Critical Micelle Temperature Research Articles

Glucose triggered enhanced solubilisation, release and cytotoxicity of poorly water soluble anti-cancer drugs fromT1307 micelles

Tetronic® 1307 (here after written as T1307) is a hydrophilic ethylene oxide-propylene oxide (EO-PO) star block copolymer with long EO chains (Total MW- 18000 and 70% EO). Although biocompatible, its use as a nanocarrier is restricted owing to its high critical micelle concentration (CMC) and temperature (CMT). We examined if the addition of glucose, a common pharmaceutical ingredient promotes micellization. Scattering and thermal studies show formation of stable unimodal micelles and cloud point (CP) decreased linearly. The solubilization of anticancer drugs viz. curcumin (CN) and quercetin (QN) demonstrates improved controlled release kinetics and cytotoxicity. On the whole, modulation in micellar behaviour by glucose opens enchanting possibility of using T1307 micelles as nanoreservoirs.

The effect of the preservative methylparaben on the thermoresponsive gelation behavior of aqueous solutions of poloxamer 407

The effects of 0.2% (w/v) methylparaben (0.2MP) on the micellization, intermicellar association and gelation characteristics of poloxamer 407 (PX) in aqueous solution as well as the water distribution in PX based samples have been investigated. Differential scanning calorimetry (DSC) studies demonstrated that 0.2MP shifted the critical micellization temperature (CMT) of PX to a lower temperature. According to sub-ambient DSC determination, 0.2MP disturbed interfacial water surrounding PX and decreased CMT. Flow curves revealed that intermicellar association of PX was promoted by 0.2MP. Since more intermicellar packing facilitated the thermoresponsive gelation, the reduction of the sol-gel transition temperature of PX was also substantiated in the presence of 0.2MP as indicated by temperature sweep tests.

Temperature, concentration and salt effect on F68 tri-block copolymer in aqueous solution: Rheological study

The rheology of the aqueous solution of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO−PPO−PEO) triblock copolymer, Pluronic F68 in the presence of KF was studied in the temperature range from 15 to 60°C. The variation of the shear stress according to the shear rate shows that independently from the temperature and concentration, the F68 solutions exhibit a Newtonian behavior. The results show that the Critical Micelle Temperature of Pluronic F68 in a KF aqueous solution decreases with the increase in the salt concentration.

Systematic characterization of Pluronic® micelles and their application for solubilization and in vitro release of some hydrophobic anticancer drugs

Abstract The utilization of polymeric micelles in oncology in the last few decades has progressed by leaps and bounds from the advances in polymer chemistry, in drug formulation and delivery (in vitro and in vivo biological models). Commercially available linear (A-B-A type) ethylene oxide-propylene oxide (EO-PO) block copolymers, Pluronics® have acquired added attention by virtue of their capability to load therapeutics, execute the delivery of the consignment to the site of action, improve the pharmacokinetics of the loaded drugs and reduce off-target cytotoxicity. The size of the hydrophobic (middle) and hydrophilic (end) blocks in copolymer molecule plays a decisive role for the drug loading capabilities. Hence, with this objective, we have examined the role of six different Pluronics® with varying molecular characteristics in the solubilization of three widely used hydrophobic anticancer drugs genistein (GEN), paclitaxel (PCL), and quercetin (QCT). Stable micelles (apparent hydrodynamic diameter ~ 15–20nm) form in case of moderately hydrophobic copolymers viz. P103 and P123 at ambient temperature while very hydrophilic F88 forms micelles at elevated temperatures due to much higher critical micelle temperature (CMT). All the three drugs showed enhanced solubility in copolymer micelles with the increase in temperature and salt concentration. The drug loading, stability and in vitro release profiles from the micelles were examined using reversed phase HPLC. Release profile demonstrated slower and sustained release. The in vitro cytotoxicity of the drug loaded micelles was investigated on MCF-7 breast cancer cells which showed higher anticancer activity as compared to free drugs. PCL loaded P123 micelles exhibited the best anticancer activity. The results of the current work will be highly commodious for the application of Pluronics® in anticancer therapeutics.

