Journal of Colloid and Interface Science 294 (2006) 234–239 www.elsevier.com/locate/jcis Effect of various factors influencing the delamination behavior of surfactant intercalated layered double hydroxides B.R. Venugopal a , C. Shivakumara b , Michael Rajamathi a,∗ a Department of Chemistry, St. Joseph’s College, Lalbagh Road, Bangalore 560 027, India b Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India Received 22 March 2005; accepted 29 June 2005 Available online 9 August 2005 Abstract The delamination–restacking behavior of a number of layered double hydroxides (LDHs) differing in [M II ]/[M III ] ratio, constituent metal ions and intercalated surfactant anions in different organic solvents has been studied. Colloidal dispersion due to delamination and the stability of the colloid obtained have been found to be not affected much by the nature of the constituent metal ions but increase with increase in the size of the surfactant anion. LDHs with low [M II ]/[M III ] ratio delaminate better than the ones with high [M II ]/[M III ] ratio. Delamination is best in alcohols such as 1-butanol, 1-hexanol, 1-octanol and 1-decanol, while a little delamination occurs in nonpolar solvents such as hexane. In all the cases, the original layered solid could be obtained through restacking of layers from the colloidal dispersion.  2005 Elsevier Inc. All rights reserved. Keywords: Layered double hydroxides; Colloids; Delamination; Restacking 1. Introduction Layered double hydroxides (LDHs), also known as hydrotalcite-like compounds (HTLCs) or anionic clays, are a class of natural and synthetic lamellar compounds hav- ing the general formula M II 1−x M III x (OH) 2 (A n− ) x/n ·mH 2 O, where M II = Mg, Co, Ni, Cu, Zn, Ca; M III = Al, Fe, Cr, Ga; A n− is anion such as CO 2− 3 , NO − 3 , SO 2− 4 , etc., and x = 0.25–0.33 [1,2]. These solids derive their struc- ture from brucite-like divalent metal hydroxides, M(OH) 2 . In brucite-like M(OH) 2, OH − ions are hexagonally close packed and the M 2+ ions occupy alternate layers of octa- hedral sites [3]. Thus, the structure can be described as a stacking of charge neutral M(OH) 2 layers. In LDHs, a part, x , of the M 2+ ions are isomorphously substituted by M 3+ ions leading to positively charged layers having the compo- sition [M II 1−x M III x (OH) 2 ] x+ . To compensate for the positive charges on the layers anions, A n− , are intercalated in the in- * Corresponding author. Fax: +91 80 22245831. E-mail address: mikerajamathi@rediffmail.com (M. Rajamathi). terlayer region along with water. Thus these solids have a structure complementary to that of smectite clays, which are made of negatively charged layers and intercalated cations. LDHs exhibit anion exchange behavior and hence find appli- cations in varied fields [4–6]. Simple inorganic and organic anions, anionic complexes and biomolecules have been in- tercalated in LDHs through anion exchange [6–8]. Delamination of layered solids in a suitable solvent lead- ing to monolayer colloidal dispersion is an important step in the preparation of large molecule intercalated layered solids and layered nanocomposites [9]. Cationic clays, due to low layer charge densities, delaminate readily in polar solvents. These solids when dispersed in water swell spontaneously and delaminate to give colloidal dispersions of monolay- ers [10]. LDHs do not swell in water due to high layer charge and hence aqueous colloidal dispersions of LDH layers are not readily formed. To overcome this shortcoming LDHs have been delaminated in organic media. In one approach, the LDH is intercalated with a large organic surfactant anion such as dodecyl sulfate ion, C 12 H 25 OSO − 3 , and the organo- inorganic hybrid obtained is refluxed in alcohols such as 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.06.086