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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
Author(s) -
Parekh Paresh,
Bahadur Pratap
Publication year - 2011
Publication title -
journal of surfactants and detergents
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.349
H-Index - 48
eISSN - 1558-9293
pISSN - 1097-3958
DOI - 10.1007/s11743-011-1247-6
Subject(s) - micelle , copolymer , chemistry , dispersity , dynamic light scattering , chemical engineering , polymer chemistry , aggregation number , critical micelle concentration , organic chemistry , aqueous solution , polymer , nanoparticle , engineering
The results on changes in the apparent hydrodynamic diameter (D h ) 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 (C 1 –C 3 ) increase solvation of PEO and thus increase micelle hydrodynamic size while higher alcohols, initially reduce D h due shrinkage of PEO followed by micellar growth at higher concentrations. Among αω‐alkanediols, C 2 and C 4 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 C 6 EO m ( m = 0, 1, 2), as the number of EO group increases, it becomes more hydrophilic and increases D h 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.