Pluronic L64 Research Articles

Biophysical Characterization of Complexation of DNA with Block Copolymers of Poly(2-dimethylaminoethyl) Methacrylate, Poly(ethylene oxide), and Poly(propylene oxide)

The interactions of DNA (salmon testes) with two new cationic block copolymers made of poly(2-dimethylaminoethyl) methacrylate and poly(ethylene oxide), PEO-pDMAEMA, or poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), L92-pDMAEMA, were studied with the aim to understand their different in vitro transfection efficiencies when used as nonviral delivery vectors. PEO-pDMAEMA does not show surface activity while L92-pDMAEMA is as surface active as its parent Pluronic L92. Surface tension, titration microcalorimetry, ethidium bromide displacement, and zeta-potential measurements were carried out in phosphate buffers at pH 5 and 7. The association of L92-pDMAEMA with DNA was strongly exothermic at both pHs; the critical aggregation concentration (CAC) corresponded to a N/P ratio of 0.3, the maximum energy evolved was reached for N/P ratios of 0.82 and 1.27 at pH 5 and pH 7, respectively, and the saturation occurred for N/P ratios close to 2. The presence of L92 in the structure of this new block copolymer apparently did not modify the thermodynamic parameters of the interaction with DNA. In contrast, the interaction with PEO-pDMAEMA was significantly less exothermic, and CAC and saturation occurred for N/Ps equal to 0.43 and 1.37, respectively. The strong affinity of L92-pDMAEMA for DNA was reflected in its capacity to displace ethidium bromide and in the jump in the values of the zeta potential when N/P is near 1. Above the N/P ratio at which electroneutral polyplexes are formed, only at pH 5 an excess of L92-pDMAEMA is incorporated in the complexes, resulting in positively charged complexes. The profile of the zeta-potential values obtained for mixtures of L92-pDMAEMA with Pluronic P123 showed a shift to a lower N/P ratio, owing to an easier interaction of L92-pDMAEMA molecules with DNA in the presence of P123. Additionally, a visual inspection of the systems indicates that P123 contributes to stabilize/solubilize the DNA/cationic polymer aggregates, by avoiding the typical phase separation near the charge neutralization point. The information obtained can be particularly useful to optimize the conditions to form efficient polyplexes for gene delivery systems.

Micellization of Pluronic L64 in salt solution by FTIR spectroscopy

The micellization of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (Pluronic L64: EO 13PO 30EO 13) with the presence of various sodium halides (NaF, NaCl, NaBr and NaI) was studied by Fourier transform infrared (FTIR) spectroscopy. The critical micelle temperature (CMT) of Pluronic L64 in the salt solution decreased with the addition of salt and the anion effect followed the sequence: F − > Cl − > Br − > I −. The deconvolution method was used to resolve the overlapping bands in the C O stretching region. The deconvoluted spectra provide information about the microenvironmental changes of ethylene oxide (EO) and propylene oxide (PO) blocks in the salt solution. Both the PEO and PPO blocks are dehydrated at lower temperature in the salt solution. The standard enthalpies (Δ H 0) and entropies (Δ S 0) of micellization for copolymer, PEO and PPO blocks, decreased by the addition of salt. Thus, it is deduced that the salt-induced decrease of enthalpy of micellization contributes to the decrease of CMT. The results reveal the leading role of salt–water interaction in promoting the micellization of PEO–PPO–PEO copolymer on addition of salt.

