Bubble generation and mechanism in polydimethylsiloxane

based polymerase chain reaction chip

       PDMS表面的疏水性和由于多孔性导致的气透性使其在某些方面的应用受到了限制，本论文以PCR芯片为例，讨论了气泡产生的原理及消除办法。首先设计了多腔室的PCR芯片，并利用MEMS加工工艺制备了芯片。利用在模具上制备的SU-8 光刻胶长方条使PDMS的对应位置产生空腔的方法很好地解决了温度传感器的植入问题。通过温控测试发现：温度的降温过程仅仅依靠其本身将会延长降温过程的时间，需要利用外界条件来缩短时间。经过氧等离子体处理后的PDMS表面的润湿性发生了很大的改变，由原来的疏水性变成了亲水性。然后通过对比PDMS表面氧等离子体处理和未经处理的芯片腔室中液体变化情况发现：经过氧等离子体处理芯片的腔室中在60-95℃没有发现气泡，而未经处理的芯片腔室中气泡随温度的升高而不断增大，经过多次循环仍有大量气泡出现。PDMS表面疏水性导致腔室内表面存在着残留气体，这些残留气体首先随温度膨胀，使腔室中的某些位置处于气固界面状态，这就为PDMS中的气体进入腔室提供了捷径，而PDMS的气透性又为腔室提供了源源不断的气源。PDMS经过氧等离子体处理后由疏水性变为亲水性，其作用不仅使PDMS内表面与水亲密接触，保证其几乎没有残留气体；而且还提高PDMS中的气体分子进入腔室中的所需的能量，这就意味着提高了PDMS中的气体分子进入腔室中的所需的温度。

         In order to explain the mechanism of bubble generationin PDMS, we investigated the crucial factors: the surface wettability andpermeability of PDMS. Two microfluidic chips were designed and fabricated: aPDMS/glass chip and a glass/PDMS/glass sandwich chip (about 1 μm in thicknessof PDMS). Then two sets of experiments were carried out: a comparison betweenthe PDMS/glass chips untreated and treated with O₂ plasma, andanother comparison between a PDMS/glass chip and a glass/PDMS/glass sandwichchip. The bubble in the PDMS/glass chip was avoided by treating with O₂plasma. After the treatment, the residual gas between the PDMS surface andwater was eliminated in that the PDMS surface became hydrophilic. In addition,the gas molecules required higher energy to enter the chambers due to thereduced contact angle of PDMS and water. The glass/PDMS/glass sandwich chip wastreated with the vacuum processing to eliminate the residual gas. And the gasoutside of the chip did not enter the chambers through the thin layer of PDMSeasily. This further verified that the surface wettability and the permeabilityof PDMS can result in the bubble generation.

Bubble generation and mechanism in polydimethylsiloxane based polymerase chain r.pdf