Alex Berlaga, Kaylyn Torkelson, Aniruddha Seal, Jim Pfaendtner, Andrew L. Ferguson
Peptoids (N-substituted glycines) are a class of sequence-defined synthetic peptidomimetic polymers with applications including drug delivery, catalysis, and biomimicry. Classical molecular simulations have been used to predict and understand the conformational dynamics of single peptoid chains and their self-assembly into diverse morphologies including sheets, tubes, spheres, and fibrils. The CGenFF-NTOID model based on the CHARMM General ForceField has demonstrated success in enabling accurate all-atom molecular modeling of the structure and thermodynamic behavior of peptoids. Extension of this force field to new peptoid side chain chemistries has historically required parameterization of new side chain bonded interactions against ab initio and/or experimental data. This fitting protocol improves the accuracy of the force field but is also burdensome and time consuming, and precludes modular extensibility of the model to arbitrary peptoid sequences. In this work, we develop and demonstrate a Modular Side Chain CGenFF-NTOID (MoSiC-CGenFF-NTOID) as an extension of CGenFF-NTOID employing a modular decomposition of the peptoid backbone and side chain parameterizations wherein arbitrary side chain chemistries within the large family of substituted methyl groups (i.e., -CH3, -CH2R, -CHRR' -CRR'R'') are directly ported from CGenFF without any additional reparameterization. We validate this approach against ab initio calculations and experimental data to to develop a MoSiC-CGenFF-NTOID model for all 20 natural amino acid side chains along with 13 commonly-used synthetic side chains, and present an extensible paradigm to efficiently determine whether a novel side chain can be directly incorporated into the model or whether refitting of the CGenFF parameters is warranted. We make the model freely available to the community along with a tool to perform automated initial structure generation.
蛋白胨（N-取代甘氨酸）是一类序列明确的合成拟肽聚合物，其应用领域包括药物输送、催化和生物仿生。经典分子模拟已被用于预测和理解单个蛋白胨链的构象动力学及其组装成片状、管状、球状和纤维状等不同形态的过程。基于 CHARMM 通用力场的 CGenFF-NTOID 模型已成功实现了类蛋白胨结构和热力学行为的精确全原子分子建模。要将该力场扩展到新的蛋白胨侧链化学成分中，历来需要根据 ab initio 和/或实验数据对新的侧链键合相互作用进行参数化。这种拟合规程提高了力场的准确性，但也很费事费时，而且无法将模型扩展到任意的类肽链序列。在这项工作中，我们开发并演示了模块化侧链 CGenFF-NTOID（MoSiC-CGenFF-NTOID），它是 CGenFF-NTOID 的扩展，采用了肽类骨架和侧链参数化的模块化分解，其中取代甲基（即 -CH3、-CH2R、-CHRR' -CRR'R''）大家族中的任意侧链化学结构都直接从 CGenFF 移植而来，无需任何额外参数化。我们根据 ab initio 计算和实验数据验证了这种方法，从而为全部 20 种天然氨基酸侧链和 13 种常用合成侧链建立了 MoSiC-CGenFF-NTOID 模型，并提出了一种可扩展的范式，以有效确定是否可以将新的侧链直接纳入模型，或者是否需要重新拟合 CGenFF 参数。我们向社区免费提供该模型以及自动生成初始结构的工具。
{"title":"A Modular and Extensible CHARMM-Compatible Model for All-Atom Simulation of Polypeptoids","authors":"Alex Berlaga, Kaylyn Torkelson, Aniruddha Seal, Jim Pfaendtner, Andrew L. Ferguson","doi":"arxiv-2409.06103","DOIUrl":"https://doi.org/arxiv-2409.06103","url":null,"abstract":"Peptoids (N-substituted glycines) are a class of sequence-defined synthetic\u0000peptidomimetic polymers with applications including drug delivery, catalysis,\u0000and biomimicry. Classical molecular simulations have been used to predict and\u0000understand the conformational dynamics of single peptoid chains and their\u0000self-assembly into diverse morphologies including sheets, tubes, spheres, and\u0000fibrils. The CGenFF-NTOID model based on the CHARMM General ForceField has\u0000demonstrated success in enabling