Journal of Colloid And Interface Science (v.373, #1)

Cover 1 (OFC).

Colloid chemistry of nanocatalysts: A molecular view by Kwangjin An; Selim Alayoglu; Trevor Ewers; Gabor A. Somorjai (1-13).
Display Omitted► Colloidal chemistry enables to control the size and shape of nanoparticles. ► Several molecular factors affect turnover frequency and reaction selectivity. ► Multipath reactions show selectivity as a function of size and shape of nanoparticles. ► In situ characterization techniques for catalysts: SFGVS, HPSTM, APXPS, and XAFS.Recent advances of a colloidal chemistry can offer great opportunities to fabricate and design nanocatalysts. Comprehensive understanding of a basic concept and theory of the colloidal synthetic chemistry facilitates to engineer elaborate nano-architectures such as bi- or multi-metallic, heterodimers, and core/shell. This colloidal solution technique not only enables to synthesize high surface mesoporous materials, but also provides a versatile tool to incorporate nanoparticles into mesoporous materials or onto substrates. For green chemistry, catalysis research has been pursued to design and fabricate a catalyst system that produces only one desired product (100% selectivity) at high turnover rates to reduce the production of undesirable wastes. Recent studies have shown that several molecular factors such as the surface structures, composition, and oxidation states affect the turnover frequency and reaction selectivity depending on the size, morphology, and composition of metal nanoparticles. Multipath reactions have been utilized to study the reaction selectivity as a function of size and shape of platinum nanoparticles. In the past, catalysts were evaluated and compared with characterizations before and after catalytic reaction. Much progress on in situ surface characterization techniques has permitted real-time monitoring of working catalysts under various conditions and provides molecular information during the reaction.
Keywords: Colloid; Nanoparticle; Surface; Catalyst; Mesoporous; Turn over; Selectivity; In situ characterization; Sum frequency generation vibrational spectroscopy (SFGVS); High pressure scanning tunneling microscopy (HPSTEM);

Eu3+ and Tb3+ codoped nearly spherical color-tunable submicron particles were synthesized via simple and low cost synthesis method. The synthesis process, mechanism of color tunability and concentration-depended luminescence quenching effect were discussed in detail.Display Omitted► Nearly uniform spherical Eu/Tb codoped Y2O3 particles were synthesized. ► The synthesis process and mechanism of color tunability were discussed in detail. ► Luminescence quenching was observed at high dopant concentrations.Eu3+ and Tb3+ codoped Y2O3 submicron particles were prepared using the simple urea homogeneous precipitation method. X-ray diffraction patterns revealed the synthesized particles to have a pure cubic Y2O3 structure. Field-emission scanning electron microscopy and field-emission transmission electron microscopy showed that the synthesized particles had almost uniform spherical shapes. The luminescence color emission of the synthesized particles could be tuned from red due to the effective 5D0  →  7F j (j  = 0, 1, 2 and 3) transitions within Eu3+ to green due to the 5D4  →  7F5 transition within Tb3+ by switching the excitation wavelength from 255 to 310 nm. Luminescence quenching was observed at high dopant concentrations. Strong and effective color-tunable emission is expected to find a wide range of applications in industry.
Keywords: Y2O3 particles; Luminescence; Urea homogeneous precipitation; Doping;

