Role of Solvent Water in the Temperature-Induced Self-Assembly of a Triblock Copolymer

Abstract

Water-soluble triblock copolymers have received much attention in industrial applications and scientific fields. We here show that femtosecond mid-IR pump-probe spectroscopy is useful to study the role of water in the temperature-induced self-assembly of triblock copolymers. Our experimental results suggest two distinct subpopulations of water molecules: those that interact with other water molecules and those involved in the hydration of a triblock copolymer surface. We find that the vibrational dynamics of bulk-like water is not affected by either micellation or gelation of triblock copolymers. The increased population of water interacting with ether oxygen atoms of the copolymer during the unimer to micelle phase transition is important evidence for the entropic role of water in temperature-induced micelle formation at a low copolymer concentration. In contrast, at the critical gelation temperature and beyond, the population of surface-associated water molecules interacting with ether oxygen atoms decreases, which indicates important enthalpic control by water. The present study on the roles of water in the two different phase transitions of triblock copolymers sheds new light on the underlying mechanisms of temperature-induced self-aggregation behaviors of amphiphiles that are ubiquitous in nature.

Micellization of Pluronic P123 in Water/Ethanol/Turpentine Oil Mixed Solvents: Hybrid Particle–Field Molecular Dynamic Simulation

“…The self-assembly of amphiphilic block copolymers has attracted considerable attention for many decades because they can form many novel structures, including spheres, cylinders, bicontinuous phases, lamellae, vesicles, and many other complex or hierarchical assemblies [1,2,3,4]. Amphiphilic block copolymers have been widely used in many industrial applications, such as detergents, dispersion stabilizers, foaming agents, emulsifiers, and lubricants [5].…”

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

“…Especially, the interfacial active polymers with large molecular weight are widely studied owing to the diversity of the structure, which can generate a strong steric barrier to inhibit drop coalescence , and stabilize emulsions. Triblock copolymers, having narrow molecular-weight distribution and nontoxicity, are focused popularly because of their irreversible interfacial adsorption characters, , salt-controlled self-assembly behaviors, − and controllable molecular structure rigidity and composition. − …”

Adsorbed Water Structure on Acrylate-Based Biocompatible Polymer Surface

“…The vibrational lifetime of the IR probe (OD stretch of HOD) is extremely sensitive to the local H-bond environment and has been utilized to probe various systems including peptides, proteins, polymeric surfaces, and Li-ion battery. ,,− The lifetime of OD stretch in the bulk water is ∼1.8 ps, but it varies significantly for different polymer surfaces. ,, The temporal profiles of the isotropic IR-PP signals of the OD stretch of HOD adsorbed in polymers (PMEA and PPEA) and their DWT-corrected profiles are shown in Figure a,c and in Figure b,d, respectively. These show that the DWT method could successfully remove the pump-induced scattering from the signal.…”

“…18,19,26−29 The lifetime of OD stretch in the bulk water is ∼1.8 ps, but it varies significantly for different polymer surfaces. 20,26,30 The temporal profiles of the isotropic IR-PP signals of the OD stretch of HOD adsorbed in polymers (PMEA and PPEA) and their DWT-corrected profiles are shown in Figure 3a,c and in Figure 3b,d, respectively. These show that the DWT method could successfully remove the pump-induced scattering from the signal.…”

“…It should be noted that the eigenspectra and the vibrational relaxation processes of two different HOD species on the polymer surfaces in this study show quite different behaviors as compared to those of HOD molecules in polymer and salt solutions in water studied previously, where it has been shown that the OD stretch modes of HOD molecules with the blue-shifted eigenspectrum have a longer lifetime than those with the red-shifted eigenspectrum in the solution phase. 19,26,32,33 Note that the blue-shifted OD stretch frequency results from a weaker Hbonding interaction of HOD with H-bonding acceptors. In stark contrast, the slowly decaying component in this study is red-shifted, which indicates that the HOD with a strong interaction with the side chain CO group has a longer lifetime.…”