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Bogris A, Burger NA, Makris KG, Loppinet B, Fytas G. Intermixed Time-Dependent Self-Focusing and Defocusing Nonlinearities in Polymer Solutions. ACS PHOTONICS 2022; 9:722-728. [PMID: 35211646 PMCID: PMC8855434 DOI: 10.1021/acsphotonics.1c01917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Indexed: 06/14/2023]
Abstract
Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.
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Affiliation(s)
- Athanasios Bogris
- FORTH,
Institute of Electronic Structure and Laser, 70013 Heraklion, Crete, Greece
- Department
of Materials Science and Technology, University
of Crete, 70013 Heraklion, Crete, Greece
| | - Nikolaos A. Burger
- FORTH,
Institute of Electronic Structure and Laser, 70013 Heraklion, Crete, Greece
- Department
of Materials Science and Technology, University
of Crete, 70013 Heraklion, Crete, Greece
| | - Konstantinos G. Makris
- FORTH,
Institute of Electronic Structure and Laser, 70013 Heraklion, Crete, Greece
- Department
of Physics, University of Crete, Heraklion 71003, Greece
| | - Benoit Loppinet
- FORTH,
Institute of Electronic Structure and Laser, 70013 Heraklion, Crete, Greece
| | - George Fytas
- FORTH,
Institute of Electronic Structure and Laser, 70013 Heraklion, Crete, Greece
- Max-Planck
Institute for Polymer Research, 55128 Mainz, Germany
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2
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Abstract
Active matter comprises self-driven units, such as bacteria and synthetic microswimmers, that can spontaneously form complex patterns and assemble into functional microdevices. These processes are possible thanks to the out-of-equilibrium nature of active-matter systems, fueled by a one-way free-energy flow from the environment into the system. Here, we take the next step in the evolution of active matter by realizing a two-way coupling between active particles and their environment, where active particles act back on the environment giving rise to the formation of superstructures. In experiments and simulations we observe that, under light-illumination, colloidal particles and their near-critical environment create mutually-coupled co-evolving structures. These structures unify in the form of active superstructures featuring a droplet shape and a colloidal engine inducing self-propulsion. We call them active droploids-a portmanteau of droplet and colloids. Our results provide a pathway to create active superstructures through environmental feedback.
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3
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Smith GN, Brok E, Schmiele M, Mortensen K, Bouwman WG, Duif CP, Hassenkam T, Alm M, Thomsen P, Arleth L. The microscopic distribution of hydrophilic polymers in interpenetrating polymer networks (IPNs) of medical grade silicone. POLYMER 2021. [DOI: 10.1016/j.polymer.2021.123671] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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4
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A Novel Multiscale Methodology for Simulating Droplet Morphology Evolution during Injection Molding of Polymer Blends. Polymers (Basel) 2020; 13:polym13010133. [PMID: 33396929 PMCID: PMC7795296 DOI: 10.3390/polym13010133] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Revised: 12/23/2020] [Accepted: 12/28/2020] [Indexed: 11/16/2022] Open
Abstract
The morphology of polymer blends plays a critical role in determining the properties of the blends and performance of resulting injection-molded parts. However, it is currently impossible to predict the morphology evolution during injection molding and the final micro-structure of the molded parts, as the existing models for the morphology evolution of polymer blends are still limited to a few simple flow fields. To fill this gap, this paper proposed a novel model for droplet morphology evolution during the mold filling process of polymer blends by coupling the models on macro- and meso-scales. The proposed model was verified by the injection molding experiment of PP/POE blends. The predicted curve of mold cavity pressure during filling process agreed precisely with the data of the corresponding pressure sensors. On the other hand, the model successfully tracked the moving trajectory and simulated morphology evolution of the droplets during the mold-filling process. After mold-filling ended, the simulation results of the final morphology of the droplets were consistent with the observations of the scanning electron microscope (SEM) experiment. Moreover, this study revealed the underlying mechanism of the droplet morphology evolution through the force analysis on the droplet. It is validated that the present model is a qualified tool for simulating the morphology evolution of polymer blends during injection molding and predicting the final microstructure of the products.
