Nanomechanical Force Research Articles

Experimental Visualization of Commercial Lithium Ion Battery Cathodes: Distinguishing Between the Microstructure Components Using Atomic Force Microscopy

The integration of lithium-ion batteries (LIB) into transportation through the implementation of hybrid and electric vehicles is driving fundamental research into improving their performance and lifetime. The rapid production of new electric vehicles by several popular brands also raises the question of how much material will eventually need to be reused or recycled. With a combination of an enhanced fundamental analysis of commercially utilized electrodes with fundamental chemical knowledge, answers to the scientific material challenges of lithium ion batteries will aid in not only the implementation of battery powered electrical transport but also the development of end of life recycling processes. Here, using quantitative nanomechanical and conductive atomic force microscopy, which are nondestructive and rapid techniques, the different components of the composite electrode are unveiled at the nanoscale, identifying the mechanism by which the active material binds together and how the conductive network is formed. Changes in the polymer binder network are observed in an aged cell and are shown to affect the mechanical integrity of the electrode structure, which can lead to the failure of the electrode. The links between nanomechanical and macro-mechanical properties were evaluated using a scratch test and optical microscopy to show that the mechanical integrity of the aged cell was weaker than that of the untouched cell.

Three-Dimensional (3D) Conductive Network of CNT-Modified Short Jute Fiber-Reinforced Natural Rubber: Hierarchical CNT-Enabled Thermoelectric and Electrically Conductive Composite Interfaces.

Jute fibers (JFs) coated with multiwall carbon nanotubes (MWCNTs) have been introduced in a natural rubber (NR) matrix creating a three-dimensional (3D) electrically conductive percolated network. The JF-CNT endowed electrical conductivity and thermoelectric properties to the final composites. CNT networks fully covered the fiber surfaces as shown by the corresponding scanning electron microscopy (SEM) analysis. NR/JF-CNT composites, at 10, 20 and 30 phr (parts per hundred gram of rubber) have been manufactured using a two-roll mixing process. The highest value of electrical conductivity (σ) was 81 S/m for the 30 phr composite. Thermoelectric measurements revealed slight differences in the Seebeck coefficient (S), while the highest power factor (PF) was 1.80 × 10−2 μW/m K−2 for the 30 phr loading. The micromechanical properties and electrical response of the composite’s conductive interface have been studied in peak force tapping quantitative nanomechanical (PFT QNM) and conductive atomic force microscopy (c-AFM) mode. The JF-CNT create an electrically percolated network at all fiber loadings endowing electrical and thermoelectric properties to the NR matrix, considered thus as promising thermoelectric stretchable materials.

Nanomechanical mapping of rejuvenated asphalt binders

To recycle reclaimed asphalt pavement (RAP) derived from porous asphalt (PA) surfacing into a new PA mix, a fundamental understanding of RAP binder properties is needed. In this paper, properties of two PA RAP binders, with and without rejuvenation, were evaluated using quantitative nanomechanical atomic force microscopy (QNM AFM) and performance grading (PG) testing. A model that describes the effect of a bio-rejuvenator on RAP microstructure was developed. A strong correlation was found between the properties measured at nanoscale and macroscale, indicating that the macro properties of RAP binders are driven by the level of polar associations and intermolecular interactions in the bitumen microstructure. This indicates that the microstructures observed in AFM are representative of the bulk properties. Addition of bio-rejuvenator in RAP resulted in the dispersion of polar associations. Finally, it was found that one percent of the rejuvenator can reduce PG critical temperatures by approximately 2 degrees.

Ultrafast DNA Sensors with DNA Framework-Bridged Hybridization Reactions.

Intracellular DNA-based hybridization reactions generally occur under tension rather than in free states, which are spatiotemporally controlled in physiological conditions. However, how nanomechanical forces affect DNA hybridization efficiencies in in-vitro DNA assays, for example, biosensors or biochips, remains largely elusive. Here, we design DNA framework-based nanomechanical handles that can control the stretching states of DNA molecules. Using a pair of tetrahedral DNA framework (TDF) nanostructured handles, we develop bridge DNA sensors that can capture target DNA with ultrafast speed and high efficiency. We find that the rigid TDF handles bind two ends of a single-stranded DNA (ssDNA) and hold it in a stretched state, with an apparent stretching length comparable to its counterpart of double-stranded DNA (dsDNA) via atomic force microscopy measurement. The DNA stretching effect of ssDNA is then monitored using single-molecule fluorescence energy transfer (FRET), resulting in decreased FRET efficiency in the stretched ssDNA. By controlling the stretching state of ssDNA, we obtained significantly improved hybridization kinetics (within 1 min) and hybridization efficiency (∼98%) under the target concentration of 500 nM. The bridge DNA sensors demonstrated high sensitivity (1 fM), high specificity (single mismatch mutation discrimination), and high selectivity (suitable for the detection in serum and blood) under the target concentration of 10 nM. Controlling the stretching state of ssDNA shows great potential in biosensors, bioimaging, and biochips applications.

