Dynamic Atomic Force Microscopy Research Articles

Incongruous Harmonics of Vibrating Solid‐Solid Interface

AbstractDeconvoluting the vibrations and harmonics in solid‐solid interfaces is crucial for designing materials with improved performance, durability, and functionality. The measured vibrating microcantilever signal in the dynamic atomic force microscopy (AFM) encompasses a multitude of distinct signatures reflecting a diverse array of material properties. Nevertheless, uncertainties persist in decoding these signatures, primarily arising from the interplay between attractive and repulsive forces. Consequently, it is challenging to correlate the generated harmonics within the solid‐solid interfaces with the imaged phase and topography of materials, as well as the occasional observed contrast reversal. In this study, the vibration harmonics produced at solid‐solid interfaces are correlated, linking them to short‐range nano‐mechanical characteristics through a comprehensive blend of theory, simulation, and experimental methods. These findings shed light on the roots of harmonic generation and contrast reversals, opening avenues for designing innovative materials with customized properties.

Reconstruction of calcite (10.4) manifests itself in the tip-assisted diffusion of water

Calcite (calcium carbonate) is the most abundant carbonate in the Earth's crust. Due to its omnipresence it plays a prominent role in fields such as geochemistry, biomineralization and industrial processes. Moreover, the interaction of water with the most stable cleavage plane, calcite (10.4), has been studied intensively, elucidating atomic-scale details of water binding and structure formation on this surface. Interestingly, calcite (10.4) reconstructs under ultrahigh vacuum conditions, exhibiting a (2 × 1) surface unit cell. Although first indications of this reconstruction have been presented more than 20 years ago, a clear confirmation of the existence has been provided only very recently. Here, we study the tip-assisted diffusion of water molecules on calcite (10.4) under ultrahigh vacuum conditions. By recording images series using dynamic atomic force microscopy we follow the movement of water molecules on the surface kept at 140 K. Analyzing the change in consecutive images allows for elucidating details of the molecular movement on the surface. Most notably, the analysis reveals that water molecules occupy one type of adsorption position exclusively, while the other type is not adopted. Our analysis thus demonstrates that the (2 × 1) reconstruction manifests itself in the movement of single water molecules on this surface.

Intracellular bactericidal activity and action mechanism of MDP1 antimicrobial peptide against VRSA and MRSA in human endothelial cells.

Staphylococcus aureus is a prominent cause of postoperative infections, often persisting within host cells, leading to chronic infections. Conventional antibiotics struggle to eliminate intracellular S. aureus due to poor cell penetration. Antimicrobial peptides are a new hope for tackling intracellular bacteria. Accordingly, this study examines the antimicrobial peptide MDP1, derived from melittin, for its efficacy against intracellular S. aureus. In this study, the physiochemical properties (Prediction of three-dimensional structure, circular dichroism and helical wheel projection analysis) were investigated. Extracellular antibacterial activity and cytotoxicity of MDP1 were also assessed. The mechanism of interaction of MDP1 with S. aureus was evaluated by molecular dynamic simulation, atomic force and confocal microscopy. Bacterial internalization into an endothelial cell model was confirmed through culture and transmission electron microscopy. The effect of the peptide on intracellular bacteria was investigated by culture and epi-fluorescence microscopy. 3D structural prediction proved the conformation of MDP1 as an α-helix peptide. Helical-wheel projection analysis indicated the proper orientation of hydrophobic amino acid residues for membrane interaction. CD spectroscopy of MDP1 showed that MDP1 in SDS 10 and 30 mM adopted 87 and 91% helical conformation. Atomic force and confocal microscopy assessments as well as molecular dynamics studies revealed the peptide-bacterial membrane interaction. MDP1, at the concentration of 0.32 μg mL-1, demonstrated a fold reduction of 21.7 ± 1.8, 1.7 ± 0.2, and 7.3 ± 0.8 in intracellular bacterial load for ATCC, VRSA, and MRSA, respectively. Molecular dynamics results demonstrate a preferential interaction of MDP1 with POPG/POPE membranes, primarily driven by electrostatic forces and hydrogen bonding. In POPC systems, two out of four MDP1 interacted effectively, while all four MDP1 engaged with POPG/POPE membranes. Gathering all data together, MDP1 is efficacious in the reduction of intracellular VRSA and MRSA proved by culture and epi-fluorescent microscopy although further studies should be performed to increase the intracellular activity of MDP1.

