An x-ray photoelectron spectroscopic study of an alumina-glucose adsorption system

Nakatani, Jiro; Ozawa, Sentaro; Ogino, Yoshisada

doi:10.1021/j100345a074

Cited by 7 publications

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“…Effects of shear flow are especially pronounced for systems near the gas-liquid critical point, due to the long-ranged character of interactions and slow diffusive motion. Scattering experiments under shear have been performed near the critical point for binary fluids [1,2], polymer blends [3][4][5][6], polymer solutions [7][8][9], and colloids [10]. Notable theoretical approaches to describe shear effects on microstructure are due to Onuki et al [11,12], Schwarzl and Hess [13], Ronis [14], and Wagner and Russell [15].…”

Section: Relaxation Of Critical Fluctuations After Cessation Of Simplmentioning

confidence: 99%

Relaxation of Critical Fluctuations after Cessation of Simple Shear Flow

1998

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Scattering experiments under shear of a near-critical system show a highly anisotropic static structure factor. We present small angle light scattering experiments on the relaxation of this anisotropic structure factor of a near-critical colloidal system after cessation of a simple shear flow. The structure factor is found to develop a scattering ring, which shifts to smaller wave vectors in time and increases in intensity. A theoretical explanation of this phenomenon is proposed. [S0031-9007(98)05367-8] PACS numbers: 61.20.Lc, 64.60.Ht, 82.20.Mj The deformation of the structure factor under shear has been of considerable interest in the last two decades. Effects of shear flow are especially pronounced for systems near the gas-liquid critical point, due to the long-ranged character of interactions and slow diffusive motion. Scattering experiments under shear have been performed near the critical point for binary fluids [1,2], polymer blends [3-6], polymer solutions [7-9], and colloids [10]. Notable theoretical approaches to describe shear effects on microstructure are due to Onuki et al. [11,12], Schwarzl and Hess [13], Ronis [14], and Wagner and Russell [15]. Only a few experimental results are available on the relaxation of long range critical microstructure. Beysens et al.describe a scattering experiment on a binary fluid at a single angle and observed pure exponential relaxation [2]. Wu et al., Dixon et al., and van Egmond et al. found that in entangled polymer systems shear flow enhances structure, leading to an increase of the turbidity [7-9]. Relaxation studies of these enhanced structures are reported.The latter kind of shear flow effects are absent in simple fluids near the critical point: for binary fluids and spherical colloids the turbidity is found to sharply decrease on applying a shear flow [2,16]. This sharp decrease in turbidity is due to the strong reduction of microstructure, contrary to the polymer systems in Refs. [7][8][9] where entanglement seems to enhance microstructural order.In this Letter we report on the first observation of an unusual equilibration scenario of a near-critical colloidal system after cessation of a simple shear flow: an optimum relaxation rate at some intermediate wave vector is found, giving rise to a scattering ring. Light scattering experiments are described, and a theoretical explanation of this new relaxation phenomenon is presented.Experiments are performed on a colloid polymer mixture. Without polymer the colloidal particles behave as hard spheres. The addition of nonadsorbing polymer induces an effective attraction between the colloidal particles due to a depletion mechanism [17,18]. The magnitude and range of the attractive forces can be tuned by the concentration and size of the polymer. Different size ratios lead to different kinds of phase behavior [19,20]. The control variable in these systems is not the temperature but rather the concentrations of polymer and colloid. Therefore, measurements are performed along so-called dilution lines, where the conce...

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