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Polymers formed by the self-assembly of a bis(urea)-basedpolymer,2,4-bis(2-ethylhexylureido)toluene (EHUT), in organic solvents suchas octane are promising systems with remarkable rheological properties.This is the first self-assembled polymer recently reported as a hydrodynamicdrag reducer for hydrocarbons. The rheology of diluted and semidilutedEHUT solutions can be tuned by specific interactions between the chains,modulated by the nature of the solvent and the presence of additives.In this article, rheological, thermal and SANS measurements were performedin order to investigate the competition between EHUT self-assemblyand its interaction with specific molecules (benzene, benzyl alcohol,and ethanol) that can interact with EHUT unimers via hydrogen bondsand π–π interactions. No substantial rheological,thermal, or structural effect is observed when benzene is added tothe systems. However, ethanol and benzyl alcohol interact with EHUTunimers through hydrogen bonds, drastically decreasing the viscoelasticityof the solutions. In addition, benzyl alcohol can interact with EHUTpolymers by π-stacking interactions, playing an important rolein tuning the rheological properties of the systems. [ABSTRACT FROM AUTHOR]

In a recent publication, we have highlighted the potentialof phosphonicacid terminated PEG oligomers to functionalize strong UV absorptioncerium oxide nanoparticles,(1) which yieldsuspensions that are stable in aqueous or organic solvents and areredispersible in different solvents after freeze-drying. In the presentwork, we highlight the interfacial activity of the functional ceriananoparticles and their potential to modify hydrophobic surfaces.We first investigated the phosphonated-PEG amphiphilic oligomers behavioras strong surface active species forming irreversibly adsorbed layers.We then show that the oligomers interfacial properties translate tothe functional nanoparticles. In particular, the addition of a smallfraction of phosphonated-PEG oligomers with an extra C16 aliphaticchain (stickers) into the formulation enabled thetuning of (i) the nanoparticles adsorption at the air/water, polystyrene/water,oil/water interfaces and (ii) the particle/particle interaction inaqueous solutions. We also found that dense and closely packed two-dimensionalmonolayers of nanoceria can be formed by spontaneous adsorption orsurface compression using a Langmuir trough. A hexagonal organizationcontrolled by reversible and repulsive interaction has been characterizedby GISAXS. Mono- or multilayers can also be stably formed or transferredon solid surfaces. Our results are key features in the field of polymersurface modification, solid-stabilized emulsions (Pickering), or supracolloidalassemblies. [ABSTRACT FROM AUTHOR]

New amphiphilic random copolymers containing hydrophobic dodecyl (C12) chain and hydrophilic l-glutamic acid were synthesized, and their self-assembly in solution as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (∼90%) self-assembled into giant vesicles with a diameter of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solutions were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphology of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate molecular design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents. [ABSTRACT FROM AUTHOR]

In this paper we report electrochemical investigations of the influence of organic solvents dissolved in aqueous solution on the permeability of nanoporous films derived from a cylinder-forming polystyrene–poly(methyl methacrylate) diblock copolymer (CF-PS-b-PMMA). The nanoporous films (ca. 30 nm in pore diameter) were prepared on planar gold electrodes via UV-based degradation of the cylindrical PMMA domains of annealed CF-PS-b-PMMA films (30–45 nm thick). The permeability of the electrode-supported nanoporous films was assessed using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The faradic current of Fe(CN)63–/4–decreased upon immersion in aqueous solutions saturated with toluene or methylene chloride (5.8 mM and 0.20 M, respectively). EIS data indicated that the decrease in faradic current mainly reflected an increase in the pore resistance (Rpore). In contrast, Rporedid not change in a saturated n-heptane solution, 0.17 M ethanol, or 5.8 mM aqueous solutions of methylene chloride, diethyl ether, methyl ethyl ketone, or ethanol. Atomic force microscopy images of a nanoporous film in aqueous solution with and without 5.8 mM toluene showed a reversible change in the surface morphology, which was consistent with a toluene-induced change in Rpore. The solvent-induced increase in Rporewas attributed to the swelling of the nanoporous films by the organic solvents, which decreased the effective pore diameter. The reversible permeability changes suggest that the surface of CF-PS-b-PMMA-derived nanoporous films can be functionalized in organic environments without destroying the nanoporous structure. In addition, the solvent-induced swelling may provide a simple means for controlling the permeability of such nanoporous films. [ABSTRACT FROM AUTHOR]

