151
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Effects of pH on shear thinning and thickening behaviors of fumed silica suspensions. Colloids Surf A Physicochem Eng Asp 2015. [DOI: 10.1016/j.colsurfa.2014.09.040] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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152
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Bharti B, Fameau AL, Velev OD. Magnetophoretic assembly of flexible nanoparticles/lipid microfilaments. Faraday Discuss 2015; 181:437-48. [DOI: 10.1039/c4fd00272e] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The directed assembly of colloidal particles into linear chains and clusters is of fundamental and practical importance. In this study we characterize and analyse the mechanism of the magnetic field driven assembly of lipid-coated iron oxide nanoparticles into flexible microfilaments. Recently we showed that nanocapillary lipid binding can form a new class of magnetic nanoparticle-lipid microfilaments with unprecedented flexibility and self-healing properties. In the presence of a uniform magnetic field, the magnetophoretic attraction of the particles combined with interparticle dipole–dipole attraction drives the microfilament assembly. The fluid like lipid layer on the particles leads to stickiness on the surface of the filaments and the magnetic field concentration overcomes the potential electrostatic repulsion in the water phase. The lipid capillary bridges formed between the particles facilitate their permanent binding and sustain the flexible microfilament structure. We demonstrate that this surface stickiness combined with the magnetic response of the filaments can be used further to twist, bend and bundle the microfilaments into unusual structures.
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Affiliation(s)
- Bhuvnesh Bharti
- Department of Chemical and Biomolecular Engineering
- North Carolina State University
- Raleigh
- USA
| | | | - Orlin D. Velev
- Department of Chemical and Biomolecular Engineering
- North Carolina State University
- Raleigh
- USA
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153
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Koos E, Kannowade W, Willenbacher N. Restructuring and aging in a capillary suspension. RHEOLOGICA ACTA 2014; 53:947-957. [PMID: 25729113 PMCID: PMC4338511 DOI: 10.1007/s00397-014-0805-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The rheological properties of capillary suspensions, suspensions with small amounts of an added immiscible fluid, are dramatically altered with the addition of the secondary fluid. We investigate a capillary suspension to determine how the network ages and restructures at rest and under applied external shear deformation. The present work uses calcium carbonate suspended in silicone oil (11 % solids) with added water as a model system. Aging of capillary suspensions and their response to applied oscillatory shear is distinctly different from particulate gels dominated by the van der Waals forces. The suspensions dominated by the capillary force are very sensitive to oscillatory flow, with the linear viscoelastic regime ending at a deformation of only 0.1% and demonstrating power-law aging behavior. This aging persists for long times at low deformations or for shorter times with a sudden decrease in the strength at higher deformations. This aging behavior suggests that the network is able to rearrange and even rupture. This same sensitivity is not demonstrated in shear flow where very high shear rates are required to rupture the agglomerates returning the apparent viscosity of capillary suspensions to the same viscosity as for the pure vdW suspension. A transitional region is also present at intermediate water contents wherein the material response depends very strongly on the type, strength, and duration of the external forcing.
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Affiliation(s)
- Erin Koos
- Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology (KIT), Straße am Forum 8, 76131 Karlsruhe, Germany
| | - Wolfgang Kannowade
- Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology (KIT), Straße am Forum 8, 76131 Karlsruhe, Germany
| | - Norbert Willenbacher
- Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology (KIT), Straße am Forum 8, 76131 Karlsruhe, Germany
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154
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Koos E. Capillary suspensions: Particle networks formed through the capillary force. Curr Opin Colloid Interface Sci 2014; 19:575-584. [PMID: 25729316 DOI: 10.1016/j.cocis.2014.10.004] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The addition of small amounts of a secondary fluid to a suspension can, through the attractive capillary force, lead to particle bridging and network formation. The capillary bridging phenomenon can be used to stabilize particle suspensions and precisely tune their rheological properties. This effect can even occur when the secondary fluid wets the particles less well than the bulk fluid. These materials, so-called capillary suspensions, have been the subject of recent research studying the mechanism for network formation, the properties of these suspensions, and how the material properties can be modified. Recent work in colloidal clusters is summarized and the relationship to capillary suspensions is discussed. Capillary suspensions can also be used as a pathway for new material design and some of these applications are highlighted. Results obtained to date are summarized and central questions that remain to be answered are proposed in this review.
