Search

The review reports an aqueous solution behavior of commercially available and easy-to-use polymers, i.e., Pluronics®- and PNIPAM-based block copolymers. Both the polymers are stimuli responsive in nature. The present review covers the different aspects of aggregation behavior of Pluronics®- and PNIPAM-based block copolymeric micelles. Here, a comparison of physical properties such as EO–PO block, CP, CMC and CMT is made. Such physical parameters can be modulated with ease by the presence of external stimuli, viz. electrolytes, organic additives such as alcohols, phenols, amides and acids, different types of surfactants and water-soluble polymers, and also by modification of end groups of Pluronics®. But in this review, our main focus is to study the addition of salts and non-electrolytes on the aggregation behavior of Pluronics®. With the help of above parameters, users can get idea about the stability, partition coefficient, solubilization capacity, etc. In analogy with Pluronics®, PNIPAM is also a thermo-responsive polymer with ~ 32 °C lower critical solution temperature (LCST). However, the LCST is independent of the degree of polymerization, i.e., molecular weight of homopolymer. However, the LCST can be tuned in the presence of external stimulus. PNIPAM-based di-block copolymers form various morphologies in different environments. An inverted morphology by double-hydrophilic-block copolymers is also possible. According to US and British Pharmacopoeia, some of the Pluronics® and PNIPAM are recognized as pharmaceutical excipients. Therefore, they have been extensively used for various pharmaceutical formulations. The other applications of these polymers are tissue engineering, bioseparation devices, active membranes, biosensors, rheological modifier, lithium batteries, etc.

The present study was undertaken to unveil the self-assembly of a polyoxyethylene alkyl ether carboxylic acids based nonionic amphiphile known as Akypo® RO90 VG (hereafter written as Akypo) in aqueous medium using cloud point (CP), solution viscosity, dynamic light scattering (DLS), small-angle neutron scattering (SANS) measurements. Surfactants belonging to Akypo family have an average formula CxEOyCH2COOH (i = 8–18, j = 2.5–10) [1] . The surfactant micellizes in aqueous media analogous to conventional surfactants but with some dissimilarity. The influence of external stimuli viz. temperature, pH and electrolyte has been examined to assess the response on the microstructural changes in micelles. SANS experiments provided the exact size and shape of micelles; the micellar growth proposed by high solution viscosity and hydrodynamic diameter (Dh) of micelles from DLS and further reinforced by SANS data. This further divulges that increase of temperature and addition of electrolyte persuade the ellipsoidal to worm-like micellar transition. Change of pH towards an alkaline medium favors the transformation of ellipsoidal micelles into spherical ones which can be correlated with deprotonation of carboxylic acid groups that results in increased solubility of Akypo. The current study authorizes how the size of Akypo micelles can effortlessly be amended in the presence of external stimuli to the desired extent.

Aqueous solution behaviour of non-ionic surfactant namely, p-tert-octylphenoxy polyethylene (9.5) ether, Triton X-100 (abbreviated as TX-100) was examined in the presence of an amphiphilic hydrophobic diol (Surfynol® 104) using viscosity, cloud point (CP), dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. Surfynol® 104 is a hydrophobic diol with limited aqueous solubility. It decreases the CP, elevates the solution viscosity of TX-100 solutions and leads to morphological changes of TX-100 micelles. The micellar transition was further confirmed from scattering techniques (DLS and SANS). With the aim to achieve different micellar transitions, the salt and the temperature effects were additional parameters used. It was revealed that the ellipsoidal to rod-like micellar transition observed at higher level of solubilization of Surfynol® 104 can be drag down to room temperature by incorporation of NaCl. Temperature and NaCl-aided micellar transitions were equally supported from SANS analysis. The observed structural transitions are explained in terms of the hydrophobic interaction between TX-100 and Surfynol® 104.