Interactions of Pluronics with phospholipid monolayers at the air–water interface

Pluronics are triblock copolymers which are extensively applied excipients shown to interact with cell membranes. The aim of our study was to apply monolayer techniques and epifluorescence microscopy to investigate the interaction behavior between selected Pluronics and phospholipid monolayers which serve as a model of cell membranes. The results showed that Pluronic L61 with hydrophobic proportions much larger than those of F68 demonstrated condensed film-like surface behavior while F68 exhibited more expanded behavior. The increments of surface pressure and the changes of image were more obvious in adding Pluronic L61 than F68 to the subphase of dipalmitoylphosphatidylcholine (DPPC) monolayers, which indicated that the interaction may be related to van der Waals forces and hydrophobic interaction. Pluronics selected with higher hydrophobicities demonstrated larger surface activities and penetration abilities while being added to the subphase of DPPC and dimyristoylphosphatidylcholine (DMPC) monolayers. Pluronic P85 and F68 were found to be squeezed to subphase at higher surface pressures, which may be attributed to their relatively higher hydrophilicities.

Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants

The mixed micellar properties of a triblock copolymer, Pluronic L64, (EO) 13(PO) 30(EO) 13, and a nonionic surfactant, Triton X-100, in aqueous solution with conventional alkyl ammonium bromides and their dimeric homologues were investigated with the help of fluorescence and cloud point measurements. The composition of mixed micelles and the interaction parameter, β, evaluated from the critical micelle concentration (cmc) data for different mixtures using Rubingh's and Motomura's theories are discussed. It has been observed that the mixed micelle formation between monomeric/dimeric alkyl ammonium bromides and L64 was due to synergistic interactions which increase with the increase in hydrophobicity of the cationic component. On the other hand, synergistic mixing was observed in the mixed micelles of Triton X-100 and monomeric cationic surfactants, the magnitude of which decreases slightly with the increase in hydrophobicity of the cationic component. Antagonistic interactions were observed in the case of Triton X-100 and dimeric cationic surfactants.

Drying of Films Formed by Ordered Poly(ethylene oxide)−Poly(propylene oxide) Block Copolymer Gels

The drying of hydrogel films formed by poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Pluronic P105 and Pluronic L64) is investigated at various air relative humidity (RH) conditions in the range 11-94%. These amphiphilic block copolymers self-assemble to form a variety of ordered (lyotropic liquid crystalline) structures as the water content decreases. The amount of water lost increases linearly with the drying time initially (constant rate region, stage I). After this linear region, a falling rate is observed (stage II). The drying rate increases with decreasing RH, thus greatly shortening the drying time. A decrease of the initial film thickness or a decrease in the initial water content shortens the drying time; however, the drying mechanism remains the same. Analysis of the experimental data shows that the hydration level in the Pluronic hydrogel mainly determines the drying rate, rather than the type of ordered structure formed. Two distinct regions (liquid/gel and solid/crystalline) are observed in the drying isotherm for PEO-PPO block copolymers and homopolymer poly(ethylene glycol)s. A model for one-dimensional water diffusion is used to fit the experimental drying results at different RH, initial film thickness, and initial water content conditions. The model accounts for the shrinkage of the film during drying and for a water diffusion coefficient that is a function of the water concentration in the film. For the experimental conditions considered here, the Biot number (Bi) is less than unity and the drying is mainly limited by evaporation at the film surface. The diffusion model is used to obtain information for cases where Bi > 1.

Structural studies of amphiphiles adsorbed at liquid–liquid interfaces using neutron reflectometry

We report the application and refinement of a recently developed method for structural studies at a liquid liquid interface using neutron reflectometry. The technique involves the entrapment of a thin oil layer between a silicon substrate and an aqueous subphase. The thin oil film is prepared by spin-coating an oil film on to an oleophilically treated silicon substrate. During the reflectivity measurement the sample is maintained in a horizontal position, and the angle of incidence of the neutron beam is varied using a supermirror. Attenuation of neutron reflectivity at the lowest angle of incidence is used to determine the oil-layer thickness. We report information regarding the structure at the interface between hexadecane and a 0.1% w/v aqueous solution of the triblock copolymer Pluronic L64 with EO13PO30EO13 (EO = ethylene oxide; PO = propylene oxide) and the interface between hexadecane and a 3.7 mmol dm(-3) (approximately critical micelle concentration) aqueous solution of the cationic surfactant tetradecyltrimethylammonium bromide (C14TAB). For the C14TAB system, the reflectivity data unambiguously reveal the presence of a region highly concentrated in C14TAB on the oil side of the interface. For the Pluronic L64 system, the data suggest that the polymer adsorbs at the interface occupying both oil and water sides of the interface. Model scattering length density profiles that capture these features are presented and further models that better fit the data are discussed.

