Conference Programme

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K-01: Soft matters & MD/ab initio applications
Monday, 19/Jun/2017:
1:30pm - 3:30pm

Session Chair: Jinju Chen, Newcastle University
Session Chair: Stephan Rudykh, Technion - Israel Institute of Technology
Location: Rm 311

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1:30pm - 2:00pm

Modeling of Microstructured Electro- and Magneto-active Soft Composites

Stephan RUDYKH

Technion - Israel Institute of Technology, Israel

We study the behavior of dielectric elastomer composites (DEC) and magnetoactive elastomers (MAE) undergoing large deformations while exited by external electric or magnetic fields. We analyze the role of the microstructures in the overall performance and stability of the soft active composites. We examine the coupled behavior of the active composites with (i) periodically and (ii) randomly distributed active particles embedded in soft matrix [1,2], and (iii) periodic laminate composites and anisotropically structured composites with chain like structures [3]. We identify the key parameters governing the electro- and magneto- mechanical couplings. Moreover, we find advantageous microstructures that give rise to significant enhancement of the coupling and actuation of the active materials [1]. Furthermore, we show that even very similar microstructures, such as periodic composites with hexagonal and rectangular representative volume elements (RVE), exhibit very different behavior both in terms of actuation, and effective properties [2].

We investigate the coupled electro- and magneto-elastic instabilities in DEC [4,5,6] and MAE [3]. These instabilities may occur at different length-scales and, potentiall, they may be exploited to achieve new functionalities such as tunable band-gaps [7,8,9,10]. We explore the role of external electric and magnetic fields, microstructure parameters, and consentient properties on the multiscale instabilities.


[1] Rudykh et al. App. Phys. Lett. 102 (2013), 151905

[2] Galipaeu et al. Int. J. Solids. Struct. 51 (2014), 3012-3024

[3] Rudykh and Bertoldi. J. Mech. Phys. Solids. 61 (2014), 949-967

[4] Rudykh and deBotton. Media. Z. Angew. Math. Phys. 62 (2011), 1131-1142

[5] Rudykh et al. Int. J. Nonlinear Mech. 47 (2012), 206-209

[6] Rudykh et al. Proc. Royal Soc. A 470 (2014), 20130618

[7] Rudykh and Boyce. Phys. Rev. Lett. 112 (2014) 034301

[8] Galich and Rudykh. Extreme Mech. Lett. 4 (2015) 156-161

[9] Galich and Rudykh. Appl. Phys. Lett. 107 (2015) 056101

[10] Galich and Rudykh. Int. J. Solids. Struct. 91, 18-25 (2016)

2:00pm - 2:30pm

Multi-physics Modelling of Bacteria Adhesion and Biofilm Development

Jinju CHEN

Newcastle University, United Kingdom

Bacteria-materials interactions are important for biofilm formation. The formation of biofilms has great impacts on a wide range of industries such as biomedical industries, marine industries and water industries. Therefore, it is important to understand how materials surface properties will affect bacteria attachment on surfaces and biofilm formation. In this study, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory has been adopted to model how surface roughness and surface topography of materials as well as appendages of bacteria will affect bacteria attachment to material surfaces. In addition, an individual based model has also been developed to predict biofilm formation, and flow induced biofilm deformation, erosion and streamer formation. In this multiphysics computational model, bacteria growth, division, decay, mechanical contact between bacteria cells and adhesion between the bacteria-extracellular polymer substance, as well as flow shear force were implemented.

2:30pm - 2:45pm

First-Principle Study of the Modification of Electronic and Optical Properties of MoS2 in the Presence of Point Defects

Ashim Kumar SAHA1, Masato YOSHIYA1,2

1Osaka University, Japan; 2Nanostructures Research Laboratory, Japan Fine Ceramics Center, Japan

Optical properties of MoS2 have been extensively studied by both experiments and first-principles electronic structures calculations. Attempts have been made to tune up the optical properties by doping rare-earth elements into monolayer MoS2. However, little attention has been paid to the native defects which may be accompanied with the intentional doping. The accompanied native defects may further modify the resultant optical properties than it is intended by doping a foreign element alone. With full understanding of the roles played by various native defects in the MoS2, it may be possible to tailor the optical properties of the material for applications in practical devices.

First principles calculations are performed to obtain correct charge density of pristine or point-defect containing MoS2. Electronic structures calculations are done based on plane-wave basis set with inner core states fixed using projector augmented wave method (PAW) using VASP code. Stability of native defect species and optical properties are quantitatively examined in order to identify possible native defect species in MoS2 and its influences on electronic structures and resultant optical properties.

Possible native defect species are identified as functions of thermodynamic environment and location of Fermi-level in MoS2. It is found that sulphur vacancies can be introduced more easily than other point defect species which will create impurity states at higher energy within bandgap. Additionally, antisite Mo and/or Mo vacancies can be created depending on chemical potential of sulphur, both of which will create impurity states at lower energy within bandgap. Those impurity states within the band gap result in pronounced photon absorption in visible light region depending on its concentration.

Thus, attention must be paid when intentional impurity doping is made to MoS2 to avoid unwanted modification of its optical properties. Those impurities may enable further exploitation of photovoltaic energy conversion at longer wavelength.