Pluronics® and Tetronics® are used in industry for solubilizing various kinds of hydrophobic compounds since decades. In present study, moderately hydrophobic linear and star block copolymer viz. Pluronic® P104 and Tetronic® T1304 are employed for the solubilization of four polycyclic aromatic hydrocarbons (PAHs) viz. naphthalene (Np), anthracene (An), phenanthrene (Ph) and pyrene (Py). The aggregation behaviour of these block copolymers in an aqueous media has been investigated by cloud point (CP), viscometry, dynamic light scattering (DLS), and small angle neutron scattering (SANS) techniques. The aqueous solubilities of these PAHs are quite poor, hence their extractions from contaminated areas are difficult. Cloud point of block copolymers linearly decreases as a function of PAHs concentration and strongly depends on the structure of PAHs. The aqueous solutions of both block copolymers are Newtonian fluid. The solubilization of PAHs in these copolymeric micelles leads to increase in the viscosity of solution suggesting the growth of micelles. The effect of concentration and temperature on the size and shapes of micelles were evaluated from DLS and SANS studies. The study provides an alternative method for the remediation of PAHs using inexpensive commercially available block copolymers.

In this paper, we have studied the mixed surfactant systems containing a cationic gemini surfactant N,N′-bis(dimethyldodecyl)-1,2-pentanediammonium dibromide (12-5-12) with several differently charged surfactants (cationic/anionic/non-ionic/zwitterionic) by using surface tension, small angle neutron scattering (SANS) under standard condition. All the surfactants have same dodecyl chain but different in polar head group viz. Sodium dodecyl trioxyethylene sulphate (SDES)(anionic), dodecyl trimethyl ammonium bromide (DTAB) (cationic), 3-[dodecyldimethyl ammonio] propane sulphonate (C12-PS)(zwitterionic), hexaethylene glycol monododecyl ether (C12E6)(non-ionic) and dimethyl dodecyl amine oxide (DMDAO) (cationic-non-ionic). The Clint, Rubingh, Maeda and Rosen approaches were employed to determine various parameters like critical micelles concentration (CMC), surface excess concentration (Гmax), surface pressure at CMC (πCMC), minimum area per molecule (Amin) etc. as well as thermodynamic parameters. Solubilization of some polycyclic aromatic hydrocarbons (PAHs) have done in single as well as in mixed surfactant systems. Order of solubilization capacity of PAHs compounds are different in pure/mixed surfactant micelles. The solubilization efficiency towards naphthalene, anthracene, and pyrene were measured and the molar solubilization ratio (MSR), deviation ratio (R) and micelle-water partition coefficient (km) were evaluated for single and mixed systems.

Aqueous solutions of cetyltrimethylammonium bromide (CTAB) show micellar growth in the presence of various organic and inorganic additives. The simultaneous presence of some of these additives exhibit synergistic effects on micellar growth in this system due to their diverse nature of influences on the critical packing parameter of CTAB micelles. In this manuscript, we report dynamic light scattering, small-angle neutron scattering and rheological studies on influences of the widely used preservative butyl paraben and NaCl on the growth and interaction of CTAB micelles. These additives show synergism in micellar growth and induce micellar attraction-driven phase separations of both upper consolute temperature and lower consolute temperature regimes in aqueous solutions of CTAB. Quite interestingly, such micellar attraction-driven phase separations are also induced in aqueous systems of other cationic and anionic surfactants in the simultaneous presence of a hydrophobic substance and NaCl. These systematic observations of micellar attraction-driven phase separation are the first of this kind in aqueous systems of ionic surfactants. The results also suggest that the use of parabens as preservatives in some ionic surfactantbased formulations can also help in tuning their rheological characteristics.

The triblock Pluronic F127 was modified by introducing poly(N-isopropylacrylamide) (PNIPAM) at both the poly(ethylene oxide) ends, and the pentablock copolymer so-prepared was characterized by gel permeation chromatography and (1)H NMR. The degree of polymerization of NIPAM blocks at the two ends was 7. The solution behavior and microstructure of copolymer aggregates in water and aqueous salt solution were examined and compared with F127 by UV-visible absorption spectroscopy, microdifferential scanning calorimetry, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The behavior of the pentablock copolymer at the air/water interface was determined by Langmuir film balance. Two lower critical solution temperatures were observed for pentablock copolymer, corresponding to poly(propylene oxide) and PNIPAM blocks, respectively. DLS studies show that micelle size increased with increase in temperature and in the presence of salt. SANS measurements provided temperature-dependent structural evolution of copolymer micelles in water and salt solution. The copolymer displays an isotherm with four classical regions (pancake, mushroom, brush, and condensed state). The study has potential applications in controlled drug delivery due to the tunable phase behavior and biocompatibility of the copolymer.

