Phase behavior of a mixture of poly(isoprene)-poly(oxyethylene) diblock copolymer and poly(oxyethylene) surfactant in water

The phase behavior of a mixture of poly(isoprene)-poly(oxyethylene) diblock copolymer (PI-PEO or C250EO70) and poly(oxyethylene) surfactant (C12EO3, C12EO5, C12EO6, C12EO7, and C12EO9) in water was investigated by phase study, small-angle X-ray scattering, and dynamic light scattering (DLS). The copolymer is not soluble in surfactant micellar cubic (I1), hexagonal (H1), and lamellar (Lalpha) liquid crystals, whereas an isotropic copolymer fluid phase coexists with these liquid crystals. Although the PI-PEO is relatively lipophilic, it increases the cloud temperatures of C12EO3-9 aqueous solutions at a relatively high PI-PEO content in the mixture. Most probably, in the copolymer-rich region, PI-PEO and C12EOn form a spherical composite micelle in which surfactant molecules are located at the interface and the PI chains form an oil pool inside. In the C12EO5/ and C12EO6/PI-PEO systems, one kind of micelles is produced in the wide range of mixing fraction, although macroscopic phase separation was observed within a few days after the sample preparation. On the other hand, small surfactant micelles coexist with copolymer giant micelles in C12EO7/ and C12EO9/PI-PEO aqueous solutions in the surfactant-rich region. The micellar shape and size are calculated using simple geometrical relations and compared with DLS data. Consequently, a large PI-PEO molecule is not soluble in surfactant bilayers (Lalpha phase), infinitely long rod micelles (H1 phase), and spherical micelles (I1 phase or hydrophilic spherical micelles) as a result of the packing constraint of the large PI chain. However, the copolymer is soluble in surfactant rod micelles (C12EO5 and C12EO6) because a rod-sphere transition of the surfactant micelles takes place and the long PI chains are incorporated inside the large spherical micelles.     

Phase polymorphism by mixing of poly(oxyethylene)-poly(dimethylsiloxane) copolymer and nonionic surfactant in water

The phase behavior of the water/poly(oxyethylene)-poly(dimethylsiloxane) copolymer (Si25C3EO51.6)/pentaoxyethylene dodecyl ether (C12EO5) ternary system has been studied. Both the silicone copolymer and the surfactant have equal volumes of hydrophilic and lipophilic parts; i.e., these are balanced amphiphiles. Although only a lamellar phase is observed in water-Si25C3EO51.6 and water-C12EO5 binary systems, a variety of liquid crystalline phases, including normal micellar cubic (I1), hexagonal (H1), bicontinuous cubic (V1), lamellar (L(alpha)), reverse bicontinuous cubic (V2), and reverse hexagonal (H2), are observed in the copolymer-rich region of the ternary phase diagram. The small C12EO5 molecules dissolve at the hydrophobic interface in the thick bilayer of the Si25C3EO51.6 L(alpha) phase occupying a large area of the total interface of the aggregates and modulate the curvature of the aggregates. Hence a variety of self-assembled structures are observed. In contrast, Si25C3EO51.6 is not dissolved in the thin bilayer of the C12EO5 lamellar phase (L'(alpha)). Hence, the C12EO5 L'(alpha) phase coexists with copolymer-rich L(alpha) and H2 phases. Consequently, small surfactant molecules are dissolved in a large silicone copolymer aggregate to induce a change in layer curvature, but a large copolymer molecule is hard to incorporate with surfactant aggregates.     

Effect of added poly(oxyethylene)dodecyl ether on the phase and rheological behavior of wormlike micelles in aqueous SDS solutions

Upon the addition of a short EO chain nonionic surfactant, poly(oxyethylene) dodecyl ether (C12EOn), to dilute micellar solution of sodium dodecyl sulfate (SDS) above a particular concentration, a sharp increase in viscosity occurs and a highly viscoelastic micellar solution is formed. The oscillatory-shear rheological behavior of the viscoselastic solutions can be described by the Maxwell model at low shear frequency and combined Maxwell-Rouse model at high shear frequency. This property is typical of wormlike micelles entangled to form a transient network. It is found that when C12EO4 in the mixed system is replaced by C12EO3 the micellar growth occurs more effectively. However, with the further decrease in EO chain length, phase separation occurs before a viscoelastic solution is formed. As a result, the maximum zero-shear viscosity is observed at an appropriate mixing fraction of surfactant in the SDS-C12EO3 system. We also investigated the micellar growth in the mixed surfactant systems by means of small-angle X-ray scattering (SAXS). It was found from the SAXS data that the one-dimensional growth of micelles was obtained in all the SDS-C12EOn (n=0-4) aqueous solutions. In a short EO chain C12EOn system, the micelles grow faster at a low mixing fraction of nonionic surfactant.     