The reaction methyl naphthalene-2-sulfonate Br−was investigated in several alkanediyl-α-ω-bis(dodecyldimethylammonium) bromide, 12-s-12,2Br−(with s= 2, 3, 4, 5, 6, 8, 10, 12), micellar solutions in the absence and in the presence of various additives. The additives were 1,2-propylene glycol, which remains in the bulk phase, N-decyl N-methylglucamide, MEGA10, which forms mixed micelles with the dimeric surfactants, and 1-butanol, which distributes between the aqueous and micellar phases. Information about the micellar reaction media was obtained by using conductivity and fluorescence measurements. In all cases, with the exception of water-1,2-prop 12-5-12,2Br−micellar solutions, with 30% weight percentage of the organic solvent, a sphere-to-rod transition takes place upon increasing surfactant concentration. In order to quantitatively explain the experimental data within the whole surfactant concentration range, a kinetic equation based on the pseudophase kinetic model was considered, together with the decrease in the micellar ionization degree accompanying micellar growth. However, theoretical predictions did not agree with the experimental kinetic data for surfactant concentrations above the morphological transition. An empirical kinetic equation was proposed in order to explain the data. It contains a parameter bwhich is assumed to account for the medium micellar kinetic effects caused by the morphological transition. The use of this empirical equation permits the quantitative rationalization of the kinetic micellar effects in the whole surfactant concentration range. [ABSTRACT FROM AUTHOR]

We have developed a simple, efficient, and highly reproducible method to fabricate the large-area biomimetic superhydrophobic polymer surfaces having hierarchical structures of micrometer-sized irregular steps and nanometer-sized fibrils. Commercial Al plates (99.0%) were etched using Beck’s dislocation etchant (mixture of HCl and HF) for different time periods in order to alter the structure of the etched Al surfaces from micrometer-sized to highly rough nanometer-sized irregular steps. These hierarchical structures could be easily replicated onto the surface of various thermoplastic polymer plates from the etched Al templates by applying heat and pressure; many polymer replicas without any significant deviations from each other could be duplicated from the same etched Al master templates. All of thermoplastic polymer replicas having hierarchical structures exhibited superhydrophobic properties with water contact angles of larger than 150°. Especially, the surfaces of the high-density polyethylene (HDPE) replicas having nanometer-sized curled strands exhibited superhydrophobicity with a static water contact angle of ∼160° and a sliding angle of less than 2°. These superhydrophobic HDPE replicas having nanometer-sized curled strands showed excellent stability after being exposed to various organic solvents and aqueous solutions of various pH. [ABSTRACT FROM AUTHOR]

Numerous methods have been reported for the preparation of liposomes, many of which, in addition to requiring time-consuming preparative steps and the use of organic solvents, result in heterogeneous liposome populations of incontrollable size. Taking into consideration the phenomenon of spontaneous vesiculation and the theory of curvature, here we present an extremely rapid and simple, solvent-free method for the preparation of monodisperse solutions of highly stable small unilamellar vesicles using both charged and zwitterionic lipids mixed with lyso-palmitoylphosphatidylcholine, exploiting a combination of a rapid pH change followed by a defined period of equilibration. Various experimental parameters and their interactions were evaluated in terms of their effect on resulting liposome size and shape, as well as on liposome stability and size distribution, with transmission electron microscope imaging being used to visualize the formed liposomes, and photon correlation spectroscopy to obtain statistical data on mean diameter and monodispersity of the liposome population. ζ potential measurements also provided information about the interpretation of vesiculation kinetics and liposome stability. The time interval of pH jump, operation temperature, equilibration time, and lipid type were shown to be the determining factors controlling the size, shape, and monodispersity of the liposomes. Buffer type was also found to be important for the long-term storage of the liposomes. Ongoing work is looking at the application of the developed method for encapsulation of bioactive molecules, such as drugs, genetic materials, and enzymes. [ABSTRACT FROM AUTHOR]

Low-molecular-mass organogelators (LMOGs) based on photochromic molecules aggregate in selected solvents to form gels through various spatio-temporal interactions. The factors that control the mode of aggregation of the chromophoric core in the LMOGs during gelation, gelation-induced changes in fluorescence, the formation of stacked superstructures of extended π-conjugated systems, and so forth are discussed with selected examples. Possible ways of generating various light-harvesting assemblies are proposed, and some unresolved questions, future challenges, and their possible solutions on this topic are presented. [ABSTRACT FROM AUTHOR]

We discuss thermally driven transport in both organic solvents and electrolyte solutions and, in particular, the variation of the thermophoretic mobility DTwith temperature. We find that the T-dependence in organic solvents arises from the viscosity η(T), in qualitative agreement with data on polystyrene in ethylbenzene. A more subtle effect occurs for charged colloids in an electrolyte, where the strong correlation of DTwith the thermal expansivity β of water is traced back to the thermoelectric effect. Our results provide an explanation for experiments on various colloidal suspensions and, in particular, for the observed change of sign of DTas a function of temperature. [ABSTRACT FROM AUTHOR]

