J. Algaba, S. Blazquez, E. Feria, J. M. Míguez, M. M. Conde, F. J. Blas
In this work, the effects of finite size on the determination of the three-phase coexistence temperature ($T_3$) of carbon dioxide (CO$_2$) hydrate have been studied by molecular dynamic simulations and using the direct coexistence technique. According to this technique, the three phases involved are placed together in the same simulation box. By varying the number of molecules of each phase it is possible to analyze the effect of simulation size and stoichiometry on the $T_3$ determination. In this work, we have determined the $T_3$ value at 8 different pressures and using 6 different simulation boxes with different numbers of molecules and sizes. In 2 of these configurations, the ratio of the number of water and CO$_2$ molecules in the aqueous solution and the liquid CO$_2$ phase is the same as in the hydrate (stoichiometric configuration). In both stoichiometric configurations, the formation of a liquid drop of CO$_2$ in the aqueous phase is observed. This drop, which has a cylindrical geometry, increases the amount of CO$_2$ available in the aqueous solution and can in some cases lead to the crystallization of the hydrate at temperatures above $T_3$, overestimating the $T_3$ value obtained from direct coexistence simulations. The simulation results obtained for the CO$_{2}$ hydrate confirm the sensitivity of $T_{3}$ depending on the size and composition of the system, explaining the discrepancies observed in the original work by M'iguez emph{et al.} Non-stoichiometric configurations with larger unit cells show convergence of $T_{3}$ values, suggesting that finite-size effects for these system sizes, regardless of drop formation, can be safely neglected. The results obtained in this work highlight that the choice of a correct initial configuration is essential to accurately estimate the three-phase coexistence temperature of hydrates by direct coexistence simulations.
{"title":"Three-phase equilibria of hydrates from computer simulation. II. Finite-size effects in the carbon dioxide hydrate","authors":"J. Algaba, S. Blazquez, E. Feria, J. M. Míguez, M. M. Conde, F. J. Blas","doi":"arxiv-2408.02069","DOIUrl":"https://doi.org/arxiv-2408.02069","url":null,"abstract":"In this work, the effects of finite size on the determination of the\u0000three-phase coexistence temperature ($T_3$) of carbon dioxide (CO$_2$) hydrate\u0000have been studied by molecular dynamic simulations and using the direct\u0000coexistence technique. According to this technique, the three phases involved\u0000are placed together in the same simulation box. By varying the number of\u0000molecules of each phase it is possible to analyze the effect of simulation size\u0000and stoichiometry on the $T_3$ determination. In this work, we have determined\u0000the $T_3$ value at 8 different pressures and using 6 different simulation boxes\u0000with different numbers of molecules and sizes. In 2 of these configurations,\u0000the ratio of the number of water and CO$_2$ molecules in the aqueous solution\u0000and the liquid CO$_2$ phase is the same as in the hydrate (stoichiometric\u0000configuration). In both stoichiometric configurations, the formation of a\u0000liquid drop of CO$_2$ in the aqueous phase is observed. This drop, which has a\u0000cylindrical geometry, increases the amount of CO$_2$ available in the aqueous\u0000solution and can in some cases lead to the crystallization of the hydrate at\u0000temperatures above $T_3$, overestimating the $T_3$ value obtained from direct\u0000coexistence simulations. The simulation results obtained for the CO$_{2}$\u0000hydrate confirm the sensitivity of $T_{3}$ depending on the size and\u0000composition of the system, explaining the discrepancies observed in the\u0000original work by M'iguez emph{et al.} Non-stoichiometric configurations with\u0000larger unit cells show convergence of $T_{3}$ values, suggesting that\u0000finite-size effects for these system sizes, regardless of drop formation, can\u0000be safely neglected. The results obtained in this work highlight that the\u0000choice of a correct initial configuration is essential to accurately estimate\u0000the three-phase coexistence temperature of hydrates by direct coexistence\u0000simulations.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141969019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Algaba, S. Blazquez, J. M. Míguez, M. M. Conde, F. J. Blas
In this work, the effect of the range of the dispersive interactions in the determination of the three-phase coexistence line of the CO$_2$ and CH$_4$ hydrates has been studied. In particular, the temperature ($T_3$) at which solid hydrate, water, and liquid CO$_2$/gas CH$_4$ coexist has been determined through molecular dynamics simulations using different cut-off values (from 0.9 to 1.6 nm) for the dispersive interactions. The $T_3$ of both hydrates has been determined using the direct coexistence simulation technique. Following this method, the three phases in equilibrium are put together in the same simulation box, the pressure is fixed, and simulations are performed at different temperatures $T$. If the hydrate melts, then $T>T_3$. Contrary, if the hydrate grows, then $T
