DOCSLIB.ORG

X) and Computer Simulation of Synthesis of Nanostructures

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
X) and Computer Simulation of Synthesis of Nanostructures FORSCHUNGSZENTRUM ROSSENDORF ml WISSENSCHAFTLICH-TECHNISCHEBERICHTE FZR-277 November 1999 DEOOGE882 RECEW?X) MN30ZO08 AAatthias Strobe/ C)STI Modeling and Computer Simulation of Ion Beam Synthesis of Nanostructures Dissertation -- *DE013741591* R: KS DEO13741591 ______.___–..—-–’––-–—- DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. FORSCHUNGSZENTRUM ROSSENDORF Institut fur Ionenstrahlphysik und Materialforschung I Modeling and Computer Simulation of Ion Beam Synthesis of Nanostructures von der Fakultat Mathematik und Naturwissenschaften der Technischen Universitat Dresden genehmigte Dissertation zur Erlangung des akademischen Grades Doctor Rerum Naturalism (Dr. rer. nat.) vorgelegt von Dipl.-Phys. MATTHIAS STROBEL geboren am 22. Februar 1969 in Wurzburg IE2R Tag der Einreichung: 30. Juni 1999 Tag der Verteidigung: 13. Oktober 1999 Vorsitzender der Prufungskommision: PROF. DR. GERHARD S OFF Gutachter: PROF. DR. WOLFHARD M.OLLER Technische Universitit Dresden PROF. HARRY BERNAS, PHD CNRS–CSNSM Orsay, Frankreich PROF. DR. SIGISMUND KOBE Technische Universitat Dresden Physic ist wahrlich das eigentliche Studium des Menschen Georg Christoph Lichtenberg (Deutscher Physiker und PhiIosoph, 1742- 1799) Contents Abbreviations ix 1 Introduction 1 2 Ion beam synthesis of nanostructures 7 2.110n implantation methods.. ...9 2.2 Principles of ion-solid interaction . 9 2.3 Formation of second-phase precipitates . 12 2.3.1 Impurity-substrate phase diagram . 12 2.3.2 Homogeneous nucleation. ..13 2.3.3 Nucleation in ion beam synthesis . - . 17 2.4 Growth, coarsening, and coalescence of nanoclusters . - 20 2.5 Modeling and simulation approaches . - . 23 2.5.1 Atomic description . .~~ 2.5.2 Mesoscopic and continuum descriptions . - . 28 3 Kinetic 3D lattice Monte-Carlo method 31 3.1 Basic description . ...31 3.2 Energetic and jump probabilities . - . 34 3.3 Intrinsic properties of the model... 35 3.4 Analysis ofsimulation data. ...38 3.5 Gauging of simulation parameters . - - . - . 39 3.5.1 Length scale . 40 3.5.2 Diffusion coefficient, time scale, and ion flux . 40 3.5.3 Nearest-neighbor bond strength, volubility, capillary length, and surface tension . ...42 3.6 A simple approach to collisional mixing . - - . 49 3.7 Simulation of ion implantation and annealing . 50 3.8 -Applicability of the K3DLMC method and discussion . 51 4 General description of Ostwald ripening 55 4.1 Characterization of Ostwald ripening and recent developments . 55 4.2 Fundamentals of the model . ...58 v vi CO~NTENTS 4.2.1 Evolution of a single nanocluster . 58 4.2.2 Evolution of an ensemble of nanoclusters . 59 4.3 Local mean-field approach to Ostwald ripening . 62 4.4 Numerical implementation. ...64 4.5 Simulation of diffusion and reaction controlled Ostwald ripening . 67 5 Nanocluster evolution during ion implantation 73 5.1 Nanocluster formation at constant implantation conditions . 73 5.2 Nanocluster formation at varying implantation conditions . 79 5.3 On the influence of collisional mixing . 82 5.3.1 Collisional mixing of a single nanocluster . 83 5.3.2 Nucleation, growth, and Ostwald ripening in the presence of colli- sional mixing . ...94 6 Combination of K3DLMC and reaction-diffusion equation methods 101 6.1 K3DLMC and reaction-diffusion equation simulations of homogeneous Ost- wald ripening . 101 6.1.1 K3DLMC simulations of homogeneous Ostwald ripening . 102 6.1.2 Comparison of K3DLlMC and reaction-diffusion equation simulations of Ostwald ripening . ...107 6.2 Late stage evolution of as-implanted samples . 111 6.3 Focused ion beam synthesis of nanocluster arrays . 115 7 Applications of the K3DLMC method in ion beam synthesis 119 7.1 Impurity redistribution in a reactive ambient . 