Water-in-oil microemulsions with greener oil solvents as sustainable nanoreactors of biopolymer nanoparticles

Microemulsions have been widely used in multidisciplinary fields, yet reverse water-in-oil microemulsions are traditionally dispersed in petroleum-based oil solvents. For greener approaches, it should be also feasible to use less toxic, bio-based hydrocarbon solvents as continuous oil phase. Herein, reverse microemulsions in different alkanes, middle-chain alkanols, middle-chain esters or combinations of nonpolar solvent with alkanol are compared, using Aerosol-OT as common surfactant. As model of bio-based solvents, ethyl caprylate, isoamyl acetate and isoamyl alcohol are proposed as a more sustainable approach of oil solvents. Various characterization techniques were used to compare the properties and stability of reverse microemulsions for the different oil phase compositions, ranging from ternary phase diagrams to conductometry and turbidity titrations, micro-Differential Scanning Calorimetry and cryo-Scanning Electron Microscopy. As sustainable application, these microemulsions in bio-based solvents were proved suitable as template phase for the synthesis of cross-linked chitosan nanoparticles. The sizes of the resulting biopolymer nanoparticles were characterized by Dynamic Light Scattering and Atomic Force Microscopy, so that the effect of different crosslinkers and different the oil phase compositions was also compared. Thus, the use bio-based alkyl esters can provide similar microemulsion properties as the conventional alkanes, especially when using a combination of nonpolar solvents with alkanols.

Probing Viscoelastic Properties and Interfaces in High-Density Polyethylene Vitrimers at the Nanoscale Using Dynamic Mode Atomic Force Microscopy.

Vitrimers are a new class of heterogeneous polymers that combine the best features of thermosets with those of thermoplastics. The introduction of cross-links strongly changes the viscoelastic behavior of vitrimer materials. However, the characterization and understanding of the nanostructures and interfaces in vitrimers resulting from dynamic cross-linking formation remain a major challenge. Here, using dynamic modes of atomic force microscopy (AFM), namely intermodulation AFM (ImAFM) and AFM-based dynamic mechanical analysis (AFM-nDMA), local viscoelastic properties and interfaces at the nanoscale length of high-density polyethylene (HDPE) vitrimer materials are reported. ImAFM imaging in combination with the k-means clustering algorithm clearly reveals two distinct phases in the vitrimer system with highly different viscoelastic properties. AFM-nDMA further provides quantitative nanoviscoelastic properties at the nanoscale to confirm that there is a cross-linking-rich aggregation area forming a nanosize network structure in the cross-linking-poor matrix phase. The cross-linking-rich region shows a similar elastic modulus but much higher adhesion force measured by AFM compared to the cross-linking-poor HDPE matrix. Furthermore, the frequency influence on the local viscoelastic properties of HDPE vitrimer at the nanoscale was initially screened. The observed HDPE vitrimer nanostructures and viscoelastic properties at the nanoscale also provide explanations on the observed bulk HDPE vitrimer crystallinity decrease and dimensional stability increase compared to HDPE. Therefore, probing the viscoelastic properties and interfaces of HDPE vitrimer provides important insights into understanding of the correlations between the vitrimer nanostructure and the bulk mechanical and rheological behaviors.

Chain-Length Dependence of Peptide-Lipid Bilayer Interaction Strength and Binding Kinetics: A Combined Theoretical and Experimental Approach.