Molar volumes and isentropic compressions of pluronics L64 and P123 in aqueous surfactant solutions, over the critical temperature range of aggregation

Interactions between triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), EO x PO y EO x , and ionic surfactants, have been investigated using density and ultrasound speed measurements over the temperature range 288.15–318.15 K. Two copolymers, denoted L64 ( x = 13, y = 30) and P123 ( x = 20, y = 69) were selected because their critical micellar temperatures (CMT) could be conveniently covered. The ionic surfactants were the sodium dodecylsulfate, SDS, and the hexadecyltrimethylammonium bromide, CTAB. The transfer molar volumes and transfer molar isentropic compressions of each copolymer from water to aqueous micellar solution were calculated and analysed at a constant copolymer concentration ( w p = 1 % ) for varying surfactant concentrations up to 0.15 mol kg −1. The trends in the variations of the transfer properties of either L64 or P123 gradually decrease from positive to negative values over the range that encompasses the critical micellar temperature. By contrast, they are remaining mostly similar apart from CMT, i.e. the copolymer is present either in monomeric or micellar state, and are weakly dependent on the temperature. The transfer values are assumed to be the sum of two contributions of opposite sign. A positive one arises from the hydrophobic interactions between the monomers and SDS and gives rise to the formation of copolymer–surfactant complexes. A negative one arises from the rehydration of the copolymer molecules expelled from the pluronic micellar core during the disruption of the pluronic micelles with increasing concentration of SDS. This negative contribution has been shown to be rigorously equivalent to the value of the micellisation properties of the pluronics in water. Results obtained in the present work for CTAB solutions reveal seemingly similar mechanisms of binding between the surfactant and the pluronics.

Thermodynamics of Temperature-Sensitive Polyether-Modified Poly(acrylic acid) Microgels

The temperature-induced structural changes and thermodynamics of ionic microgels based on poly(acrylic acid) (PAA) networks bonded with poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) (Pluronic) copolymers have been studied by small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (USANS), differential scanning calorimetry (DSC), and equilibrium swelling techniques. Aggregation within microgels based on PAA and either the hydrophobic Pluronic L92 (average composition, EO8PO52EO8; PPO content, 80%) or the hydrophilic Pluronic F127 (average composition, EO99PO67EO99; PPO content, 30%) was studied and compared to that in the solutions of the parent Pluronic. The neutron scattering results indicate the formation of micelle-like aggregates within the F127-based microgel particles, while the L92-based microgels formed fractal structures of dense nanoparticles. The microgels exhibit thermodynamically favorable volume phase transitions within certain temperature ranges due to reversible aggregation of the PPO chains, which occurs because of hydrophobic associations. The values of the apparent standard enthalpy of aggregation in the microgel suspensions indicate aggregation of hydrophobic clusters that are more hydrophobic than the un-cross-linked PPO chains in the Pluronic. Differences in the PPO content in Pluronics L92 and F127 result in a higher hydrophobicity of the resulting L92-PAA-EGDMAmicrogels and a larger presence of hydrophobic, densely cross-linked clusters that aggregate into supramolecular structures rather than micelle-like aggregates such as those formed in the F127-PAA-EGDMA microgels.

Ionophoric activity of pluronic block copolymers.

