The Origins of Enhanced and Retarded Crystallization in Nanocomposite Polymers

Controlling the crystallinity of hybrid polymeric systems has an important impact on their properties and is essential for developing novel functional materials. The crystallization of nanocomposite polymers with gold nanoparticles is shown to be determined by free space between nanoparticles. Results of large-scale molecular dynamics simulations reveal while crystallinity is affected by the nanoparticle size and its volume fraction, their combined effects can only be measured by interparticle free space and characteristic size of the crystals. When interparticle free space becomes smaller than the characteristic extended length of the polymer molecule, nanoparticles impede the crystallization because of the confinement effects. Based on the findings from this work, equations for critical particle size or volume fraction that lead to this confinement-induced retardation of crystallization are proposed. The findings based on these equations are demonstrated to agree with the results reported in experiments for nanocomposite systems. The results of simulations also explain the origin of a two-tier crystallization regime observed in some of the hybrid polymeric systems with planar surfaces where the crystallization is initially enhanced and then retarded by the presence of nanoparticles.

Download Full-text

Constraining the intergalactic medium at z ≈ 9.1 using LOFAR Epoch of Reionization observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa487 ◽

2020 ◽

Vol 493 (4) ◽

pp. 4728-4747 ◽

Cited By ~ 10

Author(s):

R Ghara ◽

S K Giri ◽

G Mellema ◽

B Ciardi ◽

S Zaroubi ◽

...

Keyword(s):

Large Scale ◽

Intergalactic Medium ◽

Volume Fraction ◽

Characteristic Size ◽

Gas Temperature ◽

Spin Temperature ◽

Simulation Code ◽

Upper Limits ◽

Credible Intervals ◽

Bayesian Inference Framework

ABSTRACT We derive constraints on the thermal and ionization states of the intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits on the 21-cm power spectrum measured by the LOFAR radio telescope and a prior on the ionized fraction at that redshift estimated from recent cosmic microwave background (CMB) observations. We have used results from the reionization simulation code grizzly and a Bayesian inference framework to constrain the parameters which describe the physical state of the IGM. We find that, if the gas heating remains negligible, an IGM with ionized fraction ≳0.13 and a distribution of the ionized regions with a characteristic size ≳ 8 h−1 comoving megaparsec (Mpc) and a full width at half-maximum (FWHM) ≳16 h−1 Mpc is ruled out. For an IGM with a uniform spin temperature TS ≳ 3 K, no constraints on the ionized component can be computed. If the large-scale fluctuations of the signal are driven by spin temperature fluctuations, an IGM with a volume fraction ≲0.34 of heated regions with a temperature larger than CMB, average gas temperature 7–160 K, and a distribution of the heated regions with characteristic size 3.5–70 h−1 Mpc and FWHM of ≲110 h−1 Mpc is ruled out. These constraints are within the 95 per cent credible intervals. With more stringent future upper limits from LOFAR at multiple redshifts, the constraints will become tighter and will exclude an increasingly large region of the parameter space.

Download Full-text

Twin-induced template effect on the inelastic deformation of hierarchically nanotwinned copper under indentation and scratch

International Journal of Damage Mechanics ◽

10.1177/1056789515574123 ◽

2015 ◽

Vol 25 (1) ◽

pp. 56-68 ◽

Cited By ~ 4

Author(s):

Yonggang Zheng ◽

Hongfei Ye ◽

Hongwu Zhang

Keyword(s):

Molecular Dynamics ◽

Inelastic Deformation ◽

Partial Dislocation ◽

Large Scale ◽

Characteristic Size ◽

Template Effect ◽

Partial Dislocations ◽

Simulation Results ◽

Dynamics Simulations ◽

Main Factor

The inelastic deformation of hierarchically nanotwinned copper that is composed of primary and secondary twins under indentation and scratch has been investigated by using large-scale molecular dynamics simulations. Simulation results show that the partial dislocation activities are the main factor that dominates the inelastic deformation. Both the indentation and scratch processes show arrest and burst behaviors of partial dislocations, which indicates that the twin boundaries have a template effect on the inelastic deformations. Moreover, it is found that the characteristic size of the inelastic deformation zone increases, respectively, with the increase of the primary and secondary twin spacings.

