Thermo-responsive triblock copolymer phase transition behaviour in imidazolium-based ionic liquids: Role of the effect of alkyl chain length of cations.
Different biophysical techniques such as fluorescence spectroscopy, dynamic light scattering (DLS), viscosity (η) and Fourier transform infrared (FTIR) spectroscopy have been carried out to characterize the effect of imidazolium-based ionic liquids (ILs) on the thermo-responsive triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly-(ethylene glycol) (PEG-PPG-PEG). In addition, to demonstrate the distinct morphological changes of various self-assembled morphologies, we further employed field emission scanning electron microscope (FESEM). To investigate the effect of alkyl chain length of the cation, concentration of the ILs and the related Hofmeister series on the phase behaviour of PEG-PPG-PEG, we used a series of ILs possessing same Cl-anion and a set of cation [Cnmim]+with increasing alkyl chain length of cation such as 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]) and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]). The critical micellization temperature (CMT) of the copolymer in the presence of well hydrated cations is directly correlated to their hydration. The overall specific ranking of ILs in decreasing the CMT of PEG-PPG-PEG in aqueous solution was [Emim][Cl]>[Bmim][Cl]>[Hmim][Cl]>[Dmim][Cl]. The trend of these ILs followed the well-known Hofmeister series of cations of ILs. The present study provides important information about the solution properties that can be helpful to tune the IL or temperature-sensitive copolymer CMT and micelle shapes which are crucial for understanding the drug delivery mechanisms.
Department of Chemistry, University of Delhi, Delhi 110007, India.
Reddicherla
R
Umapathi
Department of Chemistry, University of Delhi, Delhi 110007, India. Electronic address: venkatesup@hotmail.com.
Pannuru
P
Venkatesu
D001881:Borates / Q000737:chemistry*; D002412:Cations; D016503:Drug Delivery Systems; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D008823:Micelles; D044367:Phase Transition; D011092:Polyethylene Glycols / Q000737:chemistry*; D011409:Propylene Glycols / Q000737:chemistry*; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry*
C528767:1-hexyl-3-methylimidazolium; D001881:Borates; D002412:Cations; D007093:Imidazoles; D052578:Ionic Liquids; D008823:Micelles; D011409:Propylene Glycols; C528875:poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) copolymer; D014867:Water; D011092:Polyethylene Glycols; C502841:1-butyl-3-methylimidazolium chloride; C518739:1-ethyl-3-methylimidazolium
Aggregation studies; Critical micellization temperature; Ionic liquids; Morphological changes; Triblock copolymer