119 7.1.1 Experimental observations . 120 7.1.2 Modeling of redistribution of implanted Ge in the presence of an oxidizing atmosphere . ...123 7.2 Ion beam synthesis of compound nanoclusters . 126 7.2.1 K3DLMC model for two types of interacting impurity atoms . 126 7.2.2 On core/shell nanocluster formation by sequential ion implantation 128 7.2.3 Shifted-profile compound nanocluster synthesis . 132 8 Summary and outlook 139 A Bit encoding of Monte-Carlo lattice 145 B Derivation of nanocluster source strengths 149 B.1 General formulation . 149 B.2 Monopole approximation . 152 B.3 Source strengths in monopole approximation . 154 List of Figures 155 CONTENTS vii List of Tables 159 Bibliography 161 Danksagung / Acknowledgements 179 Erklarung 181 Thesen / Major statements of the work 183 ... VIH CONTENTS Abbreviations An author of a (scientific) publication faces the conflict of using acronyms versus writing technical or often repeated expressions always in full length. Some claim that acronyms facilitate reading while others complain about the problem memorizing them. By carefully balancing the convenience of using abbreviations versus the readability of this thesis, I finally decided to introduce the following ones which are partly standard in the physical literature: BC boundary condition BCA binary collision approximation bcc body-centered cubic CA cellular automaton CBII conventional beamline ion implantation CM collisional mixing CPU central processor unit dpa displacements per atom fcc face-centered cubic FIB focused ion beam GT GIBBS-THOMSON IA impurity atom IBS ion beam synthesis K3DLiMc kinetic three-dimensional lattice Monte-Carlo KIM kinetic Is~~G model lhs left hand side LSW LIFSHITZ-SLYOZOV-WAGNER MC Monte-Carlo MCS Monte-Carlo step MD Molecular Dynamics NC! nanocluster OR OSTWALD ripening PRD particle radius distribution RBS RUTHERFORD backscattering RDE reaction-diffusion equation rhs right hand side ix x CONTENTS Sc simple-cubic SRIM Stopping ancl Range of Ions in Matter TEM transmission electron microscopy TRIM TRansport of Ions in Matter VG VOORHEES-GLICKSMAN XTEM cross-section TEi’v1 Chapter 1 Introduction Ever since the invention of particle accelerators energetic ions have been used to explore the physical laws of ion-solid interactions [1). Besides these fundamental studies the potential of ions to modify selectively the properties of substrates has been recognized and thus found a wide area of technological applications. In modern microelectronics, for instance, current integrated circuit fabrication is based on the precise control of doping of Si wafers by implantation [2]. A further example is the hardening of steels with energetic nitrogen ions, which proceeds via the formation of nitrides close to the surface [3]. Depending mostly on the implanted fluence FO, ion beam modification of materials can be roughly grouped into three major ranges: ● For fluences -FO~ 1014cm-z the implanted ions are assumed to remain isolated within the substrate. Implanted into crystals these impurities may reside on regular lattice sites and thus change the electrical properties of the host material (doping range); ● For fluences in the range 1015 cm ‘2 ~ 1’.<1016 cm–2, in the course of implantation the deposited impurities start to exceed the volubility threshold. This causes the formation of isolated domains of a new phase [in general called nanoclusters (FJCS), precipitates, quantum dots, or, if in a crystalline state, nanocrystals], which besides the mechanical may also change the optical properties of the substrate; ● For fluences F. > 1017 cm-2 the second phase domains start to coalesce, which might result in the formation of a continuous buried layer of a new composition in a predefine depth of the substrate. Ion beam synthesis (IBS) of nanostructures refers to items two and three of the