1
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Kajouri R, Theodorakis PE, Milchev A. Durotaxis and Antidurotaxis Droplet Motion onto Gradient Gel-Substrates. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:17779-17785. [PMID: 39106075 PMCID: PMC11340025 DOI: 10.1021/acs.langmuir.4c02257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2024] [Revised: 07/23/2024] [Accepted: 07/23/2024] [Indexed: 08/07/2024]
Abstract
The self-sustained motion of fluids on gradient substrates is a spectacular phenomenon, which can be employed and controlled in applications by carefully engineering the substrate properties. Here, we report on a design of a gel substrate with stiffness gradient, which can cause the spontaneous motion of a droplet along (durotaxis) or to the opposite (antidurotaxis) direction of the gradient, depending on the droplet affinity to the substrate. By using extensive molecular dynamics simulations of a coarse-grained model, we find that the mechanisms of the durotaxis and antidurotaxis droplet motion are distinct, require the minimization of the interfacial energy between the droplet and the substrate, and share similarities with those mechanisms previously observed for brush substrates with stiffness gradient. Moreover, durotaxis motion takes place over a wider range of affinities and is generally more efficient (faster motion) than antidurotaxis. Thus, our study points to further possibilities and guidelines for realizing both antidurotaxis and durotaxis motion on the same gradient substrate for applications in microfluidics, energy conservation, and biology.
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Affiliation(s)
- Russell Kajouri
- Institute
for Computational Physics, University of
Stuttgart, 70569 Stuttgart, Germany
| | | | - Andrey Milchev
- Bulgarian
Academy of Sciences, Institute of Physical
Chemistry, 1113 Sofia, Bulgaria
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2
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Badr RGM, Hauer L, Vollmer D, Schmid F. Dynamics of Droplets Moving on Lubricated Polymer Brushes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:12368-12380. [PMID: 38834186 PMCID: PMC11192036 DOI: 10.1021/acs.langmuir.4c00400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 05/11/2024] [Accepted: 05/13/2024] [Indexed: 06/06/2024]
Abstract
Understanding the dynamics of drops on polymer-coated surfaces is crucial for optimizing applications such as self-cleaning materials or microfluidic devices. While the static and dynamic properties of deposited drops have been well characterized, a microscopic understanding of the underlying dynamics is missing. In particular, it is unclear how drop dynamics depends on the amount of uncross-linked chains in the brush, because experimental techniques fail to quantify those. Here we use coarse-grained simulations to study droplets moving on a lubricated polymer brush substrate under the influence of an external body force. The simulation model is based on the many body dissipative particle dynamics (MDPD) method and designed to mimic a system of water droplets on poly(dimethylsiloxane) (PDMS) brushes with chemically identical PDMS lubricant. In agreement with experiments, we find a sublinear power law dependence between the external force F and the droplet velocity v, F ∝ vα with α < 1; however, the exponents differ (α ∼ 0.6-0.7 in simulations versus α ∼ 0.25 in experiments). With increasing velocity, the droplets elongate and the receding contact angle decreases, whereas the advancing contact angle remains roughly constant. Analyzing the flow profiles inside the droplet reveals that the droplets do not slide but roll, with vanishing slip at the substrate surface. Surprisingly, adding lubricant has very little effect on the effective friction force between the droplet and the substrate, even though it has a pronounced effect on the size and structure of the wetting ridge, especially above the cloaking transition.
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Affiliation(s)
- Rodrique G. M. Badr
- Institut
für Physik, Johannes Gutenberg-Universität
Mainz, Staudingerweg 7-9, D-55099 Mainz, Germany
| | - Lukas Hauer
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Doris Vollmer
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Friederike Schmid
- Institut
für Physik, Johannes Gutenberg-Universität
Mainz, Staudingerweg 7-9, D-55099 Mainz, Germany
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3
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Huang Z, Gu C, Li J, Xiang P, Liao Y, Jiang BP, Ji S, Shen XC. Surface-Initiated Polymerization with an Initiator Gradient: A Monte Carlo Simulation. Polymers (Basel) 2024; 16:1203. [PMID: 38732672 PMCID: PMC11085584 DOI: 10.3390/polym16091203] [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: 03/21/2024] [Revised: 04/22/2024] [Accepted: 04/23/2024] [Indexed: 05/13/2024] Open
Abstract
Due to the difficulty of accurately characterizing properties such as the molecular weight (Mn) and grafting density (σ) of gradient brushes (GBs), these properties are traditionally assumed to be uniform in space to simplify analysis. Applying a stochastic reaction model (SRM) developed for heterogeneous polymerizations, we explored surface-initiated polymerizations (SIPs) with initiator gradients in lattice Monte Carlo simulations to examine this assumption. An initial exploration of SIPs with 'homogeneously' distributed initiators revealed that increasing σ slows down the polymerization process, resulting in polymers with lower molecular weight and larger dispersity (Đ) for a given reaction time. In SIPs with an initiator gradient, we observed that the properties of the polymers are position-dependent, with lower Mn and larger Đ in regions of higher σ, indicating the non-uniform properties of polymers in GBs. The results reveal a significant deviation in the scaling behavior of brush height with σ compared to experimental data and theoretical predictions, and this deviation is attributed to the non-uniform Mn and Đ.
