Search

Polyplexes between a double-stranded Salmon DNA and hyperbranched poly(ethyleneimine) (PEI) as well as a maltosylated PEI-Mal were incorporated into a gelatin/chitosan hydrogel scaffold. Calorimetric experiments of the polyplexes show a decrease of the melting temperature in presence of PEI and a peak splitting in presence of PEI-Mal, which can be interpreted to a partial compaction of the DNA strands in presence of PEI-Mal. When the polyplexes are incorporated into a gelatin/chitosan scaffold in the swollen state, the DNA melting peaks at 90 and 93 °C, respectively, indicate in both cases the release of the DNA at the surface of the hydrogel scaffold in a more compact form. Specific interactions between the PEI-Mal shell and gelatin are responsible for the tuning of the release properties in presence of the maltose units in the hyperbranched PEI.

Pickering emulsions with two types of nanoparticles, i.e., superparamagnetic magnetite nanoparticles dispersed in n-hexane and gold nanoparticles dispersed in water, were formed by rigorous mixing in presence of surface active polymeric surfactants. Monodisperse magnetite nanoparticles with a mean particle size of 4 nm were obtained by a microwave-assisted synthesis in n-hexane in presence of oleic acid, and gold nanoparticles were produced in aqueous solution in presence of the hyperbranched poly(ethyleneimine) (PEI) or sodium citrate as reducing and stabilizing agent. After mixing the prepared nanoparticle dispersions in presence of the Pluronics an intermediate gel-like phase is formed. The Pickering emulsion droplets in the intermediate phase are stabilized by both types of nanoparticles, as to be seen by cryo-SEM micrographs. After separating, solvent evaporation and redispersion in water highly ordered Pluronic-stabilized superparamagnetic magnetite nanoparticle aggregates with embedded gold nanoparticles can be obtained.

Polyplexes between Salmon DNA and non-modified hyperbranched poly(ethyleneimines) of varying molar mass, i.e., PEI(5 k) with 5000 g/mol and PEI(25 k) with 25,000 g/mol, and modified PEI(5 k) with maltose units (PEI-Mal) were investigated in dependence on the molar N/P ratio by using dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (mu-DSC), scanning-transmission electron microscopy (STEM), and cryo-scanning electron microscopy (cryo-SEM). A reloading of the polyplexes can be observed by adding the unmodified PEI samples of different molar mass. In excess of PEI a morphological transition from core-shell particles (at N/P 8) to loosely packed onion-like polyplexes (at N/P 40) is observed. The shift of the DSC melting peak from 88 degrees C to 76 degrees C indicates a destabilization of the DNA double helix due to the complexation with the unmodified PEI. Experiments with the maltose-modified PEI show a reloading already at a lower N/P ratio. Due to the presence of the sugar units in the periphery of the polycation electrostatic interactions between DNA become weaker, but cooperative H-bonding forces are reinforced. The resulting less-toxic, more compact polyplexes in excess of the PEI-Mal with two melting points and well distributed DNA segments are of special interest for extended gene delivery experiments. (C) 2015 Elsevier B.V. All rights reserved.

By dropping a NaH2PO4 center dot H2O precursor solution to a CaCl2 solution at 90 degrees C under continuous stirring in presence of two biopolymers, i.e. gelatin (G) and chitosan (C), supramolecular calcium phosphate (CP) card house structures are formed. Light microscopic investigations in combination with scanning electron microscopy show that the GC-based flower-like structure is constructed from very thin CP platelets. Titration experiments indicate that H-bonding between both biopolymers is responsible for the synergistic effect in presence of both polymers. Gelatin chitosan water complexes play an important role with regard to supramolecular ordering. FTIR spectra in combination with powder X-ray diffraction show that after burning off all organic components (heating up >600 degrees C) dicalcium and tricalcium phosphate crystallites are formed. From high resolution transmission electron microscopy (HR-TEM) it is obvious to conclude, that individual crystal platelets are dicalcium phosphates, which build up ball-like supramolecular structures. The results reveal that the GC guided crystal growth leads to nano-porous supramolecular structures, potentially attractive candidates for bone repair. (c) 2015 Elsevier B.V. All rights reserved.

