Nanomechanical Lab
About 600 people attended the ECF20
ISFAM2018, Trondheim, Norway
Int Symposium on Materials for Anti-icing 2019, NTNU
Welcome to the NTNU Nanomechanical Lab at Department of Structural Engineering
Hydrogen-induced transgranular to intergranular fracture transition
The manuscript demonstrates the direct transgranular to intergranular fracture transition process controlled by hydrogen-influenced plasticity, by scrutinizing the tensile responses of Ni Σ5(210)[001] GB with varied hydrogen concentration using atomistic modeling. Compared with the Σ3 coherent twin GB which traps nearly no H atoms, H will form an atmosphere at the Σ5 GB due to the high trapping energy and excess volume and induce a higher initial local stress. In the case without H, less stress is built up at the Σ5 GB region during deformation, which leads to transgranular fracture. In contrast, H suppresses the stress-releasing ability of the Σ5 GB, which causes a local stress concentration and promotes local plasticity on the GB. This further leads to early dislocation emission, severe twinning evolution, increased number of vacancies and thus enhanced nanovoiding on the GB. The growth of nanovoids with H finally completes the transgranular to intergranular-fracture transition. These findings enrich our knowledge of hydrogen-induced intergranular fracture at the microscale.
Microstructure and nanomechanical behavior of additively manufactured high entropy alloy
A new paper published in Materials Science and Engineering A
The microstructure and crystallographic orientation-dependent nanomechanical characteristics of an additively manufactured (AM-ed) high-entropy alloy (HEA) were investigated by aid of nanoindentation and SEM. Furthermore, the effect of heat treatment on AM-ed HEA was explored by comparing with as-printed HEA. Interestingly, it is found that the grain {101} has the highest hardness and elastic modulus, whereas the creep resistance of grain {111} is the greatest, with the indicators of the creep mechanism showing lattice diffusion is the dominant mechanism. Heat treatment in the current study can increase the hardness and elastic modulus but decrease the creep resistance slightly. This work elucidates the grain orientation dependence on nanomechanical properties and the role of heat treatment, and sheds light on the nanoscale creep behavior and the corresponding creep mechanisms in the AM-ed HEA.
The effect of forcefields on thermal transport in polymers
Thermal Transport in Polyethylene: The Effect of Force Fields and Crystallinity
Macromolecules, 2021, DOI: 10.1021/acs.macromol.1c00633
The local structure and heat transfer properties (thermal conductivity and interfacial conductance) in model semi-crystalline polyethylene (PE) are studied by non-equilibrium molecular dynamics. Three different force fields with different levels of detail (all-atom, all-atom with constraints, and united-atom) are compared. We find that the structure of the model PE is significantly influenced by the choice of force field. The united-atom force field results in a reduced overall crystallinity and an over-idealized organization of the polymer chains, compared to the all-atom force fields. We find that thermal transport properties are not greatly influenced when structural effects are taken into consideration, and our results suggest that united-atom models can be used to study heat transfer properties of model PE, with decreased computational cost.
Molecular dynamics simulation reveals structural disjoining pressure
Nanoparticles hold promising potentials in enhanced oil recovery. The mechanics of nanoparticles interacting with different components in confined nanochannels still awaits in-depth clarification. In the current work, atomistic modeling and molecular dynamics simulations were utilized to investigate three different nanoparticle dispersion patterns in nanochannels with trapped oil droplets, namely nanoparticles favoring in water, in oil, and in both phases. The special focus of this study is to detail the local pressure in the nanochannels induced by the injections of nanoparticles. The results reveal the key effects of different nanoparticles on altering the atomistic mechanics in the complex nanofluid system and shed light on the rational design and selection of nanoparticles in practice. Particularly, the local pressure in the three-phase contact area triggered by hydrophilic nanoparticles was found to feature the famous structural disjoining pressure, which supplied supporting evidences to the former continuum medium based analytical study from the atomistic level for the first time.