Chain Exchange Kinetics in Diblock Copolymer Micelles in Ionic Liquids: The Role of χ

Chain exchange kinetics of diblock copolymer micelles with lower critical micellization temperature (LCMT) phase behavior were investigated using time-resolved small-angle neutron scattering (TR-SANS). Three nearly identical isotopically substituted pairs of poly(methyl methacrylate)-block-poly(n-butyl methacrylate) (PMMA-b-PnBMA) diblocks were used in mixtures of the room temperature ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. In this case, the h-PnBMA and d9-PnBMA blocks form the micellar cores. The results are consistent with previous measurements in other systems, in that the barrier to chain extraction scales linearly with the core block length. By varying the ratio of the two homologous solvents in the mixture, the value of χ between the core block and the solvent is varied systematically. The results show that the solvent selectivity has a remarkable effect on the chain exchange rate, as anticipated b...

Stability and dynamics of silicate/organic hybrid micelles

The formation of silicate/organic hybrid micelles is an important milestone in the two-step synthesis of mesoporous silica with polyethyleneoxide (PEO) nonionic structure directing agents (C.R. Chimie 8 (2005) 579). Unlike many inorganic/organic hybrid micelles, these objects have the inorganic component as a diffuse layer positioned at the periphery of the initial micelles and interacting with the hydrophilic polyoxyethylene palisade. We studied how this additional inorganic layer can modify the structure and dynamics of micelles prepared with different types of nonionic surfactants using steady-state and time-resolved fluorescence and dynamic light scattering. Our results show that these hybrid micelles still possess a versatile behavior, which allows them to adapt reversibly to temperature changes. This silicate layer tends to stabilize and consolidate the micelle structure, especially close to the cloud point of critical micelle temperature for polypropyleneoxide (PPO)-based triblock copolymers. Their internal structure is only slightly disturbed by the silicate layer, which reduces the molecular exchanges a little bit. Among other results, we managed to elucidate why mesoporous silica prepared with Pluronic P123, according to our synthesis, stands a dramatic structural change from wormhole to hexagonal structure at 40 °C. Our dynamic light scattering study shows that 40 °C is a critical temperature corresponding to a sphere-to-rodlike structural transition of hybrid micelles, which is not observed with pure micelles. La formation de micelles hybrides organiques/inorganiques est une étape importante dans la synthèse en deux étapes des silices mésoporeuses obtenues avec des agents structurants de type copolymère diblock polyéthylène glycol (PEG) (C. R. Chimie 8 (2005) 579). Contrairement à la plupart des objets décrits comme micelles hybrides organique/inorganique, ces objets micellaires présentent leur composant inorganique positionné comme une couche diffuse à la périphérie de la micelle initiale, et en interaction avec la couronne hydrophile formée des chaines PEG. Nous avons étudié par fluorescence en mode statique et résolu en temps, ainsi que par spectroscopie de photocorrélation, comment l'ajout d'une telle couche inorganique peut modifier la structure et la dynamique de micelles préparées avec différents types de tensioactifs non ioniques. Nos résultats démontrent que ces micelles hybrides possèdent un comportement très versatile, leur permettant de s'adapter réversiblement aux variations de température. Ces couches de silicate tendent à stabiliser et renforcer la structure micellaire, en particulier lorsqu'on s'approche du point de trouble (CP) et de la température micellaire critique (CMT) pour les copolymères triblock à base de polypropylène oxyde. Leur structure interne est déstabilisée légèrement par la couche de silicate, avec pour conséquence une faible réduction des échanges moléculaires. Entre autres résultats, nous sommes parvenus à trouver la raison pour laquelle les silices mésoporeuses préparées avec du Pluronic™ P123, selon notre mode de synthèse, sont affectées par un changement structural majeur à 40 °C, avec la formation d'une structure hexagonale en nid d'abeille. Notre étude par spectroscopie de photocorrélation montre que 40 °C correspond à une température critique avec une transition de micelle sphérique en micelle allongée, une telle transition n’étant pas observée pour les solutions micellaires pures.

Influence of cleavage of photosensitive group on thermally induced micellization and gelation of a doubly responsive diblock copolymer in aqueous solutions: A SANS study