accurate all-atom molecular modeling of the\u0000structure and thermodynamic behavior of peptoids. Extension of this force field\u0000to new peptoid side chain chemistries has historically required\u0000parameterization of new side chain bonded interactions against ab initio and/or\u0000experimental data. This fitting protocol improves the accuracy of the force\u0000field but is also burdensome and time consuming, and precludes modular\u0000extensibility of the model to arbitrary peptoid sequences. In this work, we\u0000develop and demonstrate a Modular Side Chain CGenFF-NTOID (MoSiC-CGenFF-NTOID)\u0000as an extension of CGenFF-NTOID employing a modular decomposition of the\u0000peptoid backbone and side chain parameterizations wherein arbitrary side chain\u0000chemistries within the large family of substituted methyl groups (i.e., -CH3,\u0000-CH2R, -CHRR' -CRR'R'') are directly ported from CGenFF without any additional\u0000reparameterization. We validate this approach against ab initio calculations\u0000and experimental data to to develop a MoSiC-CGenFF-NTOID model for all 20\u0000natural amino acid side chains along with 13 commonly-used synthetic side\u0000chains, and present an extensible paradigm to efficiently determine whether a\u0000novel side chain can be directly incorporated into the model or whether\u0000refitting of the CGenFF parameters is warranted. We make the model freely\u0000available to the community along with a tool to perform automated initial\u0000structure generation.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142220622","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}
Vinay Kopnar, Adam O'Connell, Natasha Shirshova, Anders Aufderhorst-Roberts
Hybrid double-network hydrogels are a class of material that comprise transiently and permanently crosslinked polymer networks and exhibit an enhanced toughness that is believed to be governed by the yielding of the transient polymer network. The precise role of the two polymer networks in this yielding transition and their interplay remains an open question that we address here through constructing a series of hydrogel designs in which the interaction within and between the two polymer networks are systematically inhibited or enhanced. We characterise each of the hydrogel designs using large amplitude oscillatory shear rheology (LAOS). Inspecting yielding through elastic stress across hydrogel designs, we elucidate that the hybrid double-network hydrogel exhibits a two-step yielding behaviour that originates from to the presence of transient crosslinks. Examining the rheological response within each oscillatory cycle and across the hydrogel designs, we show that the micro-structural changes in the transient network are crucial in the second stage of this yielding. We surmise that the first step of yielding is determined by the intermolecular interactions between the two polymer networks by systematically altering the strength of the interactions. These interactions also influence the second step of yielding, which we show is governed by the transient intermolecular interactions within the polymer networks. Our study therefore reveals that the interactions between the polymer networks are as crucial as within the polymer networks and therefore provides insights into how the yielding mechanisms in soft composite materials can be identified, adjusted, and controlled.
