The gap between crystalline and osmotic swelling of Na-montmorillonite: A Monte Carlo study

Abstract

Although the swelling of clay during moistening is a broadly experienced occurrence, the mechanisms driving it and especially the reason for the existence of a peculiar gap between crystalline and osmotic swelling of Na-montmorillonite are not yet fully understood. We obtained a deeper insight by means of Monte Carlo simulations of Na-montmorillonite swelling, which yield the swelling curve, interaction energies between and characteristic positions of structural atoms and water molecules. We find that a chainlike structure consisting of Na cations, water molecules, and oxygens of substituted tetrahedrons of neighboring mineral layers is formed in the interlayer space of Na-montmorillonite at a layer spacing of approximately 19 A, where experimental investigations show termination of crystalline swelling. Such a persistent structure may lock the interlayer space, until excess water is able to break this chain by osmotic forces. We suggest that its formation is the reason for the existence of a gap in layer spacings between approximately 19 and approximately 40 A, which have been named "forbidden" layer spacings in experimental studies.

Mechanisms of water adsorption into partially saturated fractured shales: An experimental study

“…Swelling occurs if rock is being hydrated and shrinkage if being dehydrated [16]. Surface hydration results from the adsorption of molecular layers of water on the basal crystal surfaces and interlayer spacing of 10-22 Å [16][17][18][19]. This process is driven primarily by the energy associated with the hydration of exchangeable cations and attraction associated with solid-liquid interactions (hydrogen bonding, charged surface-dipole attraction, or a combination of both) occurring in the immediate vicinity of the clay particle surfaces [17,20].…”

Swelling pressure development and inter-aggregate porosity evolution upon hydration of a compacted swelling clay

“…The driving force for osmotic swelling is the repulsion between the electrical diffuse double-layers that form on platelet surfaces (Chapman, 1913;Gouy, 1917;Gouy, 1910;Stern, 1924). For smectites exchanged with monovalent cations, osmotic swelling manifests itself by clay platelet separation distances larger than 40 Å and that can progress continuously towards infinity for very dilute suspensions (Meleshyn and Bunnenberg, 2005;Michot et al, 2004;Norrish, 1954). For divalent smectites (Ca-or Mgmontmorillonite), osmotic swelling seems to be prohibited in the interlayer spaces due to strong ion-ion correlation forces that reduce double-layer repulsion (Kjellander et al, 1988;Wang et al, 2011).…”

Propriedades físicas de filmes à base de biopolímeros reforçados com laponita

“…A2.4 the d(001) values from X-ray diffraction measurements, are plotted together with the predicted values (d(001)) for Na-Ht by Morrow et al (2013).Experimental work on Na-Ht determined the minimum hydration of the clay in very dry atmospheres (P2O5) close to r ≈ 0.6, while in the present research on Lap RD, the lowest hydration is close to r ≈ 2.2. However, the measured interlayer space of Lap RD agrees very well with the molecular dynamics simulations of the first hydration plateau of Na-Ht which starts to form at r ≈ 2(Meleshyn & Bunnenberg, 2005), the distance d(001) remaining constant d(001) = 11.8 Å until r ≈ 5. Because Lap RD hydration is so favorable r ≈ 13 is already reached with RH = 71% with the interlayer d(001) = 16.1 Å, while with RH = 94%, d(001) = 20 Å.…”

“…It has also been reported in pioneer experiments by Norrish (1954) the existence of a gap between crystalline and osmotic swelling of Na-Mt. Recent Monte Carlo simulations of Na-Mt swelling by Meleshyn & Bunnenberg (2005) found a chainlike structure consisting of Na cations, water molecules, and oxygen formed in Na-Mt at a layer space of d ∼ 19 Å, where experimental investigations showed "termination" of crystalline swelling. The authors suppose that such a persistent structure may "lock" the interlayer space, until excess water is able to break this chain by osmotic forces.…”