矽膠複合材料透過雷射直寫轉換調控表面導電與潤濕性

Abstract

近年來，聚二甲基矽氧烷（Polydimethylsiloxane, PDMS）矽膠材料由於其化學穩定性、柔軟性與生物相容性，使其在生物醫學、柔性感測器與微流體晶片的應用日益廣泛。為了賦予PDMS更多樣的功能與增加在各領域的應用，許多研究常透過添加高分子聚合物或是具有功能性的微奈米顆粒來製作PDMS複合材料。儘管如此，要精確控制這些複合材料的特性通常需要複雜的製造流程與較高的生產成本。

本論文提出一種藉由445nm藍光二極體雷射誘導生成石墨烯(Laser-induced Graphene)的技術，在PDMS混和石墨(Graphite)所製作的PDMS/Graphite柔性基材上調控表面潤濕性與導電性的方法。為了提高PDMS在可見光波段的吸收率，我們在PDMS中加入了石墨粉末使雷射過程中有更好的轉換並且降低對焦系統的要求，也發現加入不同重量百分濃度的石墨在PDMS中經由雷射轉換過後所產生的石墨烯結構與導電性都有所差異，更高濃度所產生的石墨烯層較厚且與基材的附著力較高。為了更進一步提升導電率也加入可溶於PDMS中的TEG，製作PDMS/Graphite/TEG的複合材料，並且證實在PDMS此類矽膠材料中加入含有碳源的物質是有利於生成石墨烯。

上述方法主要是透過改變基材組成來調控表面特性，而本研究亦透過不同雷射功率來對PDMS/Graphite基材調控其表面潤濕性與導電性，較低雷射功率所產的石墨烯結構為片狀且具有超疏水特性，而使用較高雷射功率所產生之石墨烯為粉狀且為超親水表面，而藉由功率的連續調控使表面潤濕性從超疏水連續變化到超親水。

根據先前研究之成功我們可一步製作可圖案化的超疏水電極，並將此作為共平面式靜電操縱液滴的驅動電極，此裝置可用來進行液滴的傳輸與合併，而高導電率與較厚的石墨烯層所製作出的電極則可用來作為柔性應變感測器。此研究之方法不僅可一步驟在柔性基材上產生電極，並且賦予其連續潤濕性的變化，相信開拓了更多柔性電極的應用可能性。

In recent years, the silicone material Polydimethylsiloxane (PDMS) has become widely used in biomedicine, flexible sensors, and microfluidic chips due to its chemical stability, flexibility, and biocompatibility. To enhance the functionality of PDMS and increase the applications in various field, many studies often fabricate PDMS composite materials by adding high molecular polymers or functional micro- and nanoparticles.Despite these efforts, precise control composite materials properties often require complex manufacturing processes and make production costs increase.

In this study we propose a technique using 445nm blue diode laser to induce Graphene on PDMS/Graphite flexible substrates. This method allows the modulation of surface wettability and conductivity on a flexible PDMS/Graphite substrates. To improve PDMS absorption in the visible wavelength. We added graphite powder into PDMS to achieve easier conversion during the laser process and reducing the requirements of the focus system. We also found adding different weight percentage concentrations of graphite into PDMS, after laser conversion the structure and conductivity of graphene were different. The graphene have thicker structure and higher adhesion to the substrate was produced in higher concentration. In order to further improve the conductivity, TEG was added to PDMS/Graphite composite material, and it was confirmed that adding carbon source-containing substances to PDMS is beneficial to the generation of graphene.

The above methods primarily involve altering the substrate composition to regulate surface conductivity. This study also demonstrates the control of surface wettability in PDMS/Graphite substrates by using different laser powers. The graphene with superhydrophobic and flake structures characteristics was produced by lower laser power, while the graphene with a hydrophilic property was produced by higher laser power. Continuous adjustment of laser power leds to a transition in surface wettability from superhydrophobic to hydrophilic.

Based on our results, we can fabricate patternable superhydrophobic electrodes in one step and use this as a driving electrode for coplanar electrostatic manipulation of droplets. This device can be used to transport and combine droplets. Electrodes made from high conductivity and thick graphene layers can also be used as flexible strain sensors. The method in this study can generate electrodes on flexible substrates in one step and control the surface wettability. This may open up more application possibilities for flexible electrodes