Block-copolymer-induced long-range depletion interaction and clustering of silica nanoparticles in aqueous solution

Abstract

Small-angle neutron scattering (SANS) has been carried out to examine the block-copolymer-induced depletion interaction of charged silica nanoparticles in aqueous solution. The measurements have been performed on fixed concentrations (1 and 10 wt. %) of anionic Ludox silica nanoparticles having sizes of 8 and 16 nm in the presence of 0.1M NaCl and varying concentration of polyethylene oxide-polypropylene oxide-polyethylene oxide P85 [(EO)(26)(PO)(39)(EO)(26)] block copolymer. The presence of the block copolymer induces an attractive depletion interaction between charge-stabilized nanoparticles. The effective interaction of silica nanoparticles is modeled by a combination of two Yukawa potentials accounting for attractive depletion and repulsive electrostatic forces. The depletion interaction is found to be a long-range attraction whose magnitude and range increase with block-copolymer concentration. The depletion interaction is further enhanced by tuning the self-assembly of the block copolymer through the variation of temperature. The increase of the depletion interaction ultimately leads to clustering of nanoparticles and is confirmed by the presence of a Bragg peak in the SANS data. The positioning of the Bragg peak suggests simple-cubic-type packing of particles within the clusters. The scattering from the clusters in the low-Q region is governed by the Porod scattering, indicating that clusters are quite large (order of microns). The depletion interaction is also found to be strongly dependent on the size of the nanoparticles.

Small-angle neutron scattering study of differences in phase behavior of silica nanoparticles in the presence of lysozyme and bovine serum albumin proteins

“…We expect some interactional changes in the system responsible for scattering buildup at lower Q. Scattering data in are given in Table III. In this case, the attractive potential is found to be relatively long range [50]. The silica nanoparticle-BSA system becomes turbid at higher BSA concentrations (2-5 wt %) as shown in region III of the phase behavior.…”

“…3(c)]. Unlike the case of BSA, the lysozyme data show a strong scattering buildup in the low Q; such scattering is usually seen for aggregated particles [50,51]. These aggregates are believed to be responsible for the decrease in the transmission of the nanoparticle-lysozyme system in region II.…”

“…We believe nonadsorption of BSA leads to depletion induced aggregation of the nanoparticles. The aggregate size in such a case is known to depend on the depletant (BSA protein) concentration and increases with increases in concentration [50], which could give the difference in the light transmission as observed for 2 and 5 wt % of BSA in Fig. 2.…”

Structure and interaction in the polymer-dependent reentrant phase behavior of a charged nanoparticle solution

“…The buildup of scattering in the low Q region at low polymer concentrations [ Fig. 3(a)] arises because of attractive interaction induced in the system [34,48]. The corresponding S(Q) plots as calculated by dividing the data with those of nanoparticles without polymer are shown in Fig.…”

“…The fact that neutron scattering is different for hydrogenated and deuterated solvents means that their mixed solvent has been selectively used to contrast-match polymer for directly studying the interaction between nanoparticles [32]. The interaction between the nanoparticles has been modeled using a two-Yukawa potential accounting for electrostatic repulsion between charged nanoparticles along with a polymer-induced depletion interaction [33][34][35]. The choice of Yukawa potentials is useful because it establishes the range and the strength of the individual parts (repulsive and depletion) of the total potential without any predefined assumption.…”