1
|
Zou H, Zhang D, Fu Q, Yang L, Zheng K, Dong RY. Scaling variation in the pinch-off of colloid-polymer mixtures. J Colloid Interface Sci 2024; 675:848-856. [PMID: 39002235 DOI: 10.1016/j.jcis.2024.07.054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 06/13/2024] [Accepted: 07/06/2024] [Indexed: 07/15/2024]
Abstract
HYPOTHESIS The scaling laws of drop pinch-off are known to be affected by drop compositions including dissolved polymers and non-Brownian particles. When the size of the particles is comparable to the characteristic length scale of the polymer network, these particles may interact strongly with the polymer environment, leading to new types of scaling behaviors not reported before. EXPERIMENTS Using high-speed imaging, we experimentally studied the time evolution of the neck diameter hmin of drops composed of silica nanoparticles dispersed in PEO solution when extruded from a nozzle. FINDINGS After initial Newtonian necking with hmin ∼ t2/3, the subsequent stage may exhibit scaling variation, characterized by either exponential or power-law decay, depending on the nanoparticle volume fraction ϕ. The exponential decay hmin ∼ e-t/τ signifies the coil-stretch transition in typical viscoelastic suspensions. We conducted an analysis of the power-law scenario hmin ∼ tα at high ϕ, categorizing the entire process into three distinct regimes based on the exponents α. The dependences of critical thicknesses at transition points and exponents on polymer concentration offer initial insights into the potential transition from heterogeneous to homogeneous thinning in the mixture. This novel scaling variation bears implications for accurately predicting and controlling droplet fragmentation in industrial applications.
Collapse
Affiliation(s)
- Hongyi Zou
- School of Astronautics, Beihang University, Beijing 100191, China
| | - Dingwei Zhang
- School of Astronautics, Beihang University, Beijing 100191, China
| | - Qingfei Fu
- School of Astronautics, Beihang University, Beijing 100191, China; Aircraft and Propulsion Laboratory, Ningbo Institute of Technology, Beihang University, Ningbo 315100, China
| | - Lijun Yang
- School of Astronautics, Beihang University, Beijing 100191, China; Aircraft and Propulsion Laboratory, Ningbo Institute of Technology, Beihang University, Ningbo 315100, China
| | - Kaikai Zheng
- Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003, USA; Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan, South Korea.
| | - Ruo-Yu Dong
- School of Astronautics, Beihang University, Beijing 100191, China; Aircraft and Propulsion Laboratory, Ningbo Institute of Technology, Beihang University, Ningbo 315100, China.
| |
Collapse
|
2
|
Klopp C, Trittel T, Harth K, Stannarius R. Coalescence of biphasic droplets embedded in free standing smectic A films. SOFT MATTER 2024; 20:1036-1046. [PMID: 38205564 DOI: 10.1039/d3sm01549a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2024]
Abstract
We investigate micrometer-sized flat droplets consisting of an isotropic core surrounded by a nematic rim in freely suspended smectic A liquid-crystal films. In contrast to purely isotropic droplets which are characterized by a sharp edge and no long-range interactions, the nematic fringe introduces a continuous film thickness change resulting in long-range mutual attraction of droplets. The coalescence scenario is divided in two phases. The first one consists in the fusion of the nematic regions. The second phase involves the dissolution of a thin nematic film between the two isotropic cores. The latter has many similarities with the rupture of thin liquid films between droplets coalescing in an immiscible viscous liquid.
Collapse
Affiliation(s)
- Christoph Klopp
- Institute of Physics, Otto von Guericke University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany.
- MARS, Otto von Guericke University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany
| | - Torsten Trittel
- MARS, Otto von Guericke University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany
- Department of Engineering, Brandenburg University of Applied Sciences, Magdeburger Straße 50, D-14770 Brandenburg an der Havel, Germany
| | - Kirsten Harth
- MARS, Otto von Guericke University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany
- Department of Engineering, Brandenburg University of Applied Sciences, Magdeburger Straße 50, D-14770 Brandenburg an der Havel, Germany
| | - Ralf Stannarius
- Institute of Physics, Otto von Guericke University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany.
