Static structure factor of a suspension charge-stabilized colloids:Study of the liquid-glass transition phase-diagram and micellar solution

• Main Authors: Wang, Jann-Long, 王建隆
• Other Authors: S.K. Lai
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/60054929575319429990

碩士 === 國立中央大學 === 物理學系 === 86 === Charge-stabilized colliodal dispersions are modeled by a mixture of spherical charged hard spheres which interact via Coulomb forces. The static partial structure factors S(q) of this so- called primitive model (PM) have been analytically solved by the mean spherical approximation. For point-like small ions and for weak electrostatic coupling, the PM is shown in the literature to be exactly the same as an effective one-component model (OCM). Accordingly, one may apply the S(q) of macroions in conjunction with an idealized mode-coupling theory to locate the liquid-glass transition loci of charged colloids within the PM. Numerically we find along the phase boundary for volume fraction less than or equal to 0.43 that the pair correlation functions become unphsical. This inherent drawback of the mean spherical approximation has been widely discussed and can be remedied by rescaling the corresponding macroion sizes. Within the context of PM, this, however, raises the question of the additive relation between macroions and small ions. In the absence of an unambiguous means of dealing with the latter problem within PM, we propose to calculate the S(q) using an effective OCM of Belloni in which the additive property is approximately taken into account. By appealing to the OCM, we then determine the phase-diagram of the liquid-glass transition for charge- stabilized colloids. The difference between the phase transition boundaries of the OCM and PM obtained by preserving additivity property indicates qualitatively the uncertainties in the loci of the phsae-diagram. The same OCM has been applied to study the S(q) of a micellar solution, the tetramethylammonium dodecylsulfate, which has recently been measured by small angle neutron scattering. Good agreement between theory and experiment lends great credence to the model. Further evidence of the usefulness of this OCM comes from its prediction of the charge of polystyrene spheres which agrees reasonably with the values proposed by other theoretical studies on the liquid- crystal phase-diagram based on the density functional theory.