Passive Flow Control in Microchannels using Diblock Copolymer Brushes

裁剪材料使其自发地经历表面性质的变化是一个正在发展的研究领域。这些刺激反应膜可以经历表面变化，包括润湿性、粘附性、与细胞或蛋白质的相互作用以及膜的渗透性。基于双嵌段共聚物电刷的刺激响应膜已经得到了广泛的研究。这些双块刷可以在响应溶剂，温度，pH值和离子强度的表面发生成分变化。这些表面组成的可逆变化在分离技术领域具有相当大的潜力。研究了双嵌段共聚物电刷在微通道中的被动流动控制。文献中有几篇报道，其中接枝聚丙烯酰胺的响应行为已被用于控制微流体装置中的流动。二嵌段共聚物刷的可逆重排应该提供一个替代的响应系统，根据流体流的组成，表面可以改变其对不同溶质的亲和力，改变流速或调整竞争微通道之间的流量。本文的重点是聚合物刷的合成和表征在微通道中的应用。描述了几个简单的测试平台，以评估双块刷体重排对被动流动控制的有效性。具体来说，原子转移自由基聚合的硅烷基引发剂将用于在玻璃毛细血管内部或平板玻璃基底表面制备双嵌段共聚物刷。测试平台都依赖于使用市售微型泵的压力驱动流量。流量将使用液体质量流量计来确定，其流量灵敏度为nL/min。将对聚电解质均聚物进行初步的流动研究。提出了三个具体的测试平台。聚电解质均聚物的初步筛选和二嵌段重排将使用带有一个泵和一个流量计的单个玻璃毛细管进行。在第二个测试平台中，将使用软光刻技术在PDMS中创建一个简单的t型图案。PDMS模具将与具有图案刷化学的玻璃基板结合，使得两个通道在微通道的玻璃部分上具有不同的双块刷组合物。相对流量输出将由液体质量流量计监测。第三个测试平台是一个简单的分体式毛细管系统，将再次监测竞争流量。由于大多数微流控分析使用水流，我们将集中研究疏水/亲水双块刷系统，其中亲水块是阳离子或阴离子聚电解质。基于我们先前的支持结果，可以设想各种各样的附加块组合。将被检查的流体变量包括：pH值、离子强度、溶质浓度和介质极性。该研究的智力优势在于，这是第一个探索双块电刷重排作为微通道流动控制元件应用的研究。迄今为止，表面固定化聚合物在微通道中的应用主要集中在相对原始的聚合物系统上。本研究将采用最先进的聚合物合成技术，在微通道内部创建刺激响应涂层。成功控制由分析物组成变化引起的微通道内的流动将对微流体和分离技术领域产生潜在的重大影响。拟议研究的更广泛影响是一个多学科项目，将培养研究生，包括一名女性，在有机、聚合物和物理化学方面。本科生也可以在研究生的指导下，通过REU暑期补充课程参加。参与者将在ACS和Gordon研究会议上展示他们的研究结果。学生将在研究过程中学习如何使用干箱技术、核磁共振、GPC、FTIR、TGA、椭偏仪和张力测定法。本工作将通过测试和评估双块刷体重排可用于微通道被动流动控制的假设，为微流体的一般领域做出贡献。

Tailoring materials to spontaneously undergo changes in surface properties is a developing area of research. These stimuli-responsive films can undergo surface changes that include wettability, adhesion, interaction with cells or proteins and membrane permeability. There has been extensive study on stimuli-responsive films based on diblock copolymer brushes. These diblock brushes can undergo compositional changes at the surface in response to solvent, temperature, pH and ionic strength. These reversible changes in surface composition have considerable potential in the field of separation technology. Passive flow control of diblock copolymer brushes in microchannels will be studied. The literature contains several reports where the responsive behavior of grafted polyacrylamides has been used to control flow in microfluidic devices. The reversible rearrangement of diblock copolymer brushes should offer an alternative responsive system where, depending on the composition of the fluid stream, the surface can change its affinity for different solutes, alter flow rate or adjust flow between competing microchannels. The focus of this proposal is on the application of polymer brush synthesis and characterization to microchannels. Several simple testing platforms are described to assess the effectiveness of diblock brush rearrangement on passive flow control. Specifically, silane-based initiators for atom transfer radical polymerization will be used to prepare diblock copolymer brushes on the interior of glass capillaries or on the surface of flat glass substrates. The testing platforms all rely on pressure-driven flow using commercially available micropumps. Flow will be determined using liquid mass flow meters, which have nL/min flow sensitivity. Preliminary flow studies will be conducted with polyelectrolyte homopolymers. Three specific testing platforms are proposed. Initial screening of the polyelectrolyte homopolymers and diblock rearrangement will be conducted using a single glass capillary with one pump and one flow meter. In the second testing platform, a simple T-pattern will be created in PDMS using soft lithography. The PDMS mold will be combined with a glass substrate that has patterned brush chemistry so that the two channels possess different diblock brush compositions on the glass portion of the microchannel. Relative flow output will be monitored by liquid mass flow meters. The third testing platform is a simple split capillary system where competitive flow will again be monitored. Because most microfluidic analyses use aqueous streams, we will concentrate on hydrophobic/hydrophilic diblock brush systems where the hydrophilic block is a cationic or anionic polyelectrolyte. A wide variety of additional block compositions can be envisioned based on results from our prior support. Variables in the flow streams that will be examined include: pH, ionic strength, concentration of solutes, and polarity of the medium.The intellectual merit of the proposed research is that this is first study to explore the application of diblock brush rearrangement as a flow control element in microchannels. To date, the use of surface-immobilized polymers in microchannels has focused on relatively primitive polymer systems. This study will employ state-of-the-art techniques in polymer synthesis to create stimuli-responsive coatings on the interior of microchannels. Successful control of flow in microchannels that is induced by compositional changes in the analyte stream will have a potentially large impact on the field of microfluidics and separation technology. The broader impact of the proposed research is a multidisciplinary project that will train graduate students, including one woman, in organic, polymer and physical chemistry. Undergraduate students may also participate through an REU summer supplement, with mentoring by graduate students. Participants will present their results at ACS and Gordon Research conferences. Students will learn how to use dry box techniques, NMR, GPC, FTIR, TGA, ellipsometry and tensiometry during the course of their research. This work will contribute to general field of microfluidics by testing and assessing the hypothesis that diblock brush rearrangement can be used for passive flow control in microchannels.