Pluronics(®) are an important class of non-ionic surfactants because of their rich phase behavior and numerous industrial and biomedical applications. F127, an FDA approved Pluronic(®) is the most prominent member amongst them owing to its potential uses as vehicle for drug delivery and template for the fabrication of mesoporous materials. A cubic micellar gel formed by this copolymer above 15 wt% concentration is the commonly used form of self assembled structure for these applications. In this manuscript we report SANS, fluorescence and rheological studies on the effect of n-butanol on gelation characteristics of aqueous F127 solutions. The studies show that solubilization of n-butanol results in a large increase in viscosity of micellar solution at a fixed copolymer concentration, and leads to the formation of stiff gel at F127 concentration as low as 9 wt%. SANS and fluorescence studies attribute this to enhancement in micellar solvation due to solubilization of n-butanol. Quite interestingly, SANS studies show that n-butanol induced F127 gels form at significantly lower micellar volume fraction than the pure F127 gels. The observed improvement in gelation characteristics can have important bearing with the application in making mesoporous materials since n-butanol is used as co-surfactant to control pore size of such structures formed with F127 gels as template.

The commercially available polypropylene oxide (PPO)–polyethylene oxide (PEO) symmetrical triblock copolymers (Pluronics®) have been recognized as pharmaceutical excipients and used in a variety of applications. This paper reports studies on micellar and solubilization behavior of three PEO–PPO–PEO block copolymers, viz. P103, P104 and P105 (same PPO mol. wt = 3250 g·mol−1 but different % PEO = 30, 40 and 50 %, respectively) in aqueous solutions. Critical micellization concentrations (CMCs), critical micellization temperatures (CMTs), and micelle size/polydispersity for copolymers with and without the drug, nimesulide (NIM), are reported. The solubilization of NIM is significantly enhanced with increasing hydrophobicity (P103 > P104 > P105), concentration, temperature and in the presence of added salt. The copolymer hydrophobicity, temperature and the drug loading strongly affect micelle behavior. The micelle–water partition coefficient (P) and thermodynamic parameters of solubilization, viz. Gibbs energy (\( \Updelta G_{s}^{\text{o}} \)), enthalpy (\( \Updelta H_{s}^{\text{o}} \)) and entropy (\( T\Updelta S_{s}^{\text{o}} \)), were calculated. The solubilization site of the drug in different micellar solutions and its release from Pluronics® micelles in phosphate buffer saline (PBS) solution at 37 °C were examined. The kinetics of NIM exhibits burst release characteristics, which are believed to be controlled by degradation of the copolymers. These studies were carried out to investigate the feasibility of using Pluronics® as a release vehicle of nimesulide in vitro. From the results, it was concluded that Pluronic® based formulations might be practical for drug delivery.

The aqueous solution behavior of a poly(ethylene oxide)–poly(propylene oxide), PEO–PPO, star block copolymer Tetronic® T904 with solubilized phenol and benzene was examined by cloud point (CP), viscosity measurements, 1D and 2D NMR experiments, dynamic light scattering(DLS), and small angle neutron scattering (SANS) techniques. Both the solubilizates decreased the CP and the critical micelle temperature (CMT) of T904. This behavior is explained in terms of the free energy of hydration of the phenol/benzene and the replacement of water molecules from the PPO and PEO blocks by the formation of hydrogen bonds which induced micellization and phase separation at lower temperature. The effect of solubilizates on micellar growth was investigated by viscosity and DLS. Benzene molecules solubilized in T904 micelles are found in intimate contact with the PEO chain while we find that the phenol molecules are located within micelle palisade layer as well as at the micelle–water interface. The SANS data indicate that these solubilizates significantly influence the solution behavior of the copolymer; the structure of micelles stays essentially constant as a function of solubilizate concentration. On the other hand, the shell thickness changes rapidly with phenol concentration. The results showed that phenol decreased CP/CMT and had a more pronounced effect on micellar growth as compared to benzene.

The effect of 1-alcohols on aqueous solution behavior of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) triblock copolymers was investigated from cloud point (CP), viscosity, dynamic light scattering (DLS) and 1H NMR. Three triblock copolymers Pluronics® P103, P104 and P105, each having same size middle PPO block but varying PEO end blocks, were used. Short chain alcohols (methanol, ethanol and 1-propanol) increased CP and critical micellization temperature (CMT) while medium chain alcohols (1-butanol, 1-pentanol and 1-hexanol) showed a decrease. The results are explained on the basis of structure and hydrophobicity of alcohols. Short chain alcohols affect by enhancing the hydrogen bonding and hydrophobic hydration while medium chain alcohols replace water molecules from PPO core and induce micelle growth at temperatures close to CP. Nuclear Overhouser Effect Spectroscopy (NOESY) experiments reveal that the P104 chains have significant motional freedom inside the micelles, leading to a folding of the PPO chains towards methyl protons of hydrocarbon chain of C4–C6 alcohols molecules in the micelles. The added alcohols can be used to tune the micellization and micellar characteristics of these amphiphilic copolymers.

