- 學位論文
銀奈米顆粒與銀線之製備及銀懸浮液及其透明導電薄膜之開發
Fabrication of Silver Suspension and Transparent Conductive Thin Film Based on Silver Nanowire/Nanoparticle
摘要
奈米銀線或銀顆粒具有良好的導電性、導熱性以及光學性質，其分散液製備之導電薄膜可被廣泛應用於先進電子產品或是噴墨列印之領域上。本研究乃開發出兩種系統以製備透明導電薄膜，一種是水相奈米銀線穩定懸浮液，利用化學合成法、多元醇方式合成高產量且高轉化率的奈米銀線，將奈米銀線分散於添加微量的分散劑中形成穩定的奈米銀線懸浮液中；其二為係利用單軸靜電紡絲所製備奈米銀顆粒，並在未額外添加分散劑下即製備出水相奈米銀顆粒穩定懸浮液，並藉由上述分散液製備具有良好透明性之導電薄膜。 本研究第一部分為合成奈米銀線和奈米銀顆粒，其一利用多元醇方法合成出高產率之奈米銀線，並探討合成奈米銀線之變因—成核溫度、成長(最終合成)溫度、聚乙烯吡咯烷酮(PVP)與硝酸銀之莫耳比、硝酸銀之注射速率以及氯化鈉和溴化鉀之濃度。藉由調整上述之合成參數，以掃描式電子顯微鏡觀察銀之表面形態，並探討出銀之相關形貌之機制模擬。結果顯示成功合成出大量長徑比大於300之奈米銀線，其中直徑約40 nm、長為12-15 μm；其二利用單軸靜電紡絲法製備銀電紡纖維，再透過預退火處理並回溶於水，則形成直徑約60奈米的銀顆粒懸浮液。 傳統上，由於銀之密度太大，使得奈米銀線仍然難以懸浮於有機/無機溶劑中。分散劑的挑選在奈米銀線懸浮上為極重要的因素之一。本文第二部分，係開發一創新且簡單之配方製備出高分子分散劑/奈米銀線之穩定水相懸浮液，藉由添加微量高分子型的分散劑聚乙烯亞胺(PEI)或聚乙烯吡咯烷酮(PVP)或是BYK型號410分散劑與奈米銀線之作用力以懸浮具高密度的奈米銀線，將其穩定地均勻懸浮於水相中。此外，在不同的pH值與界面電位的變化下的高分子分散奈米銀線之懸浮行為，發現分散劑的高分子鏈段的伸展收縮結構明顯受pH值影響，因而影響奈米銀線的懸浮行為。 本研究第三個部分，係開發一簡易且實用之方式製備可撓性高分子/奈米銀線導電薄膜或是高分子分散劑/奈米銀顆粒導電薄膜。在奈米銀線方面，藉由添加分散劑及高分子乳膠，並利用磁石攪拌將奈米銀線均勻分散於水相中，再透過兩種不同的製膜方式(滴降式塗佈及噴霧式塗佈)以製備出導電薄膜。在奈米銀顆粒方面，因水性懸浮液中已存在分散劑，直接利用旋轉塗佈製備出透明導電薄膜。除此之外，也藉由調整噴霧式塗佈製膜參數(加熱溫度、噴霧次數及奈米銀線懸浮液濃度)以及旋轉塗佈製膜參數(旋轉速率及旋轉時間)改變導電薄膜厚度與奈米銀線/銀顆粒構成之網狀結構，來提升導電薄膜之透明度。上述方法提供一簡易、實際且有效率的製程，用於製備具良好導電性及高透明度之導電薄膜，並展現其可應用於電子元件的發展或是噴墨列印領域之潛力。
並列摘要
Silver nanowires and silver nanoparticles have received considerable attention due to their electrical, optimal and thermal properties used in various applications such as conductive thin film since bulk silver (Ag) has the highest thermal and electrical conductivity among all metals. Two methods were developed in this research to fabricate transparent conductive thin films from stable silver-nanowire or silver-nanoparticle suspensions. Chemical method was applied to synthesize silver nanowires; whereas electrospinning method was used to prepare silver nanoparticles. Three divided sections were contained in this thesis. In the first section, we demonstrated a parametric study on self-seeding polyol synthesis of optimal Ag nanowires. The effects of synthesizing temperature, molar ratio of poly(vinylpyrrolidone) (PVP) to silver nitrate, injecting rate of silver nitrate, concentrations of sodium chloride and potassium bromide, and stirring rate on the morphology of Ag nanostructures were examined. The morphologies of nanostructures and aspect ratio on synthesis parameters were shown via scanning electron microscopy (SEM) images. Ag nanowires were optimally synthesized by polyol process with a high aspect ratio of over than 300, where the average diameter and length were 40 nm and 12-15 μm, respectively. In terms of silver nanoparticle, single-jet electrospinning nethod was used to fabricate silver electrospun fibers, and the fibers were pre-annealed, and these fibers were re-disperded in water to form the stable silver nanoparticle suspension with the assistance of PVP from fibers. Traditionally, Ag nanowires were hardly suspended in polar or nonpolar solvents owing to their high density. In the second section, some innovative and facile formulas were proposed to prepare the water-based stable Ag nanowire suspensions with the addition of dispersive agent such as polyethylenimine (PEI), poly(vinylpyrrolidone) (PVP) and BYK-410 as suspending agent. When adding a little amount of polymers, polymer served as dispersion that associated with Ag nanowire, thus changing the interaction between Ag nanowires. We also examined the effect of pH values and zeta potential on the suspended behaviors of the polymer-bound Ag nanowire in aqueous solutions. The last section, a practical and general approach is described to fabricate the conductive thin films. Ag nanowires were dispersed stably in aqueous phase by the addition of dispersive agent under homogenization and Ag nanoparticles were dispersed in water phase then followed by three distinct processes including drop casting, spray coating and spin coating. Through the above-mentioned methods, good electrical and optical properties of prepared polymer-bound Ag nanowires/nanoparticles conductive thin films were performed. The proposed method provided a simple and practical approach for the fabrication of the conductive thin films with excellent transparency and showed the significant potential to apply in electronic fields generally.