Nanomechanical Behavior Research Articles

Nano mechanical behavior of bio composites

Nano mechanical behavior of bio composites

In situ TEM visualization of superior nanomechanical flexibility of shear-exfoliated phosphorene.

Recently discovered atomically thin black phosphorus (called phosphorene) holds great promise for applications in flexible nanoelectronic devices. Experimentally identifying and characterizing nanomechanical properties of phosphorene are challenging, but also potentially rewarding. This work combines for the first time in situ transmission electron microscopy (TEM) imaging and an in situ micro-manipulation system to directly visualize the nanomechanical behaviour of individual phosphorene nanoflakes. We demonstrate that the phosphorene nanoflakes can be easily bent, scrolled, and stretched, showing remarkable mechanical flexibility rather than fracturing. An out-of-plane plate-like bending mechanism and in-plane tensile strain of up to 34% were observed. Moreover, a facile liquid-phase shear exfoliation route has been developed to produce such mono-layer and few-layer phosphorene nanoflakes in organic solvents using only a household kitchen blender. The effects of surface tensions of the applied solvents on the ratio of average length and thickness (L/T) of the nanoflakes were studied systematically. The results reported here will pave the way for potential industrial-scale applications of flexible phosphorene nanoelectronic devices.

Electrochemically synthesized amorphous and crystalline nanowires: dissimilar nanomechanical behavior in comparison with homologous flat films.

The effects of constrained sample dimensions on the mechanical behavior of crystalline materials have been extensively investigated. However, there is no clear understanding of these effects in nano-sized amorphous samples. Herein, nanoindentation together with finite element simulations are used to compare the properties of crystalline and glassy CoNi(Re)P electrodeposited nanowires (ϕ ≈ 100 nm) with films (3 μm thick) of analogous composition and structure. The results reveal that amorphous nanowires exhibit a larger hardness, lower Young's modulus and higher plasticity index than glassy films. Conversely, the very large hardness and higher Young's modulus of crystalline nanowires are accompanied by a decrease in plasticity with respect to the homologous crystalline films. Remarkably, proper interpretation of the mechanical properties of the nanowires requires taking the curved geometry of the indented surface and sink-in effects into account. These findings are of high relevance for optimizing the performance of new, mechanically-robust, nanoscale materials for increasingly complex miniaturized devices.

Nanomechanical and nanotribological behavior of ultra-thin silicon-doped diamond-like carbon films

Diamond-like carbon (DLC) film with ultra-thin thickness displays high internal stress, thereby resulting in the failure of protection to the substrate. Incorporation of silicon into DLC films, which has higher adhesion to substrate and extraordinary thermal stability, can be potentially used in heat assisted magnetic recording (HAMR). The nanomechanical and nanotribological behavior of Si doped DLC films is investigated using molecular dynamic simulation method. Effects of the Si content and density of Si-DLC films on the frictional behavior and wear resistance of Si-DLC films are investigated. Surface profiles at the contact interface are identified before and after sliding.

Extreme nanomechanics: vacuum nanoindentation and nanotribology to 950 °C

Elevated temperature mechanical and tribological properties can be more relevant for practical wear situations than corresponding measurements at room temperature. However, high temperature nanomechanics and nanotribology is highly challenging experimentally. To overcome these challenges the NanoTest*** has been developed with active heating of the indenter and sample with resistive heaters, horizontal loading, patented thermal control method and stage design. By separately actively heating*** and controlling the temperatures of indenter and sample their temperatures can be precisely matched so that there is no heat flow and minimal/no thermal drift during the high temperature indentation,*** and measurements can be performed as reliably as at room temperature. Above 500 °C it is beneficial to use a cubic Boron Nitride indenter with gas purging to limit oxidation of samples. To achieve higher temperatures without indenter or sample oxidation an ultra-low drift high temperature vacuum nanomechanics/tribology system capable of testing to*** much higher temperatures has been recently developed (NanoTest Xtreme). The influence of time-dependent deformation on elevated temperature nanomechanical behaviour is discussed, using published results in Argon on glass-ceramic solid oxide fuel cell seal materials and previously unpublished nanoindentation measurements on single crystal silicon and polycrystalline tungsten using the NanoTest Xtreme in vacuum at temperatures up to 950 °C. Studies of the elevated temperature nano-/micro-tribological*** behaviour of wear-resistant*** nitride-based and MAX-phase coatings are also briefly reviewed.