In present study, we have investigated the effect of an anionic surfactant sodium dodecyl sulfate (SDS) and clay on calcium alginate beads was studied to remove methylene blue (MB) and to improve the adsorption capacity. The effects of various experimental parameters, such as shaking rate, initial dye concentration, temperature, and pH on the adsorption rate, have been studied. Equilibrium studies showed that the sorption of the dye was enhanced in presence of SDS. Scanning electron microscope (SEM) analysis showed that SDS entrapped beads have more pores and cavities which could be responsible for improved adsorption of MB. The kinetics of cationic dye adsorption nicely followed pseudo-second-order process. The evaluated thermodynamic parameters (ΔG o, ΔH o, ΔS o) suggest endothermic adsorption of MB. The results revealed that the surfactant entrapped alginate could be considered as potential adsorbents for MB removal from aqueous solutions.

The mixed surfactant systems of anionic sodium dodecyl trioxyethylene sulfate (SDES) and gemini surfactants (cationic) of the series N,N’-bis-(dimethyldodecyl)-α,ω-dialkanediammoniumdibromide, 12-s-12 (s = 2, 4, 6) at different molar ratios were studied by surface tension measurements of aqueous solution as a function of total concentration under standard condition. Various parameters like critical micelle concentration (CMC), surface excess concentration (Гmax), minimum area per molecule (Amin), interaction parameter of mixed micelle and adsorption monolayer (βm, βo) as well as thermodynamic and micellar properties have been determined using Clint, Rubingh, Maeda and Rosen approach. The strong interaction showing very low CMC and large negative interaction parameter β were due to weakening of the electrostatic head group repulsion which favors the mixed micelle formation. The results are discussed in terms of the structural characteristics and spacer chain of gemini surfactants and also in terms of the presence of EO group in SDES molecule. Gemini surfactants bind tightly with SDES by electrostatic, hydrophobic and ion–dipole interactions. Thermodynamic parameters for all three cationic–anionic mixed systems were evaluated. From excess free energy of micellization we can conclude that thermodynamically stable micelles are formed with strong synergistic interaction.

The solubilization of benzene and toluene in micellar solutions and the effects on the micellization and micelle size of ethylene oxide-propylene oxide triblock copolymers were investigated by dynamic light scattering (DLS), small angle neutron scattering (SANS), and 2D NMR spectroscopy. The copolymeric surfactants have the same size as the middle hydrophobic polypropylene oxide block (Mol. Wt. 3250) and varying polyethylene oxide end blocks (30, 40 and 50%). The solubilization and the properties of the micelles in the presence of the solubilizates were investigated; the results reveal that the more hydrophobic copolymer showed better solubilization. The cloud points of the copolymers decreased in the presence of oils; the depression in the cloud point is due to the formation of an electron donor–acceptor complex. DLS shows that the effect of benzene is dominated at high oil concentration. SANS data show that the micelles remain spherical in shape and that the micellar core size does not change with higher benzene concentration; observed changes in the low scattering vector region could be because of some small amount of benzene clusters formed at higher benzene concentration. Finally, the locus of solubilization of the oils in the copolymer micelles was determined via 2D NMR experiments. In all cases, significant nuclear Overhauser effect spectroscopy (NOESY) cross peaks were observed that appeared to correlate well with the expected loci of these solubilizates in micelles. Hence, the noninvasive NOESY technique provides important information on the location of the aromatic solubilizates in these copolymer micelles that depends on the structure of the oils.