In the present study, small-angle neutron scattering (SANS) was used to investigate the temperature and concentration dependence of micelle formation and growth of a thermo- and light-responsive hydrophilic block copolymer and the influence of removing photosensitive group. The water-soluble polymer poly(ethylene oxide)- b -poly(ethoxytri(ethylene glycol) acrylate- co - o -nitrobenzyl acrylate) (PEO- b -P(TEGEA- co -NBA) underwent sol-gel/gel-sol transitions in response to temperature changes in the range of 15–55 °C in a 25 wt% aqueous solution. The SANS data showed that individual chains existed at low temperatures and dilute solutions. Spherical micelles formed and packed into an ordered structure at elevated temperatures and high concentrations. Data fitting revealed that the micelle growth followed both micelle fusion and unimer insertion mechanisms after the critical micelle temperature was reached in moderately concentrated solutions whereas the fusion mechanism was dominant at higher temperatures. The UV exposure led to a 22% expansion in chain dimension at the unimer stage due to repulsive interactions between the ionized segments after the removal of the light sensitive group. The higher onset temperature of sol-gel transition after irradiation was mainly ascribed to the higher lower critical solution temperature (LCST). On the other hand, the lower gel-sol transition temperature upon UV exposure was due to the reduction in micelle volume fraction after the cleavage of o -nitrobenzyl group. These results correlated well with the dynamic rheological data. • SANS reveals the molecular mechanisms of polymer micellization and gelation. • The unimers stretch upon the removal of the light sensitive group. • The cleavage of the light sensitive group leads to a narrower gel zone. • The scattering data uncovers material distributions in micelles. • Micelle growth follows both micelle fusion and unimer insertion mechanisms.

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.

A multitechnique approach on adsorption, self-assembly and quercetin solubilization by Tetronics® micelles in aqueous solutions modulated by glycine

Ethylene oxide-propylene oxide (EO-PO) block copolymer micelles are useful potential nanoreservoirs for the delivery of hydrophobic drugs. Considering that glycine is an excipient and can favorably affect the surface/micellar behavior and thus improve solubilization power/dispersion stability/wetting characteristics we have reported here studies on aqueous solution behavior of two commercially available branched block copolymers (Tetronics®) with differing hydrophobicities namely Tetronics® 1307 and 1304, hereafter referred as T1307 and T1304, in the presence of glycine. Steady state fluorescence studies using pyrene as a probe, equilibrium and dynamic surface tension measurements, wetting and dispersion stability studies of Teflon (polytetrafluoroethylene; PTFE) and solubilization studies of a hydrophobic antioxidant/anticancer drug quercetin (QN) have been examined. The cloud point (CP) and critical micelle temperature (CMT) decrease while micelle hydrodynamic size (Dh) increases with the addition of glycine as well as on loading of the drug in the micelles. Water penetration through packed PTFE powder and dynamic surface tension confirm the enhanced micellization process for aqueous Tetronic® solutions in presence of glycine and accordingly restricted diffusion for the surfactant molecules towards air-water and PTFE-water interface. The contact angles for Tetronic® solutions in presence of glycine indicate moderate decrease. The pressure-area curves of the copolymers in water and glycine solutions were also constructed. Surface and micellar properties of copolymers are markedly altered in the presence of glycine and can be tuned for use of these nanocarriers in delivery systems.

The Pentablock Amphiphilic Copolymer T1107 Prevents Aggregation of Denatured and Reduced Lysozyme.

Aggregation of denatured or unfolded proteins establishes a large energy barrier to spontaneous recovery of protein form and function following traumatic injury, tissue cryopreservation, and biopharmaceutical storage. Some tissues utilize small heat shock proteins (sHSPs) to prevent irreversible aggregation, which allows more complex processes to refold or remove the unfolded proteins. It is postulated that large, amphiphilic, and biocompatible block copolymers can mimic sHSP function. Reduced and denatured hen egg white lysozyme (HEWL) is used as a model aggregating protein. The poloxamine T1107 prevents aggregation of HEWL at 37 °C by three complimentary measures. Structural analysis of denatured HEWL reveals a partially folded conformation with preserved or promoted beta-sheet structures only in the presence of T1107. The physical association of T1107 with denatured HEWL, and the ability to prevent aggregation, is linked to the critical micelle temperature of the polymer. The results suggest that T1107, or a similar amphiphilic block copolymer, can find use as a synthetic chaperone to augment the innate molecular repair mechanisms of natural cells.

The origin of anomalous positive heat capacity change upon micellization of Pluronic triblock copolymer F108 in aqueous solutions: Effect of PEO-PPO diblock impurities

