Synthesis of FDU-1 silica with narrow pore size distribution and tailorable pore entrance size in the presence of sodium chloride

Ordered silicas with large (9-15 nm), uniform, cagelike mesopores were synthesized under acidic aqueous conditions from tetraethyl orthosilicate in the presence of sodium chloride using poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer B50-6600 (EO39BO47EO39, Dow Chemicals) as a supramolecular template. Except for the use of NaCl in our case, the synthesis mixture composition was the same as that originally reported by Zhao et al. for the synthesis of FDU-1 silica, which was later shown to exhibit a cubic close-packed (Fm3m) structure with stacking faults related to the occurrence of hexagonal close-packed stacking sequences. The copolymer-templated silicas were formed at room temperature and in most cases were subjected to the hydrothermal treatment at 373 or 393 K. The calcined materials were characterized using small-angle X-ray scattering (SAXS) and nitrogen and argon adsorption at 77 K. SAXS patterns were generally similar to those reported for FDU-1 silica, indicating the cubic close-packed (Fm3m) structure, but the presence of stacking faults characteristic of a hexagonal close-packed structure cannot be precluded. The addition of the salt was found to significantly narrow the pore size distributions and to improve the uniformity of entrances to the cagelike mesopores, whereas the pore diameter, specific surface area, and pore volume were similar (in most cases slightly lower) to those for FDU-1 silicas obtained in the absence of NaCl. The materials synthesized in the presence of NaCl also appeared to have better resolved SAXS patterns. The feasibility of tailoring the pore cage diameter (from approximately 9.5 to 14.5 nm) and pore entrance diameter (from below 4 to approximately 8 nm) simply by adjusting the hydrothermal treatment temperature and time was demonstrated, indicating that these simple and convenient ways of structural design of cagelike mesopores are operative in the case of syntheses in the presence of inorganic salts.     

Selective synthesis of single-crystalline selenium nanobelts and nanowires in micellar solutions of nonionic surfactants

Single-crystalline nanobelts and nanowires of trigonal selenium (t-Se) have been selectively synthesized in micellar solutions of nonionic surfactants. In particular, t-Se nanobelts about 30 nm in thickness were obtained in micellar solutions of poly(oxyethylene(20)) octadecyl ether (C18EO20), whereas t-Se nanowires were obtained in micellar solutions of poly(oxyethylene(10)) dodecyl ether (C12EO10). The obtained t-Se nanobelts exhibit a low-energy absorption peak that is considerably red shifted from that for t-Se nanowires, which has been presumably attributed to the lower degree of crystal perfection for the t-Se nanobelts with rectangular cross sections.     

Effect of acid on the aggregation of poly(ethylene xide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers

The acid effect on the aggregation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers EO(20)PO(70)EO(20) has been investigated by transmission electron microscopy (TEM), particle size analyzer (PSA), Fourier transformed infrared, and fluorescence spectroscopy. The critical micellization temperature for Pluronic P123 in different HCl aqueous solutions increases with the increase of acid concentration. Additionally, the hydrolysis degradation of PEO blocks is observed in strong acid concentrations at higher temperatures. When the acid concentration is low, TEM and PSA show the increase of the micelle mean diameter and the decrease of the micelle polydispersity at room temperature, which demonstrate the extension of EO corona and tendency of uniform micelle size because of the charge repulsion. When under strong acid conditions, the aggregation of micelles through the protonated water bridges was observed.     

Interaction between cationic, anionic, and non-ionic surfactants with ABA block copolymer Pluronic PE6200 and with BAB reverse block copolymer Pluronic 25R4

The interaction in aqueous solution between either the normal block copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide): Pluronic PE6200 [(EO)(11)-(PO)(28)-(EO)(11)], or the reverse block copolymer poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide): Pluronic 25R4 [(PO)(19)-(EO)(33)-(PO)(19)] and the surfactants sodium decylsulfate, C(10)OS, decyltrimethyl ammonium bromide, C(10)TAB, and pentaethylene glycol monodecyl ether, C(10)E(5), was investigated and the aggregation behavior of these surfactants with Pluronics was compared. Surface tension measurements show that Pluronics in their non-aggregated state better interact with the anionic surfactant C(10)OS than with cationic and non-ionic ones. The presence of the two Pluronics induces the same lowering of the aggregation number of C(10)OS as shown by fluorescence quenching measurements. The number of polymer chains necessary to bind each C(10)OS aggregate has been estimated to be approximately 6 for PE6200 and approximately 2 for 25R4. Furthermore, this surfactant also induces the same increment in the gyration radius of the polymers as revealed by viscosimetry. Calorimetric results have been reasonably reproduced by applying a simple equilibrium model to the aggregation processes.     