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Affiliation(s)
- Zhining Huang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
| | - Caixia Gu
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
| | - Jiahao Li
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
| | - Peng Xiang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
| | - Yanda Liao
- School of Computer Science and Engineering & School of Software, Guangxi Normal University, Guilin 541004, China;
| | - Bang-Ping Jiang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
| | - Shichen Ji
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
- State Key Laboratory of Molecular Engineering of Polymers, Fudan University, Shanghai 200433, China
| | - Xing-Can Shen
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Education of China, Collaborative Innovation Center for Guangxi Ethnic Medicine, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China; (Z.H.); (B.-P.J.)
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4
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Lu G, Ni E, Jiang Y, Wu W, Li H. Room-Temperature Liquid Metals for Flexible Electronic Devices. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2304147. [PMID: 37875665 DOI: 10.1002/smll.202304147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 07/26/2023] [Indexed: 10/26/2023]
Abstract
Room-temperature gallium-based liquid metals (RT-GaLMs) have garnered significant interest recently owing to their extraordinary combination of fluidity, conductivity, stretchability, self-healing performance, and biocompatibility. They are ideal materials for the manufacture of flexible electronics. By changing the composition and oxidation of RT-GaLMs, physicochemical characteristics of the liquid metal can be adjusted, especially the regulation of rheological, wetting, and adhesion properties. This review highlights the advancements in the liquid metals used in flexible electronics. Meanwhile related characteristics of RT-GaLMs and underlying principles governing their processing and applications for flexible electronics are elucidated. Finally, the diverse applications of RT-GaLMs in self-healing circuits, flexible sensors, energy harvesting devices, and epidermal electronics, are explored. Additionally, the challenges hindering the progress of RT-GaLMs are discussed, while proposing future research directions and potential applications in this emerging field. By presenting a concise and critical analysis, this paper contributes to the advancement of RT-GaLMs as an advanced material applicable for the new generation of flexible electronics.
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Affiliation(s)
- Guixuan Lu
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), School of Materials Science and Engineering, Shandong University, Jinan, Shandong, 250061, China
| | - Erli Ni
- The Institute for Advanced Studies of Wuhan University, Wuhan University, Wuhan, Hubei, 430072, China
| | - Yanyan Jiang
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), School of Materials Science and Engineering, Shandong University, Jinan, Shandong, 250061, China
| | - Weikang Wu
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), School of Materials Science and Engineering, Shandong University, Jinan, Shandong, 250061, China
| | - Hui Li
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), School of Materials Science and Engineering, Shandong University, Jinan, Shandong, 250061, China
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5
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Smith ER, Theodorakis PE. Multiscale simulation of fluids: coupling molecular and continuum. Phys Chem Chem Phys 2024; 26:724-744. [PMID: 38113114 DOI: 10.1039/d3cp03579d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Computer simulation is an important tool for scientific progress, especially when lab experiments are either extremely costly and difficult or lack the required resolution. However, all of the simulation methods come with limitations. In molecular dynamics (MD) simulation, the length and time scales that can be captured are limited, while computational fluid dynamics (CFD) methods are built on a range of assumptions, from the continuum hypothesis itself, to a variety of closure assumptions. To address these issues, the coupling of different methodologies provides a way to retain the best of both methods. Here, we provide a perspective on multiscale simulation based on the coupling of MD and CFD with each a distinct part of the same simulation domain. This style of coupling allows molecular detail to be present only where it is needed, so CFD can model larger scales than possible with MD alone. We present a unified perspective of the literature, showing the links between the two main types of coupling, state and flux, and discuss the varying assumptions in their use. A unique challenge in such coupled simulation is obtaining averages and constraining local parts of a molecular simulation. We highlight that incorrect localisation has resulted in an error in the literature. We then finish with some applications, focused on the simulation of fluids. Thus, we hope to motivate further research in this exciting area with applications across the spectrum of scientific disciplines.