Chemically cross-linked composite gels based on bentonite clay from Manyrak deposit (Kazakhstan Republic) and nonionic polymers, i.e., poly(hydroxyethylacrylate) and poly(acrylamide), were polymerized in situ after preliminary intercalation of monomers in an aqueous suspension of bentonite clay. By means of cryo-scanning electron microscopy, it was shown that bentonite clay is well incorporated into the gel network structure with pore sizes up to 1.5 mu m. The intercalated bentonite clay can adsorb cationic surfactants as well as heavy metal ions due to electrostatic interactions. Conductometric and surface tension measurements indicate not only the adsorption of surfactants and heavy metals inside the hydrogel, but also the displacement of the critical micellization concentration (CMC) of the surfactants.

Janus emulsions, containing olive oil (OO) and silicone oil (SiO), were formed in presence of polyelectrolyte complex particles, i.e., gelatin-sodium polyacrylate (NaPAA) complexes. The diameter of completely engulfed Janus droplets can be tuned between 50 and 200 μm by varying the gelatin/NaPAA complex particle size between 200 and 400 nm. The gelatin/NaPAA complex particles adsorbed at the olive oil interface decrease the interfacial tension and stabilize the resulting completely engulfed Pickering Janus emulsions. Long-term stable Janus gels can be synthesized in presence of gelatin/sodium carboxymethylcellulose (NaCMC) mixtures. In that case Coulombic forces are of relevance with regard to the stabilization of the Janus droplets embedded in a gelatin/NaCMC gel matrix. Janus gels show elastic reological behavior and thixotropic properties.

This Letter is focused on the one-pot formation of CdS nanoparticles in aqueous medium in presence of polyethyleneimine (PEI). Quantum dots can be obtained by adding a pre-cooled aqueous Na 2 S solution to a pre-cooled aqueous CdCl 2 solution dropwise in presence of PEI. Field flow fractionation in combination with TEM experiments show a time dependent agglomeration of individual quantum dots from 1.6 nm up to 3.2 nm in size. The hyperbranched PEI of moderate molar mass (>20 000 g/mol) is an excellent polymer to prevent a further increase of the particle size. Therefore, stable fluorescent PEI-capped CdS quantum dots are available.

Polyplexes, composed of Salmon DNA and very small gold nanoparticles embedded into a dendritic glycopolymer architecture of sugar-modified poly(ethyleneimine) (PEI-Mal) with a molar mass of about 25,000 g/mol, were characterized by dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (mu-DSC) and transmission electron microscopy (TEM). The PEI-Mal-entrapped gold nanoparticles of about 2 nm in diameter influence the polyplex formation of the hyperbranched PEI containing bulky maltose, and in consequence the DNA is more compactized in the inner part of spherical polyplex particles of about 150 nm in diameter. The resulting more compact core shell polyplex particles with embedded gold nanoparticles in the outer polymer shell will be used as components in forthcoming gene delivery experiments. (C) 2017 Elsevier B.V. All rights reserved.

This paper is focused on the formation of organically and inorganically passivated cadmium sulfide (CdS) nanoparticles in two different types of microemulsions. On the one hand, we used a ternary inverse microemulsion consisting of water, heptanol, and 3-(N,N-dimethyldodecylammonio)propanesulfonate and on the other hand, a poly(ethyleneimine)-based quaternary microemulsion containing water, toluene, pentanol, and sodium dodecylsulfate. UV-vis measurements confirm the formation of CdS-ZnS core-shell nanoparticles in the ternary microemulsion. Using the quaternary microemulsion template phase, polymer capped luminescent CdS nanoparticles can be formed. After a complete solvent evaporation, the nanoparticles are redispersed in water and characterized by means of dynamic light scattering and transmission electron microscopy. From the ternary microemulsion, well-stabilized CdS-ZnS core-shell nanoparticles with diameters of about 5 nm can be redispersed, but from the quaternary microemulsion, only nanoparticle aggregates of about 100 nm.

This article is focused on the characterization of the poly(ethylene glycol) (PEG)-induced bicontinuous microemulsion of the pseudo-ternary system sodium dodecylsulfate (SDS)/xylene-pentanol/water by means of differential scanning calorimetry, rheology, and conductometry. The influence of the polymer concentration (cp) and the molecular weight (Mw) on the microstructure of the microemulsion was investigated using Cryo scanning electron microscopy. It was found that an increase of cp influences the structure of the sponge-like phase significantly. These polymer-modified microemulsions can be used as a template phase for the formation of BaSO4 nanorods, where individual nanoparticles (5 nm in size) are ordered along the polymer backbone.

