An ultra-small-angle neutron scattering study of the restructuring of sheared colloidal silica gels

Neutron scattering curves for a sheared colloidal silica gel were measured using a Bonse-Hart ultra-small-angle neutron scattering instrument. When th ey are combined with data taken from a conventional small-angle neutron sca ttering instrument, the accessible scattering vector range extends over app roximately four orders of magnitude: 3 x 10(-4) < q (nm(-1)) < 3. A peak in the scattering datais observed at q = 2.7 x 10(-3) nm(-1) corresponding to a correlation length of 2.3 mu m. The scattering curves show an approximat e power-law behaviour with an exponent of -2.9 over the range 4 x 10(-3) < q (nm(-1)) < 4 x 10(-2). These results are compared with our previously rep orted observation that an unsheared sample yields a correlation length of o nly similar to 20 nm with no observable power-law regime. The present data confirm that shear stresses induce a structural densification in gelling co lloidal silica systems.