Ordered mesoporous silica with large cage-like pores: structural identification and pore connectivity design by controlling the synthesis temperature and time

FDU-1 silicas with large cage-like pores (diameter about 10 nm) were synthesized under acidic conditions from tetraethyl orthosilicate in the presence of a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer template B50-6600 (EO(39)BO(47)EO(39)). High-resolution transmission electron microscopy and small-angle X-ray scattering provided strong evidence that FDU-1 silica synthesized under typical conditions is a face-centered cubic Fm3m structure with 3-dimensional hexagonal intergrowth and is not a body-centered cubic Im3m structure, as originally reported. Samples synthesized in a wide range of conditions (initial temperatures from 298 to 353 K; hydrothermal treatment at 333-393 K) exhibited similar XRD patterns and their nitrogen adsorption isotherms indicated a good-quality cage-like pore structure. The examination of low-pressure nitrogen adsorption isotherms for FDU-1 samples, whose pore entrance diameters were evaluated using an independent method, allowed us to conclude that low-pressure adsorption was appreciably stronger for samples with smaller pore entrance sizes. This prompted us to examine low-pressure adsorption isotherms for a wide range of samples and led us to a conclusion that the FDU-1 pore entrance size can be systematically enlarged from about 1.3 nm (perhaps even lower) to at least 2.4 nm without an appreciable loss of uniformity by increasing the temperature of the hydrothermal treatment or the initial synthesis. Further enlargement of pore entrance size was achieved for sufficiently long hydrothermal treatment times at temperatures of 373 K or higher, as seen from the shape of nitrogen desorption isotherms. This allowed us to obtain samples with uniform pore sizes, high adsorption capacity, and with pore entrances enlarged so much that their size was similar to the size of the pore itself, resulting in a highly open porous structure. However, in the latter case, there was evidence that the pore entrance size distribution was quite broad.     

Dynamics of Micelles of Polyethyleneoxide-Polypropyleneoxide-Polyethyleneoxide Block Copolymers in Aqueous Solutions

The dynamics of the micelles of five triblock poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) copolymers, the Pluronics P104 (EO27PO61EO27), P84 (EO19PO43EO19), P65 (EO18PO29EO18), P85 (EO26PO40EO26), and P103 (EO17PO60EO17), have been investigated using two chemical relaxation methods: the temperature-jump and the ultrasonic relaxation (absorption). In the frequency range investigated (0.5-50 MHz), the ultrasonic absorption spectra (absorption vs frequency plots) consisted in tails of relaxation curves, indicating characteristic times much longer than 0.3 μs for the exchange of copolymers between micelles and intermicellar solution. Absorption measurements at a fixed frequency yielded the critical micellization temperature of the solutions. The temperature-jump results obtained in this study together with those from a previous one for the copolymers L64 (EO13PO30EO13) and PF80 (EO73PO27EO73) (B. Michels et al., Langmuir 13, 3111, 1997) showed that the relaxation time associated with the formation/breakup of micelles becomes longer upon increasing copolymer molecular weight at constant composition. This time also increased when decreasing the length of the hydrophilic block at fixed hydrophobic block length or increasing the length of the hydrophobic block at fixed hydrophilic block length, similar to conventional surfactants. The dynamics of block copolymers micelles in aqueous solution are discussed. Copyright 1999 Academic Press.     

Pore size tailoring in large-pore SBA-15 silica synthesized in the presence of hexane

Large-pore SBA-15 silicas were synthesized using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer Pluronic P123 as a template and hexane as a micelle expander. The reaction was initially carried out at 15 degrees C, followed by the heating of the synthesis gel at temperatures from 40 to 130 degrees C. Small-angle X-ray scattering data indicate that highly ordered two-dimensional hexagonal material (SBA-15 structure) formed at 15 degrees C and was preserved even after 5 days of heating at 130 degrees C. The unit-cell parameter for as-synthesized SBA-15 silicas was about 16.5 nm and increased only slightly after the heat treatment, whereas the unit-cell parameter after calcination was appreciably larger (16 vs 14 nm) for materials that were subjected to the thermal treatment. The pore size distribution of SBA-15 formed at 15 degrees C was narrow and centered at approximately 9.5 nm, which is close to the upper limit of pore diameters typically reported for SBA-15. The presence of constrictions in the pores of this material was evident. The heat treatment led to the elimination of the constrictions and to the pore diameter increase to 15 nm or more, tailored by the selection of appropriate treatment temperature and time. The pore size increase was the fastest during the first day of treatment, but it continued for at least 5 days. The pore size distribution broadened as the time of the treatment increased beyond 1 day. The pore size increase appears to be primarily related to the decrease in the degree of shrinkage during the calcination (removal of the template) and the decrease in the pore wall thickness.     