above listing and consists usually of two independent steps. First, the implantation of a certain fluence F. is performed in a rather well defined parameter range, i.e. ion energy E, ion flux j, and substrate temperature ~~P. Very often this step is followed by a thermal heat treatment because (i) radiation damage is annealed out and (ii) the thermally activated redistribution of the impurities can be tailored to a large extent. As evidenced by a vast literature, a huge variety of different NC/substrate systems has been achieved by IBS. For instance, the formation of AU [4, 5], Ag [6], Cu [7] or 1 2 CILAPTER 1. INTRODUC7 Ni [8] precipitates in silica glasses or other insulators has been reported (for a revi( metallic NC formation by IBS see, e.g. MAZZOLDI et al. [9]). The synthesis of elem semiconducting hTCs in neutral (chemically inert) matrices has been observed [10], as as compound nanocrystal formation in single-type implantations due to chemical reac between impurity and substrate atoms, e.g. silicide formation for metal implantation ir [II]. Additionally, in a neutral matrix compound NCS could be detected by co- or seque implantation of various atom types, e.g. II-VI, III-V or IV-IV semiconductor N-CS in [12], AlzOS [13] or Si [14] as well as metallic compound NCS in SiOa [15]. Further exan and applications of ion beams in materials science can be found in Proceedings of ar or biannual conferences in ion beam physics (for recent examples, see Refs. [16, 17]). This work concentrates on the synthesis of NCS by ion implantation, because a p~ cclntrol of the formation of these essentially zero-dimensional structures helps to use unique physical properties in technological applications. Consisting of approximate: to 105 single atoms, the properties of N(Js are governed by a combination of effects k] from atomic and solid state physics. Hence, for their description well established con fr,~m
Load more

Recommended publications
  • Theoretical Investigation of Catalyst Stability and Deactivation
    Theoretical investigation of catalyst stability and deactivation Zur Erlangung des akademischen Grades eines DOKTORS DER NATURWISSENSCHAFTEN (Dr. rer. nat) von der KIT-Fakultät für Chemie und Biowissenschaften des Karlsruher Instituts für Technologie (KIT) genehmigte DISSERTATION von Elisabeth Maria Dietze 1. Referent: Prof. Dr. Felix Studt 2. Referent: Prof. Dr. Olaf Deutschmann Tag der mündlichen Prüfung: 09.12.2019 Abstract Oxide supported noble metal nanoparticles are commonly used as industrial heterogeneous catalysts, for example in automotive exhaust-gas after-treatment systems. To improve their lifetime is highly important to reduce natural resource exploitation. The catalyst lifetime is limited by catalyst deactivation, in particular through sintering. In this thesis, both, the thermodynamic stability of supported nanoparticles as well as their deactivation kinetics through sintering are investigated. First, the thermodynamic stability of pure unsupported metal nanoparticles is studied. Density functional theory (DFT) is used to examine cuboctahedral, octahedral and cubic nanoparticles of the late transition metals as well as Al and Mg in order to identify their stability as a function of size. A simple model is developed that not only includes the surface energies as in the commonly used Wulff construction but additionally accounts for energies related to edges and corners. Importantly, this model only requires the bulk cohesive energy and the surface energies of the fcc(111) and fcc(100) surfaces, which are used to extrapolate to lower coordination numbers. It is found that the model estimates the stability of nanoparticles with a mean absolute error of only 0.09 eV/atom. To understand how the support influences the stability of metal nanoparticles, numerous metal/oxide interfaces are investigated using DFT.
