AFM Study of Micelle Chaining in Surface Films of Polystyrene-block-Poly(ethylene oxide) Stars at the Air/Water Interface

Abstract

A series of three-arm star block copolymers were examined using atomic force microscopy (AFM). These stars consisted of a polystyrene core composed of ca. 111 styrene units/branch with poly(ethylene oxide) (PEO) chains at the star periphery. Each star contained different amounts of PEO, varying from 107 to 415 ethylene oxide units/branch. The stars were spread as thin films at the air/water interface on a Langmuir trough and transferred onto mica at various surface pressures. Circular domains representing 2D micelle-like aggregated molecules were observed at low pressures. Upon further compression, these domains underwent additional aggregation in a systematic manner, including micellar chaining. At this point, domain area and the number of molecules/domain increased with increasing pressure. In addition, it was found that longer PEO chains led to greater intermolecular separation and less aggregation. These AFM results correspond to attributes seen in the surface pressure-area isotherms of the stars. In addition, they demonstrate the viability of AFM as a quantitative characterization technique.

Synthesis and Organization of Three‐Arm‐Star PIB–PEO Block Copolymers at the Air/Water Interface: Langmuir‐ and Langmuir–Blodgett Film Investigations

“…Using Langmuir-Blodgett techniques at low surface pressures, the formation of regular patterns can be observed, which are generally accepted to represent surface aggregates [26] of the respective di-BCPs. [27,28] Besides irregular patterns, the formation of tubular-, rod-type structures can be observed, in accordance with the phase diagram of BCP microphases. [24,25] Transfer at higher pressures in the ''brush'' regime leads to crystalline PEO with finger-type morphology.…”

“…[24,25] Transfer at higher pressures in the ''brush'' regime leads to crystalline PEO with finger-type morphology. Langmuir techniques have been also applied to other di-and tri-BCPs [29][30][31] as well as star BCPs, [27,32,33] revealing similar results as the structural complexity of the molecules increases. Again, surface aggregation of the BCPs in the plateau regime is observed, leading to micellar structures as well as crystalline regions in the case of BCPs with perfluorinated chain segments.…”

Assembling hyperbranched polymerics

“…Such a phenomenon is consistently observed and governed especially by the hydrophobic-hydrophilic balance, but the stability is affected by other external variables, for example, temperature, architecture, and terminal groups. 35,38,41,[148][149][150][151][152] Except for one compound, all amphiphilic POSS-M compounds eventually formed a uniform LB monolayer at a high surface pressure. At the highest surface pressure, the overall morphology is eventually dominated by the crowding of the POSS-M cores and alkyl branches.…”

Amphiphilic 2-ethyl hexyl methacrylate-b-N ,N ′-dimethylacrylamide diblock copolymer monolayer behaviour at the air − water interface†

“…Amphiphilic diblock copolymers are versatile systems that, when in solution, can organise into several different shapes. The formation of these structures is governed by the molecular characteristics of the constituent polymers, such as their chain length, the volume fraction of each component, the degree of incompatibility between the blocks, their specific interactions with the solvent, and the temperature of the system, among other factors . Nevertheless, in the past few decades the air − water interface has received much attention as a tool for investigating the self‐assembly of various amphiphilic molecules because of its ability to mimic hydrophilic − hydrophobic interfaces…”