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5
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Siriwardane DA, Kulikov O, Batchelor BL, Liu Z, Cue JM, Nielsen SO, Novak BM. UV- and Thermo-Controllable Azobenzene-Decorated Polycarbodiimide Molecular Springs. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b00679] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Dumindika A. Siriwardane
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Oleg Kulikov
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, United States
| | - Benjamin L. Batchelor
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Zhiwei Liu
- Department of Chemistry and Biochemistry, University of the Sciences, 600 South 43rd Street, Philadelphia, Pennsylvania 19104, United States
| | - John Michael Cue
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Steven O. Nielsen
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Bruce M. Novak
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
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6
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Wang H, Zang D, Li X, Geng X. Simulation of phase separation with temperature-dependent viscosity using lattice Boltzmann method. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2017; 40:115. [PMID: 29274072 DOI: 10.1140/epje/i2017-11605-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Accepted: 12/04/2017] [Indexed: 06/07/2023]
Abstract
This paper presents an exploration of the phase separation behavior and pattern formation in a binary fluid with temperature-dependent viscosity via a coupled lattice Boltzmann method (LBM). By introducing a viscosity-temperature relation into the LBM, the coupling effects of the viscosity-temperature coefficient [Formula: see text] , initial viscosity [Formula: see text] and thermal diffusion coefficient [Formula: see text] , on the phase separation were successfully described. The calculated results indicated that an increase in initial viscosity and viscosity-temperature coefficient, or a decrease in the thermal diffusion coefficient, can lead to the orientation of isotropic growth fronts over a wide range of viscosity. The results showed that droplet-type phase structures and lamellar phase structures with domain orientation parallel or perpendicular to the walls can be obtained in equilibrium by controlling the initial viscosity, thermal diffusivity, and the viscosity-temperature coefficient. Furthermore, the dataset was rearranged for growth kinetics of domain growth and thermal diffusion fronts in a plot by the spherically averaged structure factor and the ratio of separated and continuous phases. The analysis revealed two different temporal regimes: spinodal decomposition and domain growth stages, which further quantified the coupled effects of temperature and viscosity on the evolution of temperature-dependent phase separation. These numerical results provide guidance for setting optimum temperature ranges to obtain expected phase separation structures for systems with temperature-dependent viscosity.
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Affiliation(s)
- Heping Wang
- Functional Soft Matter & Materials Group, Key Laboratory of Space Applied Physics and Chemistry of Ministry of Education, School of Science, Northwestern Polytechnical University, 710129, Xi'an, China
| | - Duyang Zang
- Functional Soft Matter & Materials Group, Key Laboratory of Space Applied Physics and Chemistry of Ministry of Education, School of Science, Northwestern Polytechnical University, 710129, Xi'an, China
| | - Xiaoguang Li
- Functional Soft Matter & Materials Group, Key Laboratory of Space Applied Physics and Chemistry of Ministry of Education, School of Science, Northwestern Polytechnical University, 710129, Xi'an, China
| | - Xingguo Geng
- Functional Soft Matter & Materials Group, Key Laboratory of Space Applied Physics and Chemistry of Ministry of Education, School of Science, Northwestern Polytechnical University, 710129, Xi'an, China.