Solvent relaxation study of pH-dependent hydration of poly(oxyethylene) shells in polystyrene-block-poly(2-vinylpyridine)-block-poly(oxyethylene) micelles in aqueous solutions

The hydration of the poly(oxyethylene) shell in polystyrene-block-poly(2-vinylpyridine)-block-poly(oxyethylene) micelles was investigated by monitoring the solvent relaxation response of a solvent-sensitive fluorophore (patman). It has been found that the relaxation occurs on the nanosecond time scale. Results for triblock copolymer micelles have been compared with those obtained for polystyrene-block-poly(2-vinylpyridine) micelles in order to evaluate the effect of the outer polyoxyethylene layer. Considerable pH-dependent changes in the hydration of poly(oxyethylene) units at the poly(2-vinylpyridine)/polyoxyethylene interface were observed. Additionally, the paper shows that the solvent relaxation technique is a suitable tool for studying polymeric nanoparticles and that the measurement of time-dependent half-width of the emission spectrum allows for estimation of the extent of relaxation process observed by a given experimental setup.     

On the molecular mechanism of clouding in aqueous solution of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) triblock copolymers

The physical aspects of the clouding phenomenon in the aqueous solution of a poly(oxyethylene)(POE) – poly(oxypropylene)(POP) – poly(oxyethylene)(POE) triblock copolymer were investigated by applying various experimental methods: viscometry, ultrasonic technique, light scattering, infrared and Raman spectroscopy. The ultrasonic absorption studies hint at a critical behaviour. In order to understand the spectroscopic findings, conformational energies of model POE molecules as well as interaction energies between oxyethylene (OE) units and water molecules were calculated by the use of the quantum chemical PCILO method. It is suggested that the clouding is connected with conformational changes of POE segments.     

Thermotropic behavior of poly(oxyethylene) cholesterol ethers

The thermotropic behavior of poly(oxyethylene) cholesterol ether surfactants was studied by differential scanning calorimetry and small-angle X-ray scattering. Contrary to what is usually observed in conventional poly(oxyethylene)-type surfactant systems, poly(oxyethylene) cholesterol ether surfactants show a change of the fusion mechanism as the chain length is varied. For long chain lengths (n > or = 15) the usual solid-liquid transition is found, but for short chain lengths (n < or = 10) the transition goes through a birefringent lamellar phase. The appearance of this liquid crystal (LC) phase seems to be related with the predominance of the cholesterol part in the short chain polyoxyethylene surfactants. On the contrary, for long polyexyethylene chains the polymer gains in importance and only a solid crystalline structure is observed at low temperatures. An antiparallel packing structure with totally overlapped chains is found for both, the solid and the LC phase. The chains seem to be in a zigzag configuration, and only for the longest surfactant here studied (n = 30) a change of the chain configuration to a much shorter meander configuration is observed.     

Hydration of short-chain poly(oxyethylene) in carbon tetrachloride: an infrared spectroscopic study