- MARS, Otto von Guericke University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany
- Department of Engineering, Brandenburg University of Applied Sciences, Magdeburger Straße 50, D-14770 Brandenburg an der Havel, Germany
| |
Collapse
|
3
|
Dolganov PV, Spiridenko NA, Zverev AS. Dynamics of viscous droplet coalescence in the confined geometry of optical cells. Phys Rev E 2024; 109:014702. [PMID: 38366422 DOI: 10.1103/physreve.109.014702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Accepted: 12/28/2023] [Indexed: 02/18/2024]
Abstract
The dynamics of quasi-two-dimensional coalescence of isotropic droplets in nematic liquid crystal environment was studied. Investigations were made in confined geometry of a Hele-Shaw optical cell with different transverse droplet sizes. The existence of three distinct dynamic regimes was found for coalescence, namely, short-, middle-, and long-time regimes. The fast dynamics of bridge transformation was visualized. At short time the dynamics of droplet transformation is similar to the transformation of free (three-dimensional) droplets. At later stages, two regimes of the coalescence at different timescales are determined by Poiseuille flow. Experimental data are discussed on the basis of existing theories.
Collapse
Affiliation(s)
- P V Dolganov
- Osipyan Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow Region, Russia
| | - N A Spiridenko
- Osipyan Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow Region, Russia
| | - A S Zverev
- Osipyan Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow Region, Russia
| |
Collapse
|
4
|
Ryu S, Zhang H, Anuta UJ. A Review on the Coalescence of Confined Drops with a Focus on Scaling Laws for the Growth of the Liquid Bridge. MICROMACHINES 2023; 14:2046. [PMID: 38004903 PMCID: PMC10673007 DOI: 10.3390/mi14112046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 10/26/2023] [Accepted: 10/28/2023] [Indexed: 11/26/2023]
Abstract
The surface-tension-driven coalescence of drops has been extensively studied because of the omnipresence of the phenomenon and its significance in various natural and engineering systems. When two drops come into contact, a liquid bridge is formed between them and then grows in its lateral dimensions. As a result, the two drops merge to become a bigger drop. The growth dynamics of the bridge are governed by a balance between the driving force and the viscous and inertial resistances of involved liquids, and it is usually represented by power-law scaling relations on the temporal evolution of the bridge dimension. Such scaling laws have been well-characterized for the coalescence of unconfined or freely suspended drops. However, drops are often confined by solid or liquid surfaces and thus are a different shape from spheres, which affects their coalescence dynamics. As such, the coalescence of confined drops poses more complicated interfacial fluid dynamics challenges compared to that of unconfined drops. Although there have been several studies on the coalescence of confined drops, they have not been systematically reviewed in terms of the properties and geometry of the confining surface. Thus, we aim to review the current literature on the coalescence of confined drops in three categories: drop coalescence on a solid surface, drop coalescence on a deformable surface, and drop coalescence between two parallel surfaces with a small gap (i.e., Hele-Shaw cell), with a focus on power-law scaling relations, and to suggest challenges and outlooks for future research on the phenomena.
Collapse
Affiliation(s)
- Sangjin Ryu
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA; (H.Z.)
- Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Haipeng Zhang
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA; (H.Z.)
| | - Udochukwu John Anuta
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA; (H.Z.)
| |
Collapse
|
5
|
Rajput AS, Varma SC, Kumar A. Sub-Newtonian coalescence in polymeric fluids. SOFT MATTER 2023. [PMID: 37325814 DOI: 10.1039/d3sm00069a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
We present a theoretical framework for capturing the coalescence of a pendant drop with a sessile drop in polymeric fluids. The framework is based on the unification of various constitutive laws under a high Weissenberg creeping flow limit. Our results suggest that the phenomenon comes under a new regime, namely, the sub-Newtonian regime followed by the limiting case of arrested coalescence with the arrest angle θarrest ∝ Ec-1/2-1, where Ec-1 is the inverse of Elasto-capillary number. Furthermore, we propose a new time scale T* integrating the continuum variable Ec-1 and the macromolecular parameter Ne, the entanglement density to describe the liquid neck evolution. Finally, we validate the framework with high-speed imaging experiments performed across different molecular weights of poly(ethylene oxide) (PEO).