The paper is focused on the formation of nanoparticles, i.e., zinc sulfide (ZnS) and hydroxylapatite, in a microemulsion template phase consisting of heptanol, water, and a surfactant with a sulfobetaine head group in the absence and presence of an added polyelectrolyte. In the absence of a polyelectrolyte, beside larger particles, spherical ZnS nanoparticles with a diameter below 10 nm can be redispersed after solvent evaporation. In the presence of the synthetic cationic polyelectrolyte poly(diallyldimethylammonium chloride), a reloading of the particle surface is observed, and cationic charged ZnS nanoparticles, of about 5 nm in size, can be redispersed as a main fraction. When hydroxylapatite is formed in the presence of the more stiff biopolymer chitosan hydroxylapatite, hybrid structures were formed. Transmission electron micrographs show fiber-like aggregate structures, consisting of individual small nanoparticles ordered along the polymer chain.

This paper is focused on the influence of anionic polyelectrolytes on the inverse micellar region (L2 phase) of the quaternary system cetyltrimethylammonium bromide/toluene–pentanol (1:1)/water. The properties of the different macromolecules have been changed by the gradual incorporation of hydrophobic side chains. Thus, commercially available poly(acrylic acid) has been hydrophobically modified by grafting with butylamine. With increasing hydrophobicity of the PAA, the charged polymers induce a clear diminution of the water solubilization capacity of the microemulsion at a given polymer concentration of 1%. The isotropic polyelectrolyte-modified L2 phase has been also investigated in much more detail by means of conductometric, rheological and calorimetric measurements. The polyelectrolyte-modified microemulsion shows a typical low shear viscosity and Newtonian flow behaviour. The conductivity measurements indicate the characteristic features of percolated microemulsion droplets. An increase of the hydrophobicity leads to a decrease of the acidity of the carboxy groups, as to be demonstrated by potentiometric measurements. However, titration experiments with a surfactant selective electrode show that the cooperativity of the interactions between the hydrophobic-modified polyelectrolyte and the surfactant molecules is decreased due to the formation of microdomains. Basing on this knowledge, the decrease of the area of the L2 phase with increasing hydrophobicity of the PAA becomes plausible due to the precipitation of more hydrophobic polyelectrolyte-surfactant complexes.

This paper focuses on the characterization and use of polymer-modified phosphatidylcholine (PC)/sodium dodecyl sulfate (SDS)-based inverse microemulsions as a template phase for BaSO4 nanoparticle formation. The area of the optically clear inverse microemulsion phase in the isooctane/hexanol/water/PC/SDS system is not significantly changed by adding polyelectrolytes, i.e., poly(diallyldimethylammonium chloride) (PDADMAC), or amphoteric copolymers of diallyldimethylammonium chloride and maleamid acid to the SDS-modified inverse microemulsion. Shear experiments show non-Newtonian flow behavior and oscillation experiments show a frequency-dependent viscosity increase (dilatant behavior) of the microemulsions. Small amounts of bulk water were identified by means of differential scanning calorimetry. One can conclude that the macromolecules are incorporated into the individual droplets, and polymer-filled microemulsions are formed. The polymer-filled microemulsions were used as a template phase for the synthesis of BaSO4 nanoparticles. After solvent evaporation the nanoparticles were redispersed in water and isooctane, respectively. The polymers incorporated into the microemulsion are involved in the redispersion process and influence the size and shape of the redispersed BaSO4 particles in a specific way. The crystallization process mainly depends on the type of solvent and the polymer component added. In the presence of the cationic polyelectrolyte PDADMAC the crystallization to larger cubic crystals is inhibited, and layers consisting of polymer-stabilized spherical nanoparticles of BaSO4 (6 nm in size) will be observed.

