奈米銀/聚乙烯醇複合膜之製備、表面形態及電阻性質

Abstract

隨著科技的日新月異，導電材料的應用日趨廣泛，為了達到不同功能與應用上的需求，擷取不同材料之間之優點進行複合材料的製備成為廣泛討論的課題與研究方向。傳統上，最廣為使用的導電材料為金屬，因其擁有良好的導電性、延展性與加工性，但其與高分子等材料之間附著力不佳，使其在不同應用面之製程開發產生阻礙，目前最廣為使用之方法為利用各種輔助系統進行的化學沉積法，但製程繁複且設備昂貴。近年來，奈米技術的迅速發展，由下而上(Bottom-up)的製程受到矚目，利用分子本身材料特性與自組裝能力，製造出不同以往利用由上而下(Top-down)製程所能得到之特性與應用。金屬銀本身擁有良好的導電性，一般利用物理或化學方法與穩定劑的兼用於原位進行氧化還原反應將銀離子還原成金屬銀，可有效控制其大小、形狀、分散情形。為結合金屬的導電性、高分子的材料特性與功能上的應用與發展，本論文係利用硝酸銀為銀之前導物與聚乙烯醇為高分子基材經由熱處理方式進行低表面電阻奈米銀粒子/聚乙烯醇複合膜之製備。在此系統中，聚乙烯醇為多功能之材料，除本身可作為高分子基材外，在還原製備奈米銀粒子過程中亦扮演還原劑與穩定劑之角色。利用聚乙烯醇於側鏈上之氫氧基，透過熱誘導方式進行氧化還原反應，將銀離子還原成銀粒子。藉由控制硝酸銀/聚乙烯醇之相對濃度、複合膜厚度、熱處理溫度與時間等條件製備之奈米銀粒子/聚乙烯醇複合膜可於表面形成特殊之蕨葉狀表面形態。透過100℃、72小時的熱處理與250℃、30分鐘的燒結，表面所生成之奈米銀粒子尺寸大小由60 nm增加至300 nm且表面片電阻值由原本未經熱處理樣本的大於2.0 × 108 Ω/sq降低至1.0 Ω/sq。透過簡單且方便的製程，低表面電阻之奈米銀粒子/聚乙烯醇複合膜的成功製備將對於未來在噴墨印刷電路等應用方面的發展。

Films with the surface silver particle interconnected patterns were fabricated from in situ reduction of silver nitrate in poly(vinyl alcohol) [PVA] aqueous solution under a mild heating at 100 ℃. The initial stage of AgNO3 dissolved in PVA solution was generated the films with fern-like morphology which subsequently directed the generated silver nanoparticles to the film surface and formed the interconnected patterns. The kinetic controls by heating promoted the migration of AgNPs to the surface and the Ag melting during the evaporation and heating. The film thickness and Ag concentration were the parameters that allowed the formation of self-organized Ag patterns on film surfaces. After heating at 100 ℃ for 72 h and annealing at 250 ℃ for 30 min, the size of AgNPs was increased averagely from 60 nm to 300 nm and the AgNPs/PVA surface sheet resistance (Rs) was significantly decreasing from > 2.0×10 8 Ω/sq of pristine PVA film to 2.0×10 0 Ω/sq. The process of forming the silver patterns on film surface was monitored by UV-visible, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM) and four point probe meter in measuring their silver melting, patterning and conductivity.