Near-Infrared Light Triggered-Release in Deep Brain Regions Using Ultra-photosensitive Nanovesicles.

Remote and minimally-invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold-coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad-PC-Rad as a tool for the delivery of bioactive molecules into brain tissue. Near-infrared picosecond laser pulses activated the gold-coating on the surface of nanovesicles, creating nanomechanical stress and leading to near-complete vesicle cargo release in sub-seconds. Compared to natural phospholipid liposomes, the photo-release was possible at 40 times lower laser energy. This high photosensitivity enables photorelease of molecules down to a depth of 4 mm in mouse brain. This promising tool provides a versatile platform to optically release functional molecules to modulate brain circuits.

Control of dielectric surface energy by dry surface treatment for high performance organic thin film transistor based on dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene semiconductor

We studied organic thin film transistors using vacuum-deposited para-sexiphenyl (p-6P) as a sublayer to reduce the surface energy of the dielectric material. The correlation between the growth mode of a thin film of the organic semiconductor dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene and the number of p-6P sublayers could be explained by a surface energy difference resulting from molecular orientation changes in the p-6P layer. A local surface energy difference was confirmed by measuring the adhesion force using a nanomechanical force measurement method.

Nanomechanical mapping reveals localized stiffening of the basilar membrane after cochlear implantation

Cochlear implantation leads to many structural changes within the cochlea which can impair residual hearing. In patients with preserved low-frequency hearing, a delayed hearing loss can occur weeks-to-years post-implantation. We explore whether stiffening of the basilar membrane (BM) may be a contributory factor in an animal model. Our objective is to map changes in morphology and Young’s modulus of basal and apical areas of the BM after cochlear implantation, using quantitative nanomechanical atomic force microscopy (QNM-AFM) after cochlear implant surgery. Cochlear implantation was undertaken in the guinea pig, and the BM was harvested at four time-points: 1 day, 14 days, 28 days and 84 days post-implantation for QNM-AFM analysis. Auditory brainstem response thresholds were determined prior to implantation and termination. BM tissue showed altered morphology and a progressive increase in Young’s modulus, mainly in the apex, over time after implantation. BM tissue from the cochlear base demonstrated areas of extreme stiffness which are likely due to micro-calcification on the BM. In conclusion, stiffening of the BM after cochlear implantation occurs over time, even at sites far apical to a cochlear implant.

Membrane-Disrupting Nanofibrous Peptide Hydrogels.

Self-assembled peptide nanofibers can form biomimetic hydrogels at physiological pH and ionic strength through noncovalent and reversible interactions. Inspired by natural antimicrobial peptides, we designed a class of cationic amphiphilic self-assembled peptides (CASPs) that self-assemble into thixotropic nanofibrous hydrogels. These constructs employ amphiphilicity and high terminal charge density to disrupt bacterial membranes. Here, we focus on three aspects of the self-assembly of these hydrogels: (a) the material properties of the individual self-assembled nanofibers, (b) emergence of bulk-scale elasticity in the nanofibrous hydrogel, and (c) trade-off between the desirable material properties and antimicrobial efficacy. The design of the supramolecular nanofibers allows for higher-order noncovalent ionic cross-linking of the nanofibers into a viscoelastic network. We determine the stiffness of the self-assembled nanofibers via the peak force quantitative nanomechanical atomic force microscopy and the bulk-scale rheometry. The storage moduli depend on peptide concentration, ionic strength, and concentration of multivalent ionic cross-linker. CASP nanofibers are demonstrated to be effective against Pseudomonas aeruginosa colonies. We use nanomechanical analysis and microsecond-time scale coarse-grained simulation to elucidate the interaction between the peptides and bacterial membranes. We demonstrate that the membranes stiffen, contract, and buckle after binding to peptide nanofibers, allowing disruption of osmotic equilibrium between the intracellular and extracellular matrix. This is further associated with dramatic changes in cell morphology. Our studies suggest that self-assembled peptide nanofibrils can potentially acts as membrane-disrupting antimicrobial agents, which can be formulated as injectable hydrogels with tunable material properties.