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Affiliation(s)
- Erin Koos
- Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology (KIT), Straße am Forum 8, 76131 Karlsruhe, Germany
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155
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Neeson MJ, Dagastine RR, Chan DYC, Tabor RF. Evaporation of a capillary bridge between a particle and a surface. SOFT MATTER 2014; 10:8489-8499. [PMID: 25238574 DOI: 10.1039/c4sm01826e] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The liquid bridge that forms between a particle and a flat surface, and the dynamics of its evaporation are pertinent to a range of physical processes including paint and ink deposition, spray drying, evaporative lithography and the flow and processing of powders. Here, using time-lapse photography, we investigate the evaporative dynamics of a sessile liquid bridge between a particle and a planar substrate. Different wetting characteristics of the particle and substrate are explored, as well as the effects of contact line pinning and stick-slip boundary conditions. A theoretical framework is developed to quantify and analyse the experimental observations. For the size range of particles and drops used in this study, gravity is by far the smallest force in the system when compared to the surface tension and capillary interactions that are present, but in certain circumstances it dictates the key evolution stages of the geometry of the particle-drop-substrate systems. Analysis of evaporation dynamics and capillary forces indicate that at low Bond numbers, surface tension forces dominate and provide unique opportunities for the control of particles on surfaces.
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Affiliation(s)
- Michael J Neeson
- Department of Mathematics and Statistics, University of Melbourne, Parkville 3010, Australia
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156
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Davies GB, Krüger T, Coveney PV, Harting J. Detachment energies of spheroidal particles from fluid-fluid interfaces. J Chem Phys 2014; 141:154902. [DOI: 10.1063/1.4898071] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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157
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Zhang Y, Wu J, Wang H, Meredith JC, Behrens SH. Stabilization of Liquid Foams through the Synergistic Action of Particles and an Immiscible Liquid. Angew Chem Int Ed Engl 2014; 53:13385-9. [DOI: 10.1002/anie.201405816] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2014] [Revised: 08/06/2014] [Indexed: 11/09/2022]
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158
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Zhang Y, Wu J, Wang H, Meredith JC, Behrens SH. Stabilization of Liquid Foams through the Synergistic Action of Particles and an Immiscible Liquid. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201405816] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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159
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Bonarius GA, Vieira JB, van der Goot AJ, Bodnár I. Rheological behaviour of fibre-rich plant materials in fat-based food systems. Food Hydrocoll 2014. [DOI: 10.1016/j.foodhyd.2014.03.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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160
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161
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Lubbers LA, Xu Q, Wilken S, Zhang WW, Jaeger HM. Dense suspension splat: monolayer spreading and hole formation after impact. PHYSICAL REVIEW LETTERS 2014; 113:044502. [PMID: 25105622 DOI: 10.1103/physrevlett.113.044502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Indexed: 06/03/2023]
Abstract
We use experiments and minimal numerical models to investigate the rapidly expanding monolayer formed by the impact of a dense suspension drop against a smooth solid surface. The expansion creates a lacelike pattern of particle clusters separated by particle-free regions. Both the expansion and the development of the spatial inhomogeneity are dominated by particle inertia and, therefore, are robust and insensitive to details of the surface wetting, capillarity, and viscous drag.