    [Show full text]
  • Ostwald Ripening of Clusters During Protein Crystallization
    week ending PRL 104, 178102 (2010) PHYSICAL REVIEW LETTERS 30 APRIL 2010 Ostwald Ripening of Clusters during Protein Crystallization Aaron M. Streets1 and Stephen R. Quake1,2,* 1Department of Applied Physics, Stanford University, Stanford, California 94305, USA 2Department of Bioengineering and Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA (Received 4 November 2009; published 26 April 2010) Contrary to classical nucleation theory, protein crystals can nucleate via a two-step process in which the molecular arrangement of the ordered solid phase is preceded by nucleation of a dense amorphous phase. We study the growth of these precrystalline clusters in lysozyme using a combination of dynamic light scattering, optical microscopy, and microfluidics. Clusters display Ostwald ripening growth kinetics but deviate from this trend after nucleation of the crystal phase. This behavior arises from the metastable relationship between clusters and the ordered solid and is explained numerically using a population balance model. DOI: 10.1103/PhysRevLett.104.178102 PACS numbers: 87.15.Zg, 64.75.Gh, 81.10.Àh The formation of an ordered solid phase from aqueous a model protein for crystallization studies [11]. We built a solution is of particular importance in structural biology, microfluidic dynamic light scattering (DLS) apparatus in where protein crystals of high purity are necessary for order to characterize growth kinetics of these submicron x-ray diffraction studies. However, the complex interaction precipitate populations involved in the crystallization of potentials of biological macromolecules have challenged HEWL. DLS was used to measure hydrodynamic radii of the formulation of a predictive theory of protein crystal- populations of small precrystalline clusters while an inte- lization [1].
    [Show full text]
  • An Overview of Recent Advances in State-Of-The-Art Techniques in the Demulsification of Crude Oil Emulsions
    processes Review An Overview of Recent Advances in State-of-the-Art Techniques in the Demulsification of Crude Oil Emulsions M. A. Saad 1,*, Mohammed Kamil 2, N. H. Abdurahman 1, Rosli Mohd Yunus 1 and Omar I. Awad 3 1 Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang, Kuantan 26300, Malaysia 2 Department of Mechanical and Nuclear Engineering, University of Sharjah, Sharjah 27272, UAE 3 State Key Laboratory of Automotive Safety and Energy of Tsinghua University, Beijing 100084, China * Correspondence: [email protected] or [email protected]; Tel.: +60-11-57608684 Received: 14 June 2019; Accepted: 18 July 2019; Published: 21 July 2019 Abstract: The processing of crude oil often requires the extraction of a large amount of water. Frequently, crude oil is mixed with water to form water-in-crude oil emulsions as the result of factors such as high shear at the production wellhead and surface-active substances that are naturally present in crude oil. These emulsions are undesirable and require demulsification to remove the dispersed water and associated inorganic salts in order to meet production and transportation specifications. Additionally, the demulsification of these crude oil emulsions mitigates corrosion and catalyst poisoning and invariably maximizes the overall profitability of crude oil production. Recently, there has been growing research interest in developing workable solutions to the difficulties associated with transporting and refining crude oil emulsions and the restrictions on produced water discharge. Therefore, this paper reviews the recent research efforts on state-of-the-art demulsification techniques. First, an overview of crude oil emulsion types, formation, and stability is presented.
