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Wang Q, Li L, Gu J, Zhang C, Lyu J, Yao W. Manipulation of a Nonconductive Droplet in an Aqueous Fluid with AC Electric Fields: Droplet Dewetting, Oscillation, and Detachment. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:12098-12111. [PMID: 34519514 DOI: 10.1021/acs.langmuir.1c01934] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Electrowetting (EW) is an effective method for droplet manipulation in microfluidics. In traditional EW, a conductive droplet is actuated, which spreads on a solid substrate. Recently, we considered an opposite phenomenon of droplet actuation in EW: inducing nonconductive droplet dewetting and detaching from the substrate. An oil/water system is used in which the oil droplet (nonconductive) is actuated on a flat substrate in surrounding water (conductive) by EW. In this work, alternating current (AC) electric fields are applied to EW, and the transient dynamics of droplet dewetting, oscillation, and detachment with the AC signals are investigated. The droplet is not in contact with electrodes, and it dances freely on the substrate. Experiments are performed in a wide range of voltages and AC frequencies. To demonstrate the droplet dynamics, we divide the full process of droplet manipulation into three distinguishable periods, that is, an initiating period, a steady oscillation period, and a detaching condition. Transient droplet dewetting is considered in the initiating period, and we obtain the distribution of the contact line friction factor. In steady oscillation, the oscillation resonance is verified from the oscillating amplitude of the contact line. Different periodical features are found for the droplet dancing at the resonance frequencies and departure from resonance. The droplet is detached at high voltages, and we provide a map for the detachable and nondetachable zones. The voltage is the dominant factor determining the droplet detachment; however, the AC frequency has notable influences on the critical voltage. The detachment is promoted when the AC frequency is within the region of the oscillation resonance (e.g., 20 < f < 75 Hz). In this region, the detaching process is not monotonic but instead, the droplet rebounds by several times before it is completely detached.
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Affiliation(s)
- Qinggong Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Long Li
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Junping Gu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Ce Zhang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Junfu Lyu
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
| | - Wei Yao
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
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Cienega-Cacerez O, García-Alcántara C, Moreno-Razo JA, Díaz-Herrera E, Sambriski EJ. Induced stabilization of columnar phases in binary mixtures of discotic liquid crystals. SOFT MATTER 2016; 12:1295-1312. [PMID: 26576703 DOI: 10.1039/c5sm01959a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Three discotic liquid-crystalline binary mixtures, characterized by their extent of bidispersity in molecular thickness, were investigated with molecular dynamics simulations. Each equimolar mixture contained A-type (thin) and B-type (thick) discogens. The temperature-dependence of the orientational order parameter reveals that A-type liquid samples produce ordered phases more readily, with the (hexagonal) columnar phase being the most structured variant. Moderately and strongly bidisperse mixtures produce globally-segregated samples for temperatures corresponding to ordered phases; the weakly bidisperse mixture displays microheterogeneities. Ordered phases in the B-type liquid are induced partially by the presence of the A-type fluid. In the moderately bidisperse mixture, order is induced through orientational frustration: a mixed prenematic-like phase precedes global segregation to yield nematic and columnar mesophases upon further cooling. In the strongly bidisperse mixture, order is induced less efficiently through a paranematic-like mechanism: a highly-ordered A-type fluid imparts order to B-type discogens found at the interface of a fully-segregated sample. This ordering effect permeates into the disordered B-type domain until nematic and columnar phases emerge upon further cooling. At sufficiently low temperatures, all samples investigated exhibit the (hexagonal) columnar mesophase.
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Affiliation(s)
- Octavio Cienega-Cacerez
- Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Avenida San Rafael Atlixco No. 186, Colonia Vicentina, Delegación Iztapalapa, México, D.F. 09340, Mexico
| | - Consuelo García-Alcántara
- Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Avenida San Rafael Atlixco No. 186, Colonia Vicentina, Delegación Iztapalapa, México, D.F. 09340, Mexico and Unidad Multidisciplinaria de Docencia e Investigación-Juriquilla, Facultad de Ciencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Boulevard Juriquilla 3001, Juriquilla, Querétaro 76230, Mexico
| | - José Antonio Moreno-Razo
- Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Avenida San Rafael Atlixco No. 186, Colonia Vicentina, Delegación Iztapalapa, México, D.F. 09340, Mexico
| | - Enrique Díaz-Herrera
- Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Avenida San Rafael Atlixco No. 186, Colonia Vicentina, Delegación Iztapalapa, México, D.F. 09340, Mexico
| | - Edward John Sambriski
- Department of Chemistry, Delaware Valley University, 700 East Butler Avenue, Doylestown, Pennsylvania 18901, USA.
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Zhang J, Li W, Yan Y, Wang Y, Liu B, Shen Y, Chen H, Liu L. Molecular insight into nanoscale water films dewetting on modified silica surfaces. Phys Chem Chem Phys 2015; 17:451-8. [DOI: 10.1039/c4cp04554h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
In this work, molecular dynamics simulations are adopted to investigate the microscopic dewetting mechanism of nanoscale water films on methylated silica surfaces.