{"title":"Three-phase equilibria of hydrates from computer simulation. III. Effect of dispersive interactions in the methane and carbon dioxide hydrates","authors":"J. Algaba, S. Blazquez, J. M. Míguez, M. M. Conde, F. J. Blas","doi":"arxiv-2408.01819","DOIUrl":"https://doi.org/arxiv-2408.01819","url":null,"abstract":"In this work, the effect of the range of the dispersive interactions in the\u0000determination of the three-phase coexistence line of the CO$_2$ and CH$_4$\u0000hydrates has been studied. In particular, the temperature ($T_3$) at which\u0000solid hydrate, water, and liquid CO$_2$/gas CH$_4$ coexist has been determined\u0000through molecular dynamics simulations using different cut-off values (from 0.9\u0000to 1.6 nm) for the dispersive interactions. The $T_3$ of both hydrates has been\u0000determined using the direct coexistence simulation technique. Following this\u0000method, the three phases in equilibrium are put together in the same simulation\u0000box, the pressure is fixed, and simulations are performed at different\u0000temperatures $T$. If the hydrate melts, then $T>T_3$. Contrary, if the hydrate\u0000grows, then $T<T_3$. The effect of the cut-off distance on the dissociation\u0000temperature has been analyzed at three different pressures for CO$_{2}$\u0000hydrate, namely, $100$, $400$, and $1000,text{bar}$. Then, we have changed\u0000the guest and studied the effect of the cut-off distance on the dissociation\u0000temperature of the CH$_{4}$ hydrate at $400,text{bar}$. Also, the effect of\u0000long-range corrections for dispersive interactions has been analyzed by running\u0000simulations with homo- and inhomogeneous corrections and a cut-off value of 0.9\u0000nm. The results obtained in this work highlight that the cut-off distance for\u0000the dispersive interactions affects the stability conditions of these hydrates.\u0000This effect is enhanced when the pressure is decreased, displacing the $T_{3}$\u0000about $2-4,text{K}$ depending on the system and the pressure.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141937376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We study the kinetics of vapor-liquid phase separation in a quasi one-dimensional confined active matter system using molecular dynamics simulations. Activity is invoked via the Vicsek rule, while passive interaction follows the Lennard-Jones potential. With the system density near the vapor branch, the evolution morphology features disconnected liquid clusters. In the passive limit, coarsening begins with nucleation, followed by an evaporation-condensation growth mechanism, leading to a metastable state without complete phase separation. We aim to understand the impact of Vicsek-like self-propulsion on the structure and growth of these clusters. Our key finding is that Vicsek activity results in a distinct growth mechanism, notably rapid cluster growth and the breakdown of the metastable state through ballistic aggregation. Relevant growth laws are analyzed and explained using appropriate theoretical models.
{"title":"Kinetics of vapor-liquid transition of active matter system under quasi one-dimensional confinement","authors":"Parameshwaran A, Bhaskar Sen Gupta","doi":"arxiv-2408.01195","DOIUrl":"https://doi.org/arxiv-2408.01195","url":null,"abstract":"We study the kinetics of vapor-liquid phase separation in a quasi\u0000one-dimensional confined active matter system using molecular dynamics\u0000simulations. Activity is invoked via the Vicsek rule, while passive interaction\u0000follows the Lennard-Jones potential. With the system density near the vapor\u0000branch, the evolution morphology features disconnected liquid clusters. In the\u0000passive limit, coarsening begins with nucleation, followed by an\u0000evaporation-condensation growth mechanism, leading to a metastable state\u0000without complete phase separation. We aim to understand the impact of\u0000Vicsek-like self-propulsion on the structure and growth of these clusters. Our\u0000key finding is that Vicsek activity results in a distinct growth mechanism,\u0000notably rapid cluster growth and the breakdown of the metastable state through\u0000ballistic aggregation. Relevant growth laws are analyzed and explained using\u0000appropriate theoretical models.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141937378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hamid Reza Tohidvand, Alexis White, Ali Khosravi, Paolo Celli
Kirigami metamaterial sheets and tubes, owing to their capacity to undergo large elastic deformations while developing three-dimensional surface textures, have enormous potential as skins for soft robots. Here, we propose to use kirigami skins with folding hinges in this same context. These recently-introduced kirigami feature counter-rotating panels connected by pop-up folding hinges. So far, researchers have only explored auxetic and highly-symmetric versions of such patterns. Yet, some of these attributes have to be relaxed in order to explore their full potential as robotic skins. Thus, we parameterize these patterns and relax symmetry constraints, with the goal of using this same platform to obtain a wide range of shape-morphing behaviors. We use a combination of: matrix analysis tools and analytical kinematic formulas to thoroughly explore the vast design space that ensues; experiments for validation purposes; and numerical simulations to explore the mechanics of selected planar and tubular patterns. We demonstrate that it is possible to tailor parameters to obtain skins that globally expand or contract due to axial elongation, and that present asymmetric pop-ups that can yield anisotropic friction -- the most desired attribute for one-way locomotion of soft robots.
