mode allows direct measurement of the tip-sample interaction stiffness and, with appropriate modeling, the set point-independent local elastic modulus. Here we discuss the advantages of bimodal tapping, coined AM-FM imaging, for modulus mapping. Results are presented for samples over a wide modulus range, from a compliant gel (∼100 MPa) to stiff materials (∼100 GPa), with the same type of cantilever. We also show high-resolution (subnanometer) stiffness mapping of individual molecules in semicrystalline polymers and of DNA in fluid. Combined with the ability to remain quantitative even at line scan rates of nearly 40 Hz, the results demonstrate the versatility of AM-FM imaging for nanomechanical characterization in a wide range of applications.

Characterization of single polyvinylidene fluoride (PVDF) nanofiber for flow sensing applications

The use of Polyvinylidene Fluoride (PVDF) based piezoelectric nanofibers for sensing and actuation has been reported widely in the past. However, in most cases, PVDF piezoelectric nanofiber mats have been used for sensing applications. This work fundamentally characterizes a single electrospun PVDF nanofiber and demonstrates its application as a sensing element for nanoelectromechanical sensors (NEMS). PVDF nanofiber mats were spun by far field electrospinning (FFES) process and complete material characterization was conducted by means of scanning electron microscope (SEM) imaging, Raman Spectroscopy and FTIR spectroscopy. An optimized recipe was developed for spinning a single suspended nanofiber on a specially designed MEMS substrate which allows the nano-mechanical and electrical characterization of a single PVDF nanofiber. Electrical characterization is conducted using a single suspended nanofiber to determine the piezoelectric coefficient (d33) of the nanofiber to be -58.77 pm/V. Also the mechanical characterization conducted using a nanoindenter revealed a Young’s Modulus and hardness of 2.2 GPa and 0.1 GPa respectively. Finally, an application that utilizes the single PVDF nanofiber as a sensing element to form a NEMS flow sensor is demonstrated. The single nanofiber flow sensor is tested in presence of various oscillatory flow conditions.

Focus on microscopy, imaging, and nanotechnology

Focus on microscopy, imaging, and nanotechnology

Nanomechanical Imaging of the Diffusion of Fullerene into Conjugated Polymer.

The large Young's modulus difference between chemically modified fullerene (PCBM) and a conjugated polymer was used to nanomechanically map the diffusion of PCBM into PTB7, a high-efficiency low-band-gap conjugated polymer. The sharp tip in nanomechanical atomic force microscopy ensures a high-resolution nanomechanical characterization of the diffusion front, with the intrinsic benefits of revealing the mechanical properties of the mixtures. Localized structure changes induced by diffusion were investigated by grazing incidence X-ray diffraction methods. We found a most unusual diffusion behavior that shows Case II characteristics, where a front of PTB7 saturated with PCBM moves into the pure PTB7 with a linear time dependence. This diffusion is due mainly to a majority fraction of the disordered PTB7 that has continuous paths for PCBM diffusion without obvious energetic barriers, and as diffusion proceeds, the paths for diffusion gets larger, leading to a step in the concentration profile. The donor/acceptor-dependent diffusion constants may also contribute to the observed Case-II-like diffusion front.

Nanomechanical Characterization of Osteogenic Differentiation of Mesenchymal Stem Cells on Bioactive Peptide Nanofiber Hydrogels

AbstractStem cell differentiation is known to be influenced by the mechanical properties of the surrounding extracellular matrix (ECM); however, little is known about the mechanical phenotypes of differentiating stem cells within the ECM. Here, this study uses osteoinductive, ECM‐mimetic peptide nanofibers to investigate the changes in the mechanical properties of rat mesenchymal stem cells (rMSCs) during osteogenic differentiation. In addition, octafluorocyclobutane (C4F8)‐coated atomic force microscopy (AFM) cantilevers are developed to minimize tip–sample adhesion during the nanomechanical characterization of rMSCs, and osteogenic differentiation is monitored through molecular analysis in conjunction with AFM measurements. rMSCs cultured on osteoinductive peptide nanofibers differentiate at substantially higher rates, form osteogenic cell clusters, deposit calcium to the surrounding matrix, and strikingly increase their Young's moduli throughout the osteogenic differentiation process compared to controls. These results show that the elasticity profiles of differentiating rMSCs may change significantly depending on environmental factors and especially the degree of biomineralization, and that the natural elasticity responses of cells cultured on scaffolds may be considerably different from those observed on non‐bioactive surfaces. This is important for the identification of cell elasticity as a biophysical marker of osteogenic differentiation of MSCs, and indicates that biomineralization might have a predominant role on cell mechanics.

Nano-mechanical characterization of the wood cell wall by AFM studies: comparison between AC- and QI\u2122 mode

BackgroundUnderstanding the arrangement and mechanical properties of wood polymers within the plant cell wall is the basis for unravelling its underlying structure–property relationships. As state of the art Atomic Force Microscopy (AFM) has been used to visualize cell wall layers in contact resonance- and amplitude controlled mode (AC) on embedded samples. Most of the studies have focused on the structural arrangement of the S2 layer and its lamellar structure.ResultsIn this work, a protocol for AFM is proposed to characterize the entire cell wall mechanically by quantitative imaging (QI™) at the nanometer level, without embedding the samples. It is shown that the applied protocol allows for distinguishing between the cell wall layers of the compound middle lamella, S1, and S2 of spruce wood based on their Young’s Moduli. In the transition zone, S12, a stiffness gradient is measured.ConclusionsThe QI™ mode pushes the limit of resolution for mechanical characterization of the plant cell wall to the nanometer range. Comparing QI™- against AC images reveals that the mode of operation strongly influences the visualization of the cell wall.