A novel method for Improving Dimensional Accuracy of Additively Manufactured Thin Channels
A new paper published at International Journal of Precision Engineering and Manufacturing-Green Technology
Powder-bed fusion additive manufacturing technology makes it possible to produce parts with complicated geometry and high accuracy. However, dimensional deviation caused by powder overmelting and dross formation is still a challenge for manufacturing thin channels. In this study, the origins of the overmelting of printed thin channels were analyzed and a concept called “melting cell” is proposed to describe and quantify the geometric error. Based on the geometrical relationship between the melting cell and target channel, a method for predicting and optimizing the fnal geometry of thin channels is outlined. In order to verify the method, geometries of thin horizontal circular channels in various sizes are studied as examples. The predicted results by the proposed method show a remarkable agreement with available experimental results. Moreover, a new egg-shaped compensated design, which is able to improve the dimensional accuracy of thin horizontal circular channels, is presented. The proposed method is simple yet very efective. It can be easily extended to the manufacturing of thin channels with various shapes, materials, and diferent powder bed fusion processes.
Simultaneously toughening and stiffening elastomers with octuple hydrogen bonding
Current synthetic elastomers suffer from the well‐known trade‐off between toughness and stiffness. By a combination of multiscale experiments and atomistic simulations, a transparent unfilled elastomer with simultaneously enhanced toughness and stiffness is demonstrated. The designed elastomer comprises homogeneous networks with ultrastrong, reversible, and sacrificial octuple hydrogen bonding (HB), which evenly distribute the stress to each polymer chain during loading, thus enhancing stretchability and delaying fracture. Strong HBs and corresponding nanodomains enhance the stiffness by restricting the network mobility, and at the same time improve the toughness by dissipating energy during the transformation between different configurations. In addition, the stiffness mismatch between the hard HB domain and the soft poly(dimethylsiloxane)‐rich phase promotes crack deflection and branching, which can further dissipate energy and alleviate local stress. These cooperative mechanisms endow the elastomer with both high fracture toughness (17016 J m−2) and high Young's modulus (14.7 MPa), circumventing the trade‐off between toughness and stiffness. This work is expected to impact many fields of engineering requiring elastomers with unprecedented mechanical performance.
Reconfigurable Mechanical Anisotropy in Self‐Assembled Magnetic Superstructures
A new paper published at Advanced Science (Impact Factor of 15.8)
Through a comprehensive Monte Carlo investigation, this study demonstrates how the mechanical properties of self‐assembled magnetic nanocubes can be controlled intrinsically by the nanoparticle magnetocrystalline anisotropy (MA), as well as by the superstructure shape anisotropy, without any need for changes in structural design (i.e., nanoparticle size, shape, and packing arrangement). The new concepts developed here pave the way for the experimental realization of smart magneto‐micromechanical systems (based, e.g., on the permanent super‐magnetostriction effect illustrated here) and inspire new design rules for applied functional materials.
Machine Learning Based Prediction of Nanoscale Ice Adhesion on Rough Surfaces
Our group is truly the first one to develop machine -learning based tool for predicting nanoscale ice adhesion. see the publicaton here.
NML Season's Greetings 2020
Self-emulsifying and demulsification of water-in-oil microemulsion droplet
Stability, deformation and rupture of Janus oligomer enabled self-emulsifying water-in-oil microemulsion droplet
Physical Chemistry and Chemiscal Physics, DOI: 10.1039/D0CP03092A
We have investigated the spontaneous emulsification process from a water, oil and surfactant mixture to form a single microemulsion droplet. By applying counter forces on the water core and the surfactant shell, the mechanical stability of microemulsion droplets was probed at different ambient temperatures. A strengthening response and a softening regime before and after a temperature-dependent peak force were identified followed by final rupture. The findings contribute to establishing an atomistic view on the previous studies on microemulsion fluids, and provide a general guide to design a stable microemulsion system, such as oil recovery and production, drug delivery, materials fabrication, chemical sensors, wastewater treatment, etc.
Timely data survey on the polysiloxane-based icephobic materials
Polysiloxane as icephobic materials – The past, present and the future
Chemical Engineering Journal, 2021, 405: 127088
Perspectives of polysiloxane low-ice adhesion materials research.
