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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. [PMID: 38834186 DOI: 10.1021/acs.langmuir.4c00400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [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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Pastorino C, Urrutia I, Fiora M, Condado F. Heat flow through a liquid-vapor interface in a nano-channel: the effect of end-grafting polymers on a wall. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:344004. [PMID: 35688142 DOI: 10.1088/1361-648x/ac77ce] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 06/10/2022] [Indexed: 06/15/2023]
Abstract
Heat transfer through a liquid-vapor interface is a complex phenomenon and crucially relevant in heat-removal and cryogenic applications. The physical coupling among confining walls, liquid and vapor phases is very important for controlling or improving cooling rates or condensation efficiency. Surface modification is a promising route, which has been explored to taylor the heat transfer through confined two-phase systems. We use coarse-grained molecular-dynamics simulations to study the heat transfer through a nano-confined liquid-vapor interface as a function of fluid filling. We set up a stationary heat flow through a liquid-vapor interface, stabilized with the liquid in contact with a colder wall and a vapor in contact with a hotter wall. For these physical conditions, we perform extensive simulations by progressively increasing the number of fluid particles, i.e. the channel filling, and measure the fluid distribution in the channel, density, pressure and temperature profiles We also compare the heat flux behavior between a bare-surfaces nano-channel and others where the hot surface was coated with end-grafted polymers, with different wetting affinities and bending properties. We take extreme cases of polymer properties to obtain a general picture of the polymer effect on the heat transfer, as compared with the bare surfaces. We find that walls covered by end-grafted solvophylic polymers change the heat flux by a factor of 6, as compared with bare walls, if the liquid phase is in contact with the polymers. Once the liquid wets the coated wall, the improve on heat flux is smaller and dominated by the grafting density. We also find that for a wall coated with stiff polymers, the jump in heat flux takes place at a significantly lower channel filling, when the polymers' free ends interact with the liquid surface. Interestingly, the morphology of the polymers induces a 'liquid bridge' between the liquid phase and the hot wall, through which heat is transported with high (liquid-like) thermal conductivity.
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Affiliation(s)
- Claudio Pastorino
- Departamento de Física de la Materia Condensada, Centro Atómico Constituyentes, CNEA, Av. Gral. Paz 1499, San Martín, Buenos Aires, 1650, Argentina
- Instituto de Nanociencia y Nanotecnología, CONICET-CNEA, CAC
| | - Ignacio Urrutia
- Departamento de Física de la Materia Condensada, Centro Atómico Constituyentes, CNEA, Av. Gral. Paz 1499, San Martín, Buenos Aires, 1650, Argentina
- Instituto de Nanociencia y Nanotecnología, CONICET-CNEA, CAC
| | - María Fiora
- INTI-Micro y Nanotecnologías, Instituto Nacional de Tecnología Industrial, Av. Gral. Paz 5445, B1650WAB San Martín, Argentina
| | - Federico Condado
- Departamento de Física de la Materia Condensada, Centro Atómico Constituyentes, CNEA, Av. Gral. Paz 1499, San Martín, Buenos Aires, 1650, Argentina
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Luo Y, Pang AP, Zhu P, Wang D, Lu X. Demonstrating the Interfacial Polymer Thermal Transition from Coil-to-Globule to Coil-to-Stretch under Shear Flow Using SFG and MD Simulation. J Phys Chem Lett 2022; 13:1617-1627. [PMID: 35142518 DOI: 10.1021/acs.jpclett.1c03866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Revealing interfacial shear-induced structural responsiveness has long been an important topic in that most fluids in nature and human life are in motion and cause interesting boundary phenomena. It is amazing how the polymer chain conformation or local structural features at a boundary change under the effective shear condition. In this study, microfluidic-assisted sum frequency generation (SFG) vibrational spectroscopy and all-atom molecular dynamics (MD) simulation are combined to reveal that the shear flow can effectively block the so-called thermal coil-to-globule transition of the poly(N-isopropylacrylamide) (PNIPAM) brushes on the solid substrate, and the normal coil-to-globule transition transfers to a coil-to-stretch one under shear flow with increasing ambient temperature. Such findings are attributed to the balance between the shear flow and the molecular interaction with respect to the polymer chains and adjacent water molecules, thus demonstrating the significant effect of the shear flow on the structural and dynamic behaviors of the polymer chains at the boundaries from the molecular level.