The influence of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) on structure formation in the inverse micellar region (L2 phase) of the ternary system 3 (N,N-dimethyldodecylammonio)propanesulfonate/alcohol/water has been investigated. Up to a polymer concentration in the aqueous phase of 10 wt %, an isotropic phase still exists. As the chain length of the alcohol component increases, the isotropic phase region is reduced and shifted in direction to the water corner. The isotropic polyelectrolyte-modified L2 phase of the heptanol-based microemulsion has been studied in much more detail by means of conductometric, rheological, and differential scanning calorimetry measurements. The polyelectrolyte-modified microemulsion phase shows a characteristic low shear viscosity and Newtonian flow behavior. The characteristic features of the nonpercolated microemulsion droplets are the low conductivity and the disappearance of bulk water. One can conclude from the experimental data that the individual nonpercolated polyelectrolyte-stuffed microemulsion droplets are approximately uniform in size. In addition, the area of the polyelectrolyte-modified inverse microemulsion phase with heptanol and octanol depends on the temperature. This means that the area of the L2 region can be increased by the temperature being increased from room temperature to 40 °C. This behavior can be explained by a change in the bending elasticity of the surface film induced by Coulombic interactions between the functional groups of the polyelectrolyte and the surfactant head groups. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 742–751, 2004

Solution polymerization of acrylonitrile was investigated in N,N'-dimethylformamide with various azo- and peroxo-initiators. Investigations were carried out in a concentration range of initiatior from 0.0016 mol/l up to 0.0160 mol/l, constant acrylonitrile concentration of 3.8 mol/l and temperatures from 40°C up to 70°C. The computer combined dilatometric equipment for long time and high conversion investigations was used for estimation of the conversion-time-reaction. By means of obtained data a mathematical model was created. The model describes sufficiently precise acrylonitrile polymerization kinetics in N,N'-dimethylformamide with various initiators in the used range of concentrations and temperatures.

Polymers can be incorporated into lamellar liquid crystalline systems without the phenomena of macroscopic phase separation occurring. By playing with the inter-membrane interactions and the polymer–bilayer interactions the properties of the lamellar system can be modified significantly. This is not only of interest as a fundamental prerequisite to life, but it also opens new fields of application.

The influence of oppositely charged polyelectrolytes and copolymers of different charge density and polyanion-polycation mixtures on the preordered lamellar liquid crystalline system sodium dodecylsulfate decanol water due to Coulombic interactions with special accentuation of aggregation and adsorption phenomena was examined. Small-angle X-ray results and rheological investigations are discussed with regard to changes in the interlayer spacing after introducing the polymers at various concentrations. The liquid crystalline phase was maintained, but the preformed lamellar structure was modified via penetration of the macromolecules between the hydrocarbon chains of the surfactant molecules. In the case of the polycation, strong Coulombic interactions cause a so-called “frozen” structure, whereas for the copolymers with decreasing charge density a “loop” conformation becomes possible, resulting in significantly increased interlayer spacings. Polyanions and polyanion-polycation mixtures showed phenomena of phase separation.

This paper focuses on two different strategies to incorporate gold nanoparticles (AuNPs) into the matrix of polyacrylamide (PAAm) hydrogels. Poly(ethyleneimine) (PEI) is used as both reducing and stabilizing agent for the formation of AuNPs. In addition, the influence of an ionic liquid (IL) (i.e., 1-ethyl-3-methylimidazolium ethylsulfate) on the stability of the nanoparticles and their immobilization in the hydrogel is investigated The results show that AuNPs surrounded by a shell containing PEI and IL, synthesized according to the one-pot approach, are much better immobilized within the PAAm hydrogel. Hereby, the IL is responsible for structural changes in the hydrogel as well as the improved stabilization and embedding of the AuNPs into the polymer gel matrix.

The influence of oppositely charged polyelectrolytes on the interlayer spacing of the lamellar liquid crystalline system hexadecyltrimethylammonium bromide/decanol/water was investigated by means of small angle X-ray diffraction and polarized microscopy. It could be demonstrated that a liquid crystalline phase was still formed by introducing a cationic polymer of low molecular weight into the lamellar structure. A disordering of the preformed structure and a decrease of the interlayer spacing occurred via penetration of the macromolecule between the hydrocarbon chains of the surfactant molecules. By using a “penetration” model for the disordering phenomena, “folded” and “telescoped” structures are discussed. The polyanion in a polyanion/polycation mixture gave the same structural change as when added alone.

