Here - Institute for Building Materials - ETH ZÃ¼rich

More documents

Recommendations

Info

Effect of size polydispersity for nanoparticle adsorption on liquid interfacesKonrad Schwenke and Emanuela Del GadoMicrostructure and Rheology, Institute for Building Materials,ETH Zurich, CH-8093 Zurich, SwitzerlandNanoparticles at liquid-liquid interfaces have stirred great interest as potentialbuilding blocks for the self-assembly of functional materials in 2 dimensions. Recentadvances in the synthesis of core-shell nanoparticles with a hard core and a soft shellof grafted polymer chains offer a new material for self-assembling structures atinterfaces [1].We present numerical data investigating the adsorption of polydisperse soft shellparticles towards the liquid interface. The nanoparticles are modeled via a repulsivepotential which allows partial overlap of particles and represents a good compromisebetween numerical simplicity and the aim to model the experimental system. Themotion of particles at the interface is simulated via Molecular Dynamics whereas weuse a Grand Canonical Monte Carlo scheme to model the process of adsorption anddesorption [2].It is elucidated how the kinetics of the adsorption process depends upon the influx ofparticles and the adsorption energy. We comment on the qualitative differences inthe adsorption characteristics for mono- and polydisperse size distributions ofparticles.References[1] L. Isa, E. Amstad, K. Schwenke, E. Del Gado, P. Ilg, M. Kröger and E.Reimhult, Soft Matter, 2011, 7, 7663-7675.[2] D. Frenkel and B. Smit, Understanding Molecular Simulation, Academic press,200260
Lattice Boltzmann Simulations of the Permeability and Capillary Adsorption ofCement Model MicrostructuresM. Zalzale 1 , P.J. McDonald 21 EPF Lausanne, Lausanne, Switzerland. 2 University of Surrey, Guildford, GU2 7XH UK.INTRODUCTION: In this work we assess thelattice Boltzmann (LB) method for solvingproblems of fluid dynamics in the context of modelcement microstructures. LB has several potentialadvantages over other numerical methods. First, itremoves the requirement to reduce themicrostructure to a network of connected cylindersso there is no inadvertent modification of the porenetworkand porosity in calculations of, forinstance, permeability. Second, it allows us toextend the modelling to the adsorption anddesorption of water liquid and vapour as a twophasefluid. In the LB approach it is not necessaryto specifically track the liquid / vapour interfacemaking it computationally efficient.METHODS: In this work, we use the LB methodto calculate the permeability and capillarycondensation part of the water adsorption /desorption isotherm in microstructures determinedusing the model µIC 1 . In both cases we use aD3Q19 LB network. For the calculation ofpermeability we used a single fluid LBimplementation with a multi-relaxation-timecollision operator 2 , forced flow and application ofDarcy’s law. For adsorption / desorption we used afree energy two-phase free energy model withsingle-relaxation-time operator 3 , with the networksurface held at successive constant relativehumidities.RESULTS: For the pressure-induced single-phaseflow the model captures the expected trends forpermeability as a function of porosity and degreeof hydration. However, the computed permeability(e.g. 10 -19 m 2 for w/c=0.4 and 10.5% capillaryporosity) is larger than expected from experiments(10 -20 -10 -21 m 2 ). Decreasing the minimum particlesize of the microstructure and increasing themagnification (voxels per particle), we increase thepore-structure complexity and LB better recoversthe hydrodynamics. Consequently, thepermeability decreases and tends closer toexperimental values, although the computationalrequirements increase prohibitively. Moreimportantly, however, the current model addressesonly the capillary porosity and does not address thegel porosity. Also, the model currently allowsunphysical “diagonal leaks”.Fig. 1: Water streamlines of a pressure-inducedflow (left) and the capillary desorption anddesorption isotherm (right) in a µICmicrostructure with a resolution (minimumparticle/pore size) of 1 µm.In multi-phase simulations of the adsorption anddesorption isotherm, hysteresis loops are generatedindicating the occurrence of capillarycondensation. However, the lack of breadth to thecapillary pore size distribution, and in particular tothe pore throat distribution, leads to an isothermwith a dramatic step at around 90% RH. Theabsence of the C-S-H intrinsic microstructure leadsto the false conclusion that the porosity is emptyby circa 80% RH.DISCUSSION & CONCLUSIONS: We believethat the LB method holds much promise for thestudy of water transport in cementitious materials.However, improvements should be made in termsof (1) computing efficiency to be able to computethe flow in highly-resolved microstructures; (2) theinclusion of gel porosity within the microstructuralmodel and LB simulations.REFERENCES:1S. Bishnoi & K.L. Scrivener; 2008; Cem ConcRes; 39:266-274.2 D. D’Humieres et al., 2002; Philos. T. R. Soc. A.;360:437-4513 A.J. Wagner & C.M. Pooley; 2007; Phys. Rev. E.;76:045702ACKNOWLEDGEMENTS: The researchleading to these results has received funding fromthe European Union Seventh FrameworkProgramme under grant agreement 264448. PJMthanks Nanocem and the UK Engineering andPhysical Sciences Research Council for financialsupport under grant number EP/H033343/1.61
Page 6 and 7:
11:20 - 12:30 POSTER SESSION12:30 L
Page 9: Mesoscopic models for flow in amorp
Page 14 and 15: Topological Excitations in Liquids
Page 16 and 17: 1. Admixtures will be used more and
Page 19 and 20: Mesoscopic simulations of clay gels
Page 21 and 22: Diffusion in soft particle suspensi
Page 26 and 27: Challenges and Innovation in the Ce
Page 28: Jamming and void space in sphere pa
Page 31 and 32: Required Subjects for the Study of
Page 33 and 34: ORALCONTRIBUTIONSSOFTCEM 201233
Page 35 and 36: Atomistic Simulations and Experimen
Page 37 and 38: Activated drying of hydrophobic nan
Page 39 and 40: Controlling building materials micr
Page 41: NANO-STRUCTURE AND -MECHANICS OF CE
Page 44 and 45: Colloidal gels under shearN. Koumak
Page 46 and 47: Microstructure of cement pastes wit
Page 48 and 49: Dissolution kinetics and rate-contr
Page 50 and 51: Molecular-Dynamics and Monte-Carlo
Page 52 and 53: Consolidation of superplasticized p
Page 54 and 55: A ROBUST METHOD TO MEASURE FRICTION
Page 56 and 57: Potential use of time domain reflec
Page 58 and 59: A MESOSCOPIC MODEL FOR C-S-H HYDRAT
Page 63 and 64: List of Participants_______________
Page 65: Prannoy Suraneni -- ETH Zurich, Swi
show all

Here - Institute for Building Materials - ETH ZÃ¼rich

Create successful ePaper yourself

Delete template?

Save as template?