Collapse
Affiliation(s)
- Abhineet Singh Rajput
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India.
| | - Sarath Chandra Varma
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India.
| | - Aloke Kumar
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India.
| |
Collapse
|
6
|
Xu H, Wang T, Che Z. Bridge evolution during the coalescence of immiscible droplets. J Colloid Interface Sci 2022; 628:869-877. [DOI: 10.1016/j.jcis.2022.08.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 07/29/2022] [Accepted: 08/02/2022] [Indexed: 10/15/2022]
|
7
|
Varma SC, Rajput AS, Kumar A. Rheocoalescence: Relaxation Time through Coalescence of Droplets. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00249] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sarath Chandra Varma
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Abhineet Singh Rajput
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Aloke Kumar
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
| |
Collapse
|
8
|
Chen S, Pirhadi E, Yong X. Viscoelastic necking dynamics between attractive microgels. J Colloid Interface Sci 2022; 618:283-289. [PMID: 35344881 DOI: 10.1016/j.jcis.2022.03.048] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 03/10/2022] [Accepted: 03/11/2022] [Indexed: 12/01/2022]
Abstract
HYPOTHESIS Microgels can deform and interpenetrate and display colloid/polymer duality. The effective interaction of microgels in the collapsed state is governed by the interplay of polymer-solvent interfacial tension and bulk elasticity. A connecting neck is shown to mediate microgel interaction, but its temporal evolution has not been addressed. We hypothesize that the necking dynamics of attractive microgels exhibits liquid-like or solid-like behavior over different time and length scales. EXPERIMENTS We simulate the merging and pinching of attractive microgels with different crosslinking densities in explicit solvent using dissipative particle dynamics. The temporal coalescence dynamics of microgels is investigated and compared with simple liquid and polymeric droplets. We model the neck growth on long time scales using Maxwell model of polymer relaxation and compare the theoretical prediction with simulation data. The mechanical strength of the neck is characterized systematically via simulated pinch-off of microgels by steered molecular dynamics. FINDINGS We evidence a crossover in the coalescence dynamics reflecting the viscoelastic signature of microgels. In contrast to the common knowledge that viscoelastic materials respond elastically on short time scales, the early expansion of the microgel neck exhibits a linear behavior, similar to the viscous coalescence of liquid droplets. However, the late regime with arrested dynamics resembles sintering of solid particles. Through an analytical model relating microgel dynamics to neck growth, we show that the long-term behavior is governed by stress relaxation of the polymers in the neck region and predict an exponential decay in the rate of growth, which agrees favorably with the simulation. Different from coalescence, the thread thinning in microgel breakup primarily highlights its polymeric characteristics.
Collapse
Affiliation(s)
- Shensheng Chen
- Department of Mechanical Engineering, Binghamton University, The State University of New York, Binghamton, NY 13902, USA
| | - Emad Pirhadi
- Department of Mechanical Engineering, Binghamton University, The State University of New York, Binghamton, NY 13902, USA
| | - Xin Yong
- Department of Mechanical Engineering, Binghamton University, The State University of New York, Binghamton, NY 13902, USA.
| |
Collapse
|
9
|
Dekker PJ, Hack MA, Tewes W, Datt C, Bouillant A, Snoeijer JH. When Elasticity Affects Drop Coalescence. PHYSICAL REVIEW LETTERS 2022; 128:028004. [PMID: 35089754 DOI: 10.1103/physrevlett.128.028004] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Accepted: 12/07/2021] [Indexed: 06/14/2023]
Abstract
The breakup and coalescence of drops are elementary topological transitions in interfacial flows. The breakup of a drop changes dramatically when polymers are added to the fluid. With the strong elongation of the polymers during the process, long threads connecting the two droplets appear prior to their eventual pinch-off. Here, we demonstrate how elasticity affects drop coalescence, the complement of the much studied drop pinch-off. We reveal the emergence of an elastic singularity, characterized by a diverging interface curvature at the point of coalescence. Intriguingly, while the polymers dictate the spatial features of coalescence, they hardly affect the temporal evolution of the bridge. These results are explained using a novel viscoelastic similarity analysis and are relevant for drops created in biofluids, coating sprays, and inkjet printing.