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.     

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.     

Highly-controlled grafting of mono and dicationic 4,4'-bipyridine derivatives on SBA-15 for potential application as adsorbent of CuCl(2) from ethanol solution

Ultra-large-pore FDU-12 (ULP-FDU-12) silica with face-centered cubic structure (Fm3m type) of spherical mesopores was synthesized using Pluronic F127 triblock copolymer (EO(106)PO(70)EO(106)) and ethylbenzene as a new micelle expander at initial temperature of 14 °C. Ethylbenzene was identified on the basis of its reported extent of solubilization in poly(ethylene oxide)-poly(propylene oxide)-type surfactant micelles, which was similar to that of xylene, the latter having been shown earlier to afford ULP-FDU-12. The unit-cell parameter of as-synthesized ULP-FDU-12 was 55 nm, which is similar to the highest value reported when xylenes (mixture of isomers) were used and larger than that achieved with trimethylbenzene. The unit-cell parameter of calcined ULP-FDU-12 reached 52 nm. For the obtained materials, the nominal pore cage diameter calculated from nitrogen adsorption reached 32 nm, whereas the actual pore cage diameter calculated using the geometrical relation was 36 nm. The pore entrance size was below 5 nm before the acid treatment, but was greatly enlarged as a result of the treatment. The sample prepared without hydrothermal treatment was converted to ordered closed-pore silica at as low as 400-450 °C. Our study confirms the ability to select micelle expanders on the basis of data on solubilization of compounds in micelle solutions.     

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.     

Aggregation behavior of pluronic triblock copolymer in 1-butyl-3-methylimidazolium type ionic liquids

Three amphiphilic poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) ethers triblock copolymers, denoted Pluronic L61 (PEO3PPO30PEO3), Pluronic L64 (PEO13PPO30PEO13), and Pluronic F68 (PEO79PPO30PEO79) were shown to aggregate and form micelles in ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). The surface tension measurements revealed that the dissolution of the copolymers in ILs depressed the surface tension in a manner analogous to aqueous solutions. The cmcs of three triblock copolymers increase following the order of L61, L64, F68, suggesting that micellar formation was driven by solvatophobic effect. cmc and gamma cmc decrease with increasing temperature because hydrogen bonds between ILs and hydrophilic group of copolymers decrease and accordingly enhance the solvatophobic interaction. Micellar droplets of irregular shape with average size of 50 nm were observed. The thermodynamic parameters DeltaGm0, DeltaHm0, DeltaSm0 of the micellization of block copolymers in bmimBF4 and bmimPF6 were also calculated. It was revealed that the micellization is a process of entropy driving, which was further confirmed by isothermal titration calorimetry (ITC) measurements.     

Poly(ethylene oxide)-poly(styrene oxide)-poly(ethylene oxide) copolymers: Micellization, drug solubilization, and gelling features

Two new poly(ethylene oxide)-poly(styrene oxide) triblock copolymers (PEO-PSO-PEO) with optimized block lengths selected on the basis of previous studies were synthesized with the aim of achieving a maximal solubilization ability and a suitable sustained release, while keeping very low material expense and excellent aqueous copolymer solubility. The self-assembling and gelling properties of these copolymers were characterized by means of light scattering, fluorescence spectroscopy, transmission electron microscopy, and rheometry. Both copolymers formed spherical micelles (12-14 nm) at very low concentrations. At larger concentration (>25 wt%), copolymer solutions showed a rich phase behavior, with the appearance of two types of rheologically active (more viscous) fluids and of physical gels depending on solution temperature and concentration. The copolymer behaved notably different despite their relatively similar block lengths. The ability of the polymeric micellar solutions to solubilize the antifungal drug griseofulvin was evaluated and compared to that reported for other structurally-related block copolymers. Drug solubilization values up to 55 mg g⁻¹ were achieved, which are greater than those obtained by previously analyzed poly(ethylene oxide)-poly(styrene oxide), poly(ethylene oxide)-poly(butylene oxide), and poly(ethylene oxide)-poly(propylene oxide) block copolymers. The results indicate that the selected SO/EO ratio and copolymer block lengths were optimal for simultaneously achieving low critical micelle concentrations (cmc) values and large drug encapsulation ability. The amount of drug released from the polymeric micelles was larger at pH 7.4 than at acidic conditions, although still sustained over 1 day.     