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8
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Böckmann M, Doltsinis NL. Towards understanding photomigration: Insights from atomistic simulations of azopolymer films explicitly including light-induced isomerization dynamics. J Chem Phys 2016; 145:154701. [DOI: 10.1063/1.4964485] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Marcus Böckmann
- Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster and Center for Multiscale Theory and Computation, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
| | - Nikos L. Doltsinis
- Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster and Center for Multiscale Theory and Computation, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
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9
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Orlishausen M, Köhler W. Competition between phase transition and thermophoretic expansion of a transient poly(N-isopropylacrylamide) network. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2016; 39:98. [PMID: 27815787 DOI: 10.1140/epje/i2016-16098-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 10/03/2016] [Indexed: 06/06/2023]
Abstract
Aqueous solutions of highly entangled ultra-high molar mass ( 2.4×106 g/mol) poly(N-isopropylacrylamide) (PNIPAM) have been subjected to an inhomogeneous temperature field by selective heating of a single embedded gold nanoparticle (GNP) by means of a focused laser beam. Randomly distributed tracer GNPs are trapped in the meshes of the transient entanglement network and serve as tracers for the monitoring of the network deformation field. Because of the positive Soret coefficient of PNIPAM in water, the viscoelastic polymer network is expanded by thermophoretic forces pointing away from the hot center. Close to the heated GNP the thermoresponsive polymer solution crosses the binodal and the network contracts, which is made visible by an inward motion of tracer GNPs, which are randomly embedded in the polymer network and not illuminated by the laser beam. Within a thin transition zone the network contraction and the competing thermophoretic network expansion cancel out in the steady state. There is, however, no cancellation during the transients due to the different time scales of both mechanisms. The network within the crossover region first undergoes an expansion that is followed by a slower contraction. From the global expansion and contraction, the local strain (stretching and compression) of the transient network can be calculated. Due to the long disentanglement times, corresponding to long lifetimes of the meshes of the network, the whole process is fully reversible.
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Affiliation(s)
- M Orlishausen
- Physikalisches Institut, Universität Bayreuth, D-95440, Bayreuth, Germany
| | - W Köhler
- Physikalisches Institut, Universität Bayreuth, D-95440, Bayreuth, Germany.
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10
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Abstract
Photomigration in azo polymers is an area of research that witnessed intensive studies owing to its potential in optical manipulation, e.g., optical tweezing, the physical mechanism of which remains unsolved since its discovery about two decades ago. In this paper, a detailed theoretical study that reproduces the phenomena associated with photomigration is presented, including the physical models and the associated master equations. Polarization effects are discussed and analytical solutions are given to describe the steady-state and the dynamics of photomigration. Such a theory leads to new theoretical experiments relating material properties to light action. A photoisomerization force which is described by a spring-type model is introduced. This force is derived from a harmonic light potential that moves the azo polymer. This force is parenting to optical tweezers, but it is quite different in the sense that it requires photoisomerization to occur. The azo polymer's motion is governed by four competing forces: the photoisomerization force, and the restoring optical gradient and elastic forces, as well as the random forces due to spontaneous diffusion.
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11
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Rodríguez-Hernández J. Wrinkled interfaces: Taking advantage of surface instabilities to pattern polymer surfaces. Prog Polym Sci 2015. [DOI: 10.1016/j.progpolymsci.2014.07.008] [Citation(s) in RCA: 218] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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12
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Jiang H, Dou N, Fan G, Zhang X, Yang Z. Orientational phase-separated domains in a polyolefin blend under a temperature gradient field. POLYMER 2014. [DOI: 10.1016/j.polymer.2014.03.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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13
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Lin WT, Sun YC, Chang CC, Lin YC, Peng CW, Juan WT, Tsai JC. Ratcheting and transitions: short granular chain in a gradient of vibration. PHYSICAL REVIEW LETTERS 2014; 112:058001. [PMID: 24580630 DOI: 10.1103/physrevlett.112.058001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Indexed: 06/03/2023]
Abstract
We report our experimental work on a one-dimensional gradient of vibration with a short granular chain. The system exhibits transitions of ratcheting dynamics from passive monotonic creeping against the gradient, to rapid stochastic head swinging with a reversed bias in its direction, and to seemingly random fluctuations. The spontaneously emerged spatial pattern reflects bifurcations of the state of the chain. Evidence from counterpart experiments using uniform vibrations confirms a nonmonotonic development of accessible modes behind the transitions, whereas the reversed ratcheting reflects an interesting dialogue between the size of the object and the spatial gradient.