Physical interactions between polypeptide chains and lipid membranes underlie critical cellular processes. Yet, despite fundamental importance, key mechanistic aspects of these interactions remain elusive. Bulk experiments have revealed a linear relationship between free energy and peptide chain length in a model system, but does this linearity extend to the interaction strength and to the kinetics of lipid binding? To address these questions, we utilized a combination of coarse-grained molecular dynamics (CG MD) simulations, analytical modeling, and atomic force microscopy (AFM)-based single molecule force spectroscopy. Following previous bulk experiments, we focused on interactions between short hydrophobic peptides (WLn, n = 1, ..., 5) with 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) bilayers, a simple system that probes peptide primary structure effects. Potentials of mean force extracted from CG MD recapitulated the linearity of free energy with the chain length. Simulation results were quantitatively connected to bulk biochemical experiments via a single scaling factor of order unity, corroborating the methodology. Additionally, CG MD revealed an increase in the distance to the transition state, a result that weakens the dependence of the dissociation force on the peptide chain length. AFM experiments elucidated rupture force distributions and, through modeling, intrinsic dissociation rates. Taken together, the analysis indicates a rupture force plateau in the WLn-POPC system, suggesting that the final rupture event involves the last 2 or 3 residues. In contrast, the linear dependence on chain length was preserved in the intrinsic dissociation rate. This study advances the understanding of peptide-lipid interactions and provides potentially useful insights for the design of peptides with tailored membrane-interacting properties.

Synthesis and evaluation of Schiff base as corrosion inhibitor for carbon steel in 1 M HCl solution

PurposeThe main purpose of the present study is to introduce new Schiff bases as corrosion inhibitor for carbon steel in 1 M HCl. The inhibitory activity of Schiff base was also assessed.Design/methodology/approach2,2′-((1Z,1′Z)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))diphenol was synthesized and it’s performance as an inhibitor was then investigated in 1 M HCl. The inhibition of this compound was studied and evaluated by the chemical methods of electrochemical impedance spectroscopy, electrochemical potential dynamic polarization and Atomic Force microscopy (AFM) method. The thermodynamics parameters were investigated for corrosion of carbon steel in both the absence and presence of Schiff base.FindingsThe results of the tests showed that this compound has a good performance as an inhibitor and the percentage of inhibition on steel corrosion will increase with increasing concentration and it will reach 70% in the presence of 2 × 10−3 M of this inhibitor. Polarization tests indicated that this compound will act as a mixed inhibitor. Nyquist curves showed that the addition of this substance to the solution increased the charge transfer resistance and decreased the capacity of the double layer. The absorption of the new Schiff base on steel follows Langmuir adsorption isotherm, and the amount of free energy of adsorption indicates the spontaneous adsorption of this inhibitor. Using AFM investigations, the results of electrochemical methods were confirmed.Originality/valueIncorporation of a new Schiff base into 1 M HCl is a promising approach for protecting the carbon steel against corrosive solution.

Ionic liquid coating for charge mitigation of solar modules in space: Electron microscopy on insulating nanosphere lithography patterned surfaces

Surfaces of satellites and spacecrafts are exposed to high energy charged particles from the solar wind, especially during space weather events. This can lead to differential charging, which is a common reason for hardware degradation and sensor errors. Solutions like coatings are required to avoid excessive cost and weight. Mimicking the electron part of space-like environments in ultra-high vacuum (UHV) chambers can be achieved by using electrons emitted by a scanning electron microscope (SEM). As a performance test for the discharge capabilities we use the quality of electron microscopy images on otherwise insulating substrates such as glass, structured by nanosphere lithography and coated with an ionic liquid (IL). Additionally, the surface potential was measured by Kelvin Probe Force Spectroscopy. The IL film (BMP DCA) was applied ex situ and a thickness of 12.8 ($\pm$0.8)\,nm was determined by reflectometry and confirmed by dynamic atomic force microscopy. Such a film of ionic liquid would lead to additional mass of below 20\,mg and negligible additional material costs. The light absorption and influence of ionic liquid coatings on the current output of an actual solar cell were investigated. The results indicate, that these coatings are promising candidates for surface charge mitigation with a high potential for application