{"title":"Tailoring anisotropy in kirigami metamaterial skins with pop-up folding hinges","authors":"Hamid Reza Tohidvand, Alexis White, Ali Khosravi, Paolo Celli","doi":"arxiv-2408.01338","DOIUrl":"https://doi.org/arxiv-2408.01338","url":null,"abstract":"Kirigami metamaterial sheets and tubes, owing to their capacity to undergo\u0000large elastic deformations while developing three-dimensional surface textures,\u0000have enormous potential as skins for soft robots. Here, we propose to use\u0000kirigami skins with folding hinges in this same context. These\u0000recently-introduced kirigami feature counter-rotating panels connected by\u0000pop-up folding hinges. So far, researchers have only explored auxetic and\u0000highly-symmetric versions of such patterns. Yet, some of these attributes have\u0000to be relaxed in order to explore their full potential as robotic skins. Thus,\u0000we parameterize these patterns and relax symmetry constraints, with the goal of\u0000using this same platform to obtain a wide range of shape-morphing behaviors. We\u0000use a combination of: matrix analysis tools and analytical kinematic formulas\u0000to thoroughly explore the vast design space that ensues; experiments for\u0000validation purposes; and numerical simulations to explore the mechanics of\u0000selected planar and tubular patterns. We demonstrate that it is possible to\u0000tailor parameters to obtain skins that globally expand or contract due to axial\u0000elongation, and that present asymmetric pop-ups that can yield anisotropic\u0000friction -- the most desired attribute for one-way locomotion of soft robots.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141937377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Based on the theory of the thermodynamic equilibrium in a system of quantum vortices in superfluids in the presence of a counterflow, the influence of a vortex tangle on various thermodynamic phenomena in quantum liquids is studied. Using the early calculated partition function we study some of the properties of He II related to counterflow, such as the distribution of vortex loops in their length, the suppression of the superfluid density $rho _{s}$ and the shift $T_{lambda}$. Good agreement with the early obtained results is a fairly strong argument in favor of the point of view that the gas of string-like topological excitations can indeed be considered as a additional kind of quasi-particles having the inner structure at high temperatures, especially near the phase transition. The application of the developed formalism to the theory of quantum turbulence is briefly discussed.
{"title":"Thermodynamics of random walking vortex loops in counterflowing superfluids","authors":"Sergey K. Nemirovskii","doi":"arxiv-2408.00680","DOIUrl":"https://doi.org/arxiv-2408.00680","url":null,"abstract":"Based on the theory of the thermodynamic equilibrium in a system of quantum\u0000vortices in superfluids in the presence of a counterflow, the influence of a\u0000vortex tangle on various thermodynamic phenomena in quantum liquids is studied.\u0000Using the early calculated partition function we study some of the properties\u0000of He II related to counterflow, such as the distribution of vortex loops in\u0000their length, the suppression of the superfluid density $rho _{s}$ and the\u0000shift $T_{lambda}$. Good agreement with the early obtained results is a fairly\u0000strong argument in favor of the point of view that the gas of string-like\u0000topological excitations can indeed be considered as a additional kind of\u0000quasi-particles having the inner structure at high temperatures, especially\u0000near the phase transition. The application of the developed formalism to the\u0000theory of quantum turbulence is briefly discussed.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141882442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natalia A. Kasian, Longin N. Lisetski, Serhii E. Ivanchenko, Vitalii O. Chornous, Halyna V. Bogatyryova, Igor A. Gvozdovskyy
It has been found that in mixtures of nematic E7 and smectogenic cholesteryl oleyl carbonate (COC) the S$_A$-N* transition temperature is substantially (by ~20 K) increased, as compared with pure COC, at E7 concentrations around ~40%. Within the same concentration range, the isotropic transition is preceded by formation of blue phase, with its maximum width of ~3.5 K clearly correlated to the increased thermal stability of the S$_A$ phase. With other cholesterol esters or cyanobiphenyls (cholesteryl nonanoate, 5CB), this effect was either much weaker or not observed. No enhancement of smectic phase was noted when E7 was replaced by N$_{tb}$-forming nematic mixture based on CB7CB with two cyanobiphenyl moieties. Selective Bragg reflection of light (BRL) spectra were measured in all three temperature regions, including the unwinding of the cholesteric helix on cooling towards S$_A$ phase and characteristic selective BRL changes in the blue phase. In the latter case, the measured {lambda}$_{max}$ values were dependent both on the helical twisting power in the cholesteric phase and on the lattice size and orientation in the blue phase. Also considered were the effects of ferroelectric BaTiO$_3$ nanoparticles accumulated at disclination lines upon the blue phase thermal stability.