Evaluation of elasto-plastic properties of ITO film using combined nanoindentation and finite element approach

Here we report for the first time the combined nanoindentation experiments and finite element modeling to investigate the in-depth nanomechanical behavior of ~1.25μm indium tin oxide (ITO) film. The ITO film is grown on silicon substrate by a reactive direct current (DC) magnetron sputtering technique. Here, the contributions of both film and substrate are considered in a power law based nonlinear material model. Based on experimental data a detailed study is carried out in the present work to investigate the stress–strain behavior, the related von-Mises stress and equivalent plastic strain of the ITO film. In addition, the effect of the nanoindentation response of the ITO film on the silicon substrate is also evaluated.

Microstructure and Nanomechanical Behaviour of Electron Beam Evaporated Yttria Stabilized Zirconia Films on Ni Base Superalloy

Yttria Stabilized Zirconia (YSZ) coating was developed using electron beam physical vapour deposition as a top coat material for thermal barrier application. In the present study, attempt to develop YSZ films by evaporating ZrO2 stabilized with 8 wt% Y2O3 powder using EBPVD technique. YSZ films were deposited on Inconel-718 (Ni-Cr-Fe) substrate by varying the substrate temperature in the range of 673 K to 1073 K. The deposited films have shown good adherence to the substrate and exhibit uniform dense microstructure. The effect of substrate temperature, phase and surface morphology were investigated by XRD, AFM and SEM. The film deposited at 673 K shows crystalline nature and the crystallinity of the deposited films increase with increasing substrate temperature. The surface roughness of the films increases with increase in the deposition temperature due to the increase in crystallinity of the films. SEM images shows that the films are grown with triangular shaped morphology. Nanomechanical characteristics of the tetragonal phase of the YSZ films were investigated by nanointendation technique and the young’s modulus of the coating was found to be 118 GPa.

Nanomechanical behavior and structural stability of a nanocrystalline CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

Abstract

Nanomechanical Behavior of CoCrFeMnNi High-Entropy Alloy

The nanomechanical behavior of the Co20Cr20Fe20Mn20Ni20 high-entropy alloy was investigated in as-cast, rolled, annealed, and thin-film forms. Dislocation nucleation was studied by repeated indents at a low load for each of the different processing conditions. Distinct displacement bursts (pop in) were observed in the loading curve marked by incipient plasticity for all the samples. The as-cast and annealed samples showed pop ins for 100% of the indents, whereas the rolled and thin-film samples showed a much lower fraction of displacement bursts. This was explained by the high density of dislocations for the cold-worked and thin-film conditions. The strong depth dependence of hardness was explained by geometrically necessary dislocations. The nanomechanical behavior and twinned microstructure indicate low stacking-fault energy for this high-entropy alloy.

Nanomechanical behaviour and thermal degradation of nanoclays and supernanoclays enhanced marine gelcoat system

Novel nanoclay reinforced unsaturated polyester gelcoats for marine vessels are evaluated in terms of their thermal and mechanical performance. In this study, mechanical and thermal tests have been employed to characterise different gelcoat systems with various loading levels of nanoclays with and without X-treatment. Differences in mechanical properties were determined by using nano-indentation testing which shown an increase in hardness compared to the control system. Thermal degradation characteristics were determined using a thermogravimetric analyser (TGA). An increase in thermal stability was observed for all nanocomposites compared to the control system. Additionally, differential scanning calorimetry (DSC) showed that the effect of inclusion of nanoclays is to hinder the structure of unsaturated polyester gelcoats and hence increase glass transition temperatures. Furthermore, X-treated supernanoclay is shown to be significantly more effective than untreated nanoclay. Enhancement of mechanical property and thermal degradation could be attributed to the grafting of hydroxyl groups (?OH) in the nanoclays with polymer chains.