The thermoresponsive gelling of the alumina suspension with PAA and the F127 copolymer was observed, unless the PAA concentration exceeded more than that needed for the saturation adsorption on the alumina surfaces. The alumina gels had excellent viscoelastic properties for fabricating the three dimensional periodic ceramic structure by a direct colloidal printing method.Display Omitted► F127 copolymer was used as thermoresponsive gelling agent to PAA–alumina suspension. ► Copolymer species had a negligible influence on adsorption state of PAA on alumina. ► Gelling behavior of alumina suspensions was influenced by PAA concentration. ► Excellent gelling of alumina suspensions was observed at suitable PAA concentrations. ► Present thermoresponsive gels were applied to a direct colloidal printing method.Thermoresponsive gelling behavior of concentrated alumina suspensions with poly(acrylic acid) (PAA) and triblock copolymer (PEO101–PPO56–PEO101, Pluronic F127) was investigated as a function of PAA concentration (0.4–1.2 mass%) for ceramic solid free forming. The copolymer species assemble into micelles at temperatures above 15 °C, yielding aqueous physical gel . In this study, the concentrated alumina aqueous suspensions (φ  = 35 vol%) were first prepared using the anionic dispersant of PAA, and then the copolymer species (10 mass%) were dissolved at a cooled temperature at 10 °C. The addition of the copolymer species had a negligible influence on the adsorption state of PAA onto the alumina surfaces. The PAA concentration needed for the saturation adsorption on the alumina surfaces was ∼0.6 mass%. When the PAA concentration was this value or slightly less, the suspension became gel state at 30 °C from low viscous state at 10 °C. The thermally induced alumina gel had excellent viscoelastic properties, and thereby the three dimensional periodic ceramic structures were successfully fabricated by a direct colloidal printing method that using the gels as “solid” inks at the room temperature. On the other hand, when it exceeded the saturation adsorption limit, the gelling behavior was not observed, indicating that the non-adsorbing PAA species may partly suppress the micellization of the copolymer on the heating.
Keywords: Ceramics; Solid free forming; Physical gel; PEO–PPO–PEO copolymer; Poly(acrylic acid);

Electrophoretic Deposition of Transparent ZnO Thin Films from Highly Stabilized Colloidal Suspensions by M. Verde; M. Peiteado; A.C. Caballero; M. Villegas; B. Ferrari (27-33).
Display Omitted► Role of PEIs molecular weight on its adsorption to ZnO nanoparticles was studied. ► PEI forms a jellyfish-like structure with the ZnO nanoflakes. ► Highly stable suspensions were obtained with PEI with the highest molecular weight. ► Densely oriented green ZnO thin films were obtained by EPD from these suspensions.The parameters that control the stability of ZnO-nanoparticles suspensions and their deposition by electrophoretic deposition were studied, so as to organize the assembly and compaction of nanoparticles. The addition of cationic polyelectrolyte – Polyethylenimine (PEI) – with different molecular weights was investigated, in order to study their effectiveness and the influence of the molecular weight of the organic chain on suspensions dispersion. It was found that PEI with the highest molecular weight provided better dispersion conditions. Cathodic EPD was performed under previously optimized suspensions conditions and over electropolished stainless steel substrates. Experimental results showed that the EPD process in these conditions allows obtaining dense transparent ZnO thin films. Deposition times and intensities were optimized by analyzing the resulting thin films characteristics. Finally, the deposits were characterized by FE-SEM, AFM, and different spectroscopic techniques.
Keywords: ZnO; Nanoflakes; Stabilization; Polyethylenimine; Electrophoretic deposition; Thin films;

Display Omitted► Effect of the alcohols solubilization on the fluorinated surfactant micelles. ► Effect of the alcohols on the structural parameters of hexagonal liquid crystal phase. ► Preparation of mesoporous materials from alcohol and fluorinated surfactant solution.In this study, we have used hydrogenated alcohols with different chain lengths and one fluorinated alcohol as additives to determine their effect on the characteristics of mesoporous materials prepared from fluorinated micelles.
Keywords: Nonionic fluorinated surfactant; Mesoporous silica material; Phase diagram; Alcohol addition; Hexagonal liquid crystal phase; Micellar solution; Cooperative templating mechanism;

