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首页> 外文期刊>PHYSICAL REVIEW E >Modeling steady-state dynamics of macromolecules in exponential-stretching flow using multiscale molecular-dynamics–multiparticle-collision simulations
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Modeling steady-state dynamics of macromolecules in exponential-stretching flow using multiscale molecular-dynamics–multiparticle-collision simulations

机译：使用多尺度分子动力学-多粒子碰撞模拟对指数伸展流中的大分子稳态动力学建模

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We introduce a method to obtain steady-state uniaxial exponential-stretching flow of a fluid (akin to extensionalnflow) in the incompressible limit, which enables us to study the response of suspended macromolecules to thenflow by computer simulations. The flow field in this flow is defined by vx = u0002x, where vx is the velocity of thenfluid and u0002 is the stretch flow gradient. To eliminate the effect of confining boundaries, we produce the flow inna channel of uniform square cross section with periodic boundary conditions in directions perpendicular to thenflow, but simultaneously maintain uniform density of fluid along the length of the tube. In experiments a perfectnelongational flow is obtained only along the axis of symmetry in a four-roll geometry or a filament-stretchingnrheometer. We can reproduce flow conditions very similar to extensional flow near the axis of symmetry bynexponential-stretching flow; we do this by adding the right amounts of fluid along the length of the flow in ournsimulations. The fluid particles added along the length of the tube are the same fluid particles which exit thenchannel due to the flow; thus mass conservation is maintained in our model by default.We also suggest a schemenfor possible realization of exponential-stretching flow in experiments. To establish our method as a useful toolnto study various soft matter systems in extensional flow, we embed (i) spherical colloids with excluded volumeninteractions (modeled by the Weeks-Chandler potential) as well as (ii) a bead-spring model of star polymers innthe fluid to study their responses to the exponential-stretched flow and show that the responses of macromoleculesnin the two flows are very similar. We demonstrate that the variation of number density of the suspended colloidsnalong the direction of flow is in tune with our expectations. We also conclude from our study of the deformationnof star polymers with different numbers of arms f that the critical flow gradient u0002c at which the star undergoesnthe coil-to-stretch transition is independent of f for f = 2, 5, 10, and 20.
机译：我们介绍了一种在不可压缩极限内获得流体的稳态单轴指数拉伸流的方法（类似于extendedalnflow），这使我们能够通过计算机模拟研究悬浮大分子对随后流动的响应。该流中的流场由vx = u0002x定义，其中vx是那么流体的速度，而u0002是拉伸流梯度。为了消除边界限制的影响，我们在垂直于nextflow的方向上产生具有周期性边界条件的均匀正方形横截面的流动通道，但同时沿管的长度保持均匀的流体密度。在实验中，仅在四辊几何形状或长丝拉伸流变仪中沿对称轴获得完美的伸长流。通过指数拉伸流，我们可以再现与对称轴附近的扩展流非常相似的流条件。我们通过在模拟中沿流的长度添加适量的流体来实现这一目的。沿着管的长度添加的流体粒子与由于流动而离开通道的流体粒子相同。因此，默认情况下，我们的模型中保持了质量守恒。我们还提出了一种在实验中可能实现指数伸展流的方案。为了建立我们的方法作为研究伸展流中各种软物质系统的有用工具，我们嵌入了（i）排除体积相互作用（由Weeks-Chandler势建模）的球形胶体，以及（ii）星形聚合物的珠弹簧模型在流体中研究它们对指数拉伸流的响应，并表明两种流中大分子的响应非常相似。我们证明了悬浮胶体沿流动方向的数量密度变化符合我们的预期。从对不同臂数f的星形聚合物的变形量的研究中，我们还得出结论，对于f = 2、5、10和20，恒星经历线圈到拉伸转变的临界流量梯度u0002c与f无关。

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  • 来源
    《PHYSICAL REVIEW E》 |2013年第4期|1-11|共11页
  • 作者

    Dhairyasheel Ghatage; Apratim Chatterji;

  • 作者单位

    Mechanical Engineering Department College of Engineering Shivajinagar Pune-411005 India;

    IISER-Pune 900 NCL Innovation Park Dr. Homi Bhaba Road Pune-411008 India;

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