We report on highly aligned graphene oxide or graphene sheets inside an alginate matrix and their structure obtained for various compositions. The order of the platelet particles with respect to one another has been verified by environmental scanning electron microscopy (ESEM) and 2-dimensional X-ray diffraction (2D XRD). The microscopic order within the platelet particles has been analyzed by X-ray diffraction (XRD) measurements in the Bragg–Brentano reflection configuration as well as in Debye–Scherrer diffraction mode. The azimuthal angle intensity profiles obtained from 2D XRD analysis have been fit to Maier–Saupe and affine deformation model predictions, and the affine deformation model proved to be the most reliable to quantify the order parameter ⟨P2⟩ values of graphene oxide/sodium alginate and graphene/calcium alginate composites with different weight fractions of the filler. The ⟨P2⟩ values for graphene oxide/sodium alginate composites were found to show little dependence on the concentration of graphene sheets above ∼10 wt %, with a maximum ⟨P2⟩ value of 0.8 at 25 wt % graphene oxide inside the sodium alginate matrix. The alignment of graphene sheets inside the calcium alginate matrix has been observed to be lower, with an average ⟨P2⟩ value of 0.7. We have not observed preferred orientation of graphene sheets inside the barium alginate matrix. The formation of a highly aligned graphene oxide/sodium alginate composite structure has been explained by the affine deformation model, whereupon drying the developed yield stress causes sheets to align in-plane with the polymer matrix. The impaired orientation of graphene sheets inside the calcium alginate matrix and absence of orientation in the barium alginate matrix have been explained by the structure development in the polymer matrix itself due to metal-ion-induced cross-linking.

We report on the production of Carbon Nano Networks (CNNs) from dense microemulsions in which catalyst nanoparticles have been synthesized. CNNs are 3D carbon networks, consisting of branches and junctions, and are mesoporous, graphitic, and conductive being suitable as electrode materials.

Microemulsions are exciting systems that are promising as tuneable self-assembling templating reaction vessels at the nanoscale. Determination of the nano-structure of microemulsions is, however, not trivial, and there are fundamental questions regarding their design. We were able to reproduce experimental data for an important microemulsion system, sodium-AOT–n-heptane–water, using coarse-grained simulations involving relatively limited computational costs. The simulation allows visualization and deeper investigation of controversial phenomena such as bicontinuity and ion mobility. Simulations were performed using the Martini coarse-grained force field. AOT bonded parameters were fine-tuned by matching the geometry obtained from atomistic simulations. We investigated several compositions with a constant ratio of surfactant to oil while the water content was varied from 10 to 60% in weight. From mean square displacement calculation of all species, it was possible to quantify caging effects and ion mobility. Average diffusion coefficients were calculated for all charged species and trends in the diffusion coefficients were used to rationalize experimental conductivity data. Especially, the diffusion coefficient of charged species qualitatively matched the variation in conductivity as a function of water content. The scattering function was calculated for the hydrophilic species and up to 40% water content quantitatively matched the experimental data obtained from small angle X-ray scattering measurements. For higher water contents, discrepancies were observed and attributed to a nearby phase separation. In particular, bicontinuity of water and oil was computationally visualized by plotting the coordinates of hydrophilic beads. Equilibrated coarse-grained simulations were reversed to atomistic models in order both to compare ion mobility and to catch finer simulation details. Especially, it was possible to capture the intimate ion pair interaction between the sodium ion and the surfactant head group.

Surfactant-free emulsion polymerization involving a nonionic, and hence uncharged initiator presents a new approach towards environmentally friendly procedures to synthesize latex particles. Under optimal solvent conditions, notably pH and ionic strength, the latex particles are stabilized by the natural development of ionic charge at the surface of the particles. We emphasize that the present process does not at all involve the addition of stabilizers such as surfactants or the creation of surface-active species from ionic initiators. The width of the size distribution is found to vary strongly with experimental conditions, notably the ionic strength and to a much lesser extent pH. The phenomenon is explained by a critical ionic strength dependence of the aggregation of the just nucleated primary particles into larger secondary particles, the so-called “coagulative nucleation” step.

Highlights•Surface coverage per layer better parameter than fill factor.•Thickness dependence due to inhomogeneous filler distribution.•There is a minimal number of layers required for optimal blocking.Homogenous, impermeable platelet dispersions significantly enhance the barrier properties of polymer composite membranes. Layer-by-layer (LbL) deposition allows achieving the highest degree of orientation in comparison to melt blending or solution casting. However, membranes produced by assisted self-assembly, exhibit a strong thickness dependence of their barrier properties. Such behavior could arise from an unevenly dispersed phase distribution in the continuous phase. Here, we analyze this anomalous thickness dependence of gas permeability in platelet–polymer composites produced by the LbL method and on the basis of this result we present a design criterion for these systems.Graphical abstract

We demonstrate that for high yield wet synthesis of monodispersed nanoparticles high surfactant content bicontinuous microemulsions offer an advantageous template as particle size is limited by the embedding matrix whereas particle aggregation is largely prohibited by its structure. We synthesized platinum nanoparticles varying the reaction rate, metal precursor and reducing agent type and concentration, and the composition of the microemulsion in water content and oil type. High yields of up to 0.4% of metal produced per weight of template were achieved without affecting the particle size, ca. 2 nm. We showed that our method is robust in the sense that particle size is hardly dependent on synthesis conditions. This is attributed to the fact that the packing of surfactant on nanoparticle surfaces is the only parameter determining the particle size. It can only be slightly varied with ionic strength, headgroup hydration, and tail solvency through oil variation. Water content mainly affects the microemulsion stability and through that the colloidal stability of the nanoparticles. Hydrazine as a reducing agent poses a special case as it causes dimerization of the surfactant and hence modifies the surfactant parameter as well as the stability. Finally, we highlighted the differences in comparison to nanoparticle synthesis in standard water-in-oil microemulsions, and we propose a mechanism of particle formation.