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Affiliation(s)
- Luuk A Lubbers
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA and Physics of Fluids Group, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Qin Xu
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Sam Wilken
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Wendy W Zhang
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Heinrich M Jaeger
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
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162
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Webb EB, Koh CA, Liberatore MW. High Pressure Rheology of Hydrate Slurries Formed from Water-in-Mineral Oil Emulsions. Ind Eng Chem Res 2014. [DOI: 10.1021/ie5008954] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Eric B. Webb
- Center for Hydrate Research,
Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Carolyn A. Koh
- Center for Hydrate Research,
Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Matthew W. Liberatore
- Center for Hydrate Research,
Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, Colorado 80401, United States
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163
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Brown E, Jaeger HM. Shear thickening in concentrated suspensions: phenomenology, mechanisms and relations to jamming. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2014; 77:046602. [PMID: 24695058 DOI: 10.1088/0034-4885/77/4/046602] [Citation(s) in RCA: 200] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Shear thickening is a type of non-Newtonian behavior in which the stress required to shear a fluid increases faster than linearly with shear rate. Many concentrated suspensions of particles exhibit an especially dramatic version, known as Discontinuous Shear Thickening (DST), in which the stress suddenly jumps with increasing shear rate and produces solid-like behavior. The best known example of such counter-intuitive response to applied stresses occurs in mixtures of cornstarch in water. Over the last several years, this shear-induced solid-like behavior together with a variety of other unusual fluid phenomena has generated considerable interest in the physics of densely packed suspensions. In this review, we discuss the common physical properties of systems exhibiting shear thickening, and different mechanisms and models proposed to describe it. We then suggest how these mechanisms may be related and generalized, and propose a general phase diagram for shear thickening systems. We also discuss how recent work has related the physics of shear thickening to that of granular materials and jammed systems. Since DST is described by models that require only simple generic interactions between particles, we outline the broader context of other concentrated many-particle systems such as foams and emulsions, and explain why DST is restricted to the parameter regime of hard-particle suspensions. Finally, we discuss some of the outstanding problems and emerging opportunities.
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164
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Heidlebaugh SJ, Domenech T, Iasella SV, Velankar SS. Aggregation and separation in ternary particle/oil/water systems with fully wettable particles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:63-74. [PMID: 24345163 DOI: 10.1021/la4039396] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report that a variety of ternary particle/liquid/liquid mixtures heavily aggregate or separate completely if (1) the particles are fully or almost fully wetted by one fluid, and (2) if the wetting fluid volume fraction is comparable to the particle volume fraction. Aggregation and separation do not happen if the particles are partially wetted by both fluids, in which case Pickering emulsions appear at all compositions. Rheological and geometric criteria for aggregation are proposed and compared with a state diagram of a ternary system composed of oil, water, and hydrophilic glass particles. Analogies are drawn to wet granulation and spherical agglomeration, two particle processing operations in which wetting phenomena are important.
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Affiliation(s)
- Samantha J Heidlebaugh
- Department of Chemical and Petroleum Engineering, University of Pittsburgh , Pittsburgh, Pennsylvania 15261, United States
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165
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Wang D, Wang X, Yuan Y, Li W, Tian H, Zhao S. Increasing the apparent shear viscosity of polymer composites by uptake of a small amount of water. RSC Adv 2014. [DOI: 10.1039/c4ra00541d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We provided a reversible, simple, inexpensive and environmentally-friendly way to control the rheology of polymer composites.
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Affiliation(s)
- Dapeng Wang
- Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Provincial Key Laboratory of Rubber-Plastics
- Qingdao University of Science & Technology
- Qingdao 266042, PR China
| | - Xiang Wang
- Department of Chemical and Biological Engineering
- University of Colorado Boulder
- Boulder, USA
| | - Yuan Yuan
- Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Provincial Key Laboratory of Rubber-Plastics
- Qingdao University of Science & Technology
- Qingdao 266042, PR China
| | - Weihua Li
- Key Laboratory of Corrosion Science
- Shandong, Institute of Oceanology
- Chinese Academy of Sciences
- Qingdao 266071, PR China
| | - Huiwen Tian
- Key Laboratory of Corrosion Science
- Shandong, Institute of Oceanology
- Chinese Academy of Sciences
- Qingdao 266071, PR China
| | - Shugao Zhao
- Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Provincial Key Laboratory of Rubber-Plastics
- Qingdao University of Science & Technology
- Qingdao 266042, PR China
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166
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Çetinel FA, Bauer W. Ceramic micro parts. Part 2: Process-related factors influencing surface finish and shape retention during thermal debinding. Ann Ital Chir 2013. [DOI: 10.1016/j.jeurceramsoc.2013.06.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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167
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How to decrease the viscosity of suspension with the second fluid and nanoparticles? Sci Rep 2013; 3:3137. [PMID: 24190438 PMCID: PMC3817430 DOI: 10.1038/srep03137] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 10/17/2013] [Indexed: 11/08/2022] Open
Abstract
According to recent research reports, addition of small amounts of a secondary fluid to a suspension could dramatically increase viscosity of suspension. Results of this study indicate another interesting behavior that the secondary fluid could form a thin hydrophobic membrane around particle surface and significantly decrease the viscosity and yield stress of the suspension. To enhance the surface hydrophobicity, hydrophobic nanoparticles (nano-CaCO3) were added to the hydrophobic membrane of particles to improve the surface roughness, and to generate composite particles having a hierarchical structure similar to the micromorphology of lotus leaf. This composite particle has a higher contact angle, and the suspension of composite particles has a lower viscosity and a lower yield stress.
