title: Sedimentation stability and aging of aqueous dispersions of Laponite in the presence of cetyltrimethylammonium bromide.
abstract: This work discusses the sedimentation stability and aging of aqueous suspensions of Laponite in the presence of cetyltrimethylammonium bromide (CTAB). The concentration of Laponite was fixed at a constant level C(l)=2%wt, which corresponds to the threshold between equilibrium gel IG(1) and glass IG(2) states. The concentration of CTAB C(s) was within 0-0.3 %wt. In the presence of CTAB, the Laponite aqueous suspensions were unstable against sedimentation and separated into the upper and bottom layers (U and B layers, respectively). The dynamic light-scattering technique has revealed that addition of CTAB even at a rather small concentration, C(s)=0.0164 %wt (0.03 cation exchange capacity), induced noticeable changes in the aging dynamics of the U layer. It was explained by equilibration of CTAB molecules that were initially nonuniformly distributed between different Laponite particles. Accelerated stability analysis by means of analytical centrifugation with rotor speed ω=500-4000 rpm revealed three sedimentation regimes: continuous (I, C(s)<0.14 %wt), zonelike (II, 0.14<C(s)<0.2%wt), and gel-like (III, C(s)>0.2%wt). It was demonstrated that the B layer was "soft" in the zonelike regime. The increase of ω resulted in its supplementary compressing and collapse of "soft" sediment above certain critical centrifugal acceleration. The physical nature of the observed behavior, accounting for enhancement of hydrophobic interactions between Laponite particles, is discussed.
authors: Taras Shevchenko Kiev National University, Department of Physics, 2, av. Academician Glushkov, Kyiv 031127, Ukraine.
authors: V
authors: V
authors: Savenko
authors: Taras Shevchenko Kiev National University, Department of Physics, 2, av. Academician Glushkov, Kyiv 031127, Ukraine.
authors: L
authors: L
authors: Bulavin
authors: Institut Charles Sadron, UPR22-CNRS, Universite de Strasbourg, 23 rue du Loess, BP 84047-67034 Strasbourg Cedex 2, France.
authors: M
authors: M
authors: Rawiso
authors: Institute of Biocolloidal Chemistry named after F.D. Ovcharenko, NAS of Ukraine, 42, blvr. Vernadskogo, Kyiv 03142, Ukraine and Departement de Genie Chimique, Universite de Technologie de Compiegne, Centre de Recherche de Royallieu, B.P. 20529-60205 Compiegne Cedex, France.
authors: M
authors: M
authors: Loginov
authors: Departement de Genie Chimique, Universite de Technologie de Compiegne, Centre de Recherche de Royallieu, B.P. 20529-60205 Compiegne Cedex, France.
authors: E
authors: E
authors: Vorobiev
authors: Institute of Biocolloidal Chemistry named after F.D. Ovcharenko, NAS of Ukraine, 42, blvr. Vernadskogo, Kyiv 03142, Ukraine and Departement de Genie Chimique, Universite de Technologie de Compiegne, Centre de Recherche de Royallieu, B.P. 20529-60205 Compiegne Cedex, France.
authors: N I
authors: NI
authors: Lebovka