Direct measurement of interaction force between hydrophilic silica surfaces in triblock copolymer solutions with salt by atomic force microscopy

• Published in: Advanced powder technology : the international journal of the Society of Powder Technology, Japan Vol. 32; no. 1; pp. 30 - 36
• Main Authors: Deguchi, Takumi, Nakahara, Takato, Imamura, Koreyoshi, Ishida, Naoyuki
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2021
• Subjects: Adsorption; Atomic force microscopy; Interaction force; Silica surface; Triblock copolymers; Atomic force microscopy; Adsorption; Interaction force; Silica surface; Triblock copolymers
• ISSN: 0921-8831; 1568-5527
• DOI: 10.1016/j.apt.2020.11.011

[Display omitted] •Forces between silica surfaces in Pluronic solutions with NaCl were measured by AFM.•Below CMC, the interactions were steric repulsion when NaCl concentration was low.•High NaCl concentration brought bridging attraction below CMC.•Above CMC, the interactions were steric repulsion caused by adsorbed micelle layers.•The length of the PEO group was found to affect considerably on the interactions. Triblock copolymers composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) are used in various fields as nonionic surfactants. In this study, we measured interaction forces between untreated hydrophilic silica surfaces in solutions with two typical triblock copolymers, Pluronic P123 (PEO20PPO70PEO20) and F127 (PEO99PPO65PEO99), in the presence of 1 mM and 500 mM NaCl using atomic force microscopy (AFM). In solutions at the copolymer concentration of 1 µM, which is below the critical micelle concentration (CMC), the measured interaction forces were monotonically repulsive in the presence of 1 mM NaCl, which suggested the brush-like conformation of copolymers on the surfaces. When the concentration of NaCl was increased to 500 mM, interaction forces became attractive, which indicated the bridging of adsorbed polymers onto surfaces, the strength of which varied depending on the affinity and adsorption density of copolymers. The interactions at the copolymer concentration of 1 mM, which were above the CMC of both copolymers, were steric repulsions between adsorbed micelles on the surfaces with 1 mM of NaCl. For 500 mM of NaCl, an attractive jump after a steric repulsion was observed only in the force curve for P123, which inferred that the displacement of micelles from the surfaces was presumably due to a decrease in the strength of adsorption caused by the dehydration of EO groups. These results indicated that the length of the EO group considerably affected the interactions.