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Affiliation(s)
- Yongsheng Luo
- State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu Province, P. R. China
| | - Ai-Ping Pang
- State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu Province, P. R. China
| | - Peizhi Zhu
- College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225009, Jiangsu Province, P. R. China
| | - Dayang Wang
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, Jilin Province, P. R. China
| | - Xiaolin Lu
- State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu Province, P. R. China
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Etha SA, Desai PR, Sachar HS, Das S. Wetting Dynamics on Solvophilic, Soft, Porous, and Responsive Surfaces. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02234] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Sai Ankit Etha
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Parth Rakesh Desai
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Harnoor Singh Sachar
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Siddhartha Das
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
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Nguyen VP, Phi PQ, Choi ST. Tribological Behavior of Grafted Nanoparticle on Polymer-Brushed Walls: A Dissipative Particle Dynamics Study. ACS APPLIED MATERIALS & INTERFACES 2019; 11:11988-11998. [PMID: 30821436 DOI: 10.1021/acsami.8b19001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two contacting surfaces grafted with polymer brushes have potential applications due to their extraordinary lubricating behavior. However, the polymer brushes may have poor mechanical stability under high normal and shear stresses, which is a challenge for practical usage of polymer brush systems. In this study, we propose the use of grafted nanoparticles as nanobearings on polymer-brush-coated surfaces to alleviate the harsh working conditions of polymer brushes and to improve their mechanical stability. We have performed dissipative particle dynamics (DPD) simulations to investigate the tribological interaction between grafted nanoparticle and parallel walls with noncharged polymer brushes in the presence of explicit solvent. The influences of several parameters (solvent quality, brush miscibility, etc.) on the tribological behavior of the system are investigated. The grafted nanoparticle obviously acts as a nanobearing that partially replaces the sliding contact between two brushed walls with rolling contact between the grafted nanoparticle and two brushed walls and reduces the number of DPD particles withstanding high force. Although the introduction of the grafted nanoparticle into polymer-brushed walls increases the friction coefficient by 20-30%, it does not greatly decrease lubrication of the brushed walls, while still helping in stabilizing the system of polymer brushes to be used with liquids with low viscosity, such as water. The DPD simulation results and analysis performed in this study would be beneficial in designing systems with polymer-brushed surfaces and grafted nanoparticles.
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Affiliation(s)
- Vinh Phu Nguyen
- School of Mechanical Engineering , Chung-Ang University , 84 Heukseok-Ro , Dongjak-Gu, Seoul 06974 , Republic of Korea
| | - Phuoc Quang Phi
- School of Mechanical Engineering , Chung-Ang University , 84 Heukseok-Ro , Dongjak-Gu, Seoul 06974 , Republic of Korea
| | - Seung Tae Choi
- School of Mechanical Engineering , Chung-Ang University , 84 Heukseok-Ro , Dongjak-Gu, Seoul 06974 , Republic of Korea
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Speyer K, Pastorino C. Pressure responsive gating in nanochannels coated by semiflexible polymer brushes. SOFT MATTER 2019; 15:937-946. [PMID: 30644495 DOI: 10.1039/c8sm02388c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We study by coarse-grained molecular-dynamics simulations the liquid flow in a slit channel with the inner walls coated by semiflexible polymer brushes. The distance between walls is close enough such that polymers grafted to opposing walls interact among each other and form bundles across the channel in poor solvent conditions. The solvent is simulated explicitly, including particles that fill the interior of the channel. The system is studied in equilibrium and under flow, by applying a constant body force on each particle of the system. A non-linear relation between external force and flow rate is observed, for a particular set of parameters. This non-linear response is linked to a morphological change of the polymer brushes. For large enough forces, the bundle structures formed across the channel break as the chains lean in the direction of the flow, and clear the middle of the channel. This morphological alteration of the polymer configurations translates in a sudden increase in the flow rate, acting as a pressure-responsive gate. The relation between flow and external force is investigated for various parameters, such as grafting density, quality of the solvent and polymer bending rigidity. We observe a non-monotonic dependence of the flow as a function of the polymer rigidity, and find an optimum value for the persistence length. We also find that the force threshold at which the morphological changes happen in the polymer brush, depends linearly on the grafting density. These findings can lead to new flow control techniques in micro and nano-fluidic devices.
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Affiliation(s)
- K Speyer
- Departamento de Física de la Materia Condensada, Centro Atómico Constituyentes, CNEA, Av. Gral. Paz 1499, 1650 Pcia. de Buenos Aires, Argentina.
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