The influence of a cationic charged polyelectrolyte, poly(diallyldimethylammonium chloride) on the interlayer spacing of the lamellar liquid crystalline system Na-dodecylsulfate (SDS)/decanol/water was investigated by means of low-angle X-ray diffraction, polarized microscopy and rheology. It could be demonstrated that a lamellar liquid crystalline phase was still formed by introducing a cationic polymer of 5000 g/mol into the mesophase, whereas different phenomena are observed in dependence on the polymer concentration. The average thickness of the layer, that means the layer repeat unit, is not influenced in the range of lower polymer concentration (up to 1%). At 2% polymer a lamellar liquid crystalline phase formed by SDS and decanol molecules and a frozen structure including polymer chains existing side by side. In a range of 5% and 10% polymer the frozen structure is the dominant one. It is assumed that electrostatic interactions determine the location of the polymer in the water layer between the surfactant head groups. Rheological investigations support the proposed model.

The phase behavior of the polyanion-polycation system, consisting of a branched polyethylene imine and a sodium salt of polyacrylic acid, was investigated as a function of the polymer concentration. At low polymer concentrations a small area of initial phase separation was observed, surrounded by a homogeneous one-phase system. The homogeneous, concentrated polyanion-polycation systems were characterized viscometrically, densitometrically, and spectroscopically. Under special mixing conditions, a significant viscosity enhancement was observed due to Coulombic interactions between the oppositely charged polyelectrolyte components. The interactions of the polyelectrolyte components with kaolin were investigated separately in the concentration range of initial phase separation as well as in the area of concentrated, optically clear polyanion-polycation systems. In the concentration range of phase separation polyanion-polycation interactions are dominant with regard to polyelectrolyte-kaolin interactions. When adding concentrated homogeneous polyanion-polycation systems to concentrated kaolin dispersions above a critical polyelectrolyte concentration, a transition to polyelectrolyte-kaolin pastes was observed. In general, these results are of practical importance for a better understanding of structuring phenomena in pigment systems.

Aqueous solutions of sodium dodecylsulfate (SDS) and poly(N,N′-diallyl-N,N′-dimethyl-alt-maleamic carboxylate) (PalH), a synthetic pH-tuneable polyelectrolyte (PEL), have been investigated by various techniques at different pH-values in absence and presence of NaCl. Potentiometric measurements using a surfactant-selective electrode indicate a quite complex interaction mechanism, which can be subdivided into different regions, where non-cooperative, electrostatic and cooperative hydrophobic interactions are of relevance. It was concluded, that in dependence on pH, conformational changes are responsible for the different interaction behavior in the NaCl-free system. Isothermal titration calorimetry (ITC) suggests that early stage hydrophobic binding is an exothermic process followed by electrostatic interactions, which are endothermic in nature and entropy driven. After NaCl addition the interaction mechanism becomes independent of pH due to a screening of (i) attractive interactions between the surfactant head groups and oppositely charged binding sites and (ii) repulsive forces between the surfactant head groups. Furthermore, the ITC investigations have revealed that after salt-addition surfactant micelles interact with the polymer instead of separated SDS molecules due to a depression of the CMC.

This paper is focused on the formation of cadmium sulfide (CdS) nanoparticles in the poly(ethylene glycol) (PEG)-modified microemulsion consisting of sodium dodecylsulfate (SDS), xylene, pentanol, and water. Due to the presence of the polymer a bicontinuous, sponge-like microemulsion is developed, which is used as a template phase for the particle formation beside the classical w/o microemulsion. The stability and size of the particles is strongly influenced by polymer concentration and molecular weight of PEG and aggregation seems to be favoured in the sponge-like template phase. However, the process of particle aggregation in the bicontinuous phase can be hindered by increasing the concentration and molecular weight of the polymer. After solvent evaporation CdS nanoparticles with diameters of 10 nm can be redispersed, which tend to build up larger aggregate clusters.

This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants. The influence of the ionic liquid on structure formation in the optically clear phase region in water/toluene/pentanol mixtures in presence of the cationic surfactant CTAB was studied in more detail. The results show a significant increase of the transparent phase region by adding the ionic liquid. Conductometric investigations demonstrate that adding the ionic liquid can drastically reduce the droplet-droplet interactions in the L(2) phase. (1)H nuclear magnetic resonance ((1)H NMR) diffusion coefficient measurements in combination with dynamic light scattering measurements clearly show that inverse microemulsion droplets still exist, but the droplet size is decreased to 2 nm. A more detailed characterisation of the isotropic phase channel by means of conductivity measurements, dynamic light scattering (DLS), (1)H NMR and cryo-scanning electron microscopy (SEM), allows the identification of a bicontinuous sponge phase between the L(1) and L(2) phase. When the poly(ethyleneimine) is added, the isotropic phase range is reduced drastically, but the inverse microemulsion range still exists.