It is well understood that the heat of micellization is monotonically decreased along with increasing temperature. However, it was found (Langmuir 2008, 24, 13858.) that the heat of micellization for Pluronic triblock copolymer in aqueous solutions abnormally increases along with the temperature at high Pluronic concentration region. The origin of this anomalous positive heat capacity change upon micellization of Pluronic F108 in aqueous solutions was explored by using differential scanning calorimetry, chromatography and dynamic light scattering. The impurities of commercial Pluronic F108, used as received, in aqueous solution form large aggregates at the temperatures well below its critical micelle temperature (CMT). At high F108 concentrations (>2.4wt.%), the aggregates almost completely dissociate and then integrate into micelles, resulting in anomalous positive relationship of heat of micellization (ΔH) with critical micelle temperature (CMT). By contrast, at low F108 concentrations (<2.4wt.%), the aggregates do not, or only partly, participate the micellization. When the impurities of F108 are separated and removed by using high performance liquid chromatography, the ΔH of purified F108 aqueous solutions monotonically decreases along with an increase in CMT. That is, a typical linear relationship of ΔH vs. CMT is resumed. It is interesting to find out that the ΔH of 0.05wt.% purified F108 aqueous solution (234.1kJ/mol) is higher than that of unpurified F108 (174.2kJ/mol) by 25.6%.

Influence of head group on the interactional behavior of cationic surface active ionic liquids with pluronic F108 in aqueous medium

The present work aims at studying the interactions between surface active ionic liquids (SAILs) 1-dodecyl-3-methylimidazolium bromide [C12mim][Br]; N-dodecyl-N-methylpiperidinium bromide, [C12mpip][Br]; N-dodecyl-N-methylpyrrolidinium bromide, [C12mpyr][Br] and pluronic F108 in aqueous medium and to draw the comparison between the effect of different SAILs with respect to head group present in them. The binding of SAILs with pluronic F108 below as well as above the critical micelle temperature (cmt) of the pluronic has been studied by isothermal titration calorimetry (ITC), dynamic light scattering (DLS) and zeta (ζ) potential measurements. A combined analysis of these techniques revealed that SAILs can bind to monomeric as well micellar pluronic F108 with [C12mim][Br] showing a higher binding affinity in comparison to the other SAILs. Further, the interactions between SAILs and pluronic F108 in mixed micelles have been studied employing surface tension and fluorescence measurements, Various micellar, interfacial and thermodynamic parameters have being obtained for mixed systems of SAILs with pluronic F108. The interactions between F108-SAIL binary mixtures have been found to be non-ideal and strongly synergistic. The modifications in the physicochemical properties of pluronic F108 upon addition of SAILs are expected to enhance and expand the industrial and pharmaceutical applications of pluronics.

Thermal and scattering studies of Tetronic® 1304 micelles in the presence of industrially important glycols, their oligomers, cellosolves, carbitols, ethers and esters

The influence of different glycol additives on the phase behaviour and micellar characteristics of a moderately hydrophobic ethylene oxide-propylene oxide(EO-PO) star block copolymer Tetronic®1304 (hereafter written as T1304) has been investigated by cloud point (CP), viscosity, high sensitivity differential scanning calorimetry (HSDSC), dynamic light scattering (DLS) and small angle neutron scattering (SANS). Glycol additives are commonly used in several industrial and pharmaceutical applications in the presence of these biocompatible, linear and branched EO-PO block copolymers functioning as dispersants, emulsifiers, detergents, defoaming agents and vehicles in pharmaceutical applications. Hence, it is essential to understand the behavior of star block copolymers in their presence (glycol additives) to optimize the performance for applications in diverse areas.In the case of short chain glycols/ethers/cyclic ethers an increase in CP, critical micelle temperature (CMT), hydrodynamic diameter (Dh) has been observed while aggregation number (Nagg) and relative viscosity decreases indicating demicellization. On the other hand, the long chain glycol ethers/aryl ethers/esters promote micellization with an increase in Nagg, micelle size, relative viscosity and decreased CMT. The influence on the micellar characteristics of T1304 is mainly dominated by the hydrophobicity and locus of solubilization of the glycol additives. The morphology of the star block copolymers can thus be customized using different glycol additives for particular applications. The information from this work will be highly lucrative for the industrial and therapeutic applications of star block copolymers using commonly used glycols to optimize their performance.

