Viscous Marangoni Effect in Coffee-ring Phenomenon
- 주제(키워드) Marangoni effect , Coffee-ring effect , surfactant , polymer
- 발행기관 고려대학교 대학원
- 지도교수 신세현
- 발행년도 2016
- 학위수여년월 2016. 8
- 학위구분 석사
- 학과 대학원 기계공학과
- 원문페이지 64 p
- 실제URI http://www.dcollection.net/handler/korea/000000068837
- 본문언어 영어
- 제출원본 000045881444
초록/요약
Uniform deposition of suspended particles in an evaporating droplet is necessary in many research fields. However, coffee-ring effect dominates internal flow in a droplet and suspended particles tend to accumulate on contact line through evaporation process. There had been many efforts to alter coffee-ring effect with adding surfactants and different shaped particles. The present study adopted a biocompatible, surfactant like polymer to break coffee-ring effect and have relatively uniform particle deposition over droplet area. For understanding internal flow in a droplet, pure water, SDS (surfactant), PVP (purely viscous polymer) and PEG (surfactant like polymer) solutions were compared with examining deposition patterns as well as movements of suspended particles in evaporating droplets on glass substrate using microscope image and video analysis. PEG and SDS droplet successfully altered the coffee-ring effect due to surface tension variation, which induced a centripetal Marangoni flow. With balancing these two phenomena, Marangoni vortex was apparently observed, pinning-and-depinning process was periodically repeated and multiple rings were regularly formed. Owing to elevated viscosity according to PEG concentration, deposition patterns of PEG droplets are more dense and uniform rather than those of SDS. Quantitative analysis of Marangoni eddies in PEG and SDS droplet was conducted with tracking change of vortex length and velocities with respect to time. Even though a small concentration of surfactant polymer was added, increased concentration of the polymer caused significant gradients of surface tension and viscosity near contact line and subsequently occurred Marangoni vortices and pinning-and-depinning led to relatively homogeneous coating at the end of evaporation compared to pure water, PVP and SDS. We think that uniform coating of suspended particles such as cells and various biomaterials would be utilized for various biomedical applications in basic analyses and clinical application in a droplet assay.
more목차
Table of Contents
List of Figures
1. Introductions 1
1.1 Coffee-ring effect 1
1.2 Importance of suppressing Coffee-ring effect 3
1.3 Methods for suppressing Coffee-ring effect 5
1.4 Objective of this study 8
2. Research background 11
2.1 Coffee-ring effect 11
2.2 Marangoni effect 13
2.3 Pinning and depinning 14
3. Materials and methods 16
3.1 Materials 16
3.2 Preparations of PEG, PVP and SDS solution 17
3.3 Preparations of glass substrate and experimental conditions 18
3.4 Analysis of deposition patterns and concentrations 19
3.5 Instruments 21
4. Results 22
4.1 Deposition patterns of tested droplets 22
4.2 Marangoni vortex 26
4.3 Multiple rings 34
5. Discussions 41
5.1 Uniformitiy 41
5.2 Modified Marangoni number 42
5.3 Contact line motion 43
5.4 Additional experiments 44
6. Conclusions 45
7. References 46
