Synchrotron X-ray Scattering and Monte Carlo Simulations of Structure and Forces in Silicate Nanoplatelet Dispersions

Mo Segad

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Clays are the world’s most widely used natural material, however, little is known regarding the microstructure as well as the forces involved in clay-water interactions, and their influence on the swelling properties. The utilization of clay platelets is nowadays a key in a number of biological and industrial applications e.g. nuclear waste management.
Bentonites from different natural sources and pure Na/Ca montmorillonite platelets have been studied experimentally and theoretically. Small angle X-ray scattering (SAXS), dynamic light scattering (DLS), nuclear magnetic resonance (NMR), X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM) and Cryogenic-TEM were applied to provide direct information about the structure of dry clays as well as clay platelets in equilibrium with a bulk solution of given ionic composition, temperature and pH. Monte Carlo (MC) simulations have been used to predict the osmotic pressure of montmorillonite dispersions. The swelling behavior is mainly regulated by counterion valency and surface charge density. Divalent counterions and high surface charge density lead to a limited swelling, while monovalent counterions favor a large swelling. This thesis has also investigated the aggregation of nanoplatelets in clay-water systems, in order to understand the effect of platelet size on the structure and swelling behavior. A new twist on aggregation phenomenon is that, really small platelets (~ 20 nm) do not form a tactoid, whereas larger platelets give rise to larger tactoids. The platelet size controls the aggregation and microstructure of silicate platelets into tactoids following an empirical relation as: N ≃ δ + α Deff, where N is the number of platelets per tactoid, Deff is the effective diameter of platelets, δ and α are constants.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Computational Chemistry
Supervisors/Advisors
  • Jönsson, Bo, Supervisor
  • Olsson, Ulf, Supervisor
Award date2014 May 22
Publisher
ISBN (Print)978-91-7422-353-8
DOIs
Publication statusPublished - 2014

Bibliographical note

Defence details

Date: 2014-05-22
Time: 10:30
Place: lecture hall C, Center for Chemistry and Chemical Engineering, Lund

External reviewer(s)

Name: Vroege, Gert Jan
Title: [unknown]
Affiliation: Debye Research Institute, Utrecht University, Utrecht, The Netherlands

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The information about affiliations in this record was updated in December 2015.
The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)

Subject classification (UKÄ)

  • Theoretical Chemistry

Free keywords

  • SAXS
  • MC simulations
  • Swelling
  • Tactoids
  • EXAFS
  • DLS
  • Cryo-TEM
  • Nanoplatelets
  • MX80
  • Na/Ca montmorillonite.

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