    [Show full text]
  • Original Paper Flavor Retention in Progressive Freeze
    _ Food Science and Technology Research, 20 (3), 547 554, 2014 Copyright © 2014, Japanese Society for Food Science and Technology doi: 10.3136/fstr.20.547 http://www.jsfst.or.jp Original paper Flavor Retention in Progressive Freeze-Concentration of Coffee Extract and Pear (La France) Juice Flavor Condensate * Mihiri GUNATHILAKE, Kiyomi SHIMMURA, Michiko DOZEN and Osato MIYAWAKI Department of Food Science, Ishikawa Prefectural University, 1-308 Suematsu, Nonoichi, Ishikawa 921-8836, Japan Received November 28, 2013 ; Accepted February 7, 2014 Concentration of coffee extract and pear (La France) juice flavor condensate was carried out by progressive freeze-concentration (PFC) and the change in flavor profiles before and after concentration was analyzed. The results were compared with those by reverse osmosis (RO) and vacuum evaporation at 50℃ (Evp). From GC/ MS analysis, nine major flavor components, all heterocyclic, were detected for coffee flavors while twelve flavor components, mostly alcohols and esters, were detected for pear flavors. In Evp, almost all flavors were lost from the concentrate. In RO, some components, especially esters and alcohols, selectively permeated through the membrane so that the flavor distribution balance was changed for the reconstituted product after concentration. In PFC, the flavor distribution balance was almost unchanged for the reconstituted product after concentration although a loss was observed to some extent because of the incorporation of solutes into the ice phase. This incorporation of solutes into the ice phase was proved to be nonselective because the flavor balance in the ice phase was also unchanged from the original. This nonselective separation mechanism between the ice and the liquid phase seemed to explain the good retention of the flavor balance in PFC.
    [Show full text]
  • Chromatin Mechanics Dictates Subdiffusion and Coarsening Dynamics of Embedded Condensates Daniel S.W
    bioRxiv preprint doi: https://doi.org/10.1101/2020.06.03.128561; this version posted June 4, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Chromatin Mechanics Dictates Subdiffusion and Coarsening Dynamics of Embedded Condensates Daniel S.W. Lee1,2,3, Ned S. Wingreen1,3, Clifford P. Brangwynne1,2,4* 1Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544, USA 2Department of Chemical and Biological Engineering, Princeton University 3Department of Molecular Biology, Princeton University 4 The Howard Hughes Medical Institute *Corresponding author, [email protected] Abstract DNA is organized into chromatin, a complex polymeric material which stores information and controls gene expression. An emerging mechanism for biological organization, particularly within the crowded nucleus, is biomolecular phase separation into condensed droplets of protein and nucleic acids. However, the way in which chromatin impacts the dynamics of phase separation and condensate formation is poorly understood. Here, we utilize a powerful optogenetic strategy to examine the interplay of droplet coarsening with the surrounding viscoelastic chromatin network. We demonstrate that droplet growth dynamics are directly inhibited by the chromatin-dense environment, which gives rise to an anomalously slow coarsening exponent, 훽~0.12, contrasting with the classical prediction of 훽~ 1⁄3. Using scaling arguments and simulations, we show how this arrested growth can arise due to subdiffusion of individual condensates, predicting 훽~훼/3 , where 훼 is the diffusion exponent.
    [Show full text]
  • Mixing Oil-Based Microencapsulation of Garlic Essential Oil: Impact of Incorporating Three Commercial Vegetable Oils on the Stability of Emulsions
    foods Article Mixing Oil-Based Microencapsulation of Garlic Essential Oil: Impact of Incorporating Three Commercial Vegetable Oils on the Stability of Emulsions Yunjiao Zhao 1, Rui Liu 1,* , Cuiping Qi 1, Wen Li 1, Mohamed Rifky 1, Min Zhang 2,*, Ping Xiao 3, Tao Wu 1 and Wenjie Sui 1 1 State Key Laboratory of Food Nutrition and Safety, Tianjin University of Science & Technology, Tianjin 300457, China; [email protected] (Y.Z.); [email protected] (C.Q.); [email protected] (W.L.); [email protected] (M.R.); [email protected] (T.W.); [email protected] (W.S.) 2 College of Food Science and Bioengineering, Tianjin Agricultural University, Tianjin 300384, China 3 Tianjin Chunfa Bio-Technology Group Co., Ltd., Tianjin 300300, China; [email protected] * Correspondence: [email protected] (R.L.); [email protected] (M.Z.) Abstract: The active components in garlic essential oil are easily degradable, which limits its ap- plication in the food industry. Vegetable oils (VOs) were used to improve the stability of garlic essential oil (GEO) emulsion. The volatile compounds of GEO and its mixtures with vegetable oils (VOs), including corn oil (CO), soybean oil (SO), and olive oil (OO) indicated that GEO-VO mixtures had a higher percentage of Diallyl disulfide and Diallyl trisulfide than pure GEO. Adding an appropriate amount of VOs promoted the GEO emulsion (whey protein concentrate and inulin as Citation: Zhao, Y.; Liu, R.; Qi, C.; Li, the wall materials) stability in order of CO > SO > OO. Evaluation of the encapsulation efficiency, W.; Rifky, M.; Zhang, M.; Xiao, P.; Wu, controlled release, and antimicrobial activity of GEO-VO microcapsules showed that the GEO was T.; Sui, W.