The micellar and phase behavior of an ethylene oxide-propylene oxide branched octablock copolymer Tetronic T 904 (hereafter written as T904) in water and NaCl solutions was examined. The copolymer shows a cloud point (CP) ranging from 74-65°C in the concentration range of 1-10% and forms aggregates (micelles) with a hydrodynamic diameter around 10-12nm in the temperature range 30-40°C. Stable, bluish solutions containing aggregates of variable size (several hundred nm in some cases) were observed even at temperatures much less than the critical micellization temperature (CMT=30°C for a 2% solution in water). The CP and the CMT markedly decrease in the presence of NaCl due to the dehydration of the polyethylene oxide shell. The size of the micelles in water or salt solutions increases at temperatures close to the CP as inferred from viscosity measurments. A model drug compound (nimesulide, NIM) was solubilized in T904 micelles which showed a remarkable increase in solubilization at higher temperature; however, a decrease in solubilization was observed in salt solutions. The thermodynamic parameters for solubilization were obtained, and the location of NIM in the copolymer micelles was investigated by UV-Visible spectroscopy.

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 (

Micelles of ABA type triblock copolymers (where A is polyethylene oxide PEO and B is polypropylene oxide PPO) viz. Pluronic® P103, P104 and P105 (each containing almost the same PPO mol wt. ∼ 3250 g/mol and 30, 40 and 50 wt.% of PEO, respectively) in the presence of p -hydroxybenzoic acid (PHBA) and its sodium salt (Na-PHBA) were examined by viscosity, dynamic light scattering (DLS), small angle neutron scattering (SANS) and NMR. Spherical polymeric micelles (apparent hydrodynamic diameter ∼ 20 nm) in water at 30 ° C grow in the presence of PHBA and transform into prolate-ellipsoidal shape with an increased aggregation number. The micellar transition was favored at higher PHBA concentration, temperature and for copolymers with more hydrophobicity. The PHBA salt, however, increased cloud point and showed only a marginal decrease in aggregation number even at much higher concentrations. The location of PHBA in micelle was elucidated by nuclear Overhauser enhancement spectroscopy (NOESY).

Pluronics® are considered as potential materials for the removal of contaminants like phenol from polluted water sources because of their superior solubilizing capacity of aromatic compounds. Systematic studies on the influence of solubilization of phenol on room temperature aggregation characteristics of Pluronics® in water are, however, conspicuous by their absence. In this manuscript, we thus report DLS, SANS and rheological studies on the influence of phenol on the aggregation characteristics of four Pluronics® viz. F127, P123, P104 and P103. The aim of this study has been to understand the role played by the composition of the Pluronics® in determining growth and interaction of the micelles induced by solubilization of phenol. The study shows that in the case of F127 and P123, phenol solubilization leads to a large increase in light scattering intensity due to an onset of attractive intermicellar interactions and consequent formation of micellar clusters. P123 being smaller than F127 shows a subsequent time dependent micellar growth, leading to a sphere-to-rod shape transitions in micelles. The copolymers P103 and P104, which are smaller and less hydrophobic than P123, respectively, exhibit a large increase in solution viscosity in the presence of phenol owing to a rapid sphere-to-rod micellar growth. The observation of such a fine interplay between the growth and interaction of the pluronic micelles in the presence of a hydrophobic solvent is first of its kind and highlights the role of composition of pluronic in determining the kinetics of the micellar restructuring process.

The influence of salicylic acid (SA) on the aggregation characteristics of Pluronic® P85 has been studied in the aqueous medium by dynamic light scattering (DLS), small angle neutron scattering (SANS), steady-state fluorescence and rheological measurements. DLS studies suggest that SA, which is used in the treatment of various skin diseases, induces a room temperature growth of the P85 micelles. Steady-state fluorescence studies and cloud point measurements attribute this to the ability of SA to stay in micellar corona and consequently dehydrate the copolymer micelles by displacing water from the corona region. A large increase in the viscosity of the P85 solutions accompanying the observed micellar growth, and SANS and rheological studies reveal that the P85 micelles undergo a sphere-to-rod shape transition in the presence of SA. Pluronics® being biomedically important surfactants, the observed effects suggest that P85 could be considered as a suitable agent as a carrier of SA, as well as a viscosity modifier of the formulations of SA. The studies also show that the effectiveness of SA in causing the observed micellar dehydration increases with a decrease in pH, which suggests that the observed effects of SA on the P85 micelles arise due to the presence of the unionized form of the SA in the micellar corona region. Rheological studies show that unlike other Pluronic® worm like micellar systems, the viscoelastic behavior of the present system shows close conformity with the Maxwell law. Such difference in the behavior has been attributed to faster restructuring and breaking processes of the P85 micelles due to the high hydrophilic PEO group content (50%) of P85 molecules.