Collapse
Affiliation(s)
- Pim J Dekker
- Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands
| | - Michiel A Hack
- Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands
| | - Walter Tewes
- Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands
| | - Charu Datt
- Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands
| | - Ambre Bouillant
- Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands
| | - Jacco H Snoeijer
- Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands
| |
Collapse
|
10
|
Dolganov PV, Zverev AS, Baklanova KD, Dolganov VK. Quasi-two-dimensional coalescence of nematic and isotropic droplets and Rayleigh-Plateau instability in flat optical cells. SOFT MATTER 2021; 18:126-136. [PMID: 34817480 DOI: 10.1039/d1sm01334c] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We investigated the coalescence of nematic droplets in an isotropic environment and that of isotropic droplets in a nematic environment in quasi-two-dimensional geometry of a flat optical cell. Two different regimes of coalescence were found. In the circular meniscus between the nematic and isotropic regions both nematic and isotropic phases exist. As a result, two bridges form at coalescence: a nematic and an isotropic bridge. In this work, we focus on the situation when nematic wets the cell surface. The coalescence of nematic droplets starts near the cell surfaces where the droplet bridge from the nematic phase is formed. An outer bridge connecting the isotropic environment is localized in the middle of the cell. When the outer bridge gets thinner it becomes unstable and breaks up. A series of pinch-offs leads to the formation of satellite droplets. On the contrary, when isotropic droplets coalesce, the coalescence starts in the middle of the cell and breaking of the bridges occurs without instability and without the formation of satellite droplets. Breakup of the outer bridge is a new example of Rayleigh-Plateau instability in addition to actively studied transformation and breaking of filaments and stretched droplets.
Collapse
Affiliation(s)
- P V Dolganov
- Institute of Solid State Physics RAS, 142432, Chernogolovka, Moscow Region, Russia.
- National Research University Higher School of Economics, Moscow, 101000, Russia
| | - A S Zverev
- Institute of Solid State Physics RAS, 142432, Chernogolovka, Moscow Region, Russia.
| | - K D Baklanova
- Institute of Solid State Physics RAS, 142432, Chernogolovka, Moscow Region, Russia.
- National Research University Higher School of Economics, Moscow, 101000, Russia
| | - V K Dolganov
- Institute of Solid State Physics RAS, 142432, Chernogolovka, Moscow Region, Russia.
| |
Collapse
|
11
|
Sivasankar VS, Etha SA, Hines DR, Das S. Coalescence of Microscopic Polymeric Drops: Effect of Drop Impact Velocities. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:13512-13526. [PMID: 34724618 DOI: 10.1021/acs.langmuir.1c02337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In this paper, we employ the direct numerical simulation (DNS) method for probing three-dimensional, axisymmetric coalescence of microscale, power-law-obeying, and shear-thinning polymeric liquid drops of identical sizes impacting a solid, solvophilic substrate with a finite velocity. Unlike the cases of drop coalescence of Newtonian liquid drops, coalescence of non-Newtonian polymeric drops has received very little attention. Our study bridges this gap by providing (1) the time-dependent, three-dimensional (3D) velocity field and 3D velocity vectors inside two coalescing polymeric drops in the presence of a solid substrate and (2) the effect of the drop impact velocity (on the solid substrate), quantified by the Weber number (We), on the coalescence dynamics. Our simulations reveal that the drop coalescence is qualitatively similar for different We values, although the velocity magnitudes involved, the time required to attain different stages of coalescence, and the time needed to attain equilibrium vary drastically for finitely large We values. Finally, we provide detailed simulation-based, as well as physics-based, scaling laws describing the growth of the height and the width of the bridge (formed due to coalescence) dictating the 3D coalescence event. Our analyses reveal distinct scaling laws for the growth of bridge height and width for early and late stages of coalescence as a function of We. We also provide simulation-based coalescence results for the case of two unequal sized drops impacting on a substrate (nonaxisymmetric coalescence) as well as results for axisymmetric coalescence for drops of different rheology. We anticipate that our findings will be critical in better understanding events such as inkjet or aerosol jet polymer printing, dynamics of polymer blends, and many more.
