Dynamic Light Scattering Studies on the Effect of 1-Alkanols, Alkanediols and Alkoxyethanols on the Micelles of a Moderately Hydrophobic/Hydrophilic PEO-PPO-PEO Triblock Copolymer

摘要

The results on changes in the apparent hydrodynamic diameter (Dh) of micelles in a solution containing 5% of a moderately hydrophobic/hydrophilic triblock PEO-PPO-PEO copolymer in the presence of several hydroxyl compounds at 23 °C from dynamic light scattering (DLS) are reported. Distribution plots show micelles with hydrodynamic diameter ~17 nm and low polydispersity (0.1) except at low concentrations where a unimer peak (~ 4 nm) was also noticed. These additives increase/decrease the micelle size and show micellar transition depending upon their hydrophilicity/hydrophobicity. The results are discussed in terms of the effect of the additives on altering water structure and their partitioning in micelle. Short chain alcohols (C1–C3) increase solvation of PEO and thus increase micelle hydrodynamic size while higher alcohols, initially reduce Dh due shrinkage of PEO followed by micellar growth at higher concentrations. Among αω-alkanediols, C2 and C4 diols increase micelle size by immobilizing water sphere around the micelles whereas higher diols form wicket like structures and reside in palisade layer. Isomeric hexanediols (1,2; 1,5; 2,5 and 1,6) alter micelle size in different ways depending on their hydrophobicity. In C6EO m (m = 0, 1, 2), as the number of EO group increases, it becomes more hydrophilic and increases Dh at higher concentration. Addition of a hydrophobic triblock copolymer leads to unfavorable mixing with a moderately hydrophobic/hydrophilic triblock copolymer which results in increase in size, while the addition of a hydrophilic counterpart increases the average hydrodynamic size and follows appearance of unimer peak.