One-Step Formation of Double Emulsions Stabilized by PNIPAM-based Microgels: The Role of Co-monomer

Abstract

Microgels have been widely used as particulate emulsifiers to stabilize emulsions due to their multiresponsiveness and deformability. Generally, microgels stabilize oil-in-water (o/w) emulsions, whereas occasionally water-in-oil (w/o) emulsions are reported using oils like n-octanol in which microgels can swell. However, the use of microgels to stabilize double emulsions (DEs) remains scarce. In this work, we report a special poly­(N-isopropylacrylamide)- (PNIPAM-) based microgel to obtain water-in-oil-in-water (w/o/w) DEs in one step with the introduction of 1-vinylimidazole (VIM) as comonomer and hydroxy silicone oil as the oily phase. By comparison, when methacrylic acid (MAA) is used, an o/w emulsion will be obtained. The same holds true even when we freeze-dry and redisperse the microgels in the oil. Compared with PNIPAM-co-MAA microgel, PNIPAM-co-VIM microgel achieves a lower interfacial tension (IFT) when dispersed in the aqueous phase. This interfacial affinity of PNIPAM-co-VIM is believed to result from acid–base interaction between VIM and hydroxyl groups of the silicone oil, the same interaction used for preparing silica–vinyl polymer composite particles. Increasing the particle concentrations from 0.05% to 0.9% (w/v), we observe the inversion from w/o to o/w/o and w/o/w emulsions. When the oil fraction is changed from 0.1 to 0.9, the emulsion morphology evolves from o/w and w/o/w to w/o emulsions. At last, we examine the emulsifying ability of PNIPAM-co-VIM microgel with other oils and find that w/o/w emulsions are obtained with edible oils as well. Considering the similarity between microgels and biopolymers, the discovery in this work will help in designing food-grade emulsifiers to form edible DEs.

Exploring water in oil emulsions simultaneously stabilized by solid hydrophobic silica nanospheres and hydrophilic soft PNIPAM microgel

“…[50][51][52] Different strategies emerged to overcome this problem: One strategy is the modification of the chemical structure of the MGs. 47,53 While remarkable success was made recently 53 , this strategy inherently bears the disadvantage that the modifications are MG specific and may not be generalized to other types of soft particles Furthermore, for most applied MGs the inherent structure is essential for their function (e.g., drug carrier MGs, proteins, etc. ), which may suffer from the modification.…”

Tuning Supramolecular Polymers’ Amphiphilicity via Host–Guest Interfacial Recognition for Stabilizing Multiple Pickering Emulsions

“…Soft colloidal particulate emulsifiers with matched polymeric amphiphilicity have also been reported to stabilize multiple Pickering emulsions, just like poly­( N -isopropylacrylamide) (PNIPAM)-based microgels, poly­(ethylene glycol)- b -polystyrene (PEG- b -PS) copolymers, amphiphilic diblock copolypeptide, and amphiphilic copolymer poly­(dodecyl acrylate- co -acrylic acid) (PDAA). , However, these covalently engineered amphiphilic polymeric stabilizers typically required sophisticated synthetic procedures and manipulations. Furthermore, the interfacial self-assembled behaviors could not be readily regulated through the stimulus-tuning amphiphilicity of polymers, further limiting the excellent modulation of interfacial energy to administrate the controllable phase behaviors.…”

“…Meanwhile, the destabilization path- way generally occurred by a two-step emulsification process, 69 further hampering the practical applications. Soft colloidal particulate emulsifiers with matched polymeric amphiphilicity have also been reported to stabilize multiple Pickering emulsions, just like poly(N-isopropylacrylamide) (PNIPAM)-based microgels, 70 poly(ethylene glycol)-b-polystyrene (PEG-b-PS) copolymers, 71 amphiphilic diblock copolypeptide, and amphiphilic copolymer poly(dodecyl acrylate-co-acrylic acid) (PDAA). 72,73 However, these covalently engineered amphiphilic polymeric stabilizers typically required sophisticated synthetic procedures and manipulations.…”

Non-covalent reconfigurable microgel colloidosomes with a well-defined bilayer shell

“…These wrinkles demonstrate a clear manifestation of the strong rheological responses of a highly elastic monolayer assembled by PNIPAM-co-MAA microgels from the oil phase; these were much stronger responses than those that have been previously reported. 15,44 This phenomenon was explained as the high surface coverage of octanol-swollen microgels led to the spontaneous buckling and jamming of the adsorption monolayer during compression. In contrast, even though water-swollen microgels are able to adsorb at the oil-water interface, very limited parts of microgels can deform and atten at the interface because of their intrinsic hydrophilicity.…”