Nano-mechanical behaviour of lithium metasilicate glass–ceramic

This paper reports the first study on the mechanical behavior of lithium metasilicate glass–ceramic using nanoindentation and in situ scanning probe imaging techniques. Indentation contact hardness, Hc, and Young’s modulus, E, were measured at 10mN peak load and 0.1–2mN/s loading rates to understand the loading rate effect on its properties. Indentation imprints were analysed with the in situ scanning probe imaging to understand indentation mechanisms. The average contact hardness increased by 112% with the loading rate (ANOVA, p<0.05) while the Young’s modulus showed the loading rate independence (ANOVA, p>0.05). A strain rate sensitivity model was applied to determine the intrinsic contact hardness. Extensive discontinuities and largest maximum, contact and final depths were also observed at the lowest loading rate. These phenomena corresponded to inhomogeneous shear-band flow and densification leading to the material strain softening. The in situ scanning probe images of indentation imprints showed plastic deformation at all loading rates and shear band-induced pileups at the lowest loading rate. With the increase in loading rate, the induced pile-ups decreased. The continuum model predicted the largest densified shear zone at the lowest loading rate. Finally, these results provide scientific insights into the abrasive machining responses of lithium metasilicate glass–ceramic during dental CAD/CAM processes using sharp diamond abrasives.

Mesoporous silica-layered biopolymer hybrid nanofibrous scaffold: a novel nanobiomatrix platform for therapeutics delivery and bone regeneration.

Nanoscale scaffolds that characterize high bioactivity and the ability to deliver biomolecules provide a 3D microenvironment that controls and stimulates desired cellular responses and subsequent tissue reaction. Herein novel nanofibrous hybrid scaffolds of polycaprolactone shelled with mesoporous silica (PCL@MS) were developed. In this hybrid system, the silica shell provides an active biointerface, while the 3D nanoscale fibrous structure provides cell-stimulating matrix cues suitable for bone regeneration. The electrospun PCL nanofibers were coated with MS at controlled thicknesses via a sol-gel approach. The MS shell improved surface wettability and ionic reactions, involving substantial formation of bone-like mineral apatite in body-simulated medium. The MS-layered hybrid nanofibers showed a significant improvement in mechanical properties, in terms of both tensile strength and elastic modulus, as well as in nanomechanical surface behavior, which is favorable for hard tissue repair. Attachment, growth, and proliferation of rat mesenchymal stem cells were significantly improved on the hybrid scaffolds, and their osteogenic differentiation and subsequent mineralization were highly up-regulated by the hybrid scaffolds. Furthermore, the mesoporous surface of the hybrid scaffolds enabled the loading of a series of bioactive molecules, including small drugs and proteins at high levels. The release of these molecules was sustainable over a long-term period, indicating the capability of the hybrid scaffolds to deliver therapeutic molecules. Taken together, the multifunctional hybrid nanofibrous scaffolds are considered to be promising therapeutic platforms for stimulating stem cells and for the repair and regeneration of bone.

Bulk and nano-mechanical behavior of silver and silver-CNT-reinforced hybrid polymer composites

The present study concerns study of the Bulk and nano-mechanical properties of Ag-CNT vis-a-vis Ag reinforced polymer composites. The Ag-CNT hybrid powder blend was prepared by mechanical milling. Variation of the bulk and nano-mechanical properties has been attributed to the morphological features and the degree of dispersion of the fillers. It has been found that dispersion of Ag-CNT hybrid particle is beneficial for improvement of both the mechanical properties. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Evaluating Molecular Interactions in Polycaprolactone-Biomineralized Hydroxyapatite Nanocomposites using Steered Molecular Dynamics