Control of quality factor of atomic force microscopy cantilever by cavity optomechanical effect

The effective quality factor of the cantilever plays a fundamental role in dynamic mode atomic force microscopy. Here we present a technique to modify the quality factor of an atomic force microscopy cantilever within a Fabry–Perot optical interferometer. The experimental setup uses two separate laser sources to detect and excite the oscillation of the cantilever. While the intensity modulation of the excitation laser drives the oscillation of the cantilever, the average intensity can be used to modify the quality factor via optomechanical force without changing the fiber-cantilever cavity length. The technique enables users to optimize the quality factor for different types of measurements without influencing the deflection measurement sensitivity. An unexpected frequency shift was observed and modelled as temperature dependence of the cantilever’s Young’s modulus, which was validated using finite element simulation. The model was used to compensate for the thermal frequency shift. The simulation provided relations between optical power, temperature, and frequency shift.

Enhanced feedback performance in off-resonance AFM modes through pulse train sampling.

Dynamic atomic force microscopy (AFM) modes that operate at frequencies far away from the resonance frequency of the cantilever (off-resonance tapping (ORT) modes) can provide high-resolution imaging of a wide range of sample types, including biological samples, soft polymers, and hard materials. These modes offer precise and stable control of vertical force, as well as reduced lateral force. Simultaneously, they enable mechanical property mapping of the sample. However, ORT modes have an intrinsic drawback: a low scan speed due to the limited ORT rate, generally in the low-kilohertz range. Here, we analyze how the conventional ORT control method limits the topography tracking quality and hence the imaging speed. The closed-loop controller in conventional ORT restricts the sampling rate to the ORT rate and introduces a large closed-loop delay. We present an alternative ORT control method in which the closed-loop controller samples and tracks the vertical force changes during a defined time window of the tip-sample interaction. Through this, we use multiple samples in the proximity of the maximum force for the feedback loop, rather than only one sample at the maximum force instant. This method leads to improved topography tracking at a given ORT rate and therefore enables higher scan rates while refining the mechanical property mapping.

5-Fluorouracil-Loaded PLGA Declined Expression of Pro-Inflammatory Genes IL-9, IL-17A, IL-23 and IFN- y; in the HT-29 Colon Cancer Cell Line.

Pro-inflammatory cytokines play critical roles in cancer pathobiology and have been considered potential targets for cancer management and therapy. Understanding the impact of cancer therapeutics such as 5-fluorouracil (5-FU) on their expression might shed light on development of novel combinational therapies. This study aimed to encapsulate 5-FU into PLGA and evaluate their effects on the expression of pro-inflammatory genes IL-9, IL-17-A, IL-23, and IFN-y; in the HT-29 cells. PLGA-5-FU NPs were constructed and characterized by Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM). The cytotoxicity was evaluated by MTT test and, the IC50 was identified. HT-29 cells were treated with different concentrations of the PLGA-5-FU NPs for 48 hours and, gene expression levels were analyzed by qRT-PCR. DLS and AFM analysis revealed that the prepared PLGA-5-FU NPs were negatively charged spherical-shaped particles with a mean size of 215.9 ± 43.3 nm. PLGA-5-FU NPs impacted the viability of HT-29 cells in a dose- and time-dependent manner. The qRT-PCR results revealed a dose-dependent decrease in the expression of IL-9, IL-17A, IL-23 and IFN-y; genes, and their expressions were significantly different in both 10 and 20 µg/mL treated groups compared to the control. However, although the treatment of HT-29 cells with 20 µg/mL free 5-FU resulted in decreased expression of the studied genes, the differences were not statistically significant compared to the control group. PLGA-5-FU NPs significantly suppressed expression of the IL-9, IL-17A, IL-23 and IFN-y; genes, and the encapsulation of 5-FU into PLGA improved considerably impact of the 5-FU on the HT-29 cells.