Counter anion induced morphologies of CeO2 synthesized under non-hydrothermal conditions show different soot oxidation activities.Display Omitted► Counter anion induced CeO2 nanorod and nanoflower morphologies were synthesized. ► The samples exhibit morphology dependent physicochemical and optical properties. ► Surface morphologies of CeO2 influence the redox property, OSC and surface acidity. ► Soot oxidation is rapid on CeO2 nanorods as compared to CeO2 nanoflowers.Advanced synthetic methods under mild and controlled conditions for the synthesis of nanocrystals with specific shapes and exposed surfaces are very important for understanding the surface related properties and to explore their structure–property relationship for various potential applications. Here, we report the synthesis of highly uniform CeO2 nanorods and nanoflowers in large scale using non-hydrothermal homogeneous precipitation method with urea as a precipitating agent and CTAB as a shape directing agent. Uniform microstructures of CeO2 samples were selectively synthesized using chloride and nitrate as the counter anions. The samples were characterized by thermal analysis, X-ray diffraction, N2 adsorption–desorption isotherms, SEM, TEM, UV–Vis-DRS, and Raman spectroscopy, and temperature programmed reduction as well as desorption methods. The results show that the physicochemical and optical properties of CeO2 samples significantly differ with their surface microstructure and morphology. They also strongly influence the redox property, oxygen storage capacity, and surface acidity of the CeO2 samples. The CeO2 samples with different morphologies were tested for their soot oxidation activity. The CeO2 sample with nanorod morphology was found to be more active due to larger CeO2/soot interface than the CeO2 sample with nanoflower morphology.
Keywords: Homogeneous precipitation; Nano-CeO2; Anion controlled morphology; Soot oxidation; Catalysis;

Complexes of nucleolipid liposomes with single-stranded and double-stranded nucleic acids by Costanza Montis; Silvia Milani; Debora Berti; Piero Baglioni (57-68).
Display Omitted► Anionic nucleolipid assemblies complex nucleic acids. ► The association is driven by Ca2+ bridging. ► Complexation driven by selective interactions for single-stranded nucleic acids. ► For double-stranded nucleic acids, no reentrant condensation is observed.We report on the association of anionic liposomes from POP-Ade:POPC (1-palmitoyl-2-oleoyl-phosphatidyladenosine and 1-palmitoyl-2-oleoyl-phosphatidylcholine, respectively) with single- and double-strand nucleic acids, mediated by Ca2+ bridging. The structural and dynamical features of such complexes are compared with those displayed when the nucleolipid is replaced by POPG (1-palmitoyl-2-oleoyl-sn-phosphatidyl-glycerol), characterized by the same apolar skeleton and negative charge as POP-Ade, but lacking the nucleic polar head. For single-stranded nucleic acids, we demonstrate that specific interactions drive the formation of complexes with nucleolipid liposomes, while no association is present for POPG-based samples. For double-stranded nucleic acids, Ca2+ bridging promotes association with both liposomal formulations, but the corresponding complexes have different structural features, in terms of size, overall charge and internal liquid–crystalline structure.
Keywords: Self-assembly; Nucleolipids; DNA delivery; Lipoplexes;

Several architectures of uricase-fatty acid ultrathin films were prepared and the enzyme activity investigated.Display Omitted► Uricase and fatty acids formed hybrid Langmuir monolayers. ► Films were transferred to solid supports as LB films in several architectures. ► Enzyme activity on uric acid was measured. ► One single enzyme–lipid layer transferred resulted in the best sensor.Preserving the enzyme structure in solid films is key for producing various bioelectronic devices, including biosensors, which has normally been performed with nanostructured films that allow for control of molecular architectures. In this paper, we investigate the adsorption of uricase onto Langmuir monolayers of stearic acid (SA), and their transfer to solid supports as Langmuir–Blodgett (LB) films. Structuring of the enzyme in β-sheets was preserved in the form of 1-layer LB film, which was corroborated with a higher catalytic activity than for other uricase-containing LB film architectures where the β-sheets structuring was not preserved. The optimized architecture was also used to detect uric acid within a range covering typical concentrations in the human blood. The approach presented here not only allows for an optimized catalytic activity toward uric acid but also permits one to explain why some film architectures exhibit a superior performance.
Keywords: Langmuir–Blodgett films; Uricase; Catalytic activity; Air–water interface;