{"title":"Mechanistic Origins of Yielding in Hybrid Double Network Hydrogels","authors":"Vinay Kopnar, Adam O'Connell, Natasha Shirshova, Anders Aufderhorst-Roberts","doi":"arxiv-2409.05765","DOIUrl":"https://doi.org/arxiv-2409.05765","url":null,"abstract":"Hybrid double-network hydrogels are a class of material that comprise\u0000transiently and permanently crosslinked polymer networks and exhibit an\u0000enhanced toughness that is believed to be governed by the yielding of the\u0000transient polymer network. The precise role of the two polymer networks in this\u0000yielding transition and their interplay remains an open question that we\u0000address here through constructing a series of hydrogel designs in which the\u0000interaction within and between the two polymer networks are systematically\u0000inhibited or enhanced. We characterise each of the hydrogel designs using large\u0000amplitude oscillatory shear rheology (LAOS). Inspecting yielding through\u0000elastic stress across hydrogel designs, we elucidate that the hybrid\u0000double-network hydrogel exhibits a two-step yielding behaviour that originates\u0000from to the presence of transient crosslinks. Examining the rheological\u0000response within each oscillatory cycle and across the hydrogel designs, we show\u0000that the micro-structural changes in the transient network are crucial in the\u0000second stage of this yielding. We surmise that the first step of yielding is\u0000determined by the intermolecular interactions between the two polymer networks\u0000by systematically altering the strength of the interactions. These interactions\u0000also influence the second step of yielding, which we show is governed by the\u0000transient intermolecular interactions within the polymer networks. Our study\u0000therefore reveals that the interactions between the polymer networks are as\u0000crucial as within the polymer networks and therefore provides insights into how\u0000the yielding mechanisms in soft composite materials can be identified,\u0000adjusted, and controlled.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"172 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142220624","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}
Flocking phase transitions found in models of polar active matter are paradigmatic examples of active phase transitions in soft matter. An interesting specialization of flocking models concerns a ``topological'' vs ``metric'' choice by which agents are considered to be interacting neighbors. While recent theoretical work suggests that the order-disorder transition in these polar aligning models is universally first order, numerical studies have suggested that topological models may instead have a continuous transition. Some recent simulations have found that some variations of topologically interacting flocking agents have a discontinuous transition, but unambiguous observations of phase coexistence using common Voronoi-based alignment remains elusive. In this work, we use a custom GPU-accelerated simulation package to perform million-particle-scale simulations of these Voronoi-Vicsek flocking models. By accessing such large systems on appropriately long time scales, we are able to show that a regime of stable phase coexistence between the ordered and disordered phases, confirming the discontinuous nature of this transition in the thermodynamic limit.
{"title":"Banded phases in topological flocks","authors":"Charles R. Packard, Daniel M. Sussman","doi":"arxiv-2409.05198","DOIUrl":"https://doi.org/arxiv-2409.05198","url":null,"abstract":"Flocking phase transitions found in models of polar active matter are\u0000paradigmatic examples of active phase transitions in soft matter. An\u0000interesting specialization of flocking models concerns a ``topological'' vs\u0000``metric'' choice by which agents are considered to be interacting neighbors.\u0000While recent theoretical work suggests that the order-disorder transition in\u0000these polar aligning models is universally first order, numerical studies have\u0000suggested that topological models may instead have a continuous transition.\u0000Some recent simulations have found that some variations of topologically\u0000interacting flocking agents have a discontinuous transition, but unambiguous\u0000observations of phase coexistence using common Voronoi-based alignment remains\u0000elusive. In this work, we use a custom GPU-accelerated simulation package to\u0000perform million-particle-scale simulations of these Voronoi-Vicsek flocking\u0000models. By accessing such large systems on appropriately long time scales, we\u0000are able to show that a regime of stable phase coexistence between the ordered\u0000and disordered phases, confirming the discontinuous nature of this transition\u0000in the thermodynamic limit.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142220626","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}
Disordered granular packings share many similarities with supercooled liquids, particu-larly in the rapid increase of structural relaxation time within a narrow range of temperature or packing fraction. However, it is unclear whether the dynamics of granular materials align with those of their corresponding thermal hard sphere liquids, and the particular influence of friction of a granular system remains largely unexplored. Here, we experimentally study the slow relaxation and the steady state of monodisperse granular sphere packings with X-ray tomography. We first quantify the thermodynamic parameters under the Edwards' ensemble, (i.e., effective temperature and configurational entropy), of granular spheres with varying friction, and measure their characteristic relaxation time during compaction processes. We then demonstrate a unified picture of the relaxation process in granular systems in which the Adam-Gibbs (AG) relationship is generally followed. These results clarify the close relation-ship between granular materials and the ideal frictionless hard sphere model.
