Laponite suspension

Mourchid, A., Delville, A., Lambard, J., Lecolier, E. and Levitz, P. (1995) Phase Diagram of Colloidal Dispersions of Anisotropic Charged Particles Equilibrium Properties, Structure, and Rheology of Laponite Suspensions. Langmuir 11, 1942-1950... 

Fig. 9a,b. Microscopic observations in polarized light of the textures of the aqueous clay suspensions a nematic threaded texture of a bentonite suspension (concentration 0.044 g/cm magnification 50x) b detail of a 1/2 disclination hne (arrow) in a laponite suspension (concentration 0.034 g/cm magnification lOOx) (Reprinted from [50], copyright (1996) from the American Chemical Society)... 

Mourchid A, Delville A, Lambard J, L 233 colier E and Levitz P 1995 Phase diagram of colloidal dispersions of anisotropic charged particles equilibrium properties, structure, and rheology of Laponite suspensions Langmuir AA 1942-50... 

Figure 36 Non-linear oscillatory behaviour of a Laponite suspension at IHz compared with a similar dispersion of Carbopol.

The major class of plate-like colloids is tliat of clay suspensions [21]. Many of tliese swell in water to give a stack of parallel, tliin sheets, stabilized by electrical charges. Natural clays tend to be quite polydisperse. The syntlietic clay laponite is comparatively well defined, consisting of discs of about 1 nm in tliickness and 25 nm in diameter. It has been used in a number of studies (e.g. [22]). 

Chemical/Physical. Endosulfan detected in Little Miami River, OH was readily hydrolyzed and tentatively identified as endosulfan diol (Eichelberger and Lichtenberg, 1971). Undergoes slow hydrolysis forming the endosulfan diol and sulfur dioxide (Worthing and Hance, 1991). The hydrolysis half-lives at pH values (temperature) of 3.32 (87.0 °C), 6.89 (68.0 °C), and 8.69 (38.0 °C) were calculated to be 2.7, 0.07, and 0.04 d, respectively (Ellington et al., 1988). Greve and Wit (1971) reported hydrolysis half-lives of P-endosulfan at 20 °C and pH values of 7 and 5.5 were 37 and 187 d, respectively. In a 1 pM sodium bicarbonate buffer solution at pH 8.15 and 28 °C, suspensions of sea sand, titanium dioxide, a-ferric oxide, a-FeOOH, laponite, and silicon dioxide catalyzed the hydrolysis of a-endosulfan to endosulfan diol. The uncatalyzed hydrolysis rate constant and half-life was 4.01 x lO Vsec and 0.20 d, respectively (Walse et al., 2002). 

Ca2 - and K+-hectorite, barasym at pH = 9 and Ca2 -laponite. For these clays the fluorescence intensity decreases with loading, following Perrin s law. Effective surface areas in aqueous suspension are estimated for the first time with Na+-hectorite as a reference. The second category is composed of Na+- and K+-laponite and barasym at pH= 7 A minimum in the... 

Spectroscopy. The important parameters, which determine the characteristic evolution of the fluorescence intensities with loading are (1) the particle size of the clays (hectorite vs. laponite) (2) the exchangeable cation (Na+, Ca2+, K+ vs. Cs+) and (3) for BS the pH. The latter is due to the extensive protonation of proflavine on the surface even in neutral suspension (Figure 3 and reference 5). 

In this way fluorescence spectroscopy of adsorbed dyes is a useful tool to characterize clays in aqueous suspension. From figures 5-8 it is noted that (1) laponites behave differently from hectorites, except Ca2+-L (2) PFH+ is the dominant species on Cs-H and Cs-L, because the fluorescence intensity is almost independent of the loading and thus no quenching due to dimers occurs (3) the difference between neutral BS suspensions and BS suspensions at pH = 9 is the presence of PFH22+ in the former case. 

A comparison with the absorption spectra of methylene blue on these clays gives interesting similarities, but also differences (4). Thus, protonation of methylene blue is found in neutral BS suspensions. The laponites are clearly distinguishable from hectorites, because of trimerization of methylene blue on laponites, which does not occur on hectorites. Finally, Cs -... 

In all that follows, the discussion will be purely classical. We now want to address the question whether the study of the (possibly anomalous) diffusion of a particle in an out-of-equilibrium medium is likely to provide information about the out-of-equilibrium properties of the latter. Generally speaking, the medium in which a diffusing particle evolves may be, or not, in a state of thermal equilibrium. For instance, when it is composed of an aging medium such as a glassy colloidal suspension of Laponite [8,12,55,56], the environment of a... 

The validity of the generalized Langevin equation (22) is restricted to a stationary medium. In other situations, for instance when the diffusing particle evolves in an aging medium such as a glassy colloidal suspension of Laponite [8,12,55,56], another equation of motion has to be used. 

Experimentally, the effective temperature of a colloidal glass can be determined by studying the anomalous drift and diffusion properties of an immersed probe particle. More precisely, one measures, at the same age of the medium, on the one hand, the particle mean-square displacement as a function of time, and, on the other hand, its frequency-dependent mobility. This program has recently been achieved for a micrometric bead immersed in a glassy colloidal suspension of Laponite. As a result, both Ax2(t) and p(co) are found to display power-law behaviors in the experimental range of measurements [12]. 

A. Knaebel, M. Bellour, J.-P. Munch, V. Viasnoff, F. Lequeux, and J. L. Harden, Aging behavior of Laponite clay particle suspensions, Europhys. Lett. 52, 73 (2000). 

The photo oxidation of several PAHs on aqueous clay suspensions (Ca montmorillonite, laponite, Na montmorillonite, kaolin and Kga-lb, a natural kaolinite from the Clay Mineral Society, USA) was reported [64], Using chrysene as a model compound, it was found that oxidation rates increased with respect to aqueous solution when Ca montmorillonite, laponite or Na... 

Fig. 12a,b. Phase diagram of clay suspensions vs clay and NaCl concentrations, (circles, F) Flocculated samples (squares, IL) isotropic liquid samples (lozenges, IG) isotropic gel samples (crosses, NG) nematic gel for a bentonite b laponite. (Reprinted from [4b], copyright (2000) from John Wiley and Sons)... 

Cryo-TEM images of a) a suspension of Laponite piateiets (the dark fiiaments are day partides seen edge-on) b,c) "hybrid iatexes synthesized by seeded emuision poiymerization of slyrene and butyi acryiate in the presence of raw Laponite (b) and 10 wt% of MPDES-functionaiized Laponite ciay piateiets (c). In b, the arrows indicate the presence of Laponite aggregates. 

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