Oscillatory and Relaxation Study of the Interfacial Rheology of Star Polymers with Low-Grafting-Density PEO Arms and Hydrophobic Poly(divinylbenzene) Cores

Abstract

Star polymers have been gaining interest due to their tunable properties. They have been used as effective stabilizers for Pickering emulsions. Herein, star polymers were synthesized via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). Poly(ethylene oxide) (PEO) with terminal α-bromoisobutyrate ATRP functionality was used as a macroinitiator and divinylbenzene as a crosslinker for the arm-first star synthesis. Stars with PEO arms with a molar mass of either 2 or 5 kDa had a relatively low density of grafted chains, i.e., ca. 0.25 chain/nm 2 . The properties of PEO stars adsorbed at oil−water interfaces were investigated using interfacial tension and interfacial rheology. The magnitude of interfacial tensions at oil−water interfaces depends on the nature of the oil phase, being lower at the m-xylene/water interface than at the n-dodecane/water interface. Small differences were observed for stars with different molecular weights of PEO arms. The overall behavior of PEO stars adsorbed at an interface can be considered as an intermediate between a particle and a linear/branched polymer. Obtained results offer an important insight into the interfacial rheology of PEO star polymers in the context of their application as stabilizers for Pickering emulsions.

Localized Surface Plasmon Resonance Sensing and its Interplay with Fluidics

“…Leveraging LSPR sensor sensitivity to changes in the refractive index at the oil–water interface can be invaluable for scrutinizing the dynamic interplay between these substances, offering potential insights into optimizing interfacial tension and, consequently, refining taste. Additionally, LSPR can facilitate the study of fluid parameters crucial for interfacial rheology, including the density and viscosity of the liquid–liquid interface. , This is due to the refractive index’s dependence on factors like density and viscosity in the context of the liquid–liquid interface.…”

Structure and Organization of Amphiphilic Mikto-Grafted Molecular Brushes at Liquid/Liquid Planar Interfaces

“…Amphiphilic polymers provide a powerful and versatile platform for designing nanostructures suitable for a wide variety of applications, such as drug delivery, − photonic crystals, , and stabilization of emulsions for food, , cosmetic , and oil recovery applications. − Linear block copolymers have been widely studied as polymeric surfactants and emulsifiers due to their simple structure. − However, it has been found that polymers with complex architectures, such as star and bottlebrush polymers, have interesting and enhanced interfacial properties. − By using polyethylene oxide (PEO) star polymers, Li et al and Huang et al have shown that stable emulsions could be generated; they measured an interfacial tension reduction and an increased dilatational modulus induced by the presence of star polymers at the fluid interfaces. In a more recent work, Olszewski et al studied PEO stars with poly­(divinylbenzene) cores at air/water and oil/water interfaces and found that the interface was viscoelastic at high polymer concentration, and it became elastic as the concentration was reduced; these star polymers were also effective emulsion stabilizers. On the other hand, Xie et al synthesized a series of heterografted bottlebrushes with hydrophobic poly­( n -butyl acrylate) (PBA) and hydrophilic PEO side chains; polymer molecular parameters were varied to evaluate the bottlebrush performance as emulsion stabilizer.…”