A survey is given of recent developments in emulsion polymerization regarding improved auxiliary materials, e.g. vinyl tensides and surface active initiators. Results of the emulsion polymerization of styrene are presented with 3-(alkyloxycarbonyl-acryloyloxy)propanesulfonates (2) as polymerizable emulsifiers and with surface active azo initiators. The results show, that the content of water soluble surface active compounds in the latexes can be reduced. Investigations of the molecular weight of the polymers show the great importance of the initiator-emulsifier system. Azo initiators leading to higher molecular weights than persulfate. Under the same conditions the highest molecular weights were obtained with a surface active azo initiator.

The paper describes the behavior of the sulfobetaine/pentanol/toluene/water system. An isotropic inverse micellar region (L2 phase) can be observed in the oil corner. The area of the L2 phase is decreased by adding an anionic polyelectrolyte, i.e. sodium polyacrylate. The incorporation of the cationic polyelectrolyte poly(diallyl-dimethylammonium chloride) (PDADMAC) induces the extension of the isotropic phase in the direction of the water corner under the formation of an isotropic phase channel. The aim of the work presented here was to study this phase channel at constant surfactant concentration (i.e. 20%) by means of electrical conductivity, 1H NMR self-diffusion experiments, rheology, polarizing microscopy, small-angle X-ray spectroscopy, and micro-differential scanning calorimetry (DSC). Macroscopically, no indication of a phase transition is observed when going from the oil-rich side to the water-rich side. However, above a critical content of the aqueous PDADMAC solution, the diffusion coefficients are changed significantly, freezable water becomes detectable in DSC measurements, and lamellar liquid-crystalline textures become visible after shearing. This behavior can be explained by a shear-induced transition from an L2 phase to a lamellar liquid-crystalline phase, and is combined by only small viscometric and conductometric effects. The transition from the L2 to the Lα phase can be explained by a significant change of the curvature of the surfactant film due to Coulombic interactions with the polycation.

This paper is focused on the characterization of polyelectrolyte-modified inverse microemulsions and their use as templates for the synthesis of magnetite nanoparticles. It is shown that the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) of low molar mass can be incorporated into the individual inverse microemulsion droplets (L2 phase) consisting of heptanol, water, and an amphoteric surfactant with a sulfobetaine head group. Up to a polymer concentration of 20% by weight in the aqueous phase and for different molecular weights of the polymer, an isotropic phase still exists. At a PDADMAC concentration of 10% the area of the isotropic L2 phase is shifted in direction to the water corner. In the percolated area of the L2 phase, i.e., at higher water content, a temperature-dependent change in the conductivity can by observed, and bulk water can be detected by means of differential scanning calorimetry measurements. The unusual temperature-dependent behavior of the polymer-modified system, i.e., the conductivity decrease with increasing temperature, can be explained by temperature-sensitive polyelectrolyte-surfactant interactions, influencing the droplet-droplet interactions. These PDADMAC-modified microemulsions can be successfully used as a template for the formation of ultrafine magnetite particles, in contrast to the nonmodified microemulsion, where the process is misdirected due to the "disturbing" effect of the surfactants. However, in the presence of PDADMAC the surfactant head groups were masked, and therefore magnetite can be synthesized. During the process of magnetite formation the PDADMAC controls the particle growing and stabilizes spherical magnetite particles with a diameter of 17 nm, which can be redispersed without a change in size.