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Affiliation(s)
- Edward R Smith
- Department of Mechanical and Aerospace Engineering, Brunel University London, Uxbridge, Middlesex UB8 3PH, UK.
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6
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Kajouri R, Theodorakis PE, Židek J, Milchev A. Antidurotaxis Droplet Motion onto Gradient Brush Substrates. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:15285-15296. [PMID: 37672007 PMCID: PMC10621003 DOI: 10.1021/acs.langmuir.3c01999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2023] [Revised: 08/28/2023] [Indexed: 09/07/2023]
Abstract
Durotaxis motion is a spectacular phenomenon manifesting itself by the autonomous motion of a nano-object between parts of a substrate with different stiffness. This motion usually takes place along a stiffness gradient from softer to stiffer parts of the substrate. Here, we propose a new design of a polymer brush substrate that demonstrates antidurotaxis droplet motion, that is, droplet motion from stiffer to softer parts of the substrate. By carrying out extensive molecular dynamics simulation of a coarse-grained model, we find that antidurotaxis is solely controlled by the gradient in the grafting density of the brush and is favorable for fluids with a strong attraction to the substrate (low surface energy). The driving force of the antidurotaxial motion is the minimization of the droplet-substrate interfacial energy, which is attributed to the penetration of the droplet into the brush. Thus, we anticipate that the proposed substrate design offers a new understanding and possibilities in the area of autonomous motion of droplets for applications in microfluidics, energy conservation, and biology.
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Affiliation(s)
- Russell Kajouri
- Institute
of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
| | | | - Jan Židek
- Central
European Institute of Technology, Brno University
of Technology, Purkyňova
656/123, 612 00 Brno, Czech Republic
| | - Andrey Milchev
- Bulgarian
Academy of Sciences, Institute of Physical Chemistry, 1113 Sofia, Bulgaria
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7
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Ricard A, Restagno F, Jang YH, Lansac Y, Raspaud E. Corrosion-driven droplet wetting on iron nanolayers. Sci Rep 2023; 13:18288. [PMID: 37880431 PMCID: PMC10600194 DOI: 10.1038/s41598-023-45547-9] [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: 08/16/2023] [Accepted: 10/19/2023] [Indexed: 10/27/2023] Open
Abstract
The classical Evans' drop describes a drop of aqueous salt solution, placed on a bulk metal surface where it displays a corrosion pit that grows over time producing further oxide deposits from the metal dissolution. We focus here on the corrosion-induced droplet spreading using iron nanolayers whose semi-transparency allowed us to monitor both iron corrosion propagation and electrolyte droplet behavior by simple optical means. We thus observed that pits grow under the droplet and merge into a corrosion front. This front reached the triple contact line and drove a non radial spreading, until it propagated outside the immobile droplet. Such chemically-active wetting is only observed in the presence of a conductive substrate that provides strong adhesion of the iron nanofilm to the substrate. By revisiting the classic Evan's drop experiment on thick iron film, a weaker corrosion-driven droplet spreading is also identified. These results require further investigations, but they clearly open up new perspectives on substrate wetting by corrosion-like electrochemical reactions at the nanometer scale.
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Affiliation(s)
- Aurelien Ricard
- Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, 91405, Orsay Cedex, France
| | - Frederic Restagno
- Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, 91405, Orsay Cedex, France
| | - Yun Hee Jang
- Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, 91405, Orsay Cedex, France
- GREMAN UMR 7347, CNRS, INSA CVL, Université de Tours, 37200, Tours, France
- Department of Energy Science and Engineering, DGIST, Daegu, 42988, Korea
| | - Yves Lansac
- Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, 91405, Orsay Cedex, France
- GREMAN UMR 7347, CNRS, INSA CVL, Université de Tours, 37200, Tours, France
- Department of Energy Science and Engineering, DGIST, Daegu, 42988, Korea
| | - Eric Raspaud
- Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, 91405, Orsay Cedex, France.
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