Effects of Salt-Controlled Self-Assembly of Triblock Copolymers F68 on Interaction Forces between Oil Drops in Aqueous Solution

Abstract

Nonionic triblock copolymers, surfactant Pluronic F68 (PEO76-PPO29-PEO76), are widely used in industrial processes, such as foaming, emulsification, and stabilization. The behaviors of triblock copolymers such as the salt-dependent self-assembly in bulk solution and the irreversible adsorption at the oil/water interface are mainly focused to explore their effects on the interaction forces between nano-spacing interfaces of oil droplets. In this study, the atomic force microscopy (AFM) technique was employed to measure the drop interaction forces with different F68 bulk concentrations. All selected bulk concentrations (≥100 μM) of copolymers can ensure the formation of a stable layer structure of stretched polymer chains ("brush") at the oil/water interface, which behaved as a mechanical barrier at the interface. This study quantified the forces caused by the space hindrance of F68 copolymers both in the bulk phase and at the interface of oil/F68 aqueous solution during drop interaction. The effects of monovalent electrolyte (NaCl)-induced self-assembly behavior of triblock copolymers F68 in bulk solution on drop interaction forces were measured through the AFM technique.

Experimental Study of the Salinity-Specific Adhesion Force between Oil Drop and Underwater Superoleophobic Polyelectrolyte Surfaces

“…However, from the topographic images acquired by AFM surface imaging, it was found that the granular sensation of the surface is enhanced with the increase in the salt concentration, as shown in Figure 4D,E. The formed granular polyelectrolyte aggregates detected on the surface can be attributed to the salt-dependent self-assembly (a "saltingout" effect 49 ) under strengthened salinity, but little effect on the surface superoleophobicity was found. Next, to carry out a new force measurement, the washout experiment was repeated and equilibrated for 20 min.…”

“…The materials (oil, deionized water, silicon wafer) used for experiments were consistent with those used in our previous study. 49 Prior to all experiments, silicon wafers were cleaned via immersion in Piranha solution (1:3 (v/v) mixture of 30% H 2 O 2 and 98% H 2 SO 4 ), followed by heating until no bubbles were released to remove possible surface contaminants. The cleaned silicon wafers were rinsed with water and dried with nitrogen.…”

“…The AFM technique (Bruker, Multimode 8) was applied to measure the interaction forces between oil droplets and PEM-capped superoleophobic surfaces in aqueous solution. The detailed measurement method of the AFM drop probe technique was described in our previous study 49 (Supporting Information, Figure S1).…”

“…This study draws primarily on the underwater wetting behavior of PEMs obtained by a LbL strategy. − The deposition of PDDA and PSS was initially accomplished on a silicon wafer. The atomic force microscopy (AFM) drop probe technique − was adopted for the direct measurement of the adhesion forces between microsized oil droplets and superoleophobic surfaces in aqueous solutions with high salinity. The measured adhesion forces between the oil droplet and PDDA/PSS-coated surface are found to be salinity-specific.…”

Probing surface interactions of underwater oleophobic polyelectrolyte multilayers

“…This study has been facilitated by the advent of the atomic force microscope (AFM) (Binnig et al 1986), which permits the direct force measurement of interactions between homoand hetero-bodies within nano-Newton scale (Mate et al 1989;Snyder et al 1997;Aston and Berg 2002;Malotky and Chaudhury 2001). Moreover, the development of probe modification technique has promoted the exploration of interactions between deformable droplets/bubbles and solid surfaces (Dagastine et al 2004a(Dagastine et al , 2006Gunning et al 2004;Vakarelski et al 2010a;Balasuriya and Dagastine 2012;Tabor et al 2011a, b;Wang et al 2015;Jin et al 2017;Shi et al 2017). One interesting study applied the drop probe AFM technique to elucidate the intrinsic wetting mechanism of polyelectrolyte surfaces with varied hydrophobicity.…”