Display Omitted► The behavior of a zwitterionic lipid layer on oil droplets is strictly dependent on the lipid molecular structure. ► Na+ and Ca2+ ions bound to the headgroups of phospholipid can affect the lipid order ► Ions act to increase attractions between the neighboring lipids and decrease the emulsion effective diameter. ► Phospholipid hydrolysis by PLA2 is enhanced by added ethanol. ► The effect of ethanol on n-tetradecane/DOPC emulsions is comparable with that when DPPC is used as stabilizer.The properties of n-tetradecane emulsions with dipalmitoylphosphatidylcholine (DPPC) or dioleoylphosphatidylcholine (DOPC) in 1 M ethanol were investigated at 20 and 37 °C. The zwitterionic phospholipids having the same headgroup bound to the apolar tail composed of two saturated or unsaturated chains were used as stabilizing agents. Both phospholipids may self-organize into aggregates, which possess different sizes and surface affinities.Electrokinetic properties of the systems at natural pH or pH 8 were investigated taking into account the effective diameter of the droplets as well as the zeta potentials using the dynamic light scattering technique. The effect of both phospholipids decreases the initially negative zeta potential of the n-tetradecane emulsion and is more evident in the case of DPPC especially at a physiological temperature near its main temperature transition. The change of zeta potential by DOPC is visible at both temperatures probably as an effect of a loose packing of this phospholipid on n-tetradecane droplets, because of the presence of double bonds in its molecule. Also, the role of ethanol dipoles on the stability of oil/phospholipid emulsions is obvious.The other aim of paper was the characterization of the phospholipase A2 influence on DOPC hydrolysis in the emulsion environment in order to emphasize the importance of such methodology. The present work is the first study that explores the effects of both electrolyte ions and ethanol molecules on DOPC hydrolysis by phospholipase. The effect of enzyme on the n-tetradecane/DOPC emulsions was investigated at pH 8 with Na+ or Ca2+ ions, which occur in the physiological fluids. The effective diameters do not always correlate with the zeta potentials. A possible reason of such behavior might a mechanism different from the electrostatic stabilization. The particular role of Ca2+ ions in the emulsions with phospholipids was confirmed. Those investigations provide insight into the properties of the PLA2 hydrolysis process enhanced by added ethanol. It is believed that the enzyme effect on the phospholipid aggregation behavior at the oil–water interface will be helpful for understanding other biological phenomena.
Keywords: n-Tetradecane emulsion; DPPC; DOPC; Phospholipase PLA2; Zeta potential; Effective diameter; Stability;

Comparison of Multilayer Formation Between Different Cellulose Nanofibrils and Cationic Polymers by Paula Eronen; Janne Laine; Janne Ruokolainen; Monika Österberg (84-93).
Display Omitted► Systematic comparison of different cellulose nanofibrils in multilayer formation. ► Nonelectrostatic interactions were decisive in build-up of cellulosic multilayers. ► Native, unmodified NFC was also successfully used in multilayers. ► The underlying cationic layer affected the interactions between NFC fibrils.The multilayer formation between polyelectrolytes of opposite charge offers possibility for creating new tailored materials. Exchanging one or both components for charged nanofibrillated cellulose (NFC) further increases the variety of achievable properties. We explored this by introducing unmodified, low charged NFC and high charged TEMPO-oxidized NFC. Systematic evaluation of the effect of both NFC charge and properties of cationic polyelectrolytes on the structure of the multilayers was performed. As the cationic component cationic NFC was compared with two different cationic polyelectrolytes, poly(dimethyldiallylammoniumchloride) and cationic starch. Quartz crystal microbalance with dissipation (QCM-D) was used to monitor the multilayer formation and AFM colloidal probe microscopy (CPM) was further applied to probe surface interactions in order to gain information about fundamental interactions and layer properties. Generally, the results verified the characteristic multilayer formation between NFC of different charge and how the properties of formed multilayers can be tuned. However, the strong nonelectrostatic affinity between cellulosic fibrils was observed. CPM measurements revealed monotonically repulsive forces, which were in good correspondence with the QCM-D observations. Significant increase in adhesive forces was detected between the swollen high charged NFC.
Keywords: Microfibrillar cellulose; Colloidal probe technique; QCM-D; Multilayer; AFM;