Pressure-induced displacement of nanofluids in confined capillaries
Insight into the pressure-induced displacement mechanism for selecting efficient nanofluids in various capillaries
Environmental Science: Nano, 2020, 7: 2785-2794
Fluids flow in porous media is ubiquitous and has important application in numerous fields, such as groundwater remediation, oil recovery, water purification, etc. Taken the oil recovery as an example, increasing the pumping pressure of injecting fluid can improve the oil recovery. However, as flooding pressure reaches a specific high value, considerable amount of oil would be trapped in the reservoir due to “fingering” phenomenon. How to overcome the “fingering” to increase the production of the residual oil is a hot topic in the research of petroleum engineering. Here we propose two distinct displacement mechanisms. Specifically, reducing the interfacial tension of fluids is beneficial to improve the displacement efficiency in hydrophobic capillary, while increasing viscosity of fluids favours for hydrophilic capillary. Based on the proposed mechanisms, we design three types of nanofluids to improve the displacement efficiency for different capillaries.
Pascal-level ice adhesion surfaces
New article by Dr. Tong Li
Self-Deicing Electrolyte Hydrogel Surfaces with Pa-level Ice Adhesion and Durable Antifreezing/Antifrost Performance
ACS Applied Materials & Interfaces, 2020, 12, 35572-35578
We have synthesized the ionic gel (IG) surfaces for everlasting anti-freezing and zero ice adhesion to ice with tuneable anti-icing temperature (down to -48.4 degree C). Moreover, we introduce the concept “deicing time” to evaluate the ice self-removal from the IG surface within 10-100 s. These excellent performances are due that the ions inside the IG diffuse to the interface between IG and water/ice to destroy ice crystals, as demonstrated by both the molecular dynamics simulations and experimental results. In summary, we first provide a possible approach to prevent ice formation and accretion in the long-term.
A novel "S-type" printing pattern developed at NML will yield lowest residual stresses in additive manufacturing of metallic materials
Tensile characteristics of carbon nitride nanothreads
New article by PhD candidate Yuequn Fu
The effects of morphology and temperature on the tensile characteristics of carbon nitride nanothreads
Nanoscale, 2020, 12, 12462-12475
We have performed comprehensive investigation on tensile mechanical characteristics of seven experimental synthesized CNNTs by using first-principle based ReaxFF molecular dynamics (MD) simulations. All the CNNTs exhibit unique tensile mechanical properties that change with molecular morphology, atomic arrangement and the distribution of nitrogen in the skeleton. CNNTs with more effective loading covalent bonds at cross-sections are more mechanically robust. The study provides physical insights into the tensile characteristics of CNNTs for the design and application of CNNT-based nanostructures as multifunctional materials.
New ionogel surfaces inhibit ice nucleation, growth and adhesion
Anti-icing Ionogel Surfaces: Inhibiting Ice Nucleation, Growth, and Adhesion
ACS Materials Letters, 2020, 2: 616-623
We have fabricated an ionogel surface that can not only inhibit the ice nucleation but also the subsequent step, the ice growth. Due to the inhibited ice growth, the ionogel surface enables an unconventional inward ice growth in water droplets from the droplet-air interface, resulting in a spherical cap ice rather than a normal pointy cap ice at cold environment. Both experiments and molecular dynamic simulations confirm that the prepared ionogel surface can efficiently generate an interfacial liquid layer due to the inward ice growth and presence of ionic liquid. Such non-frozen interfacial liquid layer is desired for lowering ice adhesion and preventing ice/frost formation. Consequently, the ionogel surface exhibits unprecedented anti-frost abilities under humid environment (-20 ºC, 60% RH). This is the first surface that can inhibit both ice nucleation and growth!
How to enhance the thermal boundary conductance of metal-polymer system
New article by PhD candidate Susanne Sandell
Enhancement of Thermal Boundary Conductance of Metal–Polymer System
Nanomaterials, 2020, 10, 670
Phase transition lubricant for oil/water separation
New article by PhD candidate Feng Wang
Enabling phase transition of infused lubricant in porous structure for exceptional oil/water separation
Journal of Hazardous Materials, 2020, 290, 122176
New Paper published at "Applied Materials Today"
NML developed an ultrafast self-healing, highly transparent mechanically durable icephobic coating.
Ultrafast self-healing and highly transparent coating with mechanically durable icephobicity
Applied Materials Today, 2020, 19, 100542
News: No ice, ice, baby!
Kjell Magne Mathisen
Professor, Administrative leader
Kjell.mathisen@ntnu.no
Professor
Fracture Mechanics and Nanomechanics
Professor
Nanomechanics
Adjunct Professor
Nanomechanics
PhD student
Fracture and Fatigue-Measurement Method