EXPLOITING THE VERSATILITY OF CHOLESTEROL IN NANOPARTICLES FORMULATION

The biocompatibility of polymers, lipids and surfactants used to formulate is crucial for the safe and sustainable development of nanocarriers (nanoparticles, liposomes, micelles, and other nanocarriers). In this study, Cholesterol (Chol), a typical biocompatible component of liposomal systems, was formulated in Chol-based solid nanoparticles (NPs) stabilized by the action of surfactant and without the help of any other formulative component. Parameters as type (Solutol HS 15, cholic acid sodium salt, poly vinyl alcohol and Pluronic-F68), concentration (0.2; 0.5 and 1% w/v) of surfactant and working temperature (r.t. and 45°C) were optimized and all samples characterized in terms of size, zeta potential, composition, thermal behavior and structure. Results demonstrated that only Pluronic-F68 (0.5% w/v) favors the organization of Chol chains in structured NPs with mean diameter less than 400nm. Moreover, we demonstrated the pivotal role of working temperature on surfactant aggregation state/architecture/stability of Chol-based nanoparticles. At room temperature, Pluronic-F68 exists in solution as individual coils. In this condition, nanoprecipitation of Chol formed the less stable NPs with a 14±3% (w/w) of Pluronic-F68 prevalently on surface (NP-Chol/0.5). On the contrary, working near the critical micelle temperature (CMT) of surfactant (45°C), Chol precipitates with Pluronic-F68 (9±5% w/w) in a compact stable matricial structure (NP-Chol/0.5-45). In vitro studies highlight the low toxicity and the affinity of NP-Chol/0.5-45 for neuronal cells suggesting their potential applicability in pathologies with a demonstrated alteration of neuronal plasticity and synaptic communication (i.e. Huntington⿿s disease).

Glycine elicited self-assembly of amphiphilic star block copolymers with contradistinct hydrophobicities

We report here calorimetric and scattering studies on two pharmaceutically important, commercially available nonlinear ethylene oxide-propylene oxide (EO-PO) octablock copolymers, Tetronic®1304 (T1304) and Tetronic®1307 (T1307) (with almost same molecular weight of polypropylene oxide (PPO) and varying % polyethylene oxide (PEO)), in the presence of amino acid, glycine. Added glycine in aqueous solution exhibits water structure-making behaviour and thus induces micellization by altering the polarity of water. Consequently, lowering of cloud point (CP), critical micelle concentration (CMC) and critical micellization temperature (CMT) of copolymer solutions with a corresponding change in solution viscosity is observed. The microstructural changes as evidenced by small angle neutron scattering (SANS) and dynamic light scattering (DLS), for Tetronic® micelles strongly depend upon their hydrophobicity, glycine concentration, temperature and pH of solution. In the case of T1304 with lesser % PEO, behaves as moderately hydrophobic and displays pronounced micellar growth as a function of glycine concentration and at alkaline pH. Such a transition in micelle size with pH is explained in terms of sticking parameter. T1307 with higher % PEO, is highly hydrophilic and does not show micellar growth even at higher concentration of glycine/alkaline pH. The measured CMTs obtained from high sensitivity differential scanning calorimetry (HSDSC) and calculated thermodynamic parameters clearly signify glycine induced micellization. The results were elucidated in terms of structure making properties of glycine. The information attained from this contribution will be potentially commodious for an efficient exploitation of Tetronic® micelles in diverse pharmaceutical applications utilizing a common excipient, glycine.

Interactions between a triblock copolymer and hydroxyethyl cellulose in aqueous solution and their use in the solubilization of Amiodarone

A physicochemical characterization of the mixtures of triblock copolymer PEO20-PPO70-PEO20, (P123) and hydroxyethyl cellulose (HEC) in aqueous solutions, with and without the hydrophobic drug amiodarone (ADA), was performed by pendant drop tensiometry, differential scanning calorimetry (DSC) and dynamic light scattering (DLS). The results allowed us to propose a detailed diagram for the formation of the different aggregates in water. The equilibrium surface tension values showed that adding HEC to P123 solutions promotes the aggregation of the P123 monomers on the HEC polymer until saturation. By adding ADA into the P123 micelles, the same equilibrium surface tension values were obtained as the ones found in the pure solution of P123. This suggests that the drug is mostly encapsulated. The DSC experiments showed that the critical micelle temperature and the enthalpy of aggregation of P123 were not modified by the presence of HEC. But the incorporation of ADA to the micelles showed a reduction of 40% in the enthalpy of aggregation, indicating a strong interaction between P123 and ADA. In contrast to the empty micelles, when HEC is added to the loaded micelles, the enthalpy of aggregation increases and the interaction of HEC-P123 becomes evident. The DLS results support that the hydrodynamic diameter of the ADA-loaded micelles is 17% smaller than the diameter of the empty P123 micelles. In the presence of HEC, the empty or loaded micelles form a larger complex. This suggests that HEC surrounds the micelles and provides the drug with a second protecting shell. This system could be a good candidate for the hydrophobic drug delivery.

