We examine the impact of confinement on the structure, dynamics, and rheology of spherically confined macromolecular suspensions, with a focus on the role played by entropic forces, by comparing the limits of strong hydrodynamics and no hydrodynamics. We present novel measurements of the osmotic pressure, intrinsic viscosity, and long-time self-diffusivity in spherical confinement and find confinement induces strong structural correlations and restrictions on configurational entropy that drive up osmotic pressure and viscosity and drive down self-diffusion. Even in the absence of hydrodynamics, confinement produces distinct short-time and long-time self-diffusion regimes. This finding revises the previous understanding that short-time self-diffusion is a purely hydrodynamic quantity. The entropic short-time self-diffusion is proportional to an entropic mobility, a direct analog to the hydrodynamic mobility. A caging plateau following the short-time regime is stronger and more durable without hydrodynamics, and entropic drift—a gradient in volume fraction—drives particles out of their cages. The distinct long-time regime emerges when an entropic mobility gradient arising from heterogeneous distribution of particle volume drives particles out of local cages. We conclude that entropic mobility gradients produce a distinct long-time dynamical regime in confinement and that hydrodynamic interactions weaken this effect. From a statistical physics perspective, confinement restricts configurational entropy, driving up confined osmotic pressure, viscosity, and (inverse) long-time dynamics as confinement tightens. We support this claim by rescaling the volume fraction as the distance from confinement-dependent maximum packing, which collapses the data for each rheological measure onto a single curve.

中文翻译：

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密闭布朗悬浮液：平衡扩散、热力学和流变学

我们通过比较强流体动力学和无流体动力学的限制，研究了约束对球形约束大分子悬浮液的结构、动力学和流变学的影响，重点关注熵力所起的作用。我们提出了球形限制中渗透压、特性粘度和长期自扩散率的新测量方法，发现限制会导致强烈的结构相关性和构型熵的限制，从而提高渗透压和粘度并降低自扩散。即使在没有流体动力学的情况下，限制也会产生不同的短时和长时自扩散机制。这一发现修正了之前的认识，即短时自扩散是一个纯粹的流体力学量。熵短时自扩散与熵流动性成正比，熵流动性是流体动力流动性的直接模拟。在没有流体动力学和熵漂移（体积分数梯度）的情况下，遵循短时机制的笼状高原更坚固、更持久，将粒子赶出它们的笼子。当粒子体积的不均匀分布引起的熵迁移率梯度将粒子赶出局部笼时，就会出现明显的长期状态。我们得出结论，熵迁移率梯度在限制中产生了明显的长期动力学机制，并且流体动力学相互作用削弱了这种效应。从统计物理学的角度来看，限制限制了构型熵，随着限制收紧，提高了限制渗透压、粘度和（逆）长期动力学。