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Affiliation(s)
- W-T Lin
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
| | - Y-C Sun
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
| | - C-C Chang
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
| | - Y-C Lin
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
| | - C-W Peng
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
| | - W-T Juan
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
| | - J-C Tsai
- Institute of Physics, Academia Sinica, Taipei, Taiwan 11529
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14
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Jiang H, Dou N, Fan G, Yang Z, Zhang X. Effect of temperature gradient on liquid-liquid phase separation in a polyolefin blend. J Chem Phys 2013; 139:124903. [PMID: 24089800 DOI: 10.1063/1.4821591] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have investigated experimentally the structure formation processes during phase separation via spinodal decomposition above and below the spinodal line in a binary polymer blend system exposed to in-plane stationary thermal gradients using phase contrast optical microscopy and temperature gradient hot stage. Below the spinodal line there is a coupling of concentration fluctuations and thermal gradient imposed by the temperature gradient hot stage. Also under the thermal gradient annealing phase-separated domains grow faster compared with the system under homogeneous temperature annealing on a zero-gradient or a conventional hot stage. We suggest that the in-plane thermal gradient accelerates phase separation through the enhancement in concentration fluctuations in the early and intermediate stages of spinodal decomposition. In a thermal gradient field, the strength of concentration fluctuation close to the critical point (above the spinodal line) is strong enough to induce phase separation even in one-phase regime of the phase diagram. In the presence of a temperature gradient the equilibrium phase diagrams are no longer valid, and the systems with an upper critical solution temperature can be quenched into phase separation by applying the stationary temperature gradient. The in-plane temperature gradient drives enhanced concentration fluctuations in a binary polymer blend system above and below the spinodal line.
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Affiliation(s)
- Hua Jiang
- Center for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, Suzhou 215006, China
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15
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Jerabek-Willemsen M, Wienken CJ, Braun D, Baaske P, Duhr S. Molecular interaction studies using microscale thermophoresis. Assay Drug Dev Technol 2012; 9:342-53. [PMID: 21812660 DOI: 10.1089/adt.2011.0380] [Citation(s) in RCA: 573] [Impact Index Per Article: 47.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Abstract The use of infrared laser sources for creation of localized temperature fields has opened new possibilities for basic research and drug discovery. A recently developed technology, Microscale Thermophoresis (MST), uses this temperature field to perform biomolecular interaction studies. Thermophoresis, the motion of molecules in temperature fields, is very sensitive to changes in size, charge, and solvation shell of a molecule and thus suited for bioanalytics. This review focuses on the theoretical background of MST and gives a detailed overview on various applications to demonstrate the broad applicability. Experiments range from the quantification of the affinity of low-molecular-weight binders using fluorescently labeled proteins, to interactions between macromolecules and multi-component complexes like receptor containing liposomes. Information regarding experiment and experimental setup is based on the Monolith NT.115 instrument (NanoTemper Technologies GmbH).
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16
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Schwaiger F, Zimmermann W, Köhler W. Transient cage formation around hot gold colloids dispersed in polymer solutions. J Chem Phys 2011; 135:224905. [DOI: 10.1063/1.3665935] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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17
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Gonnella G, Lamura A, Tiribocchi A. Thermal and hydrodynamic effects in the ordering of lamellar fluids. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2011; 369:2592-2599. [PMID: 21576175 DOI: 10.1098/rsta.2011.0020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Phase separation in a complex fluid with lamellar order has been studied in the case of cold thermal fronts propagating diffusively from external walls. The velocity hydrodynamic modes are taken into account by coupling the convection-diffusion equation for the order parameter to a generalized Navier-Stokes equation. The dynamical equations are simulated by implementing a hybrid method based on a lattice Boltzmann algorithm coupled to finite difference schemes. Simulations show that the ordering process occurs with morphologies depending on the speed of the thermal fronts or, equivalently, on the value of the thermal conductivity ξ. At large values of ξ, as in instantaneous quenching, the system is frozen in entangled configurations at high viscosity while it consists of grains with well-ordered lamellae at low viscosity. By decreasing the value of ξ, a regime with very ordered lamellae parallel to the thermal fronts is found. At very low values of ξ the preferred orientation is perpendicular to the walls in d=2, while perpendicular order is lost moving far from the walls in d=3.