Hydration of short-chain poly(oxyethylene)s, CH(3)(OCH(2)CH(2))(m)OCH(3) (abbreviated as C(1)E(m)()C(1)) (m = 1-3), in carbon tetrachloride has been studied by infrared spectroscopy. The O-H stretching vibrations of water in ternary solutions with H(2)O:C(1)E(m)C(1):CCl(4) mole ratios of 0.000418:0.005:0.995 to 0.000403:0.04:0.96 were analyzed. Two types of hydrogen bonds are formed in the interaction between water and C(1)E(m)C(1) in carbon tetrachloride; one is a monodentate hydrogen bond, in which only one of the O-H bonds of a water molecule participates in hydrogen bonding, and the other is a bidentate hydrogen bond, in which both of the O-H bonds of a water molecule participate in hydrogen bonding by bridging oxygen atoms separated by two or more monomer units on the polymer chain. An important finding is that the bidentate hydrogen-bond bridge is not formed between the nearest-neighbor oxygen atoms. This experimental observation supports the results of previous molecular dynamics simulations. The shortest oligomer of poly(oxyethylene), i.e., CH(3)OCH(2)CH(2)OCH(3) (1,2-dimethoxyethane) with a single monomer unit, is suggested not to be an adequate model for this polymer with respect to hydrogen bonding to water. The hydrogen bonding in a 1:1 C(1)E(m)C(1)-water adduct in carbon tetrachloride represents primitive incipient hydration of poly(oxyethylene). The present results indicate that both monodentate and bidentate hydrogen bonds are important and the latter is destabilized more rapidly than the former with increasing temperature. This dehydration process can be a potential mechanism of the poly(oxyethylene)-water phase separation.     

Intercalation of poly(oxyethylene) alkyl ether into a layered silicate kanemite

Poly(oxyethylene) alkyl ether (CnEOm) is intercalated into the interlayer space of a layered silicate kanemite by using layered hexadecyltrimethylammonium (C16TMA) intercalated kanemite (C16TMA-kanemite) as the intermediate. C16TMA-kanemite was treated with an aqueous solution of C16EO10, and the intercalation of C16EO10 was confirmed by the slight increase in the basal spacing (from 2.92 to 3.34 nm) with the increase in the carbon content, yielding C16EO10-C16TMA-kanemite. The product was dispersed again in a C16EO10 aqueous solution, and then 1.0 M HCl was added to the suspension to remove C16TMA ions completely. The basal spacing was further increased (from 3.34 to 5.52 nm) and the content of nitrogen was virtually zero, indicating further intercalation of C16EO10 molecules and complete elimination of C16TMA ions simultaneously. Though C16EO10 molecules are not directly intercalated into kanemite, the mutual interactions among C16TMA ions, C16EO10 molecules, and the interlayer silicate surfaces effectively induce the intercalation of C16EO10. C16EO10-kanemite shows a reversible adsorption of n-decane and water owing to the hydrophobicity and hydrophilicity of C16EO10, respectively, in the interlayer space. Layered CnEO10-kanemites (n = 12 and 18) were also synthesized in a manner similar to layered C16EO10-kanemite.     

用SAXS/WAXS研究聚氧乙烯/聚氧丁烯嵌段共聚物在n-己烷中的结晶性球形胶束结构

嵌段共聚物在选择性溶剂中能够自组装形成胶束,胶束的不同形状与嵌段共聚物的结构、溶剂和浓度有关．无定形嵌段共聚物通常形成球形胶束,在某些情况下也可以形成其它形状的胶束,关于结晶性嵌段共聚物在无定形链段选择性溶剂中的胶束结构和形状的报道非常少．由于结晶和相似相溶两种作用力的竞争,使得这类胶束的形状丰富多变．通常结晶作用较强时,结晶性嵌段共聚物形成片状的胶束,当结晶组分比较少时,可形成棒状胶束,尽管理论上已经指出存在球形胶束,但尚无关于这方面的报道。     

Vesicle formation with amphiphilic chitosan derivatives and a conventional cationic surfactant in mixed systems

In this study, molecular packing in lamellar liquid crystals in poly(oxyethylene) dodecyl ether(C(12)EO(n)) pure systems and the two surfactant mixtures of C(12)EO(8)/1-dodecanol(C(12)EO(0)), C(12)EO(8)/lipophilic sucrose laurate (L-595), hydrophilic sucrose laurate (L-1695)/C(12)EO(2) is investigated in terms of mean molecular area and partial molecular area (PMA). Lamellar liquid crystals formed in the C(12)EO(8)/C(12)EO(0) mixed system show higher melting temperatures than those in the C(12)EO(n) pure systems, even though the average number of EO units in the mixed surfactant system is the same as in the pure system. We compared the mean molecular area at the interface between hydrophilic and lipophilic moieties in the lamellar liquid crystals in each system. In the mixed system, the molecules are packed more tightly than in the pure system. Among the C(12)EO(n) and sucrose laurate mixtures, the L-1695/C(12)EO(2) mixed system showed a smaller mean molecular area per lipophilic chain than the C(12)EO(8)/L-595 mixed system. We investigated the effect of mixing two surfactants with different head group geometry on molecular packing by comparing the PMA of each surfactant.     