Pluronic block copolymers (triblock copolymers of poly(ethylene oxide) and poly(propylene oxide)) exhibit a chemosensitizing effect on multidrug resistant cell lines. Changes in membrane permeability are hypothesized to be responsible because inhibition of drug transport mediated by both the multidrug-resistance-associated protein and the P-glycoprotein drug efflux system has been observed. To test this hypothesis, we now have studied the ion conductivity mediated by Pluronic L61. Besides a detergent-like action, the copolymer was able to form regular channels and to exhibit carrier activity. Long living ion channels were formed by polymer oligomerization. Aggregate equilibrium was shifted toward L61 monomers and dimers, which operated as mobile carriers. Copolymer-induced membrane permeability for potassium ions (1 M KCl) was less than 10(-8) cm s(-1), whereas the permeability for uncharged doxorubicin molecules (1 mM) was equal to 5 x 10(-4) cm s(-1). The results are consistent with reports about an increased doxorubicin accumulation in cells (Venne, Li, S., Mandeville, R., Kabanov, A., and Alakhov, V. Y. (1996) Cancer Res. 56, 3626-3629). However, the increased permeability contrasts with the polymer-mediated decrease of drug efflux from cells. Preferential polymer binding to membrane proteins may mask the unspecific effect of L61 observed on lipid bilayers.

Studies on apparent molar volumes and heat capacities of several pluronics (triblock copolymers) in aqueous solutions of sodium dodecyl sulfate at 298.15 and 318.15 KElectronic supplementary information (ESI) available: Apparent molar properties of SDS in aqueous pluronic solutions at 298.15 and 318.15 K. See http://www.rsc.org/suppdata/cp/b3/b313717a/

Density and heat capacity measurements were performed in order to investigate the interactions between the ionic surfactant sodium dodecyl sulfate (SDS) and some triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), at 298.15 and 318.15 K. The pluronics L31, L35, 10R5, L64, F68 and P123, were selected as copolymers because of their convenient hydrophilic-hydrophobic ratio and critical micellar temperature. Molar volumes and heat capacities of transfer of either SDS or copolymer from water to an aqueous mixed solution were calculated from the density and heat capacity values and analysed as a function of the surfactant concentration. It was found that the transfer properties depend mainly on the state of the copolymers. For the unassociated copolymers, the molar volumes of transfer of both SDS and copolymer are positive. The initial sharp increase seen in the corresponding plots against surfactant molality signals the formation of a surfactant-copolymer complex up to the saturation of the copolymer. Thereafter, the constant values of transfer volumes of copolymers depend mainly on the length of the poly(propylene oxide) block. For the associated copolymers, negative volumes of transfer of either SDS or copolymer were observed. They are ascribed to interactions between SDS and copolymer micelles that give rise to a rapid breakdown of the aggregates. The profiles of the transfer heat capacity curves show more complicated trends through the critical micellar concentration region, which are interpreted as being due to the large positive contribution of the relaxation terms related to the equilibrium shifts induced by the temperature.

Association Behavior of PEO–PPO–PEO Block Copolymers in Water or Organic Solvent Observed by FTIR Spectroscopy

Fourier transform infrared (FTIR) spectroscopy is applied to investigate the association behavior of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymers in water or organic solvent as a function of temperature. In aqueous solutions, when the temperature approaches the critical micellization temperature, the antisymmetric C-H stretching vibration of methyl groups shifts toward lower wavenumber. It indicates that the methyl groups are experiencing a progressively less polar environment and the interaction of the methyl groups with water molecules is weakened by heat. At higher temperatures, the symmetric deformation vibration of methyl groups is composed of two bands, which are related to hydrated and dehydrated state. The proportion of the dehydrated methyl groups of Pluronic polymers increases with an increase of temperature, which means the exclusion of water from the micelle cores and formation of micelles with a denser PPO core at higher temperatures. A more hydrophobic Pluronic polymer would form a micelle in water with a higher proportion of dehydrated methyl groups. No changes in FTIR spectra correspond to temperature dependent gelation of Pluronic F127 in water. Based on FTIR spectroscopic results of Pluronic P104, the PPO blocks are hydrated only in a condition of lower temperature and lower polymer concentration. In the hydration process, PEO blocks would be hydrated preferentially where H2O molecules are bound easily to PEO segments. The water-induced reverse micelle formation of Pluronic L92, in p-Xylene solution has also been investigated by FTIR spectroscopic technique. The reason of reverse micelle formation is explained by the strengthening of the intermolecular interactions of copolymers, which was originated from the interactions of solubilized water.