无序颗粒填料与过冷液体有许多相似之处，特别是在狭窄的温度或填料分数范围内结构弛豫时间的快速增加。然而，颗粒材料的动力学是否与其对应的热硬球液体的动力学相一致尚不清楚，颗粒体系的特殊摩擦影响在很大程度上仍未得到探索。在此，我们利用 X 射线断层扫描技术对单分散粒状球形填料的缓慢弛豫和稳定状态进行了实验研究。我们首先量化了具有不同摩擦力的粒状球体在爱德华兹集合下的热力学参数（即有效温度和构型熵），并测量了它们在压实过程中的特征弛豫时间。然后，我们展示了颗粒系统松弛过程的统一图景，其中一般遵循亚当-吉布斯（AG）关系。这些结果阐明了颗粒材料与理想无摩擦硬球模型之间的密切关系。
{"title":"Testing Adam-Gibbs relationship in tapped Granular Packings","authors":"Xinyu Ai, Houfei Yuan, Shuyang Zhang, Zhikun Zeng, Hanyu Li, Chengjie Xia, Yujie Wang","doi":"arxiv-2409.04983","DOIUrl":"https://doi.org/arxiv-2409.04983","url":null,"abstract":"Disordered granular packings share many similarities with supercooled\u0000liquids, particu-larly in the rapid increase of structural relaxation time\u0000within a narrow range of temperature or packing fraction. However, it is\u0000unclear whether the dynamics of granular materials align with those of their\u0000corresponding thermal hard sphere liquids, and the particular influence of\u0000friction of a granular system remains largely unexplored. Here, we\u0000experimentally study the slow relaxation and the steady state of monodisperse\u0000granular sphere packings with X-ray tomography. We first quantify the\u0000thermodynamic parameters under the Edwards' ensemble, (i.e., effective\u0000temperature and configurational entropy), of granular spheres with varying\u0000friction, and measure their characteristic relaxation time during compaction\u0000processes. We then demonstrate a unified picture of the relaxation process in\u0000granular systems in which the Adam-Gibbs (AG) relationship is generally\u0000followed. These results clarify the close relation-ship between granular\u0000materials and the ideal frictionless hard sphere model.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227353","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}
Elastic structures can be designed to exhibit precise, complex, and exotic functions. While recent work has focused on the quasistatic limit governed by force balance, the mechanics at a finite driving rate are governed by Newton's equations. The goal of this work is to study the feasibility, constraints, and implications of creating disordered structures with exotic properties in the dynamic regime. The dynamical regime offers responses that cannot be realized in quasistatics, such as responses at an arbitrary phase, frequency-selective responses, and history-dependent responses. We employ backpropagation through time and gradient descent to design spatially specific steady states in disordered spring networks. We find that a broad range of steady states can be achieved with small alterations to the structure, operating both at small and large amplitudes. We study the effect of varying the damping, which interpolates between the underdamped and the overdamped regime, as well as the amplitude, frequency, and phase. We show that convergence depends on several competing effects, including chaos, large relaxation times, a gradient bias due to finite time simulations, and strong attenuation. By studying the eigenmodes of the linearized system, we show that the systems adapt very specifically to the task they were trained to perform. Our work demonstrates that within physical bounds, a broad array of exotic behaviors in the dynamic regime can be obtained, allowing for a richer range of possible applications.