This paper is focused on the use of branched poly(ethyleneimine) (PEI) as reducing as well as stabilizing agent for the formation of gold nanoparticles in different media. The process of nanoparticle formation was investigated, in the absence of any other reducing agents, in microemulsion template phase in comparison to the nucleation process in aqueous polymer solution. On the one hand, it was shown that the polyelectrolyte can be used for the controlled single-step synthesis and stabilization of gold nanoparticles via a nucleation reaction and particles with an average diameter of 7.1 nm can be produced. On the other hand, it was demonstrated that the polymer can also act as reducing and stabilizing agent in much more complex systems, i.e. in water-in-oil (w/o) microemulsion droplets. The reverse microemulsion droplets of the quaternary system sodium dodecylsulfate (SDS)/toluene-pentanol (1:1)/water were successfully used for the synthesis of gold nanoparticles. The polymer, incorporated in the droplets, exhibits reducing properties, adsorbs on the surface of the nanoparticles and prevents their aggregation. Consequently, nanoparticles of 8.6 nm can be redispersed after solvent evaporation without a change of their size. Nevertheless, the polymer acts already as a "template" during the formation of the nanoparticles in water and in microemulsion, so that an additional template effect of the microemulsion is not observed. The particle formation for both methods is checked by means of UV-vis spectroscopy and the particle size and size distribution are investigated via dynamic light scattering and transmission electron microscopy (TEM). (c) 2006 Elsevier B.V. All rights reserved.

The paper is focused on the characterization and use of phosphatidylcholine (PC)-based inverse microemulsions as a template phase for the CdS nanoparticle formation. The optically clear, isotropic phase in the oil corner was identified as a “classical” water-in-oil microemulsion by means of NMR-diffusion measurements. Because of the very small dimensions of the water droplets, the isotropic phase shows a Newtonian-like flow behavior, and adequate amounts of bulk water cannot be detected by DSC. It is demonstrated that this w/o microemulsion can be used successfully as a nanoreactor for the formation of CdS nanoparticles with diameters of 4–5 nm. During the following process of solvent evaporation the individual small CdS nanoparticles aggregate to significant larger cubic nanoparticles, with an edge length of 20–40 nm, arranged in well-defined mosaic-like superstructures. In presence of SDS the nanocubes were stable up to 800 °C. It has to be stated here that polyelectrolytes prevent the formation of such well-ordered superstructures.

In polycation-modified SDS/decanol systems, dense multilamellar structures, i.e. multilamellar vesicles are formed by self-organization, which were used as an organic template for CdS nanoparticle preparation. Specific amounts of precursors, CdCl2 and Na2S, were incorporated into the multilamellar vesicles without losing the multilamellar structure. Structural changes of the lamellar liquid crystalline template induced by the incorporation of the polycation and the inorganic precursors were investigated by differential scanning calorimetry in combination with small angle X-ray scattering. By mixing both precursors within the multilamellar vesicles CdS nanoparticles are formed. After decomposition of the vesicle template, quite different shaped and sized CdS-nanoparticles were observed by transmission electron microscopy. At lower polymer concentration spherical CdS nanoparticles of about 10 nm can be obtained. At higher polymer concentration predominantly rod-like CdS aggregates were produced with an average length of 120 nm and width of 30 nm.

The formation of gold nanoparticles and the crystal growth at the surface of mixed phosphatidylcholine (PC)–ionic surfactant vesicles was investigated. The PC-bilayer surface was negatively charged by incorporating sodium dodecyl sulfate (SDS) and positively charged by adding hexadecyltrimethylammonium chloride (CTAB). The mass ratio phosphatidylcholine:surfactant was fixed in both cases at 1:1. The gold nanoparticle formation was studied by using transmission electron microscopy (TEM) combined with dynamic light scattering (DLS) and UV–vis absorption spectroscopy. TEM micrographs confirm that the particle formation occurs on the vesicle surface. However, the reduction process depends on the ionic surfactant incorporated into the vesicles, the vesicle size distribution, as well as the temperature used for the reduction process. Thereby, it becomes possible to control the crystal growth of the individual spherical gold nanoparticles in a characteristic way. Red colored colloidal dispersions consisting of monodisperse spherical nanoparticles with an average particle size between 2 and 8 nm (determined by dynamic light scattering) can be obtained by using a monodisperse SDS-modified vesicle phase. When the temperature is increased to 45 °C, a crystallization in rod-like or triangular structures is observed. In the CTAB-based template phase in general larger gold particles of about 35 nm are formed. In similarity to the anionic vesicles a temperature increase leads to the crystallization in triangular structures.