Time-resolved nano-Newton force spectroscopy in air and vacuum using a load cell of ultra micro-balance.

We demonstrate a simple and versatile nanomechanical force measuring setup with 1 nN precision in air and vacuum using a load cell of an ultra-microbalance. We validate stability, precision, and linearity of the load cell with simple tests. The setup is customized to measure stress-strain response of biomaterials (silk, leaf, and flower) and capillary force in fluids. We isolated an optical pull force induced by a Watt-level laser reflected from a mirror/solid surface in air, in addition to optical push force. Furthermore, we add an interferometric probe to directly measure nanoscale deflection of cantilever of the load cell in real-time, thus bypassing its conventional electromagnetic readout, to improve speed and precision of the instrument. We demonstrate nanomechanical force measurement in high vacuum with the same precision and employ radiation pressure to calibrate the load cell for various precision measurements.

Top-down strategy synthesis of fluorinated graphdiyne for lithium ion battery.

As a novel carbon allotrope, graphdiyne exhibits excellent electrochemical properties such as high specific capacities, outstanding rate performances, and long cycle lives. These properties are attributed to its sp- and sp2-hybridized bonding and a natural large pore structure. Doping with light elements is a facile way to improve the electrochemical performance of graphdiyne. Herein, we report the preparation of fluorine-doped graphdiyne by exposure to XeF2 under a mild temperature. Compared to pristine graphdiyne, the capacities are doubled. We obtained reversible capacities of fluorinated graphdiyne up to 1080 mA h g−1 after 600 cycles at a current density of 500 mA g−1. At a higher current density of 1000 mA g−1, it still retained a high specific capacity of 693 mA h g−1 after 1000 cycles. Using in situ quantitative nanomechanical probe atomic force microscopy, we further analyzed the surface morphologies and elastic modulus to understand the mechanism of the electrochemical improvement. The fluorinated graphdiyne elastic modulus is doubled in contrast to pristine graphdiyne. The performance improvements are attributed to the improvement in conductivity and enhancement of the mechanical properties.

Plasmon‐Polariton Induced, “from Surface” RAFT Polymerization, as a Way toward Creation of Grafted Polymer Films with Thickness Precisely Controlled by Self‐Limiting Mechanism

AbstractPlasmon‐induced “from surface” reversible addition‐fragmentation chain‐transfer (RAFT) polymerization is reported for the first time. The gold grating surface, supporting the surface plasmon polariton excitation and propagation, is grafted with RAFT agent, immersed in the solution, containing the NIPAm monomer and AIBN and subsequently illuminated at a wavelength corresponding to plasmon absorption. The grafting of the polymer layer, its thickness, and morphology are characterized by several techniques (including the surface‐enhanced Raman spectroscopy (SERS), scanning electron microscopy and energy‐dispersive X‐ray spectroscopy (SEM‐EDX), X‐ray photoelectron spectroscopy (XPS), nanomechanical atomic force microscopy (AFM) mapping, and goniometry). It is shown that the polymerization efficiently starts only under the surface plasmon‐polariton excitation. The time‐dependent SERS and XPS measurements indicate rather self‐limiting nature of plasmon‐induced “from the surface” PNIPAm growth, namely the reaction takes place up to a certain polymer thickness and is stopped despite a significant excess of polymerization initiator and monomer in the reaction solution. The present results provide the basis for designing further experiments on plasmonic catalysis in general and offer a new way of producing ultrathin polymer films with a defined structural dimension.

In situ AFM study of low-temperature polymerization and network formation of thin film polyurea in ionic liquid

When a monomer/oligomer film composed of 4,4′-methylenebis(2-chlorophenyl isocyanate) (MBCI) and 2,7-diaminofluorene (DAF) stoichiometrically equivalent to each other is simply annealed in ionic liquid (IL), its polymerization and network formation take place at below 100 °C. It is in contrast to the case by annealing without IL in the air, in which much higher temperature is needed for the polymerization, but never happens such network formation. In situ topographic and nanomechanical atomic force microscopy (AFM), combined with separate ex situ experiments of Fourier transform infrared spectroscopy (FT-IR), is powerful to visualize this IL-assisted annealing process. The surface nanomechanical hardening behavior was first observed as a sign of the surface polymerization at a temperature as low as 45 °C prior to the formation of porous structures; many pits then appeared at around 50–55 °C, followed by a rapid emergence of porous, network structures above 60 °C.