{"title":"Induced smectic ordering and blue phase formation in mixtures of cyanobiphenyls and cholesterol esters","authors":"Natalia A. Kasian, Longin N. Lisetski, Serhii E. Ivanchenko, Vitalii O. Chornous, Halyna V. Bogatyryova, Igor A. Gvozdovskyy","doi":"arxiv-2408.00650","DOIUrl":"https://doi.org/arxiv-2408.00650","url":null,"abstract":"It has been found that in mixtures of nematic E7 and smectogenic cholesteryl\u0000oleyl carbonate (COC) the S$_A$-N* transition temperature is substantially (by\u0000~20 K) increased, as compared with pure COC, at E7 concentrations around ~40%.\u0000Within the same concentration range, the isotropic transition is preceded by\u0000formation of blue phase, with its maximum width of ~3.5 K clearly correlated to\u0000the increased thermal stability of the S$_A$ phase. With other cholesterol\u0000esters or cyanobiphenyls (cholesteryl nonanoate, 5CB), this effect was either\u0000much weaker or not observed. No enhancement of smectic phase was noted when E7\u0000was replaced by N$_{tb}$-forming nematic mixture based on CB7CB with two\u0000cyanobiphenyl moieties. Selective Bragg reflection of light (BRL) spectra were\u0000measured in all three temperature regions, including the unwinding of the\u0000cholesteric helix on cooling towards S$_A$ phase and characteristic selective\u0000BRL changes in the blue phase. In the latter case, the measured\u0000{lambda}$_{max}$ values were dependent both on the helical twisting power in\u0000the cholesteric phase and on the lattice size and orientation in the blue\u0000phase. Also considered were the effects of ferroelectric BaTiO$_3$\u0000nanoparticles accumulated at disclination lines upon the blue phase thermal\u0000stability.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"103 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141882441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The field of active matter explores the behaviors of self propelled agents out of equilibrium, with active suspensions, such as swimming bacteria in solutions, serving as impactful models. These systems exhibit spatio-temporal patterns akin to active turbulence, driven by internal energy injection. While bacterial turbulence in dense suspensions is well studied, the dynamics in growing bacterial suspensions are less understood. This work presents a phenomenological coarse-grained model for growing bacterial suspensions, incorporating hydrodynamic equations for bacterial density, orientation, and fluid velocity, with birth and death terms for colony growth. Starting with low density and random orientations, the model shows the development of local ordering as bacterial density increases. As density continues to rise, the model captures four distinct phases; dilute, clustered, turbulent, and trapped based on structural patterns and dynamics, with the turbulent phase characterized by spatio-temporal vortex structures, aligning with observations in dense bacterial suspensions.
