CAREER: in situ Polymer Gelation in Confined Flows

聚合物凝胶在许多自然和工业流程中形成：蛋白质凝胶用于制作果冻或鸡蛋等食品；塑料可以在3D打印过程中凝胶；血液蛋白质可以交联，在血管中形成凝块。当聚合物分子交联或凝胶时，流动变得复杂，将流体转变为柔软的固体。交联会导致间歇性流动或完全停止流动，导致小通道、喷嘴或血管堵塞，最终导致系统故障。预测流态的能力是评估、控制和防止间歇和堵塞的关键。这一奖项将促进我们对通过小通道的交联型聚合物流动的基本理解，从而实现这种控制。这一奖项的结果可能导致各种应用的进步，包括生物打印和3D打印，因为它能够有效地打印更多种类的聚合物。它还将有助于设计能够在从液体肥料到生物医学和制药产品的小空间中流动的聚合物。计划开展教育和外展活动，以吸引和培训高中生、本科生和研究生掌握复杂液体中的新兴主题。该奖项的目标有两个：(1)了解导致通过微通道的交联聚合物流动的间歇性和堵塞的系统参数的范围；(2)提供间歇性以及间歇性流动的流变和材料特性的定量描述。为此，将使用视频显微镜和原位流变学，并结合理论传输模型。聚合物可以通过化学或物理方法进行交联，这两种方法都可以在生物印花中找到。在化学交联中，凝胶化进行得很快，就像用钙交联的海藻酸盐一样。在物理交联中，凝胶化速度是可控制的，就像通过降低温度来交联明胶一样。将对这两种类型的凝胶化进行研究，以确定反应速度和机理的重要性。我们将研究流型与化学物质浓度和流速的关系。研究结果将为预测和控制广泛的交联型聚合物体系中的流动状态提供参数。间歇性流动状态将通过现场流变学测量来研究，以确定流动中的凝胶强度和粘弹性，并将其与同类体系的整体流变特性进行比较。这将有助于在实际系统中防止和克服间歇性流动的策略。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。

Polymer gels form in many natural and industrial flows: proteins gel in preparing foods like Jell-O or eggs; plastics can gel during 3D printing; blood proteins can crosslink to form clots in vessels. Flows become complex when polymer molecules crosslink, or gel, transforming the fluid into a soft solid. Crosslinking can result in intermittent flow or complete flow stoppage, resulting in clogging of small channels, nozzles, or vessels, and eventual failure of the system. The ability to predict flow regimes is key to assessing, controlling, and preventing intermittency and clogging. This award will advance our fundamental understanding of crosslinked polymer flows through small channels to enable such control. The outcome of this award could result in advances for a variety of applications including in bioprinting and 3D printing by enabling efficient printing of a wider variety of polymers. It will also help designing polymers to flow through small spaces, ranging from fluid fertilizers to biomedical and pharmaceutical products. Education and outreach activities are planned to engage and train high school, undergraduate, and graduate students in emerging topics in complex fluids. Curriculum development, engaging the general public, and supporting underrepresented populations in STEM are also planned.The goals of this award are twofold: (1) to understand the range of system parameters that lead to intermittency and clogging in crosslinking polymer flows through microchannels, and (2) to provide quantitative descriptions of intermittency and the rheological and material properties of intermittent flows. Video microscopy and in situ rheology combined with theoretical transport models will be employed for this purpose. Polymers can be crosslinked by chemical or physical methods, both of which are found in bioprinting. In chemical crosslinking, gelation proceeds quickly, as in alginate crosslinked by calcium. Gelation rate is controllable in physical crosslinking, as in gelatin crosslinked by lowering temperature. Both types of gelation will be investigated to determine the importance of reaction rate and mechanism. Dependence of flow regimes on chemical concentrations and flow rates will be studied. The outcome will provide parameters to predict and control flow regimes in a broad range of crosslinking polymer systems. The intermittent flow regime will be investigated by in situ rheological measurements to determine gel strength and viscoelasticity in flow, which will be compared to bulk rheological characterization of comparable systems. This will facilitate strategies to prevent and overcome intermittent flows in practical systems.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.