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168
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Webb EB, Koh CA, Liberatore MW. Rheological properties of methane hydrate slurries formed from AOT + water + oil microemulsions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:10997-11004. [PMID: 23924434 DOI: 10.1021/la4022432] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The in situ formation and flow properties of methane hydrates formed from water-in-oil microemulsions composed of water, dodecane, and aerosol OT surfactant (AOT) were studied using a unique high pressure rheometer. AOT microemulsions have high stability (order of months), well-characterized composition, and yield reproducible results compared to hydrate studies in water-in-crude oil emulsions. Viscosity increases on the order of minutes upon hydrate formation, and then decreases on the order of hours. If significant unconverted water remained after the initial formation event, then viscosity increases for a time as methane slowly dissolves and converts additional water to hydrate. In addition to transient formation measurements, yield stresses and flow curves are measured for a set of experimental conditions. Hydrate slurry viscosity and yield stress increase with increasing water volume fraction, increasing initial pressure, decreasing temperature, and decreasing formation shear rate.
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Affiliation(s)
- Eric B Webb
- Center for Hydrate Research, Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, Colorado 80401, USA
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169
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Trapping energy of a spherical particle on a curved liquid interface. J Colloid Interface Sci 2013; 405:249-55. [DOI: 10.1016/j.jcis.2013.04.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2013] [Revised: 03/28/2013] [Accepted: 04/12/2013] [Indexed: 11/24/2022]
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170
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Zylyftari G, Lee JW, Morris JF. Salt effects on thermodynamic and rheological properties of hydrate forming emulsions. Chem Eng Sci 2013. [DOI: 10.1016/j.ces.2013.02.056] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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171
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Abstract
Controlled assembly of nanoscale objects into superstructures is of tremendous interests. Many approaches have been developed to fabricate organic-nanoparticle superstructures. However, effective fabrication of inorganic-nanoparticle superstructures (such as nanoparticles linked by metals) remains a difficult challenge. Here we show a novel, general method to assemble metals and nanoparticles rationally into nanocomposite superstructures. Novel metal-nanoparticle superstructures are achieved by self-assembly of liquid metals and nanoparticles in immiscible liquids driven by reduction of free energy. Superstructures with various architectures, such as metal-core/nanoparticle-shell, nanocomposite-core/nanoparticle-shell, network of metal-linked core/shell nanostructures, and network of metal-linked nanoparticles, were successfully fabricated by simply tuning the volume ratio between nanoparticles and liquid metals. Our approach provides a simple, general way for fabrication of numerous metal-nanoparticle superstructures and enables a rational design of these novel superstructures with desired architectures for exciting applications.