Effect of copolymer structure on micellar behavior of acrylamide-octylphenylpoly (oxyethylene) acrylate surfactant

Acrylamide-octylphenylpoly (oxyethylene) acrylate copolymer (AM-C₈PhEO_nAc) surfactant is the copolymer of acrylamide (AM) and octylphenylpoly (oxyethylene) acrylate macromonomer (C₈PhEO_nAc). The effect of the copolymer structure on the micellar behavior in aqueous solution was studied using dynamic light scattering. It has been found that the length of ethylene oxide (EO) in the branch and the content of C₈PhEO_nAc in the copolymer surfactant have great effects on the size and distribution of the micelles. For AM-C₈PhEO₇Ac copolymer, at the concentration of 5 × 10⁻⁴ g/ml, the micellar size increases with the increase of C₈PhEO₇Ac content. However, for AM-C₈PhEO₁₀Ac copolymer, the result is the opposite; the micellar size decreases with the increase of C₈PhEO₁₀Ac content. Larger C₈PhEO_nAc content leads to narrower micellar distribution. For copolymer surfactants with equal C₈PhEO_nAc content, when the concentration of copolymer solution is the same, the copolymer with longer EO length forms smaller micelles. Received: 2 February 2000 Accepted: 6 October 2000     

Mixed micelles of a PEO-PPO-PEO triblock copolymer (P123) and a nonionic surfactant (C12EO6) in water. a dynamic and static light scattering study

The present article reports on static and dynamic light scattering (SLS and DLS) studies of aqueous solutions of the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) at temperatures between 25 and 45 degrees C. In water, P123 self-assembles into spherical micelles with a hydrodynamic radius of 10 nm, and at 40 degrees C, these micelles consist of 131 unimers. Addition of C12EO6 leads to an association of the surfactant molecules to the P123 micelles and mixed micelles are formed. The size and structure of the mixed micelles as well as interparticle interactions were studied by varying the surfactant-to-copolymer (C12EO6/P123) molar ratio. The novelty of this study consists of a composition-induced structural change of the mixed micelles at constant temperature. They gradually change from being spherical to polymer-like with increasing C12EO6 content. At low C12EO6/P123 molar ratios (below 12), the SLS measurements showed that the molar mass of the mixed micelles decreases with an increasing amount of C12EO6 in the micelles for all investigated temperatures. In this regime, the mixed micelles are spherical and the DLS measurements revealed a decrease in the hydrodynamic radius of the mixed micelles. An exception was found for C12EO6/P123 molar ratios between 2 and 3, where the mixed micelles become rodlike at 40 degrees C. This was the subject of a previous study and has hence not been investigated here. At high molar ratios (48 and above), the polymer-like micelles present a concentration-induced growth, similar to that observed in the pure C12EO6/water system.     

Chain propagation/step propagation polymerization. III. An XPS investigation of poly(oxyethylene)-b-poly(pivalolactone) telechelomer

A combination of chain and step propagations is being used to prepare a series of segmented copolymers containing polyoxyethylene and polypivalolactone segments each with narrow molecular weight distributions. The incompatibility of the two segments coupled with the difference in surface energies of the two segments could result in good phase separation with the polyoxyethylene segment thereby being found on the surface. Poly(oxyethylene)-co-(pivalolactone) telechelomer, which is the precursor to the segmented copolymer, is used as a model to develop an XPS method for surface analysis. An angular resolution study shows that negligible amounts of poly(pivalolactone) segments are present near the surface. Core level spectra of the telechelomer and its model compounds are presented to indicate that poly(oxyethylene) segment is richer near the surface.     