Nanometrology of Biomass for Bioenergy: The Role of Atomic Force Microscopy and Spectroscopy in Plant Cell Characterization

Ethanol production using extracted cellulose from plant cell walls (PCW) is a very promising 4 approach to biofuel production. However, efficient throughput has been hindered by the pheno5 menon of recalcitrance, leading to high costs for the lignocellulosic conversion. To overcome 6 recalcitrance, it is necessary to understand the chemical and structural properties of the plant 7 biological materials, which have evolved to generate the strong and cohesive features observed 8 in plants. Therefore, tools and methods that allow the investigation of how the different molecular 9 components of PCW are organized and distributed and how this impacts the mechanical proper10 ties of the plants are needed but challenging due to the molecular and morphological complexity 11 of PCW. Atomic force microscopy (AFM), capitalizing on the interfacial nanomechanical forces, 12 encompasses a suite of measurement modalities for nondestructive material characterization. 13 Here, we present a review focused on the utilization of AFM for imaging and determination of 14 physical properties of plant-based specimens. The presented review encompasses the AFM 15 derived techniques for topography imaging (AM-AFM), mechanical properties (QFM), and sur16 face/subsurface (MSAFM, HPFM) chemical composition imaging. In particular, the motivation and 17 utility of force microscopy of plant cell walls from the early fundamental investigations to achieve 18 a better understanding of the cell wall architecture, to the recent studies for the sake of advancing 19 the biofuel research are discussed. An example of delignification protocol is described and the 20 changes in morphology, chemical composition and mechanical properties and their correlation at 21 the nanometer scale along the process are illustrated.

Receptor-mediated endocytosis generates nanomechanical force reflective of ligand identity and cellular property.

Whether environmental (thermal, chemical, and nutrient) signals generate quantifiable, nanoscale, mechanophysical changes in the cellular plasma membrane has not been well elucidated. Assessment of such mechanophysical properties of plasma membrane may shed lights on fundamental cellular process. Atomic force microscopic (AFM) measurement of the mechanical properties of live cells was hampered by the difficulty in accounting for the effects of the cantilever motion and the associated hydrodynamic force on the mechanical measurement. These challenges have been addressed in our recently developed control-based AFM nanomechanical measurement protocol, which enables a fast, noninvasive, broadband measurement of the real-time changes in plasma membrane elasticity in live cells. Here we show using this newly developed AFM platform that the plasma membrane of live mammalian cells exhibits a constant and quantifiable nanomechanical property, the membrane elasticity. This mechanical property sensitively changes in response to environmental factors, such as the thermal, chemical, and growth factor stimuli. We demonstrate that different chemical inhibitors of endocytosis elicit distinct changes in plasma membrane elastic modulus reflecting their specific molecular actions on the lipid configuration or the endocytic machinery. Interestingly, two different growth factors, EGF and Wnt3a, elicited distinct elastic force profiles revealed by AFM at the plasma membrane during receptor-mediated endocytosis. By applying this platform to genetically modified cells, we uncovered a previously unknown contribution of Cdc42, a key component of the cellular trafficking network, to EGF-stimulated endocytosis at plasma membrane. Together, this nanomechanical AFM study establishes an important foundation that is expandable and adaptable for investigation of cellular membrane evolution in response to various key extracellular signals.

On the use of nanomechanical atomic force microscopy to characterise oil-exposed surfaces.

Oil-exposed surfaces are susceptible to carbonaceous deposits (CDs). In turn, deposits are responsible for fouling, compromising performance and reducing profitability across the hydrocarbon value chain. An understanding of the deposition behaviour of these organic molecules is therefore imperative. In this paper we address the question of understanding the deposition in upstream operation, where the CDs are known to be asphaltenes, the heaviest fraction of oil. Systematic characterisation of fouled oil-exposed surfaces constitutes an initial step towards that direction and it is a challenging task in itself. We demonstrate the use of Atomic Force Microscopy (AFM) to map surface mechanical properties and how they can be used to determine differences between deposit types. We also demonstrate that the use of an adhesion inhibitor (AI) has a dramatic effect not only on the morphology but also on the mechanical properties of asphaltene deposits.