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172
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Vakarelski IU, Marston JO, Thoroddsen ST. Foam-film-stabilized liquid bridge networks in evaporative lithography and wet granular matter. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:4966-4973. [PMID: 23534699 DOI: 10.1021/la400662n] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Evaporative lithography using latex particle templates is a novel approach for the self-assembly of suspension-dispersed nanoparticles into ordered microwire networks. The phenomenon that drives the self-assembly process is the propagation of a network of interconnected liquid bridges between the template particles and the underlying substrate. With the aid of video microscopy, we demonstrate that these liquid bridges are in fact the border zone between the underlying substrate and foam films vertical to the substrate, which are formed during the evaporation of the liquid from the suspension. The stability of the foam films and thus the liquid bridge network stability are due to the presence of a small amount of surfactant in the evaporating solution. We show that the same type of foam-film-stabilized liquid bridge network can also propagate in 3D clusters of spherical particles, which has important implications for the understanding of wet granular matter.
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Affiliation(s)
- Ivan U Vakarelski
- Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia.
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173
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Horvat M, Emin MA, Hochstein B, Willenbacher N, Schuchmann HP. Influence of medium-chain triglycerides on expansion and rheological properties of extruded corn starch. Carbohydr Polym 2013; 93:492-8. [DOI: 10.1016/j.carbpol.2012.12.052] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 12/10/2012] [Accepted: 12/13/2012] [Indexed: 10/27/2022]
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174
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Beruto D, Lagazzo A, Botter R. Nanoscopic water layers adsorbed onto mesoporous silica aggregates and their effect on the stability and the static yield stress of their dispersion in liquid paraffin. Colloids Surf A Physicochem Eng Asp 2012. [DOI: 10.1016/j.colsurfa.2012.05.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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175
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Schwarz I, Fortini A, Wagner CS, Wittemann A, Schmidt M. Monte Carlo computer simulations and electron microscopy of colloidal cluster formation via emulsion droplet evaporation. J Chem Phys 2012; 135:244501. [PMID: 22225163 DOI: 10.1063/1.3672106] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We consider a theoretical model for a binary mixture of colloidal particles and spherical emulsion droplets. The hard sphere colloids interact via additional short-ranged attraction and long-ranged repulsion. The droplet-colloid interaction is an attractive well at the droplet surface, which induces the Pickering effect. The droplet-droplet interaction is a hard-core interaction. The droplets shrink in time, which models the evaporation of the dispersed (oil) phase, and we use Monte Carlo simulations for the dynamics. In the experiments, polystyrene particles were assembled using toluene droplets as templates. The arrangement of the particles on the surface of the droplets was analyzed with cryogenic field emission scanning electron microscopy. Before evaporation of the oil, the particle distribution on the droplet surface was found to be disordered in experiments, and the simulations reproduce this effect. After complete evaporation, ordered colloidal clusters are formed that are stable against thermal fluctuations. Both in the simulations and with field emission scanning electron microscopy, we find stable packings that range from doublets, triplets, and tetrahedra to complex polyhedra of colloids. The simulated cluster structures and size distribution agree well with the experimental results. We also simulate hierarchical assembly in a mixture of tetrahedral clusters and droplets, and find supercluster structures with morphologies that are more complex than those of clusters of single particles.
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Affiliation(s)
- Ingmar Schwarz
- Theoretische Physik II, Physikalisches Institut, Universität Bayreuth, Bayreuth, Germany
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176
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Fortini A. Clustering and gelation of hard spheres induced by the Pickering effect. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:040401. [PMID: 22680411 DOI: 10.1103/physreve.85.040401] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Indexed: 05/28/2023]
Abstract
A mixture of hard-sphere particles and model emulsion droplets is studied with a Brownian dynamics simulation. We find that the addition of nonwetting emulsion droplets to a suspension of pure hard spheres can lead to both gas-liquid and fluid-solid phase separations. Furthermore, we find a stable fluid of hard-sphere clusters. The stability is due to the saturation of the attraction that occurs when the surface of the droplets is completely covered with colloidal particles. At larger emulsion droplet densities a percolation transition is observed. The resulting networks of colloidal particles show dynamical and mechanical properties typical of a colloidal gel. The results of the model are in good qualitative agreement with recent experimental findings [E. Koos and N. Willenbacher, Science 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids.
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Affiliation(s)
- Andrea Fortini
- Theoretische Physik II, Physikalisches Institut, Universität Bayreuth, Universitätsstraße 30, D-95447 Bayreuth, Germany.