Cell death induced by vaccine adjuvants containing surfactants

Many vaccine adjuvants contain surface-active agents, but the immunological roles played by these components have been essentially ignored. The objective of this study was to examine possible apoptotic and necrotic effects of the surface-active agents, Pluronic L121 and Tween 80, which are components of L121-adjuvant (a formulation we synthesized with the aim of representing several commercially produced adjuvants), on EL4 lymphoma cells. Cell viability and cytolytic effects were analyzed using the MTT and LDH release assays, and the distribution of cells in different stages of the cell cycle after treatment with these agents was analyzed by propidium iodide (PI) staining and flow cytometry. L121-adjuvant was shown to induce cell cycle arrest and inhibit cell proliferation. Treatment of EL4 cells with surface-active agents resulted in a concentration-dependent increase in the apoptotic/necrotic cell populations. Fluorescence microscopy using Hoechst 33342 staining demonstrated chromosome condensation and DNA fragmentation in cells treated with surfactants or adjuvant. The apoptotic and necrotic effects of vaccine adjuvant containing surface-active agents were confirmed by Annexin V/propidium iodide staining and flow cytometric analysis. Pretreatment of EL4 cells with zVAD-fmk, a broad range caspase inhibitor, partially prevented apoptosis induced by Pluronic L121, but did not prevent the cell death induced by Tween 80 or L121-adjuvant. These findings suggested that Tween 80 and L121-adjuvant induced apoptosis in EL4 cells via a “non-classical” caspase-independent pathway. Results presented in this study suggest mechanisms of elicitation of CD8 +, class I-restricted CTL response by soluble antigens mediated by the vaccine adjuvant containing surface-active agents.

Observation of Liquid-to-Glass and Glass-to-Glass Transitions in L64/D2O Triblock Copolymer Micellar System

We report photon correlation spectroscopy (PCS), low shear viscosity and small angle neutron scattering (SANS) studies of a Pluronic L64 micellar system in aqueous solutions at high polymer concentrations (wt%), 35.0%<c<54.4%, in a temperature range where a kinetic glass transition (KGT) has been observed. We analyze SANS intensity distributions in the liquid state assuming that the micelles are spherical and interact among themselves via an effective pair-potential consisting of a hard core plus a narrow attractive square-well, the depth of which is temperature dependent. Comparison of the potential parameters so obtained with the phase diagram predicted recently by mode coupling theory (MCT) allows us to verify the existence of the so-called “liquid to attractive glass” KGT line. We then use scaling plots of SANS intensity distributions to show the existence of another branch of the KGT line where transitions from a repulsive glass to an attractive glass occur. In particular, we show an evidence of the existence of the so-called A3 singularity end point where two glasses become identical in local structure [Sow-Hsin Chen, Wei-Ren Chen, Francesco Mallamace, “The glass–glass transition and its end point in a co-polymer micellar system”, to be published].

Smart Microgel Studies. Polyelectrolyte and Drug-Absorbing Properties of Microgels from Polyether-Modified Poly(acrylic acid)

The study dealt with microgels that consist of loosely cross-linked poly(acrylic acid) onto which poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO−PPO−PEO) copolymers such as Pluronic F127 (average composition EO99PO67EO99) or L92 (EO8PO52EO8) segments are grafted. Microgels based on the more hydrophobic Pluronic L92 exhibited highly porous structure, while the microgels containing Pluronic F127 were generally larger and possessed smooth surfaces, a homogeneous structure, and lower ion-exchange capacity. A good correlation was observed between the microgel surface potential obtained from the potentiometric titration data and the independently measured electrophoretic ζ-potential. The differences in the microgel ion-exchange capacity account for the differences in the capacity of the microgels to absorb weakly basic anticancer drugs such as mitomycin, mitoxantrone, and doxorubicin. The uptake of hydrophobic drugs such as Taxol, estradiol, progesterone, and camptothecin was dictated ...