2:45pm - 3:00pm

Ab Initio Modelling of the Hydrogen Interaction with Ferrite/Cementite Interface

Alexander MIRZOEV, Anastasiya VERKHOVYH

South Ural State University, Russian Federation

Hydrogen is one of important components in iron and steels. It has the smallest atomic radius among interstitial impurities and high diffusivity but low solubility in iron. From technical point of view hydrogen is a harmful impurity causing embrittlement, cracking etc. Hydrogen atoms' interaction with substitutional impurities, vacancies and grain boundaries have been considered in many papers previously using ab initio. In this paper we consider the hydrogen interaction with another type of defects, namely interface of ferrite/cementite. We have used the Isaichev type of orientation relationships (OR) between ferrite and cementite in pearlite. For our calculations we exploited density functional theory within generalized gradient approximation (GGA’96), as implemented in WIEN2k package. Ab initio calculations of formation energy and atomic configuration of fully relaxed ferrite/cementite interphase boundary with and without hydrogen was carried out to investigate the formation energy of interphase boundary and the binding energy of hydrogen on it. The computational results have shown that the interphase boundary act as traps to hydrogen with the binding energy of 0.25- 0.39 eV with the zero point energy correction. These values are in good agreement with the experimental values. Also the hydrogen atoms interact not only with the surrounding matrix of iron, but also with the closest carbon atom, thereby increasing the binding energy of the hydrogen with interfacial boundary.

The authors gratefully acknowledge the support from Russian Science Foundation [grant number 16-19-10252].

3:00pm - 3:15pm

Relationship between Grain Boundaries and Phonon Thermal Conduction by Molecular Dynamics

Susumu FUJII1, Masatoshi TANEMURA1, Kohei FUNAI1, Tatsuya YOKOI1, Masato YOSHIYA1,2

1Department of Adaptive Machine Systems, Osaka University, Japan; 2Nanostructures Research Laboratory, Japan Fine Ceramics Center, Japan

Grain boundaries (GBs) are one of the sources of phonon scattering especially for phonons with longer mean free paths than the distance between GBs. This scattering has been extensively exploited to reduce thermal conductivity as in thermal barrier coatings and nanostructured thermoelectric materials. However, it is still experimentally challenging to precisely determine how thermal conduction is modified at GBs since practical materials have other defects such as point defects, dislocations and stacking faults, all of which act as phonon scattering sources. Atomistic analyses without any prescribing theories are thus required to obtain physical insights and in-depth understanding on it.

Here, using perturbed molecular dynamics, we calculated phonon thermal conductivity in the presence of a single GB with various sets of internal degrees of freedoms that characterizes the GBs, in order to clarify the impact of GBs on phonon thermal conduction. MgO and cubic-ZrO2 are studied as model systems since their symmetric tilt GBs structures and bulk crystal structures are geometrically simple, so that the relationship between GBs and thermal conductivity is easy to understand. In addition, cubic-ZrO2 is well-characterized materials and used as thermal barrier coating (YSZ). Their GB structures were obtained using the simulated annealing method.

In spite of rather similar crystal structures of MgO and ZrO2 as mentioned above, calculated results suggest the impact of GB on phonon thermal conduction in its vicinity are much less in ZrO2. This can be explained in terms of mean free paths of phonons that scales phonon-phonon scattering independent of GBs. On the other hand, suppressed thermal conduction in the vicinity of GB is less affected by misorientations of neighboring crystal lattices that modify magnitude and local distribution of strains of bonds and the number of ill-coordinates atoms at GBs. More quantitative discussion will be given in the presentation.

3:15pm - 3:30pm

Influence of Transition Metal Doping on the Electronic and Optical Properties of Rhenium Disulphide and Diselenide Monolayer

Kingsley O. OBODO1, Cecil M. N. OUMA2, Joshua T. OBODO3, Moritz BRAUN1

1University of South Africa, South Africa; 2Natural Resources and Environment, Council for Scientific and Industrial Research Pretoria, South Africa; 3Physikalisches Institut (IA), RWTH Aachen University, Germany

Quantum mechanical based calculations are used to calculate the structural, electronic and optical properties of transition metal doped triclinic rhenium disulphide and diselenide (ReS2 and ReSe2) compounds with lower crystallographic symmetry unlike Molybdenum disulphide and other transition metal dichalcogenides (TMDC). The addition of single transition metal dopants ions (such as Fe, Co, Mn, Mo, W, Nb and Ta) in ReS2 and ReSe2 monolayer results in no significant lattice distortion. The calculated electronic band gap for ReS2 and ReSe2 monolayer are 1.43 eV and 1.23 eV respectively with both having a non-magnetic ground state. We found that the presence of dopant ions in the ReS2 and ReSe2 monolayer significantly modify their electronic ground states with consequent reduction of the electronic band gap and modification of the density of states profile. Different magnetic ground state was obtained depending on the dopant ions in ReS2 and ReSe2 monolayer. Also, the calculated absorbance and reflectance spectra of the doped compounds shows that this group of material would have potential application as optoelectronic and solar materials.

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