    [Show full text]
  • Evaporation) Kinetics of Fine Aerosol Particles (Droplets
    Experimental and Theoretical Characterization on the Sublimation (Evaporation) Kinetics of Fine Aerosol Particles (Droplets) Vom Fachbereich Maschinenbau und Verfahrenstechnik der Technischen Universitat¨ Kaiserslautern zur Erlangung des akademischen Grades Doktor-Ingenieur (Dr.-Ing.) genehmigte Dissertation von Ms. Sc. Haomin Ding aus Beijing/China Kaiserslautern 2008 D386 Dekan: Prof. Dr.-Ing. S. Ripperger Vorsitzender der Promotionskommission: Prof. Dr. rer. nat. R. Ulber Berichterstatter: Prof. Dr.-Ing. S. Ripperger Prof. Dr.-Ing. B. Sachweh Prof. Dr. J-F. Chen Tag der mundlichen¨ Prufung:¨ 18. Dezember 2008 Vorwort Die vorliegende Arbeit wurde in der Zeit von Juli 2005 bis Dezember 2008 an dem Lehrstuhl fur¨ mechanische Verfahrenstechnik der Technischen Universitat¨ Kaiserslautern durchgefuhrt.¨ Fur¨ das entgegengebrachte Vertrauen mochte¨ ich besonders Herrn Prof. Siegfried Ripperger danken, der mir die Moglichkeit¨ gegeben hat meine Doktorarbeit an seinem Lehrstuhl durchzufuhren.¨ Sein stetiges Interesse am Fortgang der Arbeit sowie die Bereitstellung des Arbeitsplatzes und des notigen¨ Freiraums fur¨ eigenstandiges¨ Forschen waren wichtige Bausteine zum Erfolg der Arbeit. Ebenso gilt mein herzlicher Dank Herrn Professor Bernd Sachweh, der mich durch seine konstruktiven Diskussionen und sein Vertrauen unterstutzt¨ hat. Herrn Professor JianFeng Chen mochte¨ ich fur¨ seine ideelle Unterstutzung¨ sowie fur¨ die Ubernahme¨ des Koreferates danken. Fur¨ die finazielle und materialle sowie die wissenschaftliche Forderung¨ der Arbeit be- danke ich mich bei der BASF SE, die durch die Projektkooperation mit der TU Kaiser- slautern meine Promotion ermoglicht¨ hat. Mein Dank gilt auch der Palas GmbH fur¨ die fachlichen Diskussionen und materialle Unterstutzung.¨ Mein Dank gilt auch allen Kollegen des Lehrstuhls fur¨ die schone¨ gemeinsame Zeit, die ich mit ihnen am Lehrstuhl verbringen durfte.