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Affiliation(s)
- G Gonnella
- Dipartimento di Fisica, Università di Bari, and INFN, Sezione di Bari, Via Amendola 173, 70126 Bari, Italy
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18
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Gonnella G, Lamura A, Piscitelli A, Tiribocchi A. Phase separation of binary fluids with dynamic temperature. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:046302. [PMID: 21230385 DOI: 10.1103/physreve.82.046302] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Revised: 09/09/2010] [Indexed: 05/30/2023]
Abstract
Phase separation of binary fluids quenched by contact with cold external walls is considered. Navier-Stokes, convection-diffusion, and energy equations are solved by lattice Boltzmann method coupled with finite-difference schemes. At high viscosity, different morphologies are observed by varying the thermal diffusivity. In the range of thermal diffusivities with domains growing parallel to the walls, temperature and phase separation fronts propagate toward the inner of the system with power-law behavior. At low viscosity hydrodynamics favors rounded shapes, and complex patterns with different length scales appear. Off-symmetrical systems behave similarly but with more ordered configurations.
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Affiliation(s)
- G Gonnella
- Dipartimento di Fisica, Università di Bari and INFN, Sezione di Bari, Via Amendola 173, 70126 Bari, Italy
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20
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Krekhov A. Formation of regular structures in the process of phase separation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:035302. [PMID: 19392008 DOI: 10.1103/physreve.79.035302] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 02/10/2009] [Indexed: 05/27/2023]
Abstract
Phase separation under directional quenching has been studied in a Cahn-Hilliard model. In distinct contrast to the disordered patterns which develop under a homogeneous quench, periodic stripe patterns are generated behind the quench front. Their wavelength is uniquely defined by the velocity of the quench interface in a wide range. Numerical simulations match perfectly analytical results obtained in the limit of small and large velocities of the quench interface. Additional periodic modulation of the quench interface may lead to cellular patterns. The quenching protocols analyzed are expected to be an effective tool in technological applications to design nanostructured materials.
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Affiliation(s)
- Alexei Krekhov
- Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
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Voit A, Krekhov A, Köhler W. Laser-induced structures in a polymer blend in the vicinity of the phase boundary. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:011808. [PMID: 17677485 DOI: 10.1103/physreve.76.011808] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Indexed: 05/16/2023]
Abstract
We have determined the diffusion, thermal diffusion, and Soret coefficients of a poly(dimethyl siloxane)/poly(ethyl-methyl siloxane) (PDMS/PEMS) polymer blend as a function of composition and temperature within the homogeneous phase. The critical slowing down of the diffusion and the corresponding critical divergence of the Soret coefficient are described within the pseudospinodal concept both for critical and off-critical compositions. These data are used to model in detail the channel-like structures that form due to the Soret effect when a focused laser beam is scanned across a polymer film of 100microm thickness. A moderate vertical asymmetry is attributed to solutal convection. Although heat rapidly diffuses away from the laser focus, the composition distribution in the early stage resembles the sharp profile of the laser beam. PDMS accumulates within the center of the structures, whereas a thin PEMS-rich layer is formed that isolates the central core from the windows. Experimentally, the structures are analyzed by means of phase contrast microscopy. Possible applications as rewritable optical waveguides or tunable phase plates are briefly discussed.