Collapse
Affiliation(s)
- Vishal Sankar Sivasankar
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Sai Ankit Etha
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Daniel R Hines
- Laboratory for Physical Sciences, 8050 Greenmead Drive, College Park, Maryland 20740, United States
| | - Siddhartha Das
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| |
Collapse
|
12
|
Dolganov PV, Zverev AS, Baklanova KD, Dolganov VK. Dynamics of capillary coalescence and breakup: Quasi-two-dimensional nematic and isotropic droplets. Phys Rev E 2021; 104:014702. [PMID: 34412240 DOI: 10.1103/physreve.104.014702] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 06/04/2021] [Indexed: 11/07/2022]
Abstract
We observed the formation of small satellite droplets from the bridge at droplet coalescence. Investigations were made using a Hele-Shaw cell in the two-phase region at the nematic-isotropic phase transition. In previous works on coalescence it was considered that before the start of coalescence there exists a bridge between the outer fluid connecting regions on the two sides of the droplets (outer bridge). After the start of coalescence, a bridge connecting the two droplets appears (droplet bridge) and the outer bridge is broken. We have shown that there are coalescence processes where after the start of coalescence both the droplet bridge and the outer bridge can exist. This cardinally changes the coalescence process. During the first coalescence stage the size of the outer bridge decreases and the size of the droplet bridge increases. During the second stage the outer bridge becomes unstable which leads to pinch-off, formation of pointed end domains, secondary instability, splitting of pointed end domains, and formation of satellite droplets. We found the linear dependence of the minimum bridge radius on time near bridge breakup. This behavior confirms the capillary viscous regime of bridge breakup. Our work connects two areas of fluid dynamics: coalescence and breakup with formation of satellite droplets.
Collapse
Affiliation(s)
- P V Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow district, Russia
| | - A S Zverev
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow district, Russia
| | - K D Baklanova
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow district, Russia.,National Research University Higher School of Economics, Moscow 101000, Russia
| | - V K Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow district, Russia
| |
Collapse
|
13
|
Zhai C, Hu C, Li S, Ma Y, Zhang Y, Guo T, Li H, Hu X. The formation principle of micro-droplets induced by using optical tweezers. NANOSCALE ADVANCES 2021; 3:279-286. [PMID: 36131882 PMCID: PMC9416808 DOI: 10.1039/d0na00705f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 11/15/2020] [Indexed: 06/15/2023]
Abstract
Utilizing droplets as micro-tools has become a valuable method in biology and chemistry. In previous work, we have demonstrated a novel droplet generation-manipulation method in a conventional optical tweezer system. Here, a further study of the droplet composition and its formation principle is performed. First, it is proved through Raman spectra that the principal component of the droplets is HPO4 2- solution. Considering that the generated droplet size is at the μm level, we have adopted a variety of methods in experiments to reduce external interference. Second, using a confocal microscopic video camera, the growth process of the droplet is completely recorded in a common glass-based chamber. The finite element simulations help us to further understand that the droplet generation process using optical tweezers can be divided into two stages: "capture" caused by optical force field and "aggregation" induced by a photothermal phenomenon and thermal acceleration. Through these studies, the nature of the optical tweezer-generated droplets is revealed. As a general principle for the droplet generation, this method will provide inspiration and prospects in the fields of microfluidics and biophysics-chemistry.
Collapse
Affiliation(s)
- Cong Zhai
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| | - Chunguang Hu
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| | - Shuai Li
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| | - Yanhua Ma
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| | - Yajing Zhang
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| | - Tong Guo
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| | - Hongbin Li
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Department of Chemistry, University of British Columbia 2036 Main Mall Vancouver BC V6T 1Z1 Canada
| | - Xiaotang Hu
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University Tianjin 300072 China
- Nanchang Institute for Microtechnology of Tianjin University Tianjin 300072 China
| |
Collapse
|
14
|
Varma SC, Saha A, Mukherjee S, Bandopadhyay A, Kumar A, Chakraborty S. Universality in coalescence of polymeric fluids. SOFT MATTER 2020; 16:10921-10927. [PMID: 33136111 DOI: 10.1039/d0sm01663b] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A pendant drop merging with a sessile drop and subsequently forming a single daughter drop is known to exhibit complex topologies. But their dynamics are yet to be probed for fluids exhibiting characteristic relaxation time scales while undergoing the deformation process. Here, we unveil a universal temporal evolution of the neck radius of the daughter drop during the coalescence of two polymeric drops. Such a generalization does not rely on the existence of previously explored viscous and inertial dominated regimes for simpler fluids but is fundamentally premised on a unique topographical evolution with essential features of interest exclusively smaller than the dominant scales of the flow. Our findings are substantiated by a theoretical model that considers the drops under coalescence to be partially viscous and partially elastic in nature. These results are substantiated with high-speed imaging experiments on drops of polyacrylamide (PAM), polyvinyl alcohol (PVA), polyethylene oxide (PEO), and polyethylene glycol (PEG). The observations herein are expected to hold importance for a plethora of diverse processes ranging from biophysics and microfluidics to the processing of materials in a wide variety of industrial applications.
