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Title: Formation and Restacking of Disordered Smectite Osmotic Hydrates

Clay swelling, an important phenomenon in natural systems, can dramatically affect the properties of soils and sediments. Something of particular interest in low-salinity, saturated systems are osmotic hydrates, forms of smectite in which the layer separation greatly exceeds the thickness of a single smectite layer due to the intercalation of water. In situ X-ray diffraction (XRD) studies have shown a strong link between ionic strength and average interlayer spacing in osmotic hydrates but also indicate the presence of structural disorder that has not been fully described. In the present study the structural state of expanded smectite in sodium chloride solutions was investigated by combining very low electron dose, high-resolution cryogenic-transmission electron microscopy observations with XRD experiments. Wyoming smectite (SWy-2) was embedded in vitreous ice to evaluate clay structure in aqua. Lattice-fringe images showed that smectite equilibrated in aqueous, low-ionic-strength solutions, exists as individual smectite layers, osmotic hydrates composed of parallel layers, as well as disordered layer conformations. There was no evidence found here for edge-to-sheet attractions, but significant variability in interlayer spacing was observed. Whether this variation could be explained by a dependence of the magnitude of long-range cohesive (van der Waals) forces on the number of layers in amore » smectite particle was investigated here. Calculations of the Hamaker constant for layer-layer interactions showed that van der Waals forces may span at least five layers plus the intervening water and confirmed that forces vary with layer number. The drying of the disordered osmotic hydrates induced re-aggregation of the smectite to form particles that exhibited coherent scattering domains. Clay disaggregation and restacking may be considered as an example of oriented attachment, with the unusual distinction that it may be cycled repeatedly by changing solution conditions.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [4]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Life Sciences Division
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source
  4. Univ. of California, Berkeley, CA (United States). Earth and Planetary Sciences
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Clays and Clay Minerals
Additional Journal Information:
Journal Volume: 63; Journal Issue: 6; Journal ID: ISSN 0009-8604
Publisher:
The Clay Minerals Society - Ingenta
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; clay swelling; cryogenic transmission electron microscopy; montmorillonite; van der waals forces
OSTI Identifier:
1378670