{"title":"Spatio-temporal patterns in Growing Bacterial Suspensions: Impact of Growth dynamics","authors":"Pratikshya Jena, Shradha Mishra","doi":"arxiv-2408.00403","DOIUrl":"https://doi.org/arxiv-2408.00403","url":null,"abstract":"The field of active matter explores the behaviors of self propelled agents\u0000out of equilibrium, with active suspensions, such as swimming bacteria in\u0000solutions, serving as impactful models. These systems exhibit spatio-temporal\u0000patterns akin to active turbulence, driven by internal energy injection. While\u0000bacterial turbulence in dense suspensions is well studied, the dynamics in\u0000growing bacterial suspensions are less understood. This work presents a\u0000phenomenological coarse-grained model for growing bacterial suspensions,\u0000incorporating hydrodynamic equations for bacterial density, orientation, and\u0000fluid velocity, with birth and death terms for colony growth. Starting with low\u0000density and random orientations, the model shows the development of local\u0000ordering as bacterial density increases. As density continues to rise, the\u0000model captures four distinct phases; dilute, clustered, turbulent, and trapped\u0000based on structural patterns and dynamics, with the turbulent phase\u0000characterized by spatio-temporal vortex structures, aligning with observations\u0000in dense bacterial suspensions.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"298 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141882368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bo Fan, Tivadar Pongó, Raúl Cruz Hidalgo, Tamás Börzsönyi
The flow rate of a granulate out of a cylindrical container is studied as a function of particle shape for flat and elongated ellipsoids experimentally and numerically. We find a nonmonotonic dependence of the flow rate on the grain aspect ratio a/b. Starting from spheres the flow rate grows and has two maxima around the aspect ratios of a/b = 0.6 (lentil-like ellipsoids) and a/b = 1.5 (rice-like ellipsoids) reaching a flow rate increase of about 15% for lentils compared to spheres. For even more anisometric shapes (a/b = 0.25 and a/b = 4) the flow rate drops. Our results reveal two contributing factors to the nonmonotonic nature of the flow rate: both the packing fraction and the particle velocity through the orifice are nonmonotonic functions of the grain shape. Thus, particles with slightly non-spherical shapes not only form a better packing in the silo but also move faster through the orifice than spheres. We also show that the resistance of the granulate against shearing increases with aspect ratio for both elongated and flat particles, thus change in the effective friction of the granulate due to changing particle shape does not coincide with the trend in the flow rate.
{"title":"Effect of particle shape on the flow of an hourglass","authors":"Bo Fan, Tivadar Pongó, Raúl Cruz Hidalgo, Tamás Börzsönyi","doi":"arxiv-2407.21685","DOIUrl":"https://doi.org/arxiv-2407.21685","url":null,"abstract":"The flow rate of a granulate out of a cylindrical container is studied as a\u0000function of particle shape for flat and elongated ellipsoids experimentally and\u0000numerically. We find a nonmonotonic dependence of the flow rate on the grain\u0000aspect ratio a/b. Starting from spheres the flow rate grows and has two maxima\u0000around the aspect ratios of a/b = 0.6 (lentil-like ellipsoids) and a/b = 1.5\u0000(rice-like ellipsoids) reaching a flow rate increase of about 15% for lentils\u0000compared to spheres. For even more anisometric shapes (a/b = 0.25 and a/b = 4)\u0000the flow rate drops. Our results reveal two contributing factors to the\u0000nonmonotonic nature of the flow rate: both the packing fraction and the\u0000particle velocity through the orifice are nonmonotonic functions of the grain\u0000shape. Thus, particles with slightly non-spherical shapes not only form a\u0000better packing in the silo but also move faster through the orifice than\u0000spheres. We also show that the resistance of the granulate against shearing\u0000increases with aspect ratio for both elongated and flat particles, thus change\u0000in the effective friction of the granulate due to changing particle shape does\u0000not coincide with the trend in the flow rate.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141862660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Weiyi Wang, Jonathan Barés, Jonathan Barés, Emilien Azéma
We present a series of experiments investigating the flow regimes and repose angles of highly concave particle packings in a rotating drum. By varying grain geometry from spherical to highly non-convex shapes, adjusting frictional properties and the particle number of branches, we examine how these parameters and the drum speed influence the flow behavior. Our study identifies two distinct flow regimes: the rolling regime, where granular matter exhibits solid-like behavior near the walls and flows like a liquid near the free surface, and the slumping regime, characterized by cyclic avalanches and solid body rotations. Using quantitative criteria such as the repose angle difference and the area ratio of particle packings, we construct phase diagrams delineating the cross-over between these regimes. Our findings highlight the significant effects of particle concavity, friction, and rotation speed on the flow dynamics of granular materials, providing new insights into the mechanical behaviors of emph{meta-granular matter}.