Temperature-responsive magnetite/PEO-PPO-PEO block copolymer nanoparticles for controlled drug targeting delivery

In this study, temperature-responsive magnetite/polymer nanoparticles were developed from iron oxide nanoparticles and poly(ethyleneimine)-modified poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer. The particles were characterized by TEM, XRD, DLS, VSM, FTIR, and TGA. A typical product has an approximately 20 nm magnetite core and an approximately 40 nm hydrodynamic diameter with a narrow size distribution and is superparamagnetic with large saturation magnetization (51.34 emu/g) at room temperature. The most attractive feature of the nanoparticles is their temperature-responsive volume-transition property. DLS results indicated that their average hydrodynamic diameter underwent a sharp decrease from 45 to 25 nm while evaluating the temperature from 20 to 35 degrees C. The temperature-dependent evolution of the C-O stretching band in the FTIR spectra of the aqueous nanoparticles solution revealed that thermo-induced self-assembly of the immobilized block copolymers occurred on the magnetite solid surfaces, which is accompanied by a conformational change from a fully extended state to a highly coiled state of the copolymer. Consequently, the copolymer shell could act as a temperature-controlled "gate" for the transit of guest substance. The uptake and release of both hydrophobic and hydrophilic model drugs were well controlled by switching the transient opening and closing of the polymer shell at different temperatures. A sustained release of about 3 days was achieved in simulated human body conditions. In primary mouse experiments, drug-entrapped magnetic nanoparticles showed good biocompatibility and effective therapy for spinal cord damage. Such intelligent magnetic nanoparticles are attractive candidates for widespread biomedical applications, particularly in controlled drug-targeting delivery.     

A new thioether functionalized organic-inorganic mesoporous composite as a highly selective and capacious Hg2+ adsorbent

A new thioether functionalized organic-inorganic ordered mesoporous composite as a highly selective and capacious Hg2+ adsorbent was synthesized by one-step co-condensation of (1,4)-bis(triethoxysilyl)propane tetrasufide (BTESPTS, (CH3CH2O)3Si(CH2)3S-S-S-S(CH2)3Si(OCH2CH3)3) and tetraethoxysilane (TEOS), with tri-block copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) EO20PO70EO20 as template.     

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.     

Surface patterns of block copolymers in thin layers after vapor treatment

A systematic study of formation of surface patterns in block copolymer thin layers after their exposure to solvent vapors was performed. The studied effect involves layers of thickness approximately equal to the ordering size of polymers - about 45 nm. Experiments were performed on three styrene - methacrylate derivative block copolymers, synthesized by living anionic polymerization: poly(4-octylstyrene)-block-poly(butyl methacrylate), poly(4-fluorostyrene)-block-poly(butyl methacrylate) and poly(p-octylstyrene)-block-poly(methyl methacrylate). The polymers were exposed to vapors of chloroform, 1,4-dioxane, hexane, acetone and tetrahydrofuran.     

Effect of SDS on the self-assembly behavior of the PEO-PPO-PEO triblock copolymer (EO)20(PO)70(EO)20

The mixed micellar system comprising the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-based triblock copolymer (EO)(20)(PO)(70)(EO)(20) (P123) and the anionic surfactant sodium dodecyl sulfate (SDS) has been investigated in aqueous media by small-angle neutron scattering (SANS) and viscosity measurements. The aggregation number of the copolymer in the micelles decreases upon addition of SDS, but a simultaneous enhancement in the degree of micellar hydration leads to a significant increase in the micellar volume fraction at a fixed copolymer concentration. This enhancement in the micellar hydration leads to a marked increase in the stability of the micellar gel phase until it is destroyed at very high SDS concentration. Mixed micellar systems with low and intermediate SDS concentrations form the micellar gel phase in much wider temperature and copolymer concentration ranges than the pure copolymer micellar solution. A comparison of the observed results with those for the copolymers (EO)(26)(PO)(40)(EO)(26) (P85) and (EO)(99)(PO)(70)(EO)(99) (F127) suggests that the composition of the copolymers plays a significant role in determining the influence of SDS on the gelation characteristics of the aqueous copolymer solutions. Copolymers with high PO/EO ratios show an enhancement in the stability of the gel phase, whereas copolymers with low PO/EO ratios show a deterioration of the same in the presence of SDS.     

Single-step synthesis and stabilization of metal nanoparticles in aqueous pluronic block copolymer solutions at ambient temperature

A single-step synthesis of gold nanoparticles with an average diameter of approximately 10 nm from hydrogen tetrachloroaureate(III) hydrate (HAuCl4.3H2O) has been achieved in air-saturated aqueous solutions that contain poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers but not any other reducing agent. These amphiphilic block copolymers act as both reductants and colloidal stabilizers and prove very efficient in both functions. The formation of gold nanoparticles is controlled by the overall molecular weight and relative block length of the block copolymer. The synthesis procedure reported here is environmentally benign and economic, as it involves the minimum possible number of components: it uses water as the solvent, it uses commercially available polymers, it proceeds fast to completion, and it results in a "ready-to-use" product.     

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.