Display Omitted► Novel fluorescent poly(2-(acetoacetoxy)ethyl methacrylate) latexes were synthesized by miniemulsion polymerization. ► Ammonia and the β-dicarbonyl aggregates assembled a supramolecular complex. ► PAAEMA thin films absorb and desorb ammonia in a reversible manner. ► PAAEMA thin films are sensitive to ammonia gas and have short response time.Novel fluorescent poly(2-(acetoacetoxy)ethyl methacrylate)(PAAEMA) latexes have been synthesized by miniemulsion polymerization employing a polymeric costabilizer. Nanoscale aggregates of macromolecules bearing β-dicarbonyl are formed in the prepared latex particles. Ammonia and the β-dicarbonyl aggregates assemble a supramolecular complex, which exhibits strong visible fluorescence under UV light. The formation of the complex is confirmed by the characteristic absorption peak located at about 275 nm in UV–Vis spectra. The absorption spectrum has been found to be applicable for ammonia detection. Atomic Force Microscopy (AFM) studies of surface morphology reveal that gas-sensing properties of the PAAEMA thin films involve the reversible absorption and desorption of ammonia. PAAEMA thin films are sensitive to ammonia gas and have a short response time of 80 s when exposed to 54 ppm of ammonia gas concentration.
Keywords: Fluorescent chemosensor; β-Dicarbonyl aggregation; Supramolecular complex; Polymer thin film; Ammonia sensing;

Effectiveness, against tuberculosis, of pseudo-ternary complexes: Peptide-DNA-cationic liposome by Rogério Silva Rosada; Célio Lopes Silva; Maria Helena Andrade Santana; Clóvis Ryuichi Nakaie; Lucimara Gaziola de la Torre (102-109).
Display Omitted► We designed a new synthetic peptide (NLS) to act as a nuclear localization signal. ► The peptide was included in DNAhsp65/cationic liposome as a gene vaccine. ► The peptide/DNAhsp65 complex was inserted into the liposome structure. ► Peptide inclusion presented in vivo therapeutic effects against tuberculosis. ► The pseudo-ternary complex is a promising gene vaccine for tuberculosis treatment.We report the effects of a synthetic peptide designed to act as a nuclear localization signal on the treatment of tuberculosis. The peptide contains 21 amino acid residues with the following specific domains: nuclear localization signal from SV 40T, cationic shuttle sequence, and cysteamide group at the C-terminus. The peptide was complexed with the plasmid DNAhsp65 and incorporated into cationic liposomes, forming a pseudo-ternary complex. The same cationic liposomes, composed of egg chicken l-α-phosphatidylcholine, 1,2-dioleoyl-3-trimethylammonium-propane, and 1,2-dioleoyl-3-trimethylammonium-propane (2:1:1 M), were previously evaluated as a gene carrier for tuberculosis immunization protocols with DNAhsp65. The pseudo-ternary complex presented a controlled size (250 nm), spherical-like shape, and various lamellae in liposomes as evaluated by transmission electron microscopy. An assay of fluorescence probe accessibility confirmed insertion of the peptide/DNA into the liposome structure. Peptide addition conferred no cytotoxicity in vitro, and similar therapeutic effects against tuberculosis were seen with four times less DNA compared with naked DNA treatment. Taken together, the results indicate that the pseudo-ternary complex is a promising gene vaccine for tuberculosis treatment. This work contributes to the development of multifunctional nanostructures in the search for strategies for in vivo DNA delivery.
Keywords: Cationic liposome; DNA delivery; Nuclear localization signal; Tuberculosis; Gene vaccine; Infectious disease;

The influence of particle clustering on the rheological properties of highly concentrated magnetic nanofluids by Daniela Susan-Resiga; V. Socoliuc; T. Boros; Tunde Borbáth; Oana Marinica; Adelina Han; L. Vékás (110-115).
Display Omitted► The highest solid volume fraction of the magnetite nanoparticles was 21%. ► DLS and magnetogranulometry revealed weak particle clustering. ► Viscosity versus solid particle concentration was fitted with Krieger–Dougherty formula. ► 1.3 part./cluster and 1.4 nm surfactant layer thickness were estimated from the fit.In this paper the particle volume fraction and temperature dependence of the dynamic viscosity of highly concentrated transformer oil based magnetic nanofluids was investigated in the absence of an external magnetic field. The solid particle volume fraction dependence of the relative viscosity was found to be very well fitted by the Krieger–Dougherty formula, whence the mean ellipticity of the colloidal particles and the effective surfactant layer thickness were obtained. Using the information on the particles’ size and shape statistics obtained from TEM, DLS and magnetogranulometry investigations, it was concluded that the magnetite nanoparticles agglomerate in small clusters of about 1.3 particles/cluster, due to the van der Waals interactions. The effective thickness of the oleic acid surfactant layer was estimated as about 1.4 nm, in very good agreement with the value resulted from previous SANS investigations.
Keywords: Magnetic fluid; Ferrofluid; Agglomeration; Dynamic viscosity; Magnetogranulometry; Dichroism; DLS; SLS; TEM;