{"title":"Flow regimes and repose angle in a rotating drum filled with highly concave particles","authors":"Weiyi Wang, Jonathan Barés, Jonathan Barés, Emilien Azéma","doi":"arxiv-2407.21464","DOIUrl":"https://doi.org/arxiv-2407.21464","url":null,"abstract":"We present a series of experiments investigating the flow regimes and repose\u0000angles of highly concave particle packings in a rotating drum. By varying grain\u0000geometry from spherical to highly non-convex shapes, adjusting frictional\u0000properties and the particle number of branches, we examine how these parameters\u0000and the drum speed influence the flow behavior. Our study identifies two\u0000distinct flow regimes: the rolling regime, where granular matter exhibits\u0000solid-like behavior near the walls and flows like a liquid near the free\u0000surface, and the slumping regime, characterized by cyclic avalanches and solid\u0000body rotations. Using quantitative criteria such as the repose angle difference\u0000and the area ratio of particle packings, we construct phase diagrams\u0000delineating the cross-over between these regimes. Our findings highlight the\u0000significant effects of particle concavity, friction, and rotation speed on the\u0000flow dynamics of granular materials, providing new insights into the mechanical\u0000behaviors of emph{meta-granular matter}.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141862661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kutlwano Gabana, Gillian A. Gehring, Hendrik Meyer, Goran Ungar, Xiangbing Zeng, William S. Fall
Polyethylene (PE) chains, with CH2 groups replaced by CBr2 at regular intervals ("precision PE"), have been observed to exhibit competing polymorphs driven by a preference for quantized fold lengths by Tasaki et al. Motivated by this recent discovery, the crystallisation behaviour of such precision PE chains, 400 carbons long with CBr2 groups placed regularly at every 21st carbon, is investigated using molecular dynamics simulations. The united-monomer model of PE is extended to include dibromo groups, with steric clashes at the bromines reflected in a triple-well bending potential, demonstrating its function as a preferred fold site. Different crystallisation protocols, continuous-cooling and self-seeding, reveal remarkably different crystals. Using self-seeding, the crystalline lamellar thickness increases monotonically with temperature, in quantized multiples of the distance between dibromo units. Polymer chains are observed to fold preferentially at the dibromo groups and such groups appear to be tolerated within the crystal lamellae. On quenching the bromos assemble to form registered layers, not unlike Smectic phases observed in liquid crystals, which confirms the experimental observation of competing Form I and Form I' polymorphs.
在 Tasaki 等人的研究中，观察到 CH2 基团被 CBr2 以规则间隔取代的聚乙烯（PE）链（"精密 PE"）在偏好量化折叠长度的驱动下表现出相互竞争的多态性。聚乙烯的单体模型扩展到包括二溴基团，溴的立体碰撞反映在三孔弯曲势中，证明了其作为首选折叠位点的功能。连续冷却和自播种这两种不同的结晶方案显示出明显不同的晶体。使用自播种方法时，结晶薄片厚度随温度的升高而单调增加，与二溴单位之间的距离成量化倍数关系。据观察，聚合物链优先在二溴基团处折叠，而这些基团似乎在晶体内部是可以容忍的。在淬火时，溴基团聚集形成注册层，这与液晶中观察到的 Smectic 相并不相同，从而证实了实验中观察到的相互竞争的 Form I 和 Form I' 多晶体。
{"title":"Molecular Simulations of Quantized Lamellar Thickening in Polyethylenes with Regularly Spaced Brominated Groups","authors":"Kutlwano Gabana, Gillian A. Gehring, Hendrik Meyer, Goran Ungar, Xiangbing Zeng, William S. Fall","doi":"arxiv-2407.21728","DOIUrl":"https://doi.org/arxiv-2407.21728","url":null,"abstract":"Polyethylene (PE) chains, with CH2 groups replaced by CBr2 at regular\u0000intervals (\"precision PE\"), have been observed to exhibit competing polymorphs\u0000driven by a preference for quantized fold lengths by Tasaki et al. Motivated by\u0000this recent discovery, the crystallisation behaviour of such precision PE\u0000chains, 400 carbons long with CBr2 groups placed regularly at every 21st\u0000carbon, is investigated using molecular dynamics simulations. The\u0000united-monomer model of PE is extended to include dibromo groups, with steric\u0000clashes at the bromines reflected in a triple-well bending potential,\u0000demonstrating its function as a preferred fold site. Different crystallisation\u0000protocols, continuous-cooling and self-seeding, reveal remarkably different\u0000crystals. Using self-seeding, the crystalline lamellar thickness increases\u0000monotonically with temperature, in quantized multiples of the distance between\u0000dibromo units. Polymer chains are observed to fold preferentially at the\u0000dibromo groups and such groups appear to be tolerated within the crystal\u0000lamellae. On quenching the bromos assemble to form registered layers, not\u0000unlike Smectic phases observed in liquid crystals, which confirms the\u0000experimental observation of competing Form I and Form I' polymorphs.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141862747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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