Passive Flow Control in Microchannels using Diblock Copolymer Brushes

使用二嵌段共聚物刷进行微通道中的被动流量控制

• 批准号: 0423786
• 负责人: William Brittain
• 金额: $ 31万
• 依托单位: University of Akron
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2008-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0423786&HistoricalAwards=false
• 关键词: Passive; Flow; Control; Microchannels; using

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.

定制材料以自发地经历表面性质的变化是一个发展中的研究领域。 这些刺激响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渗透性。 基于二嵌段共聚物刷的刺激响应膜已经得到了广泛的研究。 这些二嵌段刷可以在表面处响应于溶剂、温度、pH和离子强度而经历组成变化。 表面组成的这些可逆变化在分离技术领域具有相当大的潜力。 研究了嵌段共聚物刷在微通道中的被动流动控制。 文献包含几个报告，其中接枝聚丙烯酰胺的响应行为已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提供替代响应系统，其中取决于流体流的组成，表面可改变其对不同溶质的亲和力，改变流速或调节竞争微通道之间的流动。 本提案的重点是应用聚合物刷合成和表征微通道。 描述了几个简单的测试平台，以评估二块刷重排对被动流控制的有效性。 具体而言，用于原子转移自由基聚合的基于硅烷的引发剂将用于在玻璃毛细管的内部或在平坦玻璃基板的表面上制备二嵌段共聚物刷。 测试平台都依赖于使用市售微型泵的压力驱动流。 将使用具有nL/min流量灵敏度的液体质量流量计测定流量。 初步的流动研究将进行与聚苯乙烯均聚物。 提出了三种具体的测试平台。 将使用带有一个泵和一个流量计的单个玻璃毛细管进行双嵌段均聚物和二嵌段重排的初始筛选。在第二个测试平台中，将使用软光刻在PDMS中创建简单的T图案。 PDMS模具将与具有图案化刷化学的玻璃基底组合，使得两个通道在微通道的玻璃部分上具有不同的二嵌段刷组合物。 将通过液体质量流量计监测相对流量输出。 第三个测试平台是一个简单的分离毛细管系统，其中竞争性流动将再次被监测。 由于大多数微流体分析使用水流，我们将集中在疏水/亲水二嵌段刷系统，其中亲水嵌段是阳离子或阴离子的聚合物。 基于我们先前支持的结果，可以设想各种各样的附加嵌段组合物。 将被检查的流动流中的变量包括：pH值，离子强度，溶质的浓度，和极性的medium.The拟议的研究的智力价值是，这是第一次研究，探索应用二块刷重排作为微通道中的流量控制元件。 迄今为止，在微通道中使用表面固定的聚合物集中在相对原始的聚合物系统。 这项研究将采用聚合物合成中最先进的技术在微通道内部创建刺激响应涂层。 成功控制微通道中由分析物流中的组成变化引起的流动将对微流体和分离技术领域产生潜在的巨大影响。拟议研究的更广泛影响是一个多学科项目，将在有机、聚合物和物理化学方面培训研究生，包括一名妇女。 本科生也可以通过REU夏季补充参与，由研究生指导。 参与者将在ACS和Gordon Research会议上展示他们的研究结果。 学生将学习如何在研究过程中使用干箱技术，NMR，GPC，FTIR，TGA，椭偏仪和张力计。 本论文的工作将有助于微流控领域的研究，验证和评估二嵌段刷重排可用于微通道被动流动控制的假设。