    [Show full text]
  • Probing the Mechanism of Aqueous Two-Phase System Formation for R-Elastin On-Chip Yanjie Zhang, Hanbin Mao, and Paul S
    Published on Web 11/18/2003 Probing the Mechanism of Aqueous Two-Phase System Formation for r-Elastin On-Chip Yanjie Zhang, Hanbin Mao, and Paul S. Cremer* Contribution from the Department of Chemistry, Texas A&M UniVersity, College Station, Texas 77843 Received August 11, 2003; E-mail: [email protected] Abstract: The kinetics of formation of the aqueous two-phase system (ATPS) for R-elastin was studied by dark field microscopy in an on-chip linear temperature gradient. Scattering intensities of protein solutions were recorded as a function of temperature and time, simultaneously at several concentrations. It was found that the formation rate of the ATPS could be fit as a first-order process and that the apparent rate constant increased with protein concentration. The activation energy for the process was 9.5 ( 0.5 kcal/ mol, and this result was consistent with a coalescence mechanism. Experiments were also conducted with varying concentrations of sodium dodecyl sulfate, which shut off the coalescence mechanism forcing ATPS formation to proceed through Ostwald ripening. When this was done, the activation energy increased to 33 ( 2 kcal/mol and the kinetics became consistent with a second-order process. Introduction is thermoresponsive and begins to fold and form aggregates Aqueous two-phase systems (ATPS) are formed when two above its lower critical solution temperature (LCST). The components in a water-based solution, which are mutually particles in this cloudy solution then precipitate to form a clear incompatible, separate into phases of different density under viscous phase in which almost all of the polymeric material the force of gravity.1-3 Examples of this phenomenon usually resides, while an upper less dense phase consists primarily of involve either two polymers (e.g., poly(ethylene glycol) and water (Figure 1).
    [Show full text]
  • Reversed Ostwald Ripening
    Vol.46, No.4, 1983 J. Soc. Photogr. Sci. Technol. Japan 研 究 Reversed Ostwald Ripening Tadao SUGIMOTO* Research Laboratories, Ashigara, Fuji Photo Film Co., Ltd. Minamiashigara, Kanagawa 250-01 (Received March 10; Accept for Publication June 20, 1983) Abstract It was theoretically deduced that smaller particles might grow at the expense of larger particles during aging in a closed dispersion under some specific conditions. This theoretical prediction was verified with some mixed emulsions composed of two kinds of monodisperse AgBr particles; e.g., the growth of small cubic AgBr particles at the expense of larger octahedral AgBr particles during aging at a low pBr, or the growth of small octahedral particles at the expense of larger cubic particles during aging at a high pBr. As a result, the size distribution became narrower. This phenomenon was named " Reversed Ostwald Ripening." The reversed Ostwald ripening was a relatively rapid process observed at the early stage of aging until the small particles reached the equilibrium form. Then, it switched to the normal Ostwald ripen- inc. durina which the large particles grew by the dissolution of the small particles. 1. Introduction 2. Theory In the previous papers (1-4), the surface As has been derived in Refs. 1 and 2, the chemical potentials of {100} and {111} faces surface chemical potentials of a {100} face of a tetradecahedral microcrstal were intro- and a {111} face of a tetradecahedral parti- duced to describe the concepts of the equi- cle are expressed as librium form and the steady form and the relationships between the two forms.