Focused Helium Ion and Electron Beam-Induced Deposition of Organometallic Tips for Dynamic Atomic Force Microscopy of Biomolecules in Liquid.

We demonstrate the fabrication of sharp nanopillars of high aspect ratio onto specialized atomic force microscopy (AFM) microcantilevers and their use for high-speed AFM of DNA and nucleoproteins in liquid. The fabrication technique uses localized charged-particle-induced deposition with either a focused beam of helium ions or electrons in a helium ion microscope (HIM) or scanning electron microscope (SEM). This approach enables customized growth onto delicate substrates with nanometer-scale placement precision and in situ imaging of the final tip structures using the HIM or SEM. Tip radii of <10 nm are obtained and the underlying microcantilever remains intact. Instead of the more commonly used organic precursors employed for bio-AFM applications, we use an organometallic precursor (tungsten hexacarbonyl) resulting in tungsten-containing tips. Transmission electron microscopy reveals a thin layer of carbon on the tips. The interaction of the new tips with biological specimens is therefore likely very similar to that of standard carbonaceous tips, with the added benefit of robustness. A further advantage of the organometallic tips is that compared to carbonaceous tips they better withstand UV-ozone cleaning treatments to remove residual organic contaminants between experiments, which are inevitable during the scanning of soft biomolecules in liquid. Our tips can also be grown onto the blunted tips of previously used cantilevers, thus providing a means to recycle specialized cantilevers and restore their performance to the original manufacturer specifications. Finally, a focused helium ion beam milling technique to reduce the tip radii and thus further improve lateral spatial resolution in the AFM scans is demonstrated.

Impact of long-range attraction on desorption kinetics.

Desorption of molecules from surfaces is widespread both in nature and technology. Despite its omnipresence and conceptual simplicity, fundamental details can be surprisingly complex and are often poorly understood. In many cases, first-order kinetics is assumed, which implies that the adsorbates do not interact with each other and desorption is the rate-limiting process. While this might be a good approximation in some cases, it is far from reality in the case of adsorbates that form ordered structures. Here, we study the desorption of a submonolayer film of 3-nitrophenol from the natural cleavage plane of calcite kept in ultrahigh vacuum. Interestingly, two distinctly different desorption regimes are observed during isothermal desorption monitored by dynamic atomic force microscopy. Initially, at high coverages, the coverage decreases almost linearly in time, indicating a constant desorption rate. Beyond this linear regime, at low coverages, a drastic increase in desorption rate is observed until the surface is completely empty. The transition between these two regimes is associated with a critical island width. We propose an existence of a long-range attractive interaction between the molecules as a possible explanation for the sudden increase in the desorption rate when a critical island width is reached. The herein observed phenomenon of two different desorption regimes is expected to be of general nature when interactions beyond next-neighbour attraction are present.

Analysis of dynamic characteristics of cantilevers excited at the fixed end in dynamic atomic force microscopy in liquid environments

Analysis of dynamic characteristics of cantilevers excited at the fixed end in dynamic atomic force microscopy in liquid environments

Self‐Healing Polybutadienes Formed through Sigmatropic Rearrangement and Stratified H‐Bonding for Use in Polymer‐Bonded Explosives