Nanomechanical characterization and fracture toughness of FeB and Fe2B iron borides produced by gas boriding of Armco iron

FeB and Fe2B hard ceramic phases were produced in Armco iron using gas-boriding in N2–H2–BCl3 atmosphere. This process was carried out at 920°C (1193K) for 3h and caused acceleration in the diffusion of boron into the surface of a base material in comparison with other acceptable methods of diffusion boriding. FeB and Fe2B layers were characterized by a strong zonation, obtaining the average thickness of 32μm and 125μm, respectively. Young's moduli and hardness of iron borides were measured using the nanoindenter with a Berkovich diamond tip under load of 50mN. The higher average indentation hardness (HIT=20.95±0.93GPa) and Young's modulus (EIT=308.86±26.44GPa) were characteristic of FeB phase. Fe2B boride was characterized by HIT=17.42±0.80GPa, and EIT=252.96±15.57GPa. The fracture toughness of iron borides was measured by microindentation technique using a Vickers diamond indenter under load of 100gf (about 0.981N). The average fracture toughness (Kc), measured in FeB zone, was equal to 1.79±0.70MPa·m1/2. Fe2B phase was characterized by higher fracture toughness, obtaining Kc=2.42±0.66MPa·m1/2. However, at FeB/Fe2B interface the increase in brittleness was detected. Such a situation was caused by the differences in coefficients of thermal expansion of both iron borides and their mechanical properties. It could provide the preliminary cracks at this interface after cooling. During indentation, the value of shear stress probably exceeded the value of normal compressive stress. It could cause the failure at this interface, facilitating cracks' propagation.

Microstructural and Nanomechanical Characterization of In-Situ He Implanted and Irradiated fcc Materials

Journal Article Microstructural and Nanomechanical Characterization of In-Situ He Implanted and Irradiated fcc Materials Get access P Hosemann, P Hosemann University of California at Berkeley, Department of Nuclear Engineering Search for other works by this author on: Oxford Academic Google Scholar D Frazer, D Frazer University of California at Berkeley, Department of Nuclear Engineering Search for other works by this author on: Oxford Academic Google Scholar D Kaoumi, D Kaoumi North Carolina State University, Department of Nuclear Engineering Search for other works by this author on: Oxford Academic Google Scholar C Zheng C Zheng North Carolina State University, Department of Nuclear Engineering Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 756–757, https://doi.org/10.1017/S1431927617004445 Published: 04 August 2017

Microstructure and nanomechanical properties of single stalks from diatom Didymosphenia geminata and their change due to adsorption of selected metal ions.

We present topographical and nanomechanical characterization of single Didymosphenia geminata stalk. We compared the samples before and after adsorption of metal ions from freshwater samples. Transmission electron microscopy studies of single stalk cross-sections have shown three distinct layers and an additional thin extra coat on the external layer (called "EL"). Using scanning electron microscopy and atomic force microscopy (AFM), we found that topography of single stalks after ionic adsorption differed significantly from topography of pristine stalks. AFM nanoindentation studies in ambient conditions yielded elastic moduli of 214±170MPa for pristine stalks and 294±108MPa for stalks after ionic adsorption. Statistical tests showed that those results were significantly different. We conducted only preliminary comparisons between ionic adsorption of several stalks in air and in water. While the stalks with ions were on average stiffer than the pristine stalks in air, they became more compliant than the pristine stalks in water. We also heated the stalks and detected EL softening at 50°C±15°C. AFM nanoindentation in air on the softened samples yielded elastic moduli of 26±9MPa for pristine samples and 43±22MPa for stalks with absorbed metal ions. Substantial decrease of the EL elastic moduli after heating was expected. Significantly different elastic moduli for the samples after ionic adsorption in both cases (i.e., for heated and nonheated samples), as well as behavior of the stalks immersed in water, point to permanent structural EL changes due to ions.

Self-Assembled TEMPO Cellulose Nanofibers: Graphene Oxide-Based Biohybrids for Water Purification.

Nanocellulose, graphene oxide (GO), and their combinations there off have attracted great attention for the application of water purification recently because of their unique adsorption capacity, mechanical characteristics, coordination with transition metal ions, surface charge density, and so on. In the current study, (2,2,6,6-tetramethylpiperidine-1-oxylradical) (TEMPO)-mediated oxidized cellulose nanofibers (TOCNF) and GO sheets or graphene oxide nanocolloid (nanoGO) biohybrids were prepared by vacuum filtration method to obtain self-assembled adsorbents and membranes for water purification. The porous biohybrid structure, studied using advanced microscopy techniques, revealed a unique networking and self-assembling of TOCNF, GO, and nanoGO, driven by the morphology of the GO phase and stabilized by the intermolecular H-bonding between carboxyl groups and hydroxyl groups. The biohybrids exhibited a promising adsorption capacity toward Cu(II) due to TOCNF and formed a unique "arrested state" in water because of ionic cross-linking between adsorbed Cu(II) and the negatively charged TOCNF and GO phase. The mechanical performance of the freestanding biohybrid membranes investigated using PeakForce Quantative NanoMechanics characterization confirmed the enhanced modulus of the hybrid membrane compared to that of the TOCNF membrane. Besides, the TOCNF+nanoGO membrane shows unique hydrolytic stability and recyclability even under several cycles of adsorption and desorption and strong sonication. This study shows that TOCNF and nanoGO hybrids can generate new water-cleaning membranes with synergistic properties because of their high adsorption capacity, flexibility, hydrolytic stability, and mechanical robustness.

Adhesion strength and nanomechanical characterization of ZnO thin films

Abstract