{"title":"Designing precise dynamical steady states in disordered networks","authors":"Marc Berneman, Daniel Hexner","doi":"arxiv-2409.05060","DOIUrl":"https://doi.org/arxiv-2409.05060","url":null,"abstract":"Elastic structures can be designed to exhibit precise, complex, and exotic\u0000functions. While recent work has focused on the quasistatic limit governed by\u0000force balance, the mechanics at a finite driving rate are governed by Newton's\u0000equations. The goal of this work is to study the feasibility, constraints, and\u0000implications of creating disordered structures with exotic properties in the\u0000dynamic regime. The dynamical regime offers responses that cannot be realized\u0000in quasistatics, such as responses at an arbitrary phase, frequency-selective\u0000responses, and history-dependent responses. We employ backpropagation through\u0000time and gradient descent to design spatially specific steady states in\u0000disordered spring networks. We find that a broad range of steady states can be\u0000achieved with small alterations to the structure, operating both at small and\u0000large amplitudes. We study the effect of varying the damping, which\u0000interpolates between the underdamped and the overdamped regime, as well as the\u0000amplitude, frequency, and phase. We show that convergence depends on several\u0000competing effects, including chaos, large relaxation times, a gradient bias due\u0000to finite time simulations, and strong attenuation. By studying the eigenmodes\u0000of the linearized system, we show that the systems adapt very specifically to\u0000the task they were trained to perform. Our work demonstrates that within\u0000physical bounds, a broad array of exotic behaviors in the dynamic regime can be\u0000obtained, allowing for a richer range of possible applications.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227355","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 interplay among solute and solvent molecules in lyotropic mesophases governs their physicochemical properties, such as phase behaviors and viscoelasticity. In our model system, a lyotropic chromonic liquid crystal (LCLC) made by disodium cromoglycate (DSCG), charged plank-like molecules self-assemble to form elongated aggregates via non-covalent attractions in water (H$_{2}$O). The aggregates align to exhibit liquid crystalline phases: nematic and columnar phases. Here, we report the isotopic effect on the phase behavior of the LCLC when D$_2$O is substituted for H$_2$O. D$_2$O-DSCG exhibits higher nematic-to-isotropic phase transition temperatures than H$_2$O-DSCG. X-ray scattering reveals considerably longer inter-aggregate correlation lengths in D$_2$O-LCLCs. In contrast, the other microstructural properties, such as inter-aggregate distances and intra-aggregate correlation lengths, remain almost the same. Our $^{23}$Na FT-NMR measurement reveals that D$_2$O-DSCG aggregates are less charged with more counter-ions, Na$^+$, bound to them than H$_2$O-DSCG aggregates. Weaker electrostatic repulsion between aggregates may stabilize the nematic phase, and this solvent isotopic effect may generally apply to diverse aqueous lyotropic mesophases with electrostatic interactions.
{"title":"Solvent isotopic effect on the phase transition of lyotropic chromonic liquid crystals: Heavy water makes mesogens less charged","authors":"Jiyong Cheon, Joonwoo Jeong","doi":"arxiv-2409.05097","DOIUrl":"https://doi.org/arxiv-2409.05097","url":null,"abstract":"The interplay among solute and solvent molecules in lyotropic mesophases\u0000governs their physicochemical properties, such as phase behaviors and\u0000viscoelasticity. In our model system, a lyotropic chromonic liquid crystal\u0000(LCLC) made by disodium cromoglycate (DSCG), charged plank-like molecules\u0000self-assemble to form elongated aggregates via non-covalent attractions in\u0000water (H$_{2}$O). The aggregates align to exhibit liquid crystalline phases:\u0000nematic and columnar phases. Here, we report the isotopic effect on the phase\u0000behavior of the LCLC when D$_2$O is substituted for H$_2$O. D$_2$O-DSCG\u0000exhibits higher nematic-to-isotropic phase transition temperatures than\u0000H$_2$O-DSCG. X-ray scattering reveals considerably longer inter-aggregate\u0000correlation lengths in D$_2$O-LCLCs. In contrast, the other microstructural\u0000properties, such as inter-aggregate distances and intra-aggregate correlation\u0000lengths, remain almost the same. Our $^{23}$Na FT-NMR measurement reveals that\u0000D$_2$O-DSCG aggregates are less charged with more counter-ions, Na$^+$, bound\u0000to them than H$_2$O-DSCG aggregates. Weaker electrostatic repulsion between\u0000aggregates may stabilize the nematic phase, and this solvent isotopic effect\u0000may generally apply to diverse aqueous lyotropic mesophases with electrostatic\u0000interactions.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227870","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 yielding response to an imposed oscillatory shear is investigated for a model two-dimensional dense glass composed of bidisperse, deformable polymer rings, with the ring stiffness being the control parameter. In the quiescent glassy state, the more flexible rings exhibit a broader spectrum of shape fluctuations, which becomes increasingly constrained with increasing ring stiffness. Under shear, the highly packed rings yield, i.e. the thermal assembly looses rigidity, with the threshold yield strain increasing significantly with decreasing ring stiffness. Further, the rings display significant deviations in their shape compared to their unsheared counterparts. This study provides insights into the interplay between shape changes and translational rearrangements under shear, thus contributing to the understanding of yielding transition in densely packed, deformable polymer systems.