Solubilization of active ingredients of different polarity in Pluronic® micellar solutions – Correlations between solubilizate polarity and solubilization site

The solubilization of two pharmaceutically active ingredients (AI) with significantly different water solubility, namely carbamazepine and fenofibrate (solubility of 150ppm and 10ppm, respectively), has been investigated using a series of Pluronics® (Poloxamers) containing different ethylene oxide and propylene oxide (EO/PO) units in the molecule. The results show largely enhanced solubilization of fenofibrate by Pluronic® micelles that increases with the PPO chain length provided the temperature is above the critical micelle temperature (cmt). In contrast the more water-soluble carbamazepine only shows a moderate increase in solubilization upon addition of Pluronics®. Small angle neutron scattering (SANS) and pulsed field gradient (PFG) NMR experiments show that the solubilization of fenofibrate occurs in the core of the micelles, whereas carbamazepine shows no direct association with the micelles. These clearly different solubilization mechanisms for the two AIs were confirmed by Nuclear Overhauser Enhancement Spectroscopy (NOESY) experiments, which show that fenofibrate interacts only with the PPO core of the micelle, whereas carbamazepine interacts with both PPO and PEO similarly. Accordingly, the large enhancement of the solubilization of fenofibrate is related to the fact that it is solubilized within the PPO core of the Pluronic® micelles, while the much more moderate increase of carbamazepine solubility is attributed to the change of solvent quality due to the presence of the amphiphilic copolymer and the interaction with the EO and PO units in solution.

Solution Behavior of Triblock Copolymer in the Presence of Ionic Liquids: A Comparative Study of Two Ionic Liquids Possessing Different Cations with Same Anion

A comparative study of two ionic liquids (ILs) with same anion and different cations on the phase transition changes of aqueous solution of a commonly used triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG–PPG–PEG) (or Pluronic F-108), is undertaken using fluorescence spectroscopy, dynamic light scattering (DLS), viscosity (η), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) techniques. Furthermore, to demonstrate it by direct visualization of various self-assembled morphologies, we employed field emission scanning electron microscope (FESEM). The two ILs include 1-allyl-3-methylimidazolium chloride ([Amim][Cl]) and 1-benzyl-3-methylimidazolium chloride ([Bzmim][Cl]). The results demonstrate that the addition of ILs alter the critical micellization temperature (CMT) toward lower temperatures. The extent to which the CMT altered is observed to be significantly more for [Bzmim][Cl] as compared to [Amim][Cl]. The charge...

Structural insights into the effect of cholinium-based ionic liquids on the critical micellization temperature of aqueous triblock copolymers

Symmetrical poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) triblock copolymer with 82.5% PEG as the hydrophilic end blocks, and PPG as the hydrophobic middle block, was chosen to study the effect of ionic liquids (ILs) on the critical micellization temperature (CMT) of block copolymers in aqueous solution. In the present work, cholinium-based ILs were chosen to explore the effect of the anions on the copolymer CMT using fluorescence spectroscopy, dynamic light scattering (DLS), viscosity (η), FT-IR spectroscopy, nuclear magnetic resonance (NMR), and direct visualization of the various self-assembled nanostructures by scanning electron microscopy (SEM). The result suggests that ILs have the ability to decrease the CMT of the aqueous copolymer solution which is dependent on the nature of the anions of the ILs. The present study reveals that the hydrophobic part PPG of the copolymer has more influence on this behavior than the PEG hydrophilic part.

Reversible Micro- and Nano- Phase Programming of Anthraquinone Thermochromism Using Blended Block Copolymers.

Here, we present an approach to generate materials with programmable thermochromic transition temperatures (TTTs), based on the reversible microcrystallization of anthraquinone dyes with the assistance of blended Pluronic block copolymers. At temperatures above block copolymer critical micellization temperature (CMT), hydrophobic anthraquinone dyes, including Sudan blue II, were dispersed in copolymer micelles, whereas at lower temperature, the dyes formed microcrystals driven by dye-dye and dye-Pluronic molecular interactions. The crystallization process altered the optical properties of the dye with bathochromatic shifts detectable by eye and the thermochromic process was fully reversible. Not only could Pluronic reversibly incorporate the anthraquinone dyes into micelles at elevated temperatures, but it also modulated the crystallization process and resulting morphology of microcrystals via tuning the molecular interactions when the temperature was lowered. Crystal melting transition points (and TTTs) were in agreement with the CMTs, demonstrating that the thermochromism was dependent on block copolymer micellization. Thermochromism could be readily programmed over a broad range of temperatures by changing the CMT by using different types and concentrations of Pluronics and combinations thereof.