Pluronic L61 accelerates flip-flop and transbilayer doxorubicin permeation.

It has recently been found that Pluronics (block copolymers of ethylene oxide, EO, and propylene oxide, PO) favor the permeability and accumulation of anthracycline antibiotics, for example doxorubicin (Dox), in tumor cells. In an effort to understand these results, the interaction of EO(2)/PO(32)/EO(2) (Pluronic L61) with unilamellar egg yolk vesicles (80-100 nm in diameter) was examined. A partition coefficient K(p)=[Pl](membrane)/[Pl](water)=45 was determined. This corresponds to adsorption of about 20 polymer molecules to the surface of each vesicle in a 20 microM polymer solution. Despite this rather weak adsorption, Pluronic has a substantial effect upon the transmembrane permeation rate of Dox and upon the phospholipid flip-flop rate within the bilayers. Thus, the Dox permeation rate increases threefold and the flip-flop rate increases sixfold in 20 microM Pluronic. The two rates increase linearly with the amount of adsorbed polymer. The obvious ability of Pluronics to increase the mobility of membrane components may have important biomedical consequences.

Emulsion stability of PMMA particles formed by dispersion polymerization of methyl methacrylate in supercritical carbon dioxide

Poly(methyl methacrylate) (PMMA) microparticles have been made by dispersion polymerization of methyl methacrylate (MMA) using PDMS-g-pyrrolidone carboxylic acid (Monasil PCA), a CO 2-philic stabilizer, in supercritical carbon dioxide. The sizes of the resulting polymer particles were in the range of 2.6–5.0 μm. As the amount of surfactant increased, the particle size became smaller and the size distribution, more uniform. Among the three different amounts of initiator between 1 and 2% of monomer, 1% gave the best particle size, morphology as well as molar weights of polymer. These PMMA particles were stable in the aqueous buffer solution containing Pluronic L62 surfactant. By sonication the agglomerated polymer particles were disrupted to form small primary particles and the sonicated emulsion was more stable than the original one.

Effects of polyether-modified poly(acrylic acid) microgels on doxorubicin transport in human intestinal epithelial Caco-2 cell layers

Novel microgels composed of cross-linked copolymers of poly(acrylic acid) and Pluronics were evaluated as possible permeation enhancers for doxorubicin transport using Caco-2 cell monolayers as a gastrointestinal model. Pluronic, triblock copolymers of ethylene oxide (EO) and propylene oxide (PO), were chosen to represent the most hydrophobic (Pluronic L61 and L92 with average compositions of EO 3PO 30EO 3 and EO 8PO 52EO 8, respectively) and the relatively hydrophilic (Pluronic F127 with average formula EO 99PO 67EO 99) extremes of this class of block copolymers. The weight ratio of Pluronic to poly(acrylic acid) in the microgels was set at 45:55. By inhibiting the P-glycoprotein (P-gp)-mediated doxorubicin efflux from the cells and enhancing the passive influx, the microgels were shown to enhance the overall cell absorption of doxorubicin. The enhancement effect was more pronounced than with a known penetration enhancer, Pluronic L61, and was comparable to that of Pluronic L92. Microgels exhibited synergism of the doxorubicin transport enhancement with Verapamil, a known inhibitor of the P-gp. The effects of the microgels were studied using the hydrophilic marker ([ 14C]mannitol) test and the MTT assay. Transepithelial electrical resistance (TEER) studies demonstrated that the microgels decreased TEER to about 80% of initial values, but these minor effects were fully reversible, indicating viability of the cells after incubation with microgels. No significant enhancement of [ 14C]mannitol transport by microgels was observed, relative to Carbopol 934NF (control polymer). Cytotoxicity studies confirmed that the transport-enhancing properties of the microgels were not due to damage of the Caco-2 cell monolayers.

