Sodium alginate-grafted submicrometer particles display enhanced reversible aggregation/disaggregation properties

Abstract

In this article, we demonstrate that submicrometer particles with surface-grafted sodium alginate (SA) display enhanced and reversible aggregation/disaggregation properties in aqueous solution. 300 nm silica particles were first functionalized with an aminosilane coupling agent, followed by the grafting of pH-sensitive SA, as confirmed by zeta potential, XPS and FTIR analyses. The SA-modified particles show enhanced aggregation properties at acidic pH compared to unmodified silica, with a 10 times increase in average aggregate diameter. The process is reversible, as the aggregates can be broken and dispersed again when the pH is increased back to 7.0. As a result, the sedimentation rate of SA-modified particles at pH 3.0 is both significantly faster and complete compared to the unmodified particles. This enhanced aggregation is most likely due to the formation of intermolecular hydrogen bonds between neighboring SA-modified particles. This work illustrates how surface-grafted macromolecules of natural origins can be used to tune interparticle interactions, in order to improve separation processes.

Tuning particle–particle interactions to control Pickering emulsions constituents separation

“…As mentioned previously, all emulsions prepared with SP-SA particles display a thicker or more viscous texture as compared to emulsions prepared with SP particles (Figure S3e-f). In agreement with previous findings 30 , particles modified with SA could experience stronger attractive interparticle interactions due to hydrogen bond formation -especially at pH 3.0, below the pKa of SA -, which might explain the more viscous appearance. Optical microscopy was employed to calculate the average droplet size as a function of ϕo and pH.…”

“…Both  and Ɵo/w confirmed surface grafting of APTMS and TMPS silanes onto bare silica particles, followed by the covalent reaction of SA with APTMS, yielding pH-sensitive sodium alginate grafted sub-m particles. 30 XPS and FTIR characterization of the particles before and after surface modification was completed previously. 30 These experiments confirmed the sequential grafting of the silane coupling agent (APTMS) and sodium alginate onto SP particles.…”

“…30 XPS and FTIR characterization of the particles before and after surface modification was completed previously. 30 These experiments confirmed the sequential grafting of the silane coupling agent (APTMS) and sodium alginate onto SP particles. The presence of grafted APTMS was confirmed by two different components related to N-H bonds observable in the spectra (extracted from the N1s peak in high resolution XPS) and one component linked to C-N bonds.…”

“…The enhanced soft gel properties (soft solid in the previous section), along with the droplet-droplet and particle-particle attractive interactions in emulsions prepared with SP-SA particles, 30 led us to hypothesize that the separation of constituents could be realized by filtration -i.e. separating the continuous water phase from the oil droplets.…”

“…This behavior in aqueous solution is due to the reversible hydrogen bond formed between neighboring particles -these "sticky" particles form significantly larger flocs as compared to unmodified particles, resulting in easier and faster sedimentation. 30 Chen et al have also synthesized pHresponsive SA grafted silica nanoparticles in applications related to drug delivery, exploiting the formation of a threedimensional network of grafted SA chains to create highstability systems. 31 In the present work, we hypothesize that these "sticky" particles could not only enhance interparticle interactions in solution, but also droplet-droplet interactions when adsorbed at the oil/water interface in Pickering emulsions.…”