An experimental and modeling study of a complex nanoclay-based polymeric scaffold system is presented here. A representative molecular model of polymeric nanocomposite scaffold system for bone tissue engineering applications was developed. Polymeric scaffolds were synthesized using organically modified montmorillonite clay (OMMT) with biomineralized hydroxyapatite and polycaprolactone (OMMT–HAP–PCL). The OMMT–HAP–PCL representative model was constructed and validated using transmission electron microscopy, x-ray diffraction and material density results. We observed strong molecular interactions between OMMT, hydroxyapatite (HAP) and polycaprolactone (PCL) in the OMMT–HAP–PCL system. Attractive and repulsive interactions between PCL and different constituents of OMMT and HAP indicate influence of OMMT–HAP on PCL. Polymeric scaffolds were found to have improved nanomechanical properties as compared to pristine PCL due to the introduction of OMMT–HAP. Stress–strain response for the representative OMMT–HAP–PCL model was evaluated using constant force steered molecular dynamics (SMD) simulations. Two distinct stress–strain responses observed in the system indicate a two-phase nanomechanical behavior of OMMT–HAP–PCL obtained at low and high applied stresses. The results obtained from the MD and SMD simulations provide quantitative understanding of molecular interactions between different constituents of OMMT, HAP and PCL and mechanical response in the OMMT–HAP–PCL system.

Aggrecan nanoscale solid-fluid interactions are a primary determinant of cartilage dynamic mechanical properties.

Poroelastic interactions between interstitial fluid and the extracellular matrix of connective tissues are critical to biological and pathophysiological functions involving solute transport, energy dissipation, self-stiffening and lubrication. However, the molecular origins of poroelasticity at the nanoscale are largely unknown. Here, the broad-spectrum dynamic nanomechanical behavior of cartilage aggrecan monolayer is revealed for the first time, including the equilibrium and instantaneous moduli and the peak in the phase angle of the complex modulus. By performing a length scale study and comparing the experimental results to theoretical predictions, we confirm that the mechanism underlying the observed dynamic nanomechanics is due to solid-fluid interactions (poroelasticity) at the molecular scale. Utilizing finite element modeling, the molecular-scale hydraulic permeability of the aggrecan assembly was quantified (kaggrecan = (4.8 ± 2.8) × 10(-15) m(4)/N·s) and found to be similar to the nanoscale hydraulic permeability of intact normal cartilage tissue but much lower than that of early diseased tissue. The mechanisms underlying aggrecan poroelasticity were further investigated by altering electrostatic interactions between the molecule's constituent glycosaminoglycan chains: electrostatic interactions dominated steric interactions in governing molecular behavior. While the hydraulic permeability of aggrecan layers does not change across species and age, aggrecan from adult human cartilage is stiffer than the aggrecan from newborn human tissue.

Dynamic nanomechanical behaviour of healthy and OI human cortical bone

Viscoelasticity of bone has been of interest for many years because this time-dependent mechanical property relates to the fracture risk of bone under dynamic loading. Several factors have been claimed to contribute to this property including the nature of different constituents of bone and their interactions, as well as moisture content. In the present study, intact normal human cortical bone was demineralised, and molecular structures were identified using infrared spectroscopy. Osteogenesis imperfecta (OI) human cortical bone was also selected for comparison because OI bone has severe defects in collagen molecules, while its mineral phase is almost identical to that of normal bone. The dynamic nanomechanical behaviours of the intact, demineralised and OI human cortical bone specimens were examined using dynamic nanoindentation. Loss tangent, tan δ, was considered as a measure of the degree of the viscoelastic response. Variable dynamic load tests show that the viscoelastic responses of all bone specimens increase with frequency. With demineralisation, bone specimens show greater viscoelastic response than intact specimens. OI bone shows similar viscoelastic response as normal bone. Results suggest that the viscoelasticity of bone is mostly attributable to the mineral phase. The present study adds to the understanding of the viscoelastic response of bone material. In addition, the dynamic mechanical properties of OI bone are firstly reported here.