Study of the Formation of the Mesoporous Material SBA-15 by EPR Spectroscopy

SBA-15 is an hexagonal mesoporous material which is synthesized with nonionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers (Pluronics, EOyPOxEOy), templates. Pore diameters in the range of 2−30 nm can be obtained with a relatively thick silica wall (up to 6 nm). This material possesses both large, uniform, and ordered channels, along with a complementary net of micropores which provides connectivity between the ordered channels through the silica. This study focuses on the investigation of the formation mechanism of SBA-15 with emphasis on the PEO interactions with the silica and the initiation of the micropores. This was achieved using in situ X-band EPR spectroscopy in combination with electron spin−echo envelope modulation (ESEEM) experiments. The paramagnetic centers were introduced as spin-labeled Pluronic L62 (EO6PO30EO6) where nitroxides replace the OH groups at the end of the polypropylene oxide (PEO) blocks (L62-NO). Initially, the acidic reaction conditions we...

Simulation of the Phase Behavior of the (EO)13(PO)30(EO)13(Pluronic L64)/Water/p-Xylene System Using MesoDyn

The phase behavior of the (EO)13(PO)30(EO)13(Pluronic L64)/water/p-xylene system in the mesoscopic region was investigated using MesoDyn, a new dynamic density functional method. The “equivalent chain” method was used to perform the parametrization of the Gaussian chain. In this paper, we compare the mesoscopic morphology formations of systems at different concentrations of solvents and discuss the effect of water on the formation of micelles. The calculated results show that Pluronic L64 does not form polymolecular micelles in pure p-xylene or in the presence of a small amount of water, but with an increase in the concentration of water, polymolecular micelles in different shapes were formed. By analyzing the water distributions of the systems after 1000 simulation steps, we prove that free water does exist in the micellar core. The effects of temperature and PEO and PPO block sizes are also investigated. The results indicate that the formation of reverse micelles is exothermic, and so the formation of reverse micelles becomes more difficult and the rate becomes slower with increasing temperature. Moreover, PEO block size has a stronger effect on the formation of reverse micelles compared with that of the PPO block size. In the microscopic region, phase behavior can be modeled using a detailed molecular description, often with techniques such as molecular dynamics (MD) and Monte Carlo (MC) simulations. In the macroscopic region, phase separation models can be based on equations of state, which are fitted to macroscopic phase diagrams. In the mesoscopic region, local concentration fields can be used as collective variables to obtain a description of self-assembly structures. The mesoscopic dynamics models are receiving increasing attention as they form

Small-angle neutron scattering study of the temperature-dependent attractive interaction in dense L64 copolymer micellar solutions and its relation to kinetic glass transition.

We made small-angle neutron scattering (SANS) study of a Pluronic L64 micellar system in aqueous solution at high polymer concentrations (wt %), 35%<c<53%, in a temperature range where a kinetic glass transition has been observed by photon correlation spectroscopy and zero shear viscosity measurements. We analyze SANS intensity distributions assuming that the micelles are spherical and interact among themselves by an effective pair potential, consisting of a hard core plus a narrow attractive square well, the depth of which is temperature dependent. The theory is able to account for the intensity distribution quantitatively when the micellar system is in the liquid phase (but qualitatively when the micellar system is in the glass state), giving values of four parameters: the aggregation number of the micelle N, the volume fraction occupied by the micelles phi, the fractional width of the square well epsilon, and the effective temperature T*=k(B)T/u, where -u is the depth of the square well. Thus, we are able to assign a point in the phase diagram (the T*-phi plane) for each measured micellar liquid and glass state. Comparison with a phase diagram predicted recently by mode coupling theory calculation allows us to identify the existence of the so-called liquid-to-attractive-glass transition line. We also found the evidence of glass-to-glass transition at volume fraction of 0.54 predicted by the mode coupling theory.