In this paper we present small-angle neutron scattering (SANS) studies on liquidlike ordered binary
colloidal suspensions. Using perfluorinated (σ
PFA = 162 nm) and polystyrene (σ
PS = 79 nm) particles, we
prepared samples made of the same colloids as in the preceding paper. All system parameters of the
mixtures were as before. Via neutron contrast variation we directly obtained all three partial intensities
I
PFA-PFA
(Q), I
PFA-PS
(Q), and I
PS
-
PS
(Q) and partial structure factors S
PFA-PFA
(Q), S
PFA-PS
(Q), and S
PS
-
PS
(Q).
The experimental results are compared with theoretical predictions for binary colloidal mixtures, based
on the pure repulsive part of the DLVO potential. Within the hypernetted chain (HNC) closure an accurate
agreement is achieved. The particle correlation in the mixtures is clarified by means of the partial distribution
functions g
ij
(r) and the one-component effective pair potentials
(r) and
(r). From this we
deduce for the examined suspensions a partial clustering or local demixing by attractive interaction
contributions of depletion origin.
In this and the following paper we present scattering studies on binary colloidal mixtures made of
charge-stabilized polystyrene (PS) and perfluorinated (PFA) particles with diameters σ = 79 and 162 nm,
respectively. Both colloidal species were mixed to well-defined compositions. The total concentration was
about 9 vol % fraction. By using ultra-small-angle X-ray scattering, we directly obtained the partial scattering
intensities of only the PFA particles in liquidlike ordered suspensions. Furthermore, after dividing intensities
by the PFA particle form factor P
PFA
(Q), we got the partial structure factor S
PFA-PFA
(Q) without any
additional treatment. The experimental results are compared with theoretical predictions obtained from
the pure repulsive DLVO potentials and the hypernetted chain (HNC) integral equation, as applied to
charged colloidal mixtures. It is shown that all measured intensities and extracted structure factors are
in good agreement with the theoretical results.
Neutron diffraction from charge stabilized shear ordered colloidal dispersions at rest and under sheared conditions are presented. A newly designed shear cell is used to generate a linear shear profile. Hexagonal scattering patterns were observed both at rest and under sheared conditions. The stacking probability A is determined by measuring the intensity dependence of the Bragg spots as a function of the angle between the incoming neutron beam and the sample cell. The shear experiments are discussed in terms of a continuous distortion [W. Loose and B. J. Ackerson, J. Chem. Phys. 101, 7211 (1994)] at small shear rates, and shear melting at higher shear rates.
Recently, it has been pointed out that the structure of shear ordered colloidal dispersions can adequately be accounted for by the intensity distribution I(l) along Bragg rods [Phys. Rev. Lett. 75, 763 (1995)]. Information concerning packing of the shear induced layers and on their stacking order is contained in I(l). In this paper I(l) is determined by measuring the small angle neutron scattering distribution as a function of the sample orientation. For the investigated charge stabilized system with particle diameter σ=143 nm and a distance of nearest neighbors in the layers a=237 nm, a structure close to random close-packed hexagonal layers is found. As compared with close-packed systems the distance between the layers c is elongated so that c≊a. Further, it is shown that the application of shear leads to a more uniform distribution of I(l) along the rods, which demonstrates that the loss of correlation between the hexagonal layers under sheared conditions can also be determined by small angle neutron scattering.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.