Experimental study of the conformation and dynamics of active colloidal polymers

活性流体是自驱动颗粒在液体介质中的分散。这种类型的流体与广泛的生物和物理系统有关，包括游泳微生物的悬浮液、合成胶体游泳器和振动颗粒棒。最近的理论和模拟已将由致密固体颗粒组成的简单活性流体的研究扩展到细长的柔性物体，如软链和细丝。这样的研究改变了我们对非平衡条件下柔性物体(例如活细胞内的生物聚合物)动力学的理解，并揭示了活动流体的意外集体动力学。然而，能够定量验证广泛的理论和数字预测的基准实验仍然缺乏。本研究项目旨在解决这一差距，并进行实验，研究活性DNA连接的胶体颗粒长链的形状和动力学，即所谓的胶体聚合物，类似于线性聚合物分子。这些研究中包括的两个具体系统是浸泡在光动力细菌悬浮液中的被动胶体聚合物和活性Janus胶体聚合物，其活性在内部通过化学反应从单个Janus粒子中产生。最终目的是探索使用自驱动活性胶体聚合物作为人造鞭毛的可能性。该项目包括为本科流体课程和工业从业者参加的暑期短期课程设计演示的外联工作。该项目还旨在建立学术和工业研究人员之间的密切合作。DNA连接的胶体链为聚合物分子的经典珠弹簧模型提供了一个具体的例子。通过将活性传递到DNA连接的胶体聚合物，研究小组将研究活性胶体聚合物的构象和动力学，并了解基本的聚合物平衡标度关系。研究人员将验证有关活性聚合物异常行为的重要理论和数值预测，如具有活性的聚合物链膨胀、发夹结构的自组装以及活性诱导的软化和线团到球体的转变。此外，通过利用相互关联的活跃Janus粒子的集体动力学，项目参与者将研究一种新的方法，以创建具有周期性非互易跳动的自驱动人造鞭毛。然后，这种鞭毛结构将被测试以驱动合成微泳者的运动。综上所述，该项目不仅提供了基准实验，证实了现有的理论和模拟，而且还提供了一种新的方法来设计合成微泳者，以便在微观尺度上运送货物。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

An active fluid is a dispersion of self-driven particles in a liquid medium. This type of fluid is relevant to a broad class of biological and physical systems including suspensions of swimming microorganisms, synthetic colloidal swimmers and vibrated granular rods. Recent theories and simulations have greatly extended the study of simple active fluids made of compact solid particles to elongated flexible objects such as soft chains and filaments. Such research has transformed our understanding of the dynamics of flexible objects in nonequilibrium conditions (for example, biopolymers within living cells) and revealed unexpected collective dynamics of active fluids. Nevertheless, benchmark experiments that can quantitatively verify the wide range of theoretical and numerical predictions are still missing. This research project aims to address this gap and to perform experiments that study the shape and dynamics of active DNA-linked long chains of colloidal particles, the so-called colloidal polymers in analogy of linear polymer molecules. Two specific systems included in these studies are passive colloidal polymers immersed in light-powered bacterial suspensions and active Janus colloidal polymers whose activity arises internally from individual Janus particles via chemical reactions. The ultimate objective is to explore the possibility of using self-driven active colloidal polymers as artificial flagella. The project includes outreach efforts on designing demos for undergraduate fluid classes and for summer short courses attended by industrial practitioners. The project also aims to forge close collaborations between academic and industrial researchers.DNA-linked colloidal chains provide a concrete example of the classic bead-spring model of polymer molecules. By conveying activity to DNA-linked colloidal polymers, the research team will investigate the conformation and dynamics of active colloidal polymers and understand the fundamental polymer scaling relations out of equilibrium. The researchers will verify important theoretical and numerical predictions on the unusual behaviors of active polymers such as the swelling of polymer chains with activity, the self-assembly of hairpin structures, and the activity-induced softening and coil-to-globule transition. Moreover, by exploiting the collective dynamics of linked active Janus particles, the project participants will study a new approach for creating self-driven artificial flagella with periodic non-reciprocal beating motions. Such a flagellar structure would then be tested for driving the locomotion of synthetic microswimmers. Taken together, the project provides not only benchmark experiments corroborating existing theories and simulations but also a new way to engineer synthetic microswimmers for cargo delivery at microscopic scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.