Stabilizing bubble and droplet interfaces using dipeptide hydrogels

Abstract

Hydrophobic dipeptide molecules can be used to create interfacial films covering bubbles and droplets made from a range of oils. At high pH, the dipeptide molecules form micelles which transform into a hydrogel of fibres in response to the addition of salt. We characterize the properties of the hydrogel for two different salt (MgSO) concentrations and then we use these gels to stabilize interfaces. Under high shear, the hydrogel is disrupted and will reform around bubbles or droplets. Here, we reveal that at low dipeptide concentration, the gel is too weak to prevent ripening of the bubbles; this then reduces the long-term stability of the foam. Under the same conditions, emulsions prepared from some oils are highly stable. We examine the wetting properties of the oil droplets at a hydrogel surface as a guide to the resulting emulsions.

Widely Adaptable Oil‐in‐Water Gel Emulsions Stabilized by an Amphiphilic Hydrogelator Derived from Dehydroabietic Acid

“…The chiral fibers with length of over 2 μm can be clearly seen, and the morphology of the fibers is the same as that formed in pure water (Figure A). Since fibers can also stabilize emulsions, it is important to establish whether R‐6‐AO molecules or self‐assembled fibers are responsible for emulsion stabilization. To answer this, gel emulsions at 5, 10 and 15 m m R‐6‐AO were prepared and held at 45 °C (over T gel ) at and beyond which fibrils will not be formed.…”

“…Since R‐6‐AO monomers with low concentrations coexist with fibers as proved by the regular surface tension curves (Figure B) and the above experiment, it can be concluded that at room temperature it is still R‐6‐AO molecules that stabilize emulsion droplets, where the hydrated headgroup layer covering droplet interfaces endows steric stabilization to approaching droplets. These results indicate that in the gel emulsions reported here R‐6‐AO molecules not only gel the continuous phase by forming fibers, but also adsorb at the oil–water interface, which is quite different from other gel emulsions stabilized solely by fibrils . For example, the gel emulsions stabilized by fibers formed by dipeptide derivatives demulsified when kept at 60 °C for 3 h …”

Directed Discovery of Tetrapeptide Emulsifiers

“…Development of new peptide materials without the presence of large aromatic capping groups showed that similar materials could be formed with similar tunable properties ( Frederix et al, 2015 ). Furthermore, these materials can be utilized in multi-solvent systems to created stable emulsions ( Scott et al, 2016 ; Aviño et al, 2017 ; Castelletto et al, 2019 ; García-Moreno et al, 2020 ; Wychowaniec et al, 2020 ).…”

“…Previous examples of short peptide based emulsifiers have relied on longer peptides (9–26 amino acids in length) that have a classical surfactant like structure ( Castelletto et al, 2019 ) or alternatively form identifiable structural motifs that are present in naturally occurring emulsifiers ( García-Moreno et al, 2020 ). In the case where shorter (di-tetrapeptides) have been identified, or designed as emulsifiers a recurring theme is the presence of aromatic amino acids such as phenylalanine and tyrosine ( Scott et al, 2016 ; Aviño et al, 2017 ; Wychowaniec et al, 2020 ). In this work a new approach for the discovery of peptides emulsifiers that are able to break these design rules is explored.…”

Self-assembled low-molecular-weight gelator injectable microgel beads for delivery of bioactive agents

“… 7 There have also been reports of LMWG microshells in which self-assembly is mediated at the interface of an oil-in-water emulsion. 8 AT the sub-micron level, in 2017, Miravet and co-workers reported the generation of nanosized spherical objects by injecting an LMWG dissolved in a good solvent into a poor solvent, and suggested the objects obtained were particles formed in the initial stages of the nucleation of self-assembly. 9 Maintaining the stability of these LMWG nanoparticles over time was challenging as a result of their tendency to aggregate.…”