Micellization of several surfactants in water−organic solvent mixtures has been investigated. Only solvents localized mainly in the bulk phase of the micellar solutions (they do not incorporate into the micelles) were studied, with either higher or lower permittivity than that of pure water. Results show that the influence of organic solvent addition on the aggregation process can be approximately accounted for by considering the changes in the bulk phase cohesive energy density, described by the Gordon parameter, G. To our knowledge, this is the first time that, for a given surfactant, the Gibbs energies of micellization, Δ GM°, obtained in several water−organic solvent mixtures have been fitted together. It is worth noting that data from different research groups have been considered. The Δ GM° versus Gcorrelation will permit the estimation of the variations in the Gibbs energy of micellization upon addition of known quantities of a given polar organic solvent. Speaking in a general way, organic solvent addition results in the bulk phase becoming a better solvent for the surfactant molecules. This would make the hydrophobic tail transfer from the bulk phase into the micelles less favorable and, as a consequence, Δ GM° increases (becomes less negative), making the aggregation process less spontaneous. [ABSTRACT FROM AUTHOR]

A stoichiometric MgAl 2O 4spinel (MAS) powder was synthesized by heat treating at 1400 °C for 2 h a compacted mixture of α-Al 2O 3and calcined caustic MgO, followed by crushing and milling. The surface of this powder was then passivated against hydrolysis with H 3PO 4and Al(H 2PO 4) 3in an ethanol solution. The as-passivated powder could then be dispersed in water using tetramethylammonium hydroxide (TMAH) and an ammonium salt of poly(acrylic acid) (Duramax D-3005) as dispersing agents and gelcast to form green consolidates with relatively high strength (>15 MPa). The good dispersing behavior of the passivated powder in water was confirmed by the low viscosity of its suspension containing 41−45 vol % solids, demonstrating the viability of replacing organic solvents by water in colloidal processing of MAS-based ceramics. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and energy dispersive X-ray (EDAX) studies revealed that only negligible amounts of phosphate ions at the surface are required to effectively protect the powder from reacting with water. [ABSTRACT FROM AUTHOR]

A systematically varying series of monolayer-protected clusters (MPCs) was prepared by exposing small gold nanoparticles (∼2 nm in diameter) to the following four adsorbates: n-octadecanethiol ( n- C18), 2-hexadecylpropane-1,3-dithiol ( C18C2), 2-hexadecyl-2-methylpropane-1,3-dithiol ( C18C3), and 1,1,1-tris(mercaptomethyl)heptadecane ( t- C18). The resultant MPCs were characterized by solubility studies, UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FT-IR). All of the MPCs were soluble in common organic solvents; moreover, analysis by TEM showed that the core dimensions were unaffected by exposure to any of the adsorbates. Separate studies by XPS revealed that the sulfur atoms in all MPCs were predominantly bound to the surface of gold (i.e., ∼85% or better). Analysis by FT-IR showed that MPCs functionalized with n- C18possessed alkyl chains having the greatest conformational order in both the solid-state and dispersed in solution; in contrast, those generated from the other three adsorbates were more liquid-like with reduced conformational order (or crystallinity). The rate of nanoparticle decomposition induced by cyanide ions was monitored by UV−vis spectroscopy. While MPCs functionalized with n- C18showed the fastest rate of decomposition, those functionalized with C18C3were the most resistant to decomposition. Overall, the following trend in chemical stability was observed, C18C3≫ C18C2> t- C18≫ n- C18. [ABSTRACT FROM AUTHOR]

The synthesis of stable, monodisperse, shaped copper nanoparticles has been difficult, partially because of copper's propensity for oxidation. This article reports the findings of an investigation of a synthetic route for the synthesis of size-controllable and potentially shape-controllable molecularly capped copper nanoparticles. The approach involved the manipulation of reaction temperature for the synthesis of copper nanoparticles in organic solvents in the presence of amine and acid capping agents. By manipulating the reaction temperature, this route has been demonstrated for the production of copper nanoparticles ranging from 5 to 25 nm. The size dependence of the melting temperature of copper nanoparticles, especially for surface melting, is believed to play an important role in interparticle coalescence, leading to size growth as the reaction temperature is increased. Control of the reaction temperature and capping molecules has also been demonstrated to produce copper nanoparticles with different shapes such as rods and cubes. The previously proposed combination of the selective formation of a seed precursor and a selective growth direction due to the preferential adsorption of capping agents on certain nanocrystal facets is believed to be responsible for shape formation by kinetically controlling the growth rates of crystal facets. The nanoparticles are characterized using TEM, XRD, and UV−visible techniques. A mechanistic consideration of the size control and shape formation is also discussed. [ABSTRACT FROM AUTHOR]