Phase-Selective Gelation of the Water Phase in an Oil–Water Mixture: An Approach Based on Oil-Activated Nanoparticle Assembly in Water

Abstract

Phase-selective gelation refers to the selective gelation of one phase in an immiscible mixture. Thus far, all such examples have involved a molecular gelator forming nanofibers in (and thus gelling) the oil phase in an oil/water mixture. Here, for the first time, we report the counterpart to the above phenomenon, i.e., selective gelation of the water phase in an oil/water mixture (while leaving the oil undisturbed). This has been a challenging problem because moieties that gel water tend to be either amphiphilic or oil-soluble; thus, if combined with an oil/ water mixture, they invariably form an emulsion. Our approach solves this problem by exploiting the tunable self-assembly of laponite (LAP) nanoparticles. Initially, LAP nanoparticles (25 nm disks) are dispersed in water, where they remain unaggregated due to the steric stabilization provided by a triblock copolymer (Pluronic P123) adsorbed on their surface. Thus, the dispersion is initially a low-viscosity sol. When an immiscible oil such as hexadecane is introduced above the sol, the mixture remains biphasic, and both phases remain unaffected. Next, an organic acid such as butanoic acid (BA) is added to the oil. The BA is oil-soluble but also has limited solubility in the water. Over about 30 min, some of the BA enters the water, whereupon it "activates" the self-assembly of LAP particles into a three-dimensional "house-of-cards" network. Ultimately, the water phase is converted into a homogeneous gel with a sufficient yield stress: the aqueous gel holds its weight in the inverted vial while the oil phase remains a thin liquid that can be poured out of the vial. On the whole, the concept advanced here is about activating nanoparticle assembly in water through an adjacent, immiscible phase. This concept could prove useful in conducting certain separations or reactions in the laboratory as well as in enhanced oil recovery.

Virtual Special Issue Honoring the Legacy of Dr. Bettye Washington Greene

“…Robertson and Minh report on novel gold nanoparticle-embedded peptoid nanosheets as a platform for plasmonic-based sensing applications. We also include in this section Yue et al reporting on the phase-selective gelation of water toward creating a tunable self-assembly of laponite (LAP) nanoparticles and Eze and Milam reporting on competitive displacement events of nucleic acids immobilized on microspheres. Finally, we include Wang et al as they describe a new approach for drug delivery across the blood–brain barrier to the central nervous system by designing nanoparticles that are conjugated with neural tract tracer proteins.…”

“…Dr. Phillips’ reflection provides a unique perspective on the lasting influence and legacy of Dr. Greene. Following this personal reflection, we present invited research articles submitted to this VSI to honor Dr. Greene and further recognize the importance of her work in advancing the discipline. − We then include selected recent articles published in Langmuir that showcase advances within research areas related to those that Dr. Greene devoted her scientific career to advancing. − This collection of articles is divided into four sections that reflect the breadth of topics influenced by Dr. Greene’s accomplishments (Table ).…”

Smart supramolecular photoresponsive gelator with long-alkyl chain azobenzene incorporated sugar derivatives for recycling aromatic solvents and sequestration of cationic dyes

“…29 Phase-selective gelators (PSGs) specially gelate one solvent over others from a given mixture at room temperature and have also been reported in the literature. 30–32 Because of their reusability, PSGs are appealing alternatives to conventional dispersants, solidifiers, and sorbents for removing organic solvents and dyes from polluted water. The properties of the gel can be further tuned by the post-modification of gels.…”