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Affiliation(s)
- A Voit
- Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
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23
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Rauch J, Hartung M, Privalov AF, Köhler W. Correlation between thermal diffusion and solvent self-diffusion in semidilute and concentrated polymer solutions. J Chem Phys 2007; 126:214901. [PMID: 17567216 DOI: 10.1063/1.2738467] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have performed measurements of thermal diffusion coefficients DT and solvent self-diffusion coefficients Dss in semidilute to concentrated polymer solutions. Solutes of different glass transition temperatures and solvents of different solvent qualities have been used. The investigated systems are in detail: poly(dimethyl-siloxane) in toluene, tristyrene in toluene, polystyrene in toluene, polystyrene in tetrahydrofuran, polystyrene in benzene, and polystyrene in cyclohexane. The thermal diffusion data are compared to our data and literature data for solvent self-diffusion coefficients. In all systems the concentration dependence of DT closely parallels the one of Dss which may be viewed as a local probe for friction on a length scale of the size of one polymer segment. This identifies local friction as the dominating parameter determining the concentration dependence of DT. Solvent quality, in contrast, has no influence on DT.
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Affiliation(s)
- J Rauch
- Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
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24
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Duhr S, Braun D. Why molecules move along a temperature gradient. Proc Natl Acad Sci U S A 2006; 103:19678-82. [PMID: 17164337 PMCID: PMC1750914 DOI: 10.1073/pnas.0603873103] [Citation(s) in RCA: 578] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Indexed: 11/18/2022] Open
Abstract
Molecules drift along temperature gradients, an effect called thermophoresis, the Soret effect, or thermodiffusion. In liquids, its theoretical foundation is the subject of a long-standing debate. By using an all-optical microfluidic fluorescence method, we present experimental results for DNA and polystyrene beads over a large range of particle sizes, salt concentrations, and temperatures. The data support a unifying theory based on solvation entropy. Stated in simple terms, the Soret coefficient is given by the negative solvation entropy, divided by kT. The theory predicts the thermodiffusion of polystyrene beads and DNA without any free parameters. We assume a local thermodynamic equilibrium of the solvent molecules around the molecule. This assumption is fulfilled for moderate temperature gradients below a fluctuation criterion. For both DNA and polystyrene beads, thermophoretic motion changes sign at lower temperatures. This thermophilicity toward lower temperatures is attributed to an increasing positive entropy of hydration, whereas the generally dominating thermophobicity is explained by the negative entropy of ionic shielding. The understanding of thermodiffusion sets the stage for detailed probing of solvation properties of colloids and biomolecules. For example, we successfully determine the effective charge of DNA and beads over a size range that is not accessible with electrophoresis.
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Affiliation(s)
- Stefan Duhr
- Chair for Applied Physics, Ludwig Maximilians Universität, Amalienstrasse 54, 80799 Munich, Germany
| | - Dieter Braun
- Chair for Applied Physics, Ludwig Maximilians Universität, Amalienstrasse 54, 80799 Munich, Germany
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25
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Voit A, Krekhov A, Köhler W. Quenching a UCST Polymer Blend into Phase Separation by Local Heating. Macromolecules 2006. [DOI: 10.1021/ma062205j] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A. Voit
- Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
| | - A. Krekhov
- Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
| | - W. Köhler
- Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
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26
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Duhr S, Braun D. Thermophoretic depletion follows Boltzmann distribution. PHYSICAL REVIEW LETTERS 2006; 96:168301. [PMID: 16712279 DOI: 10.1103/physrevlett.96.168301] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2005] [Indexed: 05/09/2023]
Abstract
Thermophoresis, also termed thermal diffusion or the Soret effect, moves particles along temperature gradients. For particles in liquids, the effect lacks a theoretical explanation. We present experimental results at moderate thermal gradients: (i) Thermophoretic depletion of 200 nm polystyrene spheres in water follows an exponential distribution over 2 orders of magnitude in concentration; (ii) Soret coefficients scale linearly with the sphere's surface area. Based on the experiments, it is argued that local thermodynamic equilibrium is a good starting point to describe thermophoresis.
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Affiliation(s)
- Stefan Duhr
- Applied Physics, Center for Nanoscience, Ludwig Maximilians University München, Amalienstr. 54, D-80799 München, Germany
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