The Structure of Percolating Lipid Monolayers by D. Risović; S. Frka; Z. Kozarac (116-121).
Display Omitted► A new approach for determination of lattice structure of lipid monolayers. ► Application of percolation theory and fractal analysis provides monolayer structure. ► Lattice structures determined from percolation thresholds conform to GIXD results.The lattice structure and in plane molecular organization of Langmuir monolayer of amphiphilic material is usually determined from grazing incidence X-ray diffraction (GIXD) or neutron reflectivity. Here we present results of a different approach for determination of monolayer lattice structure based on application of fractal analysis and percolation theory in combination with Brewster angle microscopy. The considerations of compressibility modulus and fractal dimension dynamics provide information on percolation threshold and consequently by application of percolation theory on the lattice structure of a monolayer. We have applied this approach to determine the monolayer lattice structures of single chain and double chain lipids. The compressibility moduli were determined from measured π-A isotherms and fractal dimensions from corresponding BAM images. The monolayer lattice structures of stearic acid, 1-hexadecanol, DPPC and DPPA, obtained in this way conform to the corresponding lattice structures determined previously by other authors using GIXD.
Keywords: Lipid monolayers; Lattice structure; Percolation; Fractal; Brewster angle microscopy; Compressibility; DPPC; DPPA; Hexadecanol; Stearic acid;

Utilization of Smart Hydrogel–Metal Composites as Catalysis Media by Nurettin Sahiner; Sultan Butun; Ozgur Ozay; Burak Dibek (122-128).
Poly(1-vinyl imidazole) (p(VI)) hydrogel network were used as template for metal nano- particle/cluster preparation such as Cu, Co and Ni. Moreover, these hydrogel-M (M:Cu, Co, and Ni) composites were also employed as reactor e.g., in generation of hydrogen from the hydrolysis of various boron compounds (NaBH4 and NH3BH3), and in reduction of nitro phenols such as 4-nitrophenol to 4-aminophenol. The p(VI)-M composite can further be made magnetic field responsive by in situ preparation of magnetic ferrites inside p(VI) for magnetic field responsive hydrogel-M composite catalyst systems.Display Omitted► P(VI) hydrogel network for metal ion absorption and reduction. ► In situ metal nanoparticle synthesis within hydrogel. ► Soft and flexible nanoreactors.Various metal nanoparticles such as, Cu, Co, Ni, and Fe were prepared inside poly(1-vinyl imidazole) p(VI) hydrogel by the absorption of the corresponding metal ions from aqueous solutions and the reduction with suitable reducing agents such as NaBH4 and/or NaOH. TGA and ICP–AES were used to determine the metal particle content of p(VI)–M (M: Cu, Co, and Ni) composites. The prepared hydrogel–metal nanoparticle composites were proven to be resourceful as reaction container for the catalysis of various organic reactions. It was illustrated that p(VI)–M hydrogel–metal composites can be successfully used in the hydrolysis of NaBH4 for the generation hydrogen form NaBH4 and NH3BH3. Additionally, p(VI)–M composites were also illustrated in the catalysis of different organic reactions; e.g., these hydrogel-M are very effective in the reduction nitro aromatic compounds such 2-nitrophenol (2-NP) and 4-nitrophenol (4-NP) to their corresponding amine forms in the presence of aqueous NaBH4. Various parameters in the catalysis of hydrogen production and 4-NP reduction were determined.
Keywords: Hydrogels; Soft network; Polymeric network; Catalysis; Composite; P(1-vinyl imidazole);