Collapse
Affiliation(s)
- Sarath Chandra Varma
- Department of Mechanical Engineering, Indian Institute of Science, Bengaluru, Karnataka-560012, India.
| | | | | | | | | | | |
Collapse
|
15
|
Akella V, Gidituri H. Universal scaling laws in droplet coalescence: A dissipative particle dynamics study. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.137917] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
|
16
|
Dolganov PV, Shuravin NS, Dolganov VK, Kats EI. Dynamics of island-meniscus coalescence in free-standing smectic films. SOFT MATTER 2020; 16:8506-8511. [PMID: 32840550 DOI: 10.1039/d0sm00791a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In free-standing smectic films islands (regions of larger thickness than the film) can be considered as two-dimensional analogues of liquid droplets in a three-dimensional medium. The dynamics of droplet coalescence is an important but up to now incompletely solved problem in non-equilibrium mechanics. Here, we report on our investigations of island coalescence with the film meniscus. This phenomenon is analogous to the coalescence of a 3D droplet with a flat liquid surface. We found that the time evolution of island dimension is described by universal power-law dependencies for different stages of coalescence. Limited agreement with existing theory was found. In particular, in the final stage of coalescence the domain dynamics differs from theoretical predictions.
Collapse
Affiliation(s)
- P V Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russia.
| | - N S Shuravin
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russia.
| | - V K Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russia.
| | - E I Kats
- Landau Institute for Theoretical Physics, Russian Academy of Sciences, Moscow Region, 142432, Chernogolovka, Russia
| |
Collapse
|
17
|
Hack MA, Tewes W, Xie Q, Datt C, Harth K, Harting J, Snoeijer JH. Self-Similar Liquid Lens Coalescence. PHYSICAL REVIEW LETTERS 2020; 124:194502. [PMID: 32469577 DOI: 10.1103/physrevlett.124.194502] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 04/28/2020] [Indexed: 06/11/2023]
Abstract
A basic feature of liquid drops is that they can merge upon contact to form a larger drop. In spite of its importance to various applications, drop coalescence on prewetted substrates has received little attention. Here, we experimentally and theoretically reveal the dynamics of drop coalescence on a thick layer of a low viscosity liquid. It is shown that these so-called "liquid lenses" merge by the self-similar vertical growth of a bridge connecting the two lenses. Using a slender analysis, we derive similarity solutions corresponding to the viscous and inertial limits. Excellent agreement is found with the experiments without any adjustable parameters, capturing both the spatial and temporal structures of the flow during coalescence. Finally, we consider the crossover between the two regimes and show that all data of different lens viscosities collapse on a single curve capturing the full range of the coalescence dynamics.
Collapse
Affiliation(s)
- Michiel A Hack
- Physics of Fluids Group, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Walter Tewes
- Physics of Fluids Group, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Qingguang Xie
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Charu Datt
- Physics of Fluids Group, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Kirsten Harth
- Physics of Fluids Group, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
- Institute of Physics, Otto von Guericke University, 39106 Magdeburg, Germany
| | - Jens Harting
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
- Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, Fürther Str. 248, 90429 Nuremberg, Germany
| | - Jacco H Snoeijer
- Physics of Fluids Group, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| |
Collapse
|
18
|
Dolganov PV, Shuravin NS, Dolganov VK. Coalescence of holes in two-dimensional free-standing smectic films. Phys Rev E 2020; 101:052701. [PMID: 32575317 DOI: 10.1103/physreve.101.052701] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 03/31/2020] [Indexed: 06/11/2023]
Abstract
We investigate in free-standing smectic films coalescence of holes (circular regions with thickness smaller than the surrounding film). This process can be considered as a two-dimensional analog of coalescence of bubbles in a three-dimensional fluid. A high speed video camera was used to study the evolution of domains at different stages of coalescence. Special attention was given to investigations of the dependence of the size of the bridge between two holes at the initial stage of coalescence, which was considered in numerous theoretical works and bears information on the coalescence mechanism. It is established that the scaling law is applicable for the description of the transformation of bridges for holes of different radius R. We found that in the regime corresponding to the experimental situation the length of the bridge H increases with the scaling law H/R=(t/τ_{R})^{1/2}. The characteristic time τ_{R} determined from the scaling law is larger than the theoretical time, which can be connected with dissipation of energy both in the film and inside the holes.
Collapse
Affiliation(s)
- P V Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russia
| | - N S Shuravin
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russia
| | - V K Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russia
| |
Collapse
|
19
|
|