Micellization Thermodynamics of Pluronic P123 (EO20PO70EO20) Amphiphilic Block Copolymer in Aqueous Ethylammonium Nitrate (EAN) Solutions

Abstract

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (commercially available as Pluronics or Poloxamers) can self-assemble into various nanostructures in water and its mixtures with polar organic solvents. Ethylammonium nitrate (EAN) is a well-known protic ionic liquid that is expected to affect amphiphile self-assembly due to its ionic nature and hydrogen bonding ability. By proper design of isothermal titration calorimetry (ITC) experiments, we determined the enthalpy and other thermodynamic parameters of Pluronic P123 (EO 20 PO 70 EO 20 ) micellization in aqueous solution at varied EAN concentration. Addition of EAN promoted micellization in a manner similar to increasing temperature, e.g., the addition of 1.75 M EAN lowered the critical micelle concentration (CMC) to the same extent as a temperature increase from 20 to 24 • C. The presence of EAN disrupts the water solvation around the PEO-PPO-PEO molecules through electrostatic interactions and hydrogen bonding, which dehydrate PEO and promote micellization. At EAN concentrations lower than 1 M, the PEO-PPO-PEO micellization enthalpy and entropy increase with EAN concentration, while both decrease above 1 M EAN. Such a change can be attributed to the formation by EAN of semi-ordered nano-domains with water at higher EAN concentrations. Pyrene fluorescence suggests that the polarity of the mixed solvent decreased linearly with EAN addition, whereas the polarity of the micelle core remained unaltered. This work contributes to assessing intermolecular interactions in ionic liquid + polymer solutions, which are relevant to a number of applications, e.g., drug delivery, membrane separations, polymer electrolytes, biomass processing and nanomaterial synthesis.

Self‐Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

“…. The sigmoidal curve can be broken into three distinct portions (He and Alexandridis, ). The lower plateau at low surfactant concentration covers a region where the micellar titrant is diluted (following injection into the sample cell) to a concentration that is less than the CMC.…”

“…A Microcal ITC200 calorimeter (Malvern, Worcestershire, UK) was used to perform isothermal titration calorimetry (ITC) experiments (He et al, ; He and Alexandridis, ; Juhász et al, ). The sample cell was filled with deionized water and maintained at 20 °C.…”

“…A linear fit of the first and last several data points of the enthalpogram was used to generate extrapolation lines. The points where the linear extrapolation lines diverged from the enthalpogram defined the end of the micelle dissociation region and the start of the micelle dilution region (He and Alexandridis, ).…”

Surfactant‐assisted‐water‐exposed versus surfactant‐aqueous‐solution‐exposed electrospinning of novel super hydrophilic Polycaprolactone‐based fibers: Cell culture studies

“…In other words, P123 are not anchored to the PCL in the bulk of SASE fibers. Hence P123 micellization and its leakage into the water happen easily and P123 detaches from fibers after immersion in water . Therefore, hydrophilicity of SASE leans toward to that of neat PCL.…”

“…Hence P123 micellization and its leakage into the water happen easily and P123 detaches from fibers after immersion in water. 28 Therefore, hydrophilicity of SASE leans toward to that of neat PCL. It is noteworthy to mention that P123 leakage from SASE fibers is highly dependent on the thickness of the scaffolds, which means by increasing the thickness of SASE scaffold, leaked P123 gets entrapped inside the scaffolds for a while, and results into a gentler decrease in the slope of the swelling curve.…”