Responsive Telechelic Block Copolymers for Enhancing the Elasticity of Nanoemulsions

Abstract

The rheology of emulsions dictates their performance in many scientific and industrial applications. Here, we demonstrate that high-molecular-weight telechelic triblock copolymers composed of polystyrene end blocks with a poly(ethylene oxide) midblock effectively modify the rheology of a suspension of cyclohexane nanodroplets. Because of their telechelic structure, these polymers bridge between droplets to generate elastic networks with shear moduli on the order of 1000 Pa. The network elasticity increases with polymer concentration and molecular weight as the polymers more effectively form bridges. Furthermore, we tune the nanoscale interactions that control the polymer partitioning by decreasing the temperature below the cloud point of the system. At low temperatures, the polystyrene end blocks no longer preferentially partition into the cyclohexane droplets, and the emulsions begin to exhibit terminal viscous relaxations. These results identify key properties of telechelic block copolymers that can be exploited to significantly enhance nanoemulsion elasticity to improve the processability and transport of complex fluids in applications ranging from 3D printing to functional hydrogels.

Effects of Polymer Molecular Weight on Structure and Dynamics of Colloid–Polymer Bridging Systems

“…Our results confirm that the polymer M w alters the size of flocs, as found in earlier studies, ,, and the microscopic dynamics. The methods employed here may prove useful to elucidate size effects of other types of bridging agents, such as microgel particles, , and other types of particles, such as emulsions, ,, on particle structure and dynamics. Further, the biphasic behavior occurring at selected M w and c / c * may offer an alternative route to obtaining favorable combinations of rheological properties for extrusion-based processes such as 3-D printing .…”

“…Further, when the surfaces of particles become fully saturated with adsorbed polymer, addition of polymer can also lead to depletion attractions. , Thus, particulate suspensions containing adsorbing polymers exhibit a rich phase behavior, including flocs and networks. Flocculation processes driven by polymers or macromolecules adsorbed to the particle surface appear in filtration applications, , beer fermentation, , and rapid diagnostics for infectious diseases. , Bridging interactions are also observed in suspensions of grafted nanoparticles or nanoemulsions, for which the solvent condition for chains, grafting density, bridging mechanism, and polymer molecular weight affect the gelation and rheological behavior of the suspensions. Control over flocculation in these settings requires understanding how the interactions induced by the bridging polymers affect the microscopic properties of the suspension.…”

Bridging Heterogeneity Dictates the Microstructure and Yielding Response of Polymer-Linked Emulsions

“…42,43 Increasing the size of the endblocks, however, generates permanent elasticity, as thermal fluctuations are no longer sufficient to drive chain rearrangements between droplets. 39 As a result, the linked networks are kinetically trapped with static polymer conformations. It remains unclear, however, how the application of shear disrupts these kinetically trapped structures and how these structures evolve under stress.…”

“…Emulsions were prepared as described in our previous work. 39 Briefly, a nonionic surfactant mixture of Span 20 (hydrophilic−lipophilic balance (HLB) = 8.6) and Tween 20 (HLB = 16.7) was prepared at a weight ratio of 1:4 to achieve an HLB of 15.0. This mixture was diluted with water to a ratio of 1:29 surfactant:water.…”

Shear Viscosity Overshoots in Polymer Modified Asphalts

“…Since the physical bonds among the end caps are weak, the detachment of an end from the hydrophobic core of the flower, with a subsequent jump to form a bridge between two micelles, can be induced by an applied shear [ 25 , 26 ]. This effect favours the formation of an interconnected network, responsible for the shear thickening, among the nodes; this network is composed of telechelic chains, and the ends of these chains belong to neighbouring micelles [ 27 , 28 , 29 ]. Due to the weak nature of the bridges, excessive stress causes disruptions of the network, with subsequent shear thinning.…”