{"title":"Two-dimensional squishy glass: yielding under oscillatory shear","authors":"Sayantan Ghosh, Rahul Nayak, Satyavani Vemparala, Pinaki Chaudhuri","doi":"arxiv-2409.04725","DOIUrl":"https://doi.org/arxiv-2409.04725","url":null,"abstract":"The yielding response to an imposed oscillatory shear is investigated for a\u0000model two-dimensional dense glass composed of bidisperse, deformable polymer\u0000rings, with the ring stiffness being the control parameter. In the quiescent\u0000glassy state, the more flexible rings exhibit a broader spectrum of shape\u0000fluctuations, which becomes increasingly constrained with increasing ring\u0000stiffness. Under shear, the highly packed rings yield, i.e. the thermal\u0000assembly looses rigidity, with the threshold yield strain increasing\u0000significantly with decreasing ring stiffness. Further, the rings display\u0000significant deviations in their shape compared to their unsheared counterparts.\u0000This study provides insights into the interplay between shape changes and\u0000translational rearrangements under shear, thus contributing to the\u0000understanding of yielding transition in densely packed, deformable polymer\u0000systems.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142220628","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}
Antonio Tavera-Vázquez, Danai Montalvan-Sorrosa, Gustavo Perez-Lemus, Otilio E. Rodriguez-Lopez, Jose A. Martinez-Gonzalez, Vinothan N. Manoharan, Juan J. de Pablo
Motile liquid crystal (LC) colloids show peculiar behavior due to the high sensitivity to external stimuli driven by the LC elastic and surface effects. However, few studies focus on harnessing the LC phase transitions to propel colloidal inclusions by the nematic-isotropic (NI) interface. We engineer a quasi-2D active system consisting of solid micron-sized light-absorbent platelets immersed in a thermotropic nematic LC. The platelets self-propel in the presence of light while self-inducing a localized NI phase transition. The sample's temperature, light intensity, and confinement determine three different regimes: a 2D large regime where the platelet-isotropic phase bubble is static and the NI interface remains stable; a compact motile-2D regime where the NI interface lies closer to the platelet's contour; and a motile-3D-confinement regime characterized by the emergence of multipolar configurations of the LC. We perform continuum-theory simulations that predict stationary platelet-LC states when confined in 3D. Our study in an intrinsically far-from-equilibrium landscape is crucial for designing simple synthetic systems that contribute to our understanding of harnessing liquid crystals' phase transitions to propel colloidal inclusions and trigger tunable topological reconfigurations leading to photonic responses.