Nanomechanical and tribological behavior of hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposites for biomedical applications

ABSTRACTA hydroxyapatite (HA) particulate reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposite is fabricated by internal mixer at 180°C and using of paraffin oil as a processing aid to overcome the high viscosity of melted UHMWPE. The reinforcing effects of nano‐HA are investigated on nanomechanical properties of HA/UHMWPE nanocomposites by nanoindentation and nanoscratching methods. Results show that the nanocomposite with 50 wt % nano‐HA exhibits a Young's modulus and hardness of 362.5% and 200% higher, and a friction coefficient of 38.86% lower than that of pure UHMWPE, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42052.

Nanomechanical behavior of MoS2 and WS2 multi-walled nanotubes and carbon nanohorns.

Nano-objects have been investigated for drug delivery, oil detection, contaminant removal, and tribology applications. In some applications, they are subjected to friction and deformation during contact with each other and their surfaces on which they slide. Experimental studies directly comparing local and global deformation are lacking. This research performs nanoindentation (local deformation) and compression tests (global deformation) with a nanoindenter (sharp tip and flat punch, respectively) on molybdenum disulfide (MoS2) multi-walled nanotubes (MWNTs), ~500 nm in diameter. Hardness of the MoS2 nanotube was similar to bulk and does not follow the “smaller is stronger” phenomenon as previously reported for other nano-objects. Tungsten disulfide (WS2) MWNTs, ~300 nm in diameter and carbon nanohorns (CNHs) 80–100 nm in diameter were of interest and also selected for compression studies. These studies aid in understanding the mechanisms involved during global deformation when nano-objects are introduced to reduce friction and wear. For compression, highest loads were required for WS2 nanotubes, then MoS2 nanotubes and CNHs to achieve the same displacement. This was due to the greater number of defects with the MoS2 nanotubes and the flexibility of the CNHs. Repeat compression tests of nano-objects were performed showing a hardening effect for all three nano-objects.

AFM nanomechanical properties and durability of new hybrid fluorinated sol-gel coatings

Microscopically homogeneous and thin fluorinated hybrid coatings showing significantly high mechanical and photochemical durability are prepared through the sol-gel chemistry and studied in this work. Their physico-chemical and nanomechanical properties are investigated. In this study, a special focus is given to the effects of organic/inorganic ratio and inorganic precursor type on surface and mechanical properties at the nanoscale. Different coatings containing low and high contents of silica as well as a mixed oxide composed of high amount of titania and low amount of silica are investigated. Nanoscratch and nanoindentation tests are performed by atomic force microscopy (AFM) and employed to assess the nanomechanical behavior of the hybrid coatings at a proper scale. Dynamic hardness results obtained from AFM are found to be in good agreement with technological pencil scratch tests performed at a macroscopic scale. Owing to the high inorganic content and good cross-linking degree achieved, coatings with a high amount of silica show considerably high dynamic hardness (nearly 2GPa), which remains unchanged even after a long-term UV-vis light exposure. Notwithstanding the comparable inorganic amount, the hardness of mixed oxide coatings is markedly lower than high silica coatings and is subjected to modifications when exposed to UV-vis light in the long term, as also corroborated by x-ray photoelectron spectroscopy (XPS). Young's modulus results obtained by AFM nanoindentations appear to be dependent mostly on the inorganic/organic ratio. Higher moduli are determined for samples with higher inorganic/organic ratio, and no particular effect of the nature of inorganic precursor upon such property is observed.

Extreme resilience in cochleate nanoparticles.

Cochleates, prospective nanoscale drug delivery vehicles, are rolls of negatively charged phospholipid membrane layers. The membrane layers are held together by calcium ions; however, neither the magnitude of membrane interaction forces nor the overall mechanical properties of cochleates have been known. Here, we manipulated individual nanoparticles with atomic force microscopy to characterize their nanomechanical behavior. Their stiffness (4.2-12.5 N/m) and membrane-rupture forces (45.3-278 nN) are orders of magnitude greater than those of the tough viral nanoshells. Even though the fundamental building material of cochleates is a fluid membrane, the combination of supramolecular geometry, the cross-linking action of calcium, and the tight packing of the ions apparently lead to extreme mechanical resilience. The supramolecular design of cochleates may provide efficient protection for encapsulated materials and give clues to understanding biomolecular structures of similar design, such as the myelinated axon.