A Quantitative Multiscale Approach to Nanofluidics

Santtu T.T. Ollila

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Nanofluidics is a cross-disciplinary field of science that deals with the controlled transport of small amounts of fluid in confined geometries. Due to the confinement, interactions with the channel walls are a dominant factor in the physics of the system and the size of the solute being transported with respect to the channel dimensions is highly relevant for the observed behavior. Multiscale modeling of soft matter system has become a popular approach of addressing problems that involve disparate time and length scales. However, such models are seldom quantitatively accurate and may contain algorithmic (fitting) parameters whose values are not physically justified. Here, we develop a multiscale model that couples a fluctuating Lattice-Boltzmann solvent and molecular dynamics particles of finite size. We consider in detail how thermal fluctuations should be implemented in the solvent model. Most importantly, we entertain the question of how the coupling should be calibrated in order for the solute particles to have a well-defined hydrodynamic size. We do this by requiring the hybrid model to reproduce both several well-known hydrodynamic steady states, which are sensitive to the particle size but do not depend on fluctuations, and several consistency checks, which do. The dissipation of energy due to the coupling is examined as well. The model is applied to five different cases. First, porous particles oscillating in a quiescent fluid are examined and new analytical expressions for the hydrodynamic force on porous particles are derived in the case of two different internal mass distributions. We then study colloids bifurcating in a letter T-shaped microfluidic channel. Second, the model is examined in the context of polymers and nanofluidics in the limit where thermal fluctuations are important. We verify the computational model in bulk by reproducing both static and time-dependent results of polymer physics. The necessity of hydrodynamic boundary conditions for agreement with experiments is observed when a lone polymer is confined into a thin film. Last, polymers driven in a corrugated nanochute by a pressure differential are found to exhibit entropic trapping and length and topology-dependent mobilities.
Translated title of the contributionNanofluidistiikan kvantitatiivista moniskaalamallinnusta
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Ala-Nissilä, Tapio, Supervising Professor
  • Denniston, Colin, Supervising Professor, External person
  • Denniston, Colin, Thesis Advisor, External person
  • Ala-Nissilä, Tapio, Thesis Advisor
Publisher
Print ISBNs978-952-60-5198-7
Electronic ISBNs978-952-60-5199-4
Publication statusPublished - 2013
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • nanofluidics
  • microfluidics
  • Lattice Boltzmann
  • hydrodynamics
  • consistency

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