运动液晶胶体由于对液晶弹性和表面效应驱动的外部刺激具有高度敏感性而表现出奇特的行为。然而，很少有研究关注利用液晶相变通过向列-各向同性（NI）界面推动胶体内含物。我们设计了由浸入热致性向列液相中的固体微米级吸光小板组成的水生二维活性系统。小板在光的作用下自我推进，同时自我诱导局部的 NI 相变。样品的温度、光照强度和封闭性决定了三种不同的状态：二维大状态，其中血小板-各向同性相泡是静态的，NI 界面保持稳定；二维紧凑运动状态，其中 NI 界面更接近于血小板的轮廓；以及三维封闭状态，其特征是 LC 的多极配置的出现。我们进行了连续理论模拟，预测了在三维约束下血小板-低密度层的稳态。我们在远离平衡的内在环境中进行的研究对于设计模拟合成系统至关重要，有助于我们理解如何利用液晶的相变推动胶体夹杂物并触发可调的拓扑重构，从而产生光子响应。
{"title":"Light-Activated Motion, Geometry- and Confinement-Induced Optical Effects of 2D Platelets in a Nematic Liquid Crystal","authors":"Antonio Tavera-Vázquez, Danai Montalvan-Sorrosa, Gustavo Perez-Lemus, Otilio E. Rodriguez-Lopez, Jose A. Martinez-Gonzalez, Vinothan N. Manoharan, Juan J. de Pablo","doi":"arxiv-2409.04912","DOIUrl":"https://doi.org/arxiv-2409.04912","url":null,"abstract":"Motile liquid crystal (LC) colloids show peculiar behavior due to the high\u0000sensitivity to external stimuli driven by the LC elastic and surface effects.\u0000However, few studies focus on harnessing the LC phase transitions to propel\u0000colloidal inclusions by the nematic-isotropic (NI) interface. We engineer a\u0000quasi-2D active system consisting of solid micron-sized light-absorbent\u0000platelets immersed in a thermotropic nematic LC. The platelets self-propel in\u0000the presence of light while self-inducing a localized NI phase transition. The\u0000sample's temperature, light intensity, and confinement determine three\u0000different regimes: a 2D large regime where the platelet-isotropic phase bubble\u0000is static and the NI interface remains stable; a compact motile-2D regime where\u0000the NI interface lies closer to the platelet's contour; and a\u0000motile-3D-confinement regime characterized by the emergence of multipolar\u0000configurations of the LC. We perform continuum-theory simulations that predict\u0000stationary platelet-LC states when confined in 3D. Our study in an\u0000intrinsically far-from-equilibrium landscape is crucial for designing simple\u0000synthetic systems that contribute to our understanding of harnessing liquid\u0000crystals' phase transitions to propel colloidal inclusions and trigger tunable\u0000topological reconfigurations leading to photonic responses.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"38 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142220627","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}
Keith G. Hedlund, Vikina Martinez, Xi Chen, Cheol S. Park, Joseph E. Maclennan, Matthew A. Glaser, Noel A. Clark
We show that stable, freely suspended liquid crystal films can be made from the ferroelectric nematic ($mathrm{N_F}$) phase and from the recently discovered polar, lamellar $mathrm{SmZ_A}$ and $mathrm{SmA_F}$ phases. The $mathrm{N_F}$ films display two-dimensional, smectic-like parabolic focal conic textures comprising director/polarization bend that are a manifestation of the electrostatic suppression of director splay in the film plane. In the $mathrm{SmZ_A}$ and $mathrm{SmA_F}$ phases, the smectic layers orient preferentially normal to the film surfaces, a condition never found in typical thermotropic or lyotropic lamellar LC phases, with the $mathrm{SmZ_A}$ films exhibiting focal-conic fan textures mimicking the appearance of typical smectics in glass cells when the layers are oriented normal to the plates, and the $mathrm{SmA_F}$ films showing a texture of plaquettes of uniform in-plane orientation where both bend and splay are suppressed, separated by grain boundaries. The $mathrm{SmA_F}$ phase can also be drawn into thin filaments, in which X-ray scattering reveals that the smectic layer planes are normal to the filament axis. Remarkably, the filaments are mechanically stable even if they break, forming free-standing, fluid filaments supported only at one end. The unique architectures of these films and filaments are stabilized by the electrostatic self-interaction of the liquid crystal polarization field, which enables the formation of confined, fluid structures that are fundamentally different from those of their counterparts made using previously known liquid crystal phases.