AbstractThe accomplishment of self‐healing polybutadienes (PB) is decisive for multitude of aerospace applications. We here present the first‐time report on a self‐healing PB derived from a blend of allyloxy end functionalized PB elicited through intramolecular thermally activated sigmatropic Claisen rearrangement coupled with stratified hydrogen bonding for use in polymer bonded explosives (PBX). Heteronuclear Single Quantum Correlation (HSQC), Heteronuclear Multiple Bond Coherence (HMBC), Total Correlation Spectroscopy (TOCSY) and Fourier Transform Infrared spectroscopy (FTIR) Spectroscopy were utilized to confirm the mechanistic aspects of the rearrangement for the proposed application. The mechanism of self‐healing is further elucidated using density functional theory (DFT) computations and confirmed through Raman spectroscopy. The biphasic polymer network architecture is disclosed through two glass transitions at −54 °C and 15–25 °C, as confirmed by Dynamic Mechanical Analysis (DMA) and Atomic Force Microscopy (AFM). The polymer exhibited healing efficiency of 85 % suitable for adhesive or coating applications. Self‐healing in bonding formulations of insensitive polymer bonded explosives was also expedited which exhibited a healing efficiency of 49–54 %.

Rapid method for detection of Vibrio cholerae from drinking water with nanomaterials enhancing electrochemical biosensor

Cholera is a potentially fatal diarrheal disease caused by Vibrio cholerae and is spread to humans from contaminated food and water. In order to prevent spread of epidemic chlorea, the development of novel sensitive, selective, user-friendly, cost-effective and rapid detection systems to detect of V. cholerae are necessary. Therefore, in this study, it was aimed to develop a specific, electrochemical immunoassay with high selectivitiy and sensitivity for detection of V. cholerae from drinking water using in house synthesized Gold Nanoparticles (AuNPs). The synthesized AuNPs were characterized by UV/Vis spectroscopy, Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM) and electrochemical techniques were applied to confirm the succesful fabrication of the immunosensor. Also, this study focuses on the development of an antibody sensor for V. cholerae detection using a standard immunoassay without using nanoparticle. To accomplish that, in house spherical synthesized AuNPs at various sizes were synthesized, conjugated with secondary antibody-horseradish peroxidase enzyme (HRP) complex and their possible effect on the lowest detection limit of V. cholerae was investigated in comparison to commercially available AuNPs. The AuNPs-immunosensor on the results enabled the quantification of V. cholerae in a wide concentration range with a high sensitivity limit of detection (1 Colony-Forming Units/Milliliter) and specificity. Although the effect of 33 and 54 nm AuNPs on the process is close to each other, it has been observed that there is a 34% loss of efficiency when the size of the nanoparticle increases. With this study, a novel V. cholerae specific immunosensor was developed and the effects of in house synthesized AuNPs with various diameter on this developed biosensor were investigated in detail.

Chemo-mechanical forces modulate the topology dynamics of mesoscale DNA assemblies

The intrinsic complexity of many mesoscale (10–100 nm) cellular machineries makes it challenging to elucidate their topological arrangement and transition dynamics. Here, we exploit DNA origami nanospring as a model system to demonstrate that tens of piconewton linear force can modulate higher-order conformation dynamics of mesoscale molecular assemblies. By switching between two chemical structures (i.e., duplex and tetraplex DNA) in the junctions of adjacent origami modules, the corresponding stretching or compressing chemo-mechanical stress reversibly flips the backbone orientations of the DNA nanosprings. Both coarse-grained molecular dynamics simulations and atomic force microscopy measurements reveal that such a backbone conformational switch does not alter the right-handed chirality of the nanospring helix. This result suggests that mesoscale helical handedness may be governed by the torque, rather than the achiral orientation, of nanospring backbones. It offers a topology-based caging/uncaging concept to present chemicals in response to environmental cues in solution.

Poly(glycidyl methacrylate) modified cellulose nanocrystals and their PBAT-based nanocomposites

