We present a neutron-scattering study of depletion interactions in a mixture of a hard-sphere-like colloid and a nonadsorbing polymer. By matching the scattering length density of the solvent with that of the polymer, we measured the partial structure factor S c (Q) for the colloidal particles. It is found that the measured S c (Q) for different colloid and polymer concentrations can be well described by an effective interaction potential U(r) for the polymer-induced depletion attraction between the colloidal particles. The magnitude of the attraction is found to increase linearly with the polymer concentration, but it levels off at higher polymer concentrations. This reduction in the depletion attraction presumably arises from the polymer-polymer interactions. The experiment demonstrates the effectiveness of using a nonadsorbing polymer to control the magnitude as well as the range of the interaction between the colloidal particles.
We report a neutron scattering study of depletion interactions in a mixture of colloid and nonadsorbing polymer. It is found that the measured colloidal structure factor can be well described by an effective interaction potential for the polymer-induced depletion attraction between the colloidal particles. The amplitude of the attraction is found to increase linearly with the polymer concentration but it levels off at higher polymer concentrations. [S0031-9007(96)00388-2]
We report sedimentation measurements of small colloidal particles through a nonadsorbing polymer solution. The experiment reveals that the particles "feel" the single-chain viscosity rather than the solvent viscosity when their radius R c is smaller than the correlation length j of the polymer solution. The particles experience the macroscopic viscosity of the polymer solution when R c ¿ j. In the transition region, the particle's friction coefficient does not have the predicted scaling form. Instead, a new switch function is found to be of universal form independent of the polymer molecular weight.[S0031-9007(97)
Dynamic light scattering and sedimentation measurements are carried out to study the motion of probe particles in neutral and adsorbing polymer solutions. By varying the microscopic interaction between the colloidal particle and the polymer molecule, we observe three different behaviors to the Stokes−Einstein (SE) equation in the same colloid−polymer system. The measurements clearly delineate the sample conditions under which the three different behaviors are observed, respectively. It is shown that the three different behaviors can be explained consistently in terms of the microstructures formed in the colloid−polymer mixture. The experiment demonstrates the importance of restraining the particle−medium interaction in the measurement of the microrheological properties of complex fluids.
Small-angle neutron scattering is used to study the interaction between the colloidal particles when they are suspended in an end-functionalized polymer solution. By matching the scattering length density of the solvent with that of the polymer, we measured the partial structure factor S c(Q) of the colloidal particles. The measurements reveal that the polymer molecules in the colloidal suspension partition themselves between the bulk solution and the adsorbed state. The free polymer molecules in the solution induce a depletion attraction between the colloidal particles, but the magnitude of the attraction is suppressed considerably by the adsorbed polymer chains on the colloidal surfaces. It is found that the measured S c(Q) can be well described by an effective interaction potential, which includes both the depletion attraction and the repulsion due to the polymer adsorption. The experiment demonstrates the effectiveness of using a polymer to control the colloidal interaction.
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