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177
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Cheng TL, Wang YU. Spontaneous formation of stable capillary bridges for firming compact colloidal microstructures in phase separating liquids: a computational study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:2696-2703. [PMID: 22220683 DOI: 10.1021/la2044152] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Computer modeling and simulations are performed to investigate capillary bridges spontaneously formed between closely packed colloidal particles in phase separating liquids. The simulations reveal a self-stabilization mechanism that operates through diffusive equilibrium of two-phase liquid morphologies. Such mechanism renders desired microstructural stability and uniformity to the capillary bridges that are spontaneously formed during liquid solution phase separation. This self-stabilization behavior is in contrast to conventional coarsening processes during phase separation. The volume fraction limit of the separated liquid phases as well as the adhesion strength and thermodynamic stability of the capillary bridges are discussed. Capillary bridge formations in various compact colloid assemblies are considered. The study sheds light on a promising route to in situ (in-liquid) firming of fragile colloidal crystals and other compact colloidal microstructures via capillary bridges.
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Affiliation(s)
- Tian-Le Cheng
- Department of Materials Science and Engineering, Michigan Technological University, Houghton, Michigan 49931, United States
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178
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Wang D, Yordanov S, Paroor HM, Mukhopadhyay A, Li CY, Butt HJ, Koynov K. Probing diffusion of single nanoparticles at water-oil interfaces. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2011; 7:3502-7. [PMID: 22072585 DOI: 10.1002/smll.201101823] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Indexed: 05/21/2023]
Abstract
The diffusion of nanoparticles at a water-alkane interface is studied using fluorescence correlation spectroscopy. Hydrophilic and hydrophobic quantum dots of 5, 8, and 11 nm radius are used. A slow-down of nanoparticle diffusion at the liquid-liquid interface is observed. The effect is most evident when the viscosities of both liquid phases are similar, here, at the water-decane interface. In this case, the interfacial diffusion coefficients of the hydrophilic particles are 1.5 times and those of the hydrophobic particles 2 times lower than the corresponding bulk values.
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Affiliation(s)
- Dapeng Wang
- Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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179
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Brown E, Zhang H, Forman NA, Maynor BW, Betts DE, DeSimone JM, Jaeger HM. Shear thickening and jamming in densely packed suspensions of different particle shapes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 84:031408. [PMID: 22060372 DOI: 10.1103/physreve.84.031408] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Revised: 09/04/2011] [Indexed: 05/31/2023]
Abstract
We investigated the effects of particle shape on shear thickening in densely packed suspensions. Rods of different aspect ratios and nonconvex hooked rods were fabricated. Viscosity curves and normal stresses were measured using a rheometer for a wide range of packing fractions for each shape. Suspensions of each shape exhibit qualitatively similar discontinuous shear thickening. The logarithmic slope of the stress vs shear rate increases dramatically with packing fraction and diverges at a critical packing fraction φ(c) which depends on particle shape. The packing fraction dependence of the viscosity curves for different convex shapes can be collapsed when the packing fraction is normalized by φ(c). Intriguingly, viscosity curves for nonconvex particles do not collapse on the same set as convex particles, showing strong shear thickening over a wider range of packing fraction. The value of φ(c) is found to coincide with the onset of a yield stress at the jamming transition, suggesting the jamming transition also controls shear thickening. The yield stress is found to correspond with trapped air in the suspensions, and the scale of the stress can be attributed to interfacial tension forces which dramatically increase above φ(c) due to the geometric constraints of jamming. Using this connection we show that the jamming transition can be identified by simply looking at the surface of suspensions. The relationship between shear and normal stresses is found to be linear in both the shear thickening and jammed regimes, indicating that the shear stresses come from friction. In the limit of zero shear rate, normal stresses pull the rheometer plates together due to the surface tension of the liquid below φ(c), but push the rheometer plates apart due to jamming above φ(c).
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Affiliation(s)
- Eric Brown
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
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Affiliation(s)
- Hans-Jürgen Butt
- Polymer Physics, Max Planck Institute for Polymer Research Mainz, 55128 Germany
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