It is generally believed that surfactant-free emulsion polymerization involves four steps: initiation, nucleation into primary particles, coagulation into secondary particles, and growth. By high resolution SEM-imaging of the intermediate polymerization products, the evolution of the morphology of the polymer particles has been followed. This allowed us, to our best knowledge for the first time, to visualize “coagulative nucleation”, which is the process where the primary nanoparticles aggregate into larger entities. The obtained visual information and data on particle size, number, and zeta potential, strongly suggest that coagulative termination is responsible for the coagulative nucleation phenomenon, resulting in a dispersion of fine, relatively uniform polymer particles.

This article demonstrates that bicontinuous microemulsions are optimal templates for high yield production of metal nanoparticles. We have verified this for a variety of microemulsion systems having AOT (sodium bis (2-ethyhexyl) sulphosuccinate) or a fluorocarbon (perfluoro (4-methyl-3,6-dioxaoctane)sulphonate) as surfactant mixed with water and oils like n-heptane or n-dodecane. Several types of metal nanoparticles, including platinum, gold and iron, were produced in these microemulsions having a size range spanning 1.8 − 17 nm with a very narrow size distribution of ±1 nm. Remarkably high mass concentrations up to 3% were reached. Size and concentration of the nanoparticles could be varied with the stoichiometries of the reagents that constituted them. The optimization towards high yield while maintaining low size polydispersity is due to the decoupling of the time scales for the precipitation reaction and for coarsening. In actual fact, coalescence is essentially prevented by the immobilization of nanoparticles within the bicontinuous microemulsion structure.Graphical abstractHighlights► Bicontinuous microemulsions as optimal nanoparticle templates. ► Size range = 1.8 − 17 nm with narrow distribution = ±1 nm. ► Mass yield of nanoparticles = 3% of template. ► Nanoparticle uniformity and immobilization guarantee long-term stability.

In a previous article published in Langmuir 27 (2011) 7783–7787, we reported on a novel synthesis route to make magnetic noble metal nanoparticles and nanoparticle clusters. In this article we demonstrate an enhanced method of recovering the magnetic particles after synthesis and give an insight into the temperature dependence of their magnetization. Based on our findings, we conclude that the magnetism induced by our method has a dominant contribution from the surface instead of the bulk as is common for classical magnetism.Graphical abstractHighlights► Tanomalous magnetic properties noble metal (nano)particles. ► Ferromagnetism strongly temperature dependent. ► Curie temperature close to melting point.

Aggregation behavior and thermodynamic properties of two novel homologous aromatic moiety bearing hybrid fluorocarbon surfactants, sodium 2-(2-(4-ethylphenyl)-1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoroethanesulfonate (1) and sodium 2-(1,1,2,2-tetrafluoro-2-(4-vinylphenyl)ethoxy)-1,1,2,2-tetrafluoroethanesulfonate (2) were studied using surface tension measurements and isothermal titration calorimetry (ITC) in dilute aqueous solutions at room temperature. Because of the aromatic group in the hydrophobic tail, both surfactants are soluble at room temperature unlike their starting precursor, 5-iodooctafluoro-3-oxapentanesulfonate as well as several other fluorocarbon sulfonic acid salts. Moreover, the surfactant 2 has the ability that it can be polymerized once microemulsions are formed with it. The ionic conductivity measurements of 1 at five different temperatures from 288 to 313 K were carried out to study the effect of temperature on the micellization and its thermodynamics. The pseudophase separation model was applied to estimate thermodynamic quantities from conductivity data. The Gibbs energy of micellization versus temperature exhibited the characteristic U-shaped behavior with a minimum at 306 K. The micellization process was found to be largely entropy driven. Because of its hybrid structure, the entropy change of micellization for 1 was larger than what is common for hydrocarbon surfactants like SDS but less than for fully fluorinated surfactants like NaPFO. The micellization process was found to be following the entropy–enthalpy compensation phenomena.

Noble metal particles can be made strongly ferromagnetic or diamagnetic provided that they are synthesized in a sufficiently strong magnetic field. Here we outline two synthesis methods that are fast, reproducible, and allow broad control over particle sizes ranging from nanometers to millimeters. From magnetometry and light spectroscopy, it appears that the cause of this anomalous magnetism is the surface anisotropy in the noble metal particles induced by the applied magnetic field. This work offers an elegant alternative to composite materials of noble metals and magnetic impurities.

This article reviews our understanding of ionization processes of weak polyelectrolytes. The emphasis is put on a general introduction to site binding models, which are able to account for many experimental features of linear and branched polyelectrolytes, including dendrimers. These models are fully compatible with the classical description of acid–base equilibria. The review further discusses the nature of the site–site interaction and role of conformational equilibria. Experimental charging data of numerous weak polyelectrolytes are discussed in terms of these models in detail.Figure optionsDownload full-size imageDownload as PowerPoint slide

We report on the production of Carbon Nano Networks (CNNs) from dense microemulsions in which catalyst nanoparticles have been synthesized. CNNs are 3D carbon networks, consisting of branches and junctions, and are mesoporous, graphitic, and conductive being suitable as electrode materials.