Abstract
The associative properties of methoxy (CH3O-) ended E58B11 and hydroxyl (-OH) ended E56B19 oxyethylene-oxybuty- lene diblock copolymers in aqueous solution at different temperature are reported in this paper. For both copolymers, E represents an oxyethylene (-[CH2CH2O]-) unit and B an oxybutylene (-[CH(C2H5)CH2O]-) unit while the subscripts denote the number average block length. Surface tension measurements were used to find out surface excess concentrations (Γm), area per molecule (αs1 ) at air/water interface and Gibbs free energy for adsorption (△G0ads ) for the pre-micellar region at four temperatures. Likewise thermodynamic parameters of micellization such as, critical micelle concentrations (CMC), enthalpy of micellization (△H0mic ), standard free energy of micellization (△G0mic) and entropy of micellization (△S0mic ), were also obtained using surface tension measurements. Solution densities were used to deter-mine the partial specific volume of micelle ( Vmic) and micellar density (ρmic). Dilute solution viscosities have been used to estimate the intrinsic viscosities [η], solute-solvent interaction parameter (KH) and hydration value of micelle (Wh) at various temperatures. The effect of temperature on the micelle properties is also discussed.
Highlights
Due to their academic as well as promising industrial applications, block copolymers self assembly in selective solvents has been drawn considerable attention of physicist and chemists in the recent decades
In some cases the surface tension does not remain fairly constant after critical micelle concentration (CMC) for block copolymers solutions; this is due to the formation of dimers and trimers or the lack of large micelles [32]
We have studied the association and surface active behaviour of the methoxy (CH3O-) ended E58B11 and hydroxyl (-OH) ended E56B19 at different temperatures in water
Summary
Due to their academic as well as promising industrial applications, block copolymers self assembly in selective solvents has been drawn considerable attention of physicist and chemists in the recent decades. Self assembled aggregates of various morphologies have been reported ranging from spherical micelles to vesicle, tubules and complex super-aggregates Such morphologies can be well tuned by relative block length, solvent composition, polymer concentration, additives and temperature [1]. Polymeric micelles are core shell structures formed through the self assembly of amphiphilic polymers in a solvent that is hostile toward either moiety In aqueous media, these micelles have an internal hydrophobic core surrounded by an outer hydrophilic corona which shields the nonaqueous core from external medium. A variety of super-structures like body-centered cubic (bcc) or face-centered cubic (fcc) arrays of spherical micelles, hexagonal arrays of elongated micelles and lamellar structures can be formed [3,4,5] Some of these aggregates are bilayered and biomimetic [6]. The present work has been carried out to see the application of these fundamental experimental techniques to the association behaviour of two E-B block copolymers with different E/B block ratio and hydrophilic ends at various solution temperatures
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