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Affiliation(s)
- Jun Zhang
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
| | - Wen Li
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
| | - Youguo Yan
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
| | - Yefei Wang
- School of Petroleum Engineering
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
| | - Bing Liu
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
| | - Yue Shen
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
| | - Haixiang Chen
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
| | - Liang Liu
- College of Science
- China University of Petroleum
- 266580 Qingdao
- People's Republic of China
- Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong
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Gbabode G, Dumont N, Quist F, Schweicher G, Moser A, Viville P, Lazzaroni R, Geerts YH. Substrate-induced crystal plastic phase of a discotic liquid crystal. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:658-662. [PMID: 22174161 DOI: 10.1002/adma.201103739] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 11/07/2011] [Indexed: 05/31/2023]
Abstract
A new phase of a known discotic liquid crystal is observed at the interface with a rigid substrate. The structure of the substrate-induced phase has been characterized by atomic force microscopy, specular X-ray diffraction, and small-angle and wide-angle grazing incidence X-ray diffraction. The substrate-induced phase, which has a thickness of ∼30 nm and a tetragonal symmetry, differs notably from the bulk phase. The occurrence of such phase casts a new light on alignment of discotic liquid crystals.
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Affiliation(s)
- Gabin Gbabode
- Laboratoire de Chimie des Polymères, Faculté des Sciences, Université Libre de Bruxelles (ULB), CP206/1, Boulevard du Triomphe, 1050 Brussels, Belgium
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Li X, Zhan MS, Wang K. A hexagonal columnar phase formed in lateral fluorinated bent-shaped molecules based on a 1,7-naphthalene central core. NEW J CHEM 2012. [DOI: 10.1039/c2nj21072j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lamarra M, Muccioli L, Orlandi S, Zannoni C. Temperature dependence of charge mobility in model discotic liquid crystals. Phys Chem Chem Phys 2012; 14:5368-75. [DOI: 10.1039/c2cp23178f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Gentili D, Foschi G, Valle F, Cavallini M, Biscarini F. Applications of dewetting in micro and nanotechnology. Chem Soc Rev 2012; 41:4430-43. [DOI: 10.1039/c2cs35040h] [Citation(s) in RCA: 203] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Pisula W, Tomović Z, Kolb U, Müllen K. Melt processing of hexa-peri-hexabenzocoronene on the water surface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:1524-1529. [PMID: 21162519 DOI: 10.1021/la1044255] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A discotic polycyclic aromatic hydrocarbon, hexa-peri-hexabenzocoronene, was oriented by slow cooling from the isotropic phase on a water surface as a film. For melt processing at low temperatures, an HBC derivative with long swallow-tailed alkyl side chains was chosen. The supramolecular organization in the resulting thin layer was investigated by electron microscopy. In high-resolution mode, the structural study showed large domains in which the columnar structures were oriented uniaxially with an edge-on arrangement of the hydrophobic molecules. The length of the stacks exceeded several hundred nanometers without obvious defects. The small-area analysis by TEM allowed the direct visualization of individual packed molecules. Electron diffraction revealed a high in-plane order of the columnar superstructures in which the discs were tilted by ca. 40° with respect to the stacking direction. This is the first example of a discotic system melt processed on the water surface yielding a pronounced order.
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Calò A, Stoliar P, Matacotta FC, Cavallini M, Biscarini F. Time-temperature integrator based on the dewetting of polyisobutylene thin films. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:5312-5315. [PMID: 20334414 DOI: 10.1021/la1008279] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
This work reports the application of a patterned thin film of polyisobutylene (PIB) irradiated with an electron beam as a time-temperature integrator, i.e., a device that is able to record the thermal history of a product. The device is fabricated by irradiation with an electron beam of regions of a PIB thin film to different doses of electrons. A different dewetting behavior occurs at these regions upon thermal exposure, depending on the dose. The experimental results are quantified by means of a model of dewetting based on nucleation and growth of holes in a strong slippage regime.
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Grelet E, Dardel S, Bock H, Goldmann M, Lacaze E, Nallet F. Morphology of open films of discotic hexagonal columnar liquid crystals as probed by grazing incidence X-ray diffraction. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2010; 31:343-349. [PMID: 20411293 DOI: 10.1140/epje/i2010-10586-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 02/24/2010] [Accepted: 03/03/2010] [Indexed: 05/29/2023]
Abstract
The structure and the orientation of thermotropic hexagonal columnar liquid crystals are studied by grazing incidence X-ray diffraction (GIXD) for different discotic compounds in the geometry of open supported thin films. Whatever the film deposition mode (either spin-coating or vacuum evaporation) and the film thickness, a degenerate planar alignment with the liquid crystalline columns parallel to the substrate is found. However, if a specific thermal process is applied to the liquid crystal film, homeotropic anchoring (columns normal to the interface) can be stabilized in a metastable state.
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Affiliation(s)
- Eric Grelet
- Centre de Recherche Paul-Pascal, CNRS -Université de Bordeaux, 115 Avenue Schweitzer, 33600, Pessac, France.
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Calò A, Stoliar P, Cavallini M, Geerts YH, Biscarini F. Synchronized optical and electrical characterization of discotic liquid crystals thin films. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2010; 81:033907. [PMID: 20370192 DOI: 10.1063/1.3327820] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We describe a setup suitable for simultaneously measuring optical and electrical properties of a liquid crystal mesophase upon temperature variation, and the difference in the order parameters between the bulk and the interface with the substrate. It integrates high-resolution polarized light optical microscopy, temperature regulation, and electrical measurements in a controlled atmosphere with a software kernel that controls the instruments and synchronizes the data streams. A user-friendly interface allows us to program multistep experiments controlling all the instruments and data acquisition by a specifically designed scheduler. We tested our system on a thin film of alkoxy-substituted phthalocyanines deposited on a test pattern with interdigitated electrodes. We studied the optical and electrical behavior in the proximity of the bulk phase transition to isotropic liquid, identifying a few ordered monolayers anchored to the substrate above the transition temperature.
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Affiliation(s)
- Annalisa Calò
- CNR-Institute for the Study of Nanostructured Materials, Via Gobetti 101, I-40129 Bologna, Italy
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