A calorimetry and light scattering study of the formation and shape transition of mixed micelles of EO20PO68EO20 triblock copolymer (P123) and nonionic surfactant (C12EO6)

The interaction between the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) has been investigated by means of isothermal titration and differential scanning calorimetry (DSC) as well as static and dynamic light scattering (SLS and DLS). P123 self-assembles in water into spherical micelles at ambient temperatures. At raised temperatures, the DSC data revealed a sphere-to-rod transition of the P123 micelles around 60 degrees C. C12EO6 interacts strongly with P123 micelles in aqueous solution to give mixed micelles with a critical micelle concentration (cmc) well below the cmc for pure C12EO6. The presence of C12EO6 also lowers the critical micelle temperature of P123 so aggregation starts at significantly lower temperatures. A new phenomenon was observed in the P123-C12EO6 system, namely, a well-defined sphere-to-rod transition of the mixed micelles. A visual phase study of mixtures containing 1.00 wt % P123 showed that in a narrow concentration range of C12EO6 both the sphere-to-rod transition and the liquid-liquid phase separation temperature are strongly depressed compared to the pure P123-water system. The hydrodynamic radius of spherical mixed micelles at a C12EO6/P123 molar ratio of 2.2 was estimated from DLS to be 9.1 nm, whereas it is 24.1 nm for the rodlike micelles. Furthermore, the hydrodynamic length of the rods at a molar ratio of 2.2 is in the range of 100 nm. The retarded kinetics of the shape transition was detected in titration calorimetric experiments at 40 degrees C and further studied by using time-resolved DLS and SLS. The rate of growth, which was slow (>2000 s), was found to increase with the total concentration.     

Conformational analysis of poly(oxyethylene) chain in aqueous solution as a hydrophilic moiety of nonionic surfactants

Conformational states of poly(oxyethylene) chain in aqueous solution are examined in connection with hydrophilic property of nonionic surfactants. The Raman spectra in various states are analyzed on the basis of comprehensive normal coordinate treatment. The poly(oxyethylene) chain is more ordered in more dilute aqueous solution. This conformational ordering is further promoted by lowering temperature. The ordered structure, which is similar, at least in part, to that in the solid state, is substantiated by the hydrogen bonds making the gauche conformation of the OCH₂-CH₂O group more favorable. The hydration has no significant effect on the conformation of the CH₂O-CH₂CH₂ group.     

Synthesis of poly(oxyethylene phosphonate)s bearing oxirane groups in the side chain

The interaction between poly(oxyethylene phosphonate)s and 1,2-epoxy-7-octene has been investigated. It has been established that in the presence of benzoyl peroxide there proceeds a selective addition of the P( )H group to the C()C double bond. Poly(oxyethylene phosphonate)s bearing oxirane groups in the side chain have been synthesized. The new polymers can be used as polymer carriers of drugs. © 1997 John Wiley & Sons, Inc.     

Molecular dynamics simulation of a poly(oxyethylene) chain dissolved in benzene

Molecular dynamics simulations of pure benzene and a poly(oxyethylene) chain in benzene are performed. The simulation of pure benzene is found to agree excellently with previous simulations despite using a different force field. A comparison is made between the results of simulations of the poly(oxyethylene) chain in benzene and in water and of stochastic simulations with respect to mean torsional angles, trans/gauche fractions, and transition rates. Characteristic deviations are found for the simulation in water and explained by specific atomic interactions, while there is satisfactory agreement with a stochastic simulation based upon the simple Langevin equation using a friction coefficient of 1 ps^?1. The characteristic ratio of poly(oxyethylene) in benzene is calculated on the basis of the rotational isomeric state model. © 1992 by John Wiley & Sons, Inc.     

Viscoelastic wormlike micellar solutions made from nonionic surfactants: structural investigations by SANS and DLS

A highly viscoelastic micellar solution of nonionic surfactants in a dilute region was recently reported. A transient network of wormlike micelles formed with the addition of short-EO-chain poly(oxyethylene) dodecyl ether surfactants (C12EO(j), j = 1-4) to poly(oxyethylene) cholesteryl ethers (ChEO(m), m = 10 and 15). A gradual increase in micellar length with an increasing C12EO(j) concentration was assumed from the results of model calculations and rheological measurements. We report in this study the results of structural investigations with small-angle neutron scattering (SANS) to confirm this assumption. Tuning from spherical to wormlike and to locally flat structures can be achieved by way of three methods. One can either increase the C12EO(j) concentration or decrease j (smaller headgroup size) at a fixed concentration of C12EO(j). The third possibility is to increase the temperature at a fixed composition. All three methods result in the same structural transition. The formation of a transient network of wormlike micelles analogous to polymer solutions can be observed with dynamic light scattering (DLS). A stretched exponential approach was applied to fit the correlation functions.