    [Show full text]
  • Emulsion Ripening Through Molecular Exchange at Droplet Contacts
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Open Archive Toulouse Archive Ouverte OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible This is an author’s version published in: http://oatao.univ-toulouse.fr/20343 Official URL: http://doi.org/10.1002/anie.201407858 To cite this version: Roger, Kevin and Olsson, Ulf and Schweins, Ralf and Cabane, Bernard Emulsion Ripening through Molecular Exchange at Droplet Contacts. (2015) Angewandte Chemie International Edition, 54 (5). 1452-1455. ISSN 1433-7851 Any correspondence concerning this service should be sent to the repository administrator: [email protected] DOI: 10.1002/anie.201407858 Emulsion Ripening through Molecular Exchange at Droplet Contacts Kevin Roger,* Ulf Olsson, Ralf Schweins, and Bernard Cabane Abstract: Two coarsening mechanisms of emulsions are well take place during collisions, through the exchange of oil established: droplet coalescence (fusion of two droplets) and molecules across the droplet–droplet interface.[2,3,5] Ostwald ripening (molecular exchange through the continuous If such a mechanism exists, it has serious consequences on phase). Here a third mechanism is identified, contact ripening, the various uses of emulsions, both for industrial and which operates through molecular exchange upon droplets academic purposes. Indeed, the existing formulation tools to collisions. A contrast manipulated small-angle neutron scatter- hinder coalescence, by using surfactant layers of high ing experiment was performed to isolate contact ripening from preferred curvature,[7,8] and Ostwald ripening, by trapping coalescence and Ostwald ripening.
    [Show full text]
  • Quantification of Ostwald Ripening in Emulsions Via Coarse-Grained
    Quantification of Ostwald Ripening in Emulsions via Coarse-Grained Simulations Abeer Khedr and Alberto Striolo* Chemical Engineering Department, University College London, United Kingdom ABSTRACT Ostwald ripening is a diffusional mass transfer process that occurs in polydisperse emulsions, often with the result of threatening the emulsion stability. In this work, we design a simulation protocol that is capable of quantifying the process of Ostwald ripening at the molecular level. To achieve experimentally relevant time scales, the Dissipative Particle Dynamics (DPD) simulation protocol is implemented. The simulation parameters are tuned to represent two benzene droplets dispersed in water. The coalescence between the two droplets is prevented via the introduction of membranes, which allow diffusion of benzene from one droplet to the other. The simulation results are quantified in terms of the changes of the droplets volume as a function of time. The results are in qualitative agreement with experiments. The agreement with the Lifshitz-Slyozov-Wagner theory becomes quantitative when the simulated solubility and diffusion coefficient of benzene in water are considered. The effect of two different surfactants was also investigated. In agreement with both experimental observations and theory, the addition of surfactants at moderate concentrations decreased the Ostwald ripening rate because of the reduction in the interfacial tension between benzene and water; as the surfactant film becomes dense, other phenomena are likely to further delay Ostwald ripening. In fact, the results suggest that the surfactant that yields higher density at the benzene-water interface delayed more effectively Ostwald ripening. The formation of micelles can also affect the ripening rate, in qualitative agreement with experiments, although our simulations are not conclusive on such effects.
    [Show full text]
  • Influence of the Production Process Conditions on the Specific Surface Area of Olivine Nano-Silicas
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by SocioEconomic Challenges Journal (Sumy State University) PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 1, 01PCN29(4pp) (2012) Influence of the Production Process Conditions on the Specific Surface Area of Olivine Nano-Silicas A. Lazaro1,*, J.W. Geus2, H.J.H. Brouwers1 1 Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2 Institute for Nanomaterials Science, University of Utrecht, Utrecht, The Netherlands (Received 19 June 2012; published online 24 August 2012) The production of nano-silica by the olivine route is a cheaper and greener method than the commer- cial methods (neutralization of sodium silicate solutions and the flame hydrolysis) because of the low cost of raw materials and the low energy requirements. The produced olivine nano-silica has a specific surface area between 100-400 m2/g and primary particles between 10 to 25 nm (agglomerated in clusters). The pro- cess conditions and the ripening process influence the properties of nano-silica in the following ways i) the cleaner the nano-silica is the higher the specific surface area is; ii) the higher the filtration pressure is the higher the surface area is (unless the pressure is so high that the voids of the material collapse reducing drastically the SSA); iii) the ripening process diminishes the specific surface of nano-silica by two thirds and could be even further reduced. Thus, modifying the process conditions and/or adding an Ostwald ripen- ing process, nano-silicas with different specific surface areas can be synthesized.
    [Show full text]