{"title":"Freely Suspended Nematic and Smectic Films and Free-Standing Smectic Filaments in the Ferroelectric Nematic Realm","authors":"Keith G. Hedlund, Vikina Martinez, Xi Chen, Cheol S. Park, Joseph E. Maclennan, Matthew A. Glaser, Noel A. Clark","doi":"arxiv-2409.04019","DOIUrl":"https://doi.org/arxiv-2409.04019","url":null,"abstract":"We show that stable, freely suspended liquid crystal films can be made from\u0000the ferroelectric nematic ($mathrm{N_F}$) phase and from the recently\u0000discovered polar, lamellar $mathrm{SmZ_A}$ and $mathrm{SmA_F}$ phases. The\u0000$mathrm{N_F}$ films display two-dimensional, smectic-like parabolic focal\u0000conic textures comprising director/polarization bend that are a manifestation\u0000of the electrostatic suppression of director splay in the film plane. In the\u0000$mathrm{SmZ_A}$ and $mathrm{SmA_F}$ phases, the smectic layers orient\u0000preferentially normal to the film surfaces, a condition never found in typical\u0000thermotropic or lyotropic lamellar LC phases, with the $mathrm{SmZ_A}$ films\u0000exhibiting focal-conic fan textures mimicking the appearance of typical\u0000smectics in glass cells when the layers are oriented normal to the plates, and\u0000the $mathrm{SmA_F}$ films showing a texture of plaquettes of uniform in-plane\u0000orientation where both bend and splay are suppressed, separated by grain\u0000boundaries. The $mathrm{SmA_F}$ phase can also be drawn into thin filaments,\u0000in which X-ray scattering reveals that the smectic layer planes are normal to\u0000the filament axis. Remarkably, the filaments are mechanically stable even if\u0000they break, forming free-standing, fluid filaments supported only at one end.\u0000The unique architectures of these films and filaments are stabilized by the\u0000electrostatic self-interaction of the liquid crystal polarization field, which\u0000enables the formation of confined, fluid structures that are fundamentally\u0000different from those of their counterparts made using previously known liquid\u0000crystal phases.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227844","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}
Liang Peng, Thibault Roch, Daniel Bonn, Bart Weber
The key parameter for describing frictional strength at the onset of sliding is the static friction coefficient. Yet, how the static friction coefficient at the macroscale emerges from contacting asperities at the microscale is still an open problem. Here, we present friction experiments in which the normal load was varied over more than three orders of magnitude, so that a transition from a single asperity contact at low loads to multi-asperity contacts at high loads was achieved. We find a remarkable drop in static friction coefficient with increasing normal load. Using a simple stick-slip transition model we identify the presence of pre-sliding and subcritical contact points as the cause of smaller static friction coefficient at increased normal loads. Our measurements and model bridge the gap between friction behavior commonly observed in atomic force microscopy (AFM) experiments at microscopic forces, and industrially relevant multi-asperity contact interfaces loaded with macroscopic forces.
{"title":"Why Static Friction Decreases From Single to Multi-asperity Contacts","authors":"Liang Peng, Thibault Roch, Daniel Bonn, Bart Weber","doi":"arxiv-2409.04280","DOIUrl":"https://doi.org/arxiv-2409.04280","url":null,"abstract":"The key parameter for describing frictional strength at the onset of sliding\u0000is the static friction coefficient. Yet, how the static friction coefficient at\u0000the macroscale emerges from contacting asperities at the microscale is still an\u0000open problem. Here, we present friction experiments in which the normal load\u0000was varied over more than three orders of magnitude, so that a transition from\u0000a single asperity contact at low loads to multi-asperity contacts at high loads\u0000was achieved. We find a remarkable drop in static friction coefficient with\u0000increasing normal load. Using a simple stick-slip transition model we identify\u0000the presence of pre-sliding and subcritical contact points as the cause of\u0000smaller static friction coefficient at increased normal loads. Our measurements\u0000and model bridge the gap between friction behavior commonly observed in atomic\u0000force microscopy (AFM) experiments at microscopic forces, and industrially\u0000relevant multi-asperity contact interfaces loaded with macroscopic forces.","PeriodicalId":501146,"journal":{"name":"arXiv - PHYS - Soft Condensed Matter","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227354","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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