Melt processing of cellulose nanocrystals (CNCs) reinforced nanocomposites is still a serious challenge due to the hydrophilic nature of CNCs and their severe agglomeration tendency within the polymer melt. In this study, chemical modification of CNC through grafting poly(glycidyl methacrylate) (PGMA) with various degrees was implemented. Wettability of the modified CNCs (mCNCs) were controlled and their structure was characterized through Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), optical microscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The nanocomposites of polybutylene adipate terephthalate (PBAT) with 3 wt% CNC and mCNC were prepared using an internal melt mixer. To differentiate the effects of CNC and PGMA molecules on the final properties of nanocomposites, PBAT/PGMA compounds were separately prepared. To confirm the chain characterization and molecular weight of the synthesized PGMAs, 1H NMR and gel permeation chromatography (GPC) analysis were conducted. Melt rheological analysis, dynamic mechanical analysis (DMA), DSC, and atomic force microscopy (AFM) were used to monitor the mCNC dispersion quality and the effect of PGMA modification in PBAT compounds. The results revealed that grafting CNC with longer PGMA considerably improved the CNCs' dispersion quality within PBAT. Such dispersion enhancement of long-chain mCNCs and interfacial interaction of PGMA and PBAT resulted in a noticeable increase in storage modulus and complex viscosity of the final nanocomposites.

Microstructural characteristics evolution of asphalt mastics under cyclic environmental temperature variations

Environmental temperature-effect is the primary factor responsible for asphalt pavement failure. Asphalt pavement exposed to the atmosphere is constantly subjected to the thermal cycles induced by environmental temperature fluctuations, and the resulting thermal cracks significantly reduce the durability of asphalt pavement. Nevertheless, the influence of cyclic temperature variations on the performance degradation of asphalt binder materials is often overlooked. To address this, accelerated thermal cycling test was conducted on two asphalt mastics to simulate repeated environmental temperature variations. Dynamic shear rheological test (DSR) and atomic force microscopy test (AFM) were performed to characterize the evolution of the macroscopic rheological properties and microstructural characteristics under five cyclic temperature ranges. Pearson correlation analysis was utilized to explore the correlation between macro and micro properties. Following thermal cycling, it was observed that the two asphalt mastics experienced a decline in their viscous properties and became more elastic, resulting in a decrease in their stress relaxation capacity and asphalt-aggregate interaction on a macroscopic level. The microstructure transitioned from a multiphase to a homogeneous structure, while the expansion of the valley structure indicated the accumulation of microscopic defects. The larger the temperature variations and the higher the cyclic temperatures are, the more severe the deterioration in the viscoelasticity and microstructures of asphalt mastics is; the degradation of the micromechanical characteristics directly affects the macroscopic rheological properties. The bee structure ratio, the adhesion, and relaxation properties are sensitive to cyclic temperature variations and recommended to characterize the thermal cycling resistance. In comparison to 90# asphalt mastic, the SBS modified asphalt mastic exhibits great resistance to thermal deterioration. This study deepens the understanding of the causes of asphalt pavement performance deterioration in regions with frequent environmental temperature fluctuations.

Dielectric constant measurement sensitivity in electrostatic force and force gradient microscopy-based modes

Understanding the nanoscale electrostatic interaction between a conductive atomic force microscopy (AFM) probe and a dielectric film is central to the operation of various nanoscale dielectric microscopies and determination of dielectric properties of the film. There is no simple analytical description of the electrostatic interaction generated in the confined probe-sample geometry for neither static nor dynamic AFM modes used in dielectric measurements. An accurate description of the involved physics is obtained only by means of a finite element analysis modeling of the system. However, the alternative to using the numerical analysis is not very popular due to being slower and requiring relatively high computation resources. In this work, we revised the contributions from different parts of the AFM probe to the probe-sample capacitance by both analytical and numerical methods. We tried to reconciliate the two approaches and observed the differences as a function of geometry and material parameters. Under various noise levels, the efficiency of an analytical model was tested against a finite element analysis that captures in detail the electrostatic interaction in AFM-based dielectric measurements. The investigation was performed in both spectroscopic force-distance curves and constant height scans with measurements for deflection and frequency of the AFM probe. The obtained measurement sensitivities are relevant in selecting the optimal scanning mode and its operational parameters for a given film thicknesses and dielectric constants but also show the critical role of the numerical analysis to the correct interpretation of the measurements.