Download Full-text

Effect of Nanoscale rods on the Kinetics of Phase-Separating Multi-Component Fluids

MRS Proceedings ◽

10.1557/proc-856-bb7.7 ◽

2004 ◽

Vol 856 ◽

Cited By ~ 1

Author(s):

Michael J.A. Hore ◽

Mohamed Laradji

Keyword(s):

Phase Separation ◽

Large Scale ◽

Volume Fraction ◽

Three Dimensions ◽

Domain Growth ◽

Slowing Down ◽

Nanoparticles Volume Fraction ◽

Scale Particle ◽

Dynamics Simulations ◽

Kinetics Of

ABSTRACTUsing large scale particle dynamics simulations, we investigated the effect of nanoscale rods on the dynamics of phase separation dynamics of two-component fluids in three dimensions. We found that when the nanoparticles interact more attractively with one of the two segregating component, they lead to a reduction of the rate of domain growth, and that this decrease is intensified as the nanoparticles volume fraction is increased. Furthermore, our results show that nanorods are much more effective in slowing down the kinetics than nanosphres. The dramatic effect of nanorods on the dynamics of phase separation of multi-component fluids, as opposed to nanospheres, implies that they may be used as an efficacious emulsifying agent of multi-component polymer blends.

Download Full-text

Elucidating the Onset of Plasticity in Sliding Contacts Using Differential Computational Orientation Tomography

Tribology Letters ◽

10.1007/s11249-021-01451-9 ◽

2021 ◽

Vol 69 (3) ◽

Author(s):

S. J. Eder ◽

P. G. Grützmacher ◽

M. Rodríguez Ripoll ◽

J. F. Belak

Keyword(s):

Grain Boundary ◽

Large Scale ◽

Surface Deformation ◽

Boundary Migration ◽

Material Design ◽

Lattice Rotation ◽

Time Resolved ◽

Near Surface ◽

Color Saturation ◽

Dynamics Simulations

Abstract Depending on the mechanical and thermal energy introduced to a dry sliding interface, the near-surface regions of the mated bodies may undergo plastic deformation. In this work, we use large-scale molecular dynamics simulations to generate “differential computational orientation tomographs” (dCOT) and thus highlight changes to the microstructure near tribological FCC alloy surfaces, allowing us to detect subtle differences in lattice orientation and small distances in grain boundary migration. The analysis approach compares computationally generated orientation tomographs with their undeformed counterparts via a simple image analysis filter. We use our visualization method to discuss the acting microstructural mechanisms in a load- and time-resolved fashion, focusing on sliding conditions that lead to twinning, partial lattice rotation, and grain boundary-dominated processes. Extracting and laterally averaging the color saturation value of the generated tomographs allows us to produce quantitative time- and depth-resolved maps that give a good overview of the progress and severity of near-surface deformation. Corresponding maps of the lateral standard deviation in the color saturation show evidence of homogenization processes occurring in the tribologically loaded microstructure, frequently leading to the formation of a well-defined separation between deformed and undeformed regions. When integrated into a computational materials engineering framework, our approach could help optimize material design for tribological and other deformation problems. Graphic Abstract .

Download Full-text

Large-Scale Membrane Permeability Prediction of Cyclic Peptides Crossing a Lipid Bilayer Based on Enhanced Sampling Molecular Dynamics Simulations

Journal of Chemical Information and Modeling ◽

10.1021/acs.jcim.1c00380 ◽

2021 ◽

Author(s):

Masatake Sugita ◽

Satoshi Sugiyama ◽

Takuya Fujie ◽

Yasushi Yoshikawa ◽

Keisuke Yanagisawa ◽

...

