William A. Brookshire Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204.
Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899.
Proc Natl Acad Sci U S A. 2022 Aug 9;119(32):e2203483119. doi: 10.1073/pnas.2203483119. Epub 2022 Aug 4.
Many biopolymers are highly charged, and as in the case of many polymer mixtures, they tend to phase separate as a natural consequence of chain connectivity and an associated relatively low entropy of polymer mixing. Recently, it has become appreciated that the phase-separated structures formed by such polyelectrolyte blends, called "complex coacervates," underlie numerous biological structures and processes essential to living systems, and there has been intense interest in understanding the unique physical features of this type of phase-separation process. In the present work, we are particularly concerned with the field responsiveness of stabilized coacervate droplets formed after the phase separation of polyelectrolyte blend solution and then exposed to deionized water, making the droplet interfacial layer acquire a viscoelastic character that strongly stabilizes it against coalescence. We show that we can precisely control the positions of individual droplets and arrays of them with relatively low-voltage electric fields (on the order of 10 V/cm) and that the imposition of an oscillatory field gives rise to chain formation with coarsening of these chains into long fibers. Such a phase-separation-like process is generally observed in electrorheological fluids of solid colloidal particles subjected to much larger field strengths. The key to these coacervates' electrorheological properties is the altered interfacial viscoelastic properties when the droplets are introduced into deionized water and the associated high polarizability of the droplets, similar to the properties of many living cells. Since many different molecular payloads can be incorporated into these stable droplets, we anticipate many applications.
许多生物聚合物带有很高的电荷，而且与许多聚合物混合物的情况一样，由于链的连接性以及相关聚合物混合的熵相对较低，它们往往会自然地分相。最近，人们开始意识到，这种聚电解质混合物形成的分相结构，称为“复杂凝聚物”，是许多对生命系统至关重要的生物结构和过程的基础，因此人们对理解这种分相过程的独特物理特性产生了浓厚的兴趣。在目前的工作中，我们特别关注的是聚电解质混合溶液分相后形成的稳定凝聚物液滴在暴露于去离子水后的场响应性，这使得液滴界面层具有粘弹性特征，从而强烈稳定其不发生聚并。我们表明，我们可以用相对较低的电场（约 10 V/cm）精确控制单个液滴及其阵列的位置，而施加振荡电场会导致链的形成，这些链会粗化为长纤维。这种类似相分离的过程通常在固体胶体颗粒的电流变流体中观察到，这些颗粒会受到更大的场强作用。这些凝聚物的电流变特性的关键在于液滴进入去离子水时界面粘弹性的变化以及液滴的高极化率，这类似于许多活细胞的特性。由于许多不同的分子有效载荷可以被整合到这些稳定的液滴中，因此我们预计会有许多应用。