Electron-induced reactive processing of polyamide 6/polypropylene blends: Morphology and properties

Electron-induced reactive processing (EIReP) recently has appeared as an advanced processing technology to modify several polymer compounds at melt state by its spatial and temporal precise energy input. In the present work, an attempt was made to prepare a compatible blend from polar polyamide 6 (PA6) and non-polar polypropylene (PP) using EIReP without any chemical crosslinking and chemical additives. EIReP modified blends were prepared at different doses (5, 10 and 20 kGy) and dose per revolutions (3, 6 and 12 kGy/rev) while keeping constant the values of mass ratio (PA6/PP 50/50 w/w), electron energy (1.5 MeV), rotor speed (60 rpm) and temperature (230 °C). EIReP process parameters-morphology-property relationship of this blend was studied. Interestingly, co-continuous morphology of the blend was converted to droplet-matrix morphology after EIReP whether PA6 was continuous phase. Influence of dose and dose per revolution on the DMT modulus (Derjaguin-Muller-Toporov) at different phases of the blends was also measured and analyzed using advanced PeakForce Quantitative Nanomechanical Mapping atomic force microscopy (PF QNM AFM) technique. Improved nano- and macroscopic properties of EIReP modified blends were originated from the properties of the continuous matrix phase, electron-induced branching and also from the reduction of domain size of PP phase with increased dose.

Nanomechanical Force Mapping of Restricted Cell-To-Cell Collisions Oscillating between Contraction and Relaxation.

Contact-mediated cell migration strongly determines the invasiveness of the corresponding cells, collective migration, and morphogenesis. The quantitative study of cellular response upon contact relies on cell-to-cell collision, which rarely occurs in conventional cell culture. Herein, we developed a strategy to activate a robust cell-to-cell collision within smooth muscle cell pairs. Nanomechanical traction force mapping reveals that the collision process is promoted by the oscillatory modulations between contraction and relaxation and orientated by the filopodial bridge composed of nanosized contractile machinery. This strategy can enhance the occurrence of cell-to-cell collision, which renders it advantageous over traditional methods that utilize micropatterned coating to confine cell pairs. Furthermore, modulation of the balance between cell tugging force and traction force can determine the repolarization of cells and thus the direction of cell migration. Overall, our approach could help to reveal the mechanistic contribution in cell motility and provide insights in tissue engineering.

Polymersomes at the solid-liquid interface: Dynamic morphological transformation and lubrication

Polymersomes are hollow spheres self-assembled from amphiphilic block copolymers of certain molecular architecture. Whilst they have been widely studied for biomedical applications, relatively few studies have reported their interfacial properties. In particular, lubrication by polymersomes has not been previously reported. Here, interfacial properties of polymersomes self-assembled from poly(butadiene)-poly(ethylene oxide) (PBD-PEO; molecular weight 10,400 g mol−1) have been studied at both hydrophilic and hydrophobic surfaces. Their morphology at silica and mica surfaces was imaged with quantitative nanomechanical property mapping atomic force microscopy (QNM AFM), and friction and surface forces they mediate under confinement between two surfaces were studied using colloidal probe AFM (CP-AFM). We find that the polymersomes remained intact but adopted flattened conformation once adsorbed to mica, with a relatively low coverage. However, on silica these polymersomes were unstable, rupturing to form donut shaped residues or patchy bilayers. On a silica surface hydrophobized with a 19 nm polystyrene (PS) film, the polymer vesicles formed a more stable layer with a higher surface coverage as compared to the hydrophilic surface, and the interfacial structure also evolved over time. Moreover, friction was greatly reduced on hydrophobized silica surfaces in the presence of polymersomes, suggesting their potential as effective aqueous lubricants.

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.

Standardized Nanomechanical Atomic Force Microscopy Procedure (SNAP) for Measuring Soft and Biological Samples

We present a procedure that allows a reliable determination of the elastic (Young’s) modulus of soft samples, including living cells, by atomic force microscopy (AFM). The standardized nanomechanical AFM procedure (SNAP) ensures the precise adjustment of the AFM optical lever system, a prerequisite for all kinds of force spectroscopy methods, to obtain reliable values independent of the instrument, laboratory and operator. Measurements of soft hydrogel samples with a well-defined elastic modulus using different AFMs revealed that the uncertainties in the determination of the deflection sensitivity and subsequently cantilever’s spring constant were the main sources of error. SNAP eliminates those errors by calculating the correct deflection sensitivity based on spring constants determined with a vibrometer. The procedure was validated within a large network of European laboratories by measuring the elastic properties of gels and living cells, showing that its application reduces the variability in elastic moduli of hydrogels down to 1%, and increased the consistency of living cells elasticity measurements by a factor of two. The high reproducibility of elasticity measurements provided by SNAP could improve significantly the applicability of cell mechanics as a quantitative marker to discriminate between cell types and conditions.