The influence of branched poly(ethyleneimine) on the phase behavior of the system sodium dodecylsulfate/toluene–pentanol (1:1)/water has been studied. The isotropic microemulsions still exist when water is replaced with aqueous solutions of PEI (up to 30% in weight), but their stability is significantly influenced. From a polymer concentration of 20 wt%, the polymer enhances the solubilization of water in oil, changes the sign of the spontaneous curvature of the surfactant film, and induces an inversion of the microemulsion type from water-in-oil (L 2 ) to oil-in-water (L 1 ), by the formation of a bicontinuous channel. Further investigations show that the addition of polymer in the L 2 phase changes the droplet–droplet interactions as the conductivity drops and the percolation disappears. In the bicontinuous channel, higher viscosities can be detected, as well as a weak percolation followed by a steep increase of the conductivity, which can be related to evident structural changes in the system. DSC measurements allow then to follow the changes of the water properties in the system, from interfacial-water in the L 2 phase to free-water in the sponge-like phase. Finally, all the measurements performed permit to characterize the structural transitions in the system and to understand the role of the added polymer.

The influence of the water soluble polymer poly(ethylene glycol) (PEG) on structure formation in the quasiternary system sodium dodecylsulfate (SDS)/pentanol-xylene/water was checked by means of conductometry, rheology, and micro differential calorimetry. The polymer induces the formation of an isotropic phase channel between the o/w and w/o microemulsion. The transition from the normal as well as from the inverse micellar to the bicontinuous phase range can be detected by conductometry, rheology as well as micro-DSC. As a result of polymer-surfactant interactions, the spontaneous curvature of the surfactant film is changed and a sponge phase is formed. The bicontinuous phase is characterized by a moderate shear viscosity, a Newtonian flow behaviour, and the disappearence of interphasal water in the heating curve of the micro-DSC. When the polymer-modified bicontinuous phase is used as a template phase for the nanoparticle formation, spherical BaSO4 nanoparticles were formed. During the following solvent evaporation process the primarily formed spherical nanoparticles aggregate to nanorods and triangular structures due to the non-restriction of the bicontinuous template phase in longitudinal direction

This paper is focused on the synthesis and characterization of hydrophobically modified polyelectrolytes and their use as reducing as well as stabilizing agents for the formation of gold nanoparticles. Commercially available poly(acrylic acid) has been hydrophobically modified with various degrees of grafting of butylamine introduced randomly along the chain. Different analytical methods are performed, i.e., IR and 1H-NMR spectroscopy in combination with elemental analysis to determine the degree of grafting. The modified polymers can successfully be used for the controlled single-step synthesis and stabilization of gold nanoparticles. The process of nanoparticle formation is investigated by means of UV-vis spectroscopy. The size and shape of the particles obtained in the presence of unmodified or modified polyelectrolytes are characterized by dynamic light scattering, zeta potential measurements and transmission electron microscopy. The polyelectrolytes were involved in the crystallization process of the nanoparticles, and in the presence of hydrophobic microdomains at the particle surface, a better stabilization at higher temperature can be observed.

The paper is focused on the formation and redispersion of monodisperse BaSO4 nanoparticles in polyelectrolyte- modified microemulsions. It is shown that a cationic polyelectrolyte of low molar mass, e.g. poly(dially1dimethylammonium chloride) (PDADMAC), can be incorporated into the individual inverse microemulsion droplets (L2 phase) consisting of heptanol, water, and an amphoteric surfactant with a sulfobetaine head group. These PDADMAC- filled microemulsion droplets can be successfully used as a template phase for the nanoparticle formation. The monodisperse BaSO4 nanoparticles are produced by a simple mixing procedure and can be redispersed after solvent evaporation without a change in particle dimensions. Dynamic and electrophoretical light scattering in combination with sedimentation experiments in the analytical Ultracentrifuge of the redispersed powder show polyelectrolyte-stabilized nanoparticles with diameters of about 6 nm. The polyelectrolyte shows a "size control effect", which can be explained by the polyelectrolyte-surfactant interactions in relation to the polyelectrolyte-nanoparticle interactions during the particle growth, solvent evaporation and redispersion process. However, the approach used here opens away to produce different types of polyelectrolyte-stabilized nanoparticles (including rare metals, semiconductors, carbonates or oxides) of very small dimensions. (C) 2004 Elsevier B.V. All rights reserved

The chapter describes the behavior of polymer-modified phospholipid-based w/o micro emulsions and its use for nanocrystal synthesis. We focused our interest on the naturally occurring crude soybean lecithin in presence of isooctane and water. In the case of the unmodified system an isotropic inverse micellar region can be observed in the oil corner. By