粗糙度對奈米粒子沉積樣貌之影響研究

A study on the influence of surface roughness on the nano-particle deposition morphology

陳昱修(Yu-Shiou Chen)

指導教授 ： 陳立仁

國立臺灣大學/工學院/化學工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202203148

摘要

本研究討論不同微米尺度柱狀表面對純水液滴之濕潤行為以及奈米粒子沉積物的影響。使用PDMS (聚二甲基矽烷)作為基材，改變不同微米方柱陣列之大小、間隙以及高度調整表面粗糙度，並透過埋針法與蒸發法量測表面之濕潤現象以及奈米粒子沉積物之形貌。其形貌隨表面粗糙度從八角形環狀結構以及較大的環型沉積物逐漸轉換為直徑較小的坍塌小球結構，提供印刷、觸媒小球製備以及咖啡環沉積圖譜之應用參考。而表面粗糙度可簡單分為四個區間，分別為Wenzel區間， 玫瑰花瓣區間，假性荷葉區間以及Cassie區間。其中在玫瑰花瓣區間使用埋針法可觀察到兩個前進角，假性荷葉區間透過蒸發法可發現兩個後退角之濕潤結果。
另一方面，使用大小約400奈米之二氧化矽以及聚苯乙烯之奈米懸浮溶液進行蒸發實驗。二氧化矽奈米粒子溶液在蒸發過程中較易於堆積於三相之接觸線，使環狀沉積物易於產生。聚苯乙烯粒子因密度較小，可以透過降低環境濕度，增加表面捕捉效應，減少環狀沉積物形成。最後，實驗調整不同懸浮溶液之濃度，環境濕度，表面性質改變最後沉積物之形貌。在粒子密度較低及環境濕度較低條件下，易於平坦化之沉積物生成，而增加表面疏水性及懸浮液濃度，容易發現球狀沉積物。

關鍵字

蒸發 ； 接觸角 ； 表面粗糙度 ； 前進角及後退角 ； 咖啡環效應

並列摘要

This study discusses the effects of micron-scale pillar structure surfaces on the wetting behavior of pure water droplets and nanoparticle deposits. Using PDMS (polydimethylsiloxane) as the substrate, changing the size, gap, and height of different micro-square column arrays to adjust the surface roughness, measuring the surface wetting phenomenon, and observing nanoparticle deposits by embedded needle method and evaporation method of appearance.
The surface roughness can be divided into four regions: the Wenzel region, petal region, pseudo lotus region, and Cassie region. Among them, the embedded needle method in the petal region can observe and measure two advancing contact angles. The wetting behaviors of the two receding angles can be found by the evaporation method in the pseudo lotus region.
On the other hand, nanosuspensions of silica and polystyrene with a size of 400 nm are used as suspensions to investigate the deposition morphology. During the evaporation process, the silica nanoparticle solution is more likely to accumulate on the solid-liquid-gas contact line so the ring-shaped deposit is easy to generate. Due to its low density, the ring formation could be eliminated by enhancing the surface capture effect by lowering the ambient humidity.
Finally, the concentration of suspension solutions, the environmental humidity, and the surface hydrophobicity are changed to alter the morphology of the final deposit. Under the conditions of low particle density and low ambient humidity, it is prone to flattened deposits, while increasing the surface hydrophobicity and the concentration of the suspension, tend to obtain spherical deposits.

並列關鍵字

contact angle ； embedded needle contact angle measurement ； evaporation ； coffee-ring effect ； nano-particle ； surface roughness ； advancing contact angle and receding contact angle ； Cassie state ； Wenzel state ； wetting behavior ； wetting transition

參考文獻

REFERENCES

1. Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Capillary flow as the cause of ring stains from dried liquid drops. Nature 1997, 389 (6653), 827-829.

2. Larson, R. G. Re‐Shaping the Coffee Ring. Angewandte Chemie International Edition 2012, 51 (11), 2546-2548.

3. Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Contact line deposits in an evaporating drop. Physical Review E 2000, 62 (1), 756

4. Deegan, R. D. Pattern formation in drying drops. Physical Review E 2000, 61 (1), 475.