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Membrane Permeability ◽

Lipid Bilayer ◽

Cyclic Peptides ◽

Large Scale ◽

Enhanced Sampling ◽

Permeability Prediction ◽

Dynamics Simulations

Download Full-text

Study on the High-Speed Milling Performance of High-Volume Fraction SiCp/Al Composites

Materials ◽

10.3390/ma14154143 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4143

Author(s):

Youzheng Cui ◽

Shenrou Gao ◽

Fengjuan Wang ◽

Qingming Hu ◽

Cheng Xu ◽

...

Keyword(s):

High Speed ◽

Large Scale ◽

Volume Fraction ◽

Simulation Analysis ◽

Cutting Temperature ◽

High Volume ◽

Cutting Parameters ◽

High Volume Fraction ◽

High Wear Resistance ◽

Element Analysis

Compared with other materials, high-volume fraction aluminum-based silicon carbide composites (hereinafter referred to as SiCp/Al) have many advantages, including high strength, small change in the expansion coefficient due to temperature, high wear resistance, high corrosion resistance, high fatigue resistance, low density, good dimensional stability, and thermal conductivity. SiCp/Al composites have been widely used in aerospace, ordnance, transportation service, precision instruments, and in many other fields. In this study, the ABAQUS/explicit large-scale finite element analysis platform was used to simulate the milling process of SiCp/Al composites. By changing the parameters of the tool angle, milling depth, and milling speed, the influence of these parameters on the cutting force, cutting temperature, cutting stress, and cutting chips was studied. Optimization of the parameters was based on the above change rules to obtain the best processing combination of parameters. Then, the causes of surface machining defects, such as deep pits, shallow pits, and bulges, were simulated and discussed. Finally, the best cutting parameters obtained through simulation analysis was the tool rake angle γ0 = 5°, tool clearance angle α0 = 5°, corner radius r = 0.4 mm, milling depth ap = 50 mm, and milling speed vc= 300 m/min. The optimal combination of milling parameters provides a theoretical basis for subsequent cutting.

Download Full-text

The Low-redshift Intergalactic Medium

Publications of the Astronomical Society of Australia ◽

10.1071/as99095 ◽

1999 ◽

Vol 16 (1) ◽

pp. 95-99 ◽

Cited By ~ 11

Author(s):

J. Michael Shull ◽

Steven V. Penton ◽

John T. Stocke

Keyword(s):

Galaxy Formation ◽

Large Scale ◽

Intergalactic Medium ◽

Hubble Space Telescope ◽

Characteristic Size ◽

Baryon Density ◽

Frequency Space ◽

Physical Conditions ◽

Low Metallicity ◽

Set Up

AbstractThe low-redshift Lyα forest of absorption lines provides a probe of large-scale baryonic structures in the intergalactic medium, some of which may be remnants of physical conditions set up during the epoch of galaxy formation. We discuss our recent Hubble Space Telescope (HST) observations and interpretation of low-z Lyα clouds toward nearby Seyferts and QSOs, including their frequency, space density, estimated mass, association with galaxies, and contribution to Ωb. Our HST/GHRS detections of ∼ 70 Lyα absorbers with Nhi ≥ 1012·6 cm−2 along 11 sightlines covering pathlength Δ(cz) = 114,000 km s−1 show f (>Nhi) α Nhi−0·63±0·04 and a line frequency dN/dz = 200 ± 40 for Nhi > 1012·6 cm−2 (one every 1500 km s−1 of redshift). A group of strong absorbers toward PKS 2155–304 may be associated with gas (400–800) kpc from four large galaxies, with low metallicity (≤0·003 solar) and D/H ≤ 2 × 10−4. At low-z, we derive a metagalactic ionising radiation field from AGN of J0 = × 10−23 erg cm−2 s−1 Hz−1 sr−1 and a Lyα-forest baryon density Ωb =(0·008 ± 0·004)[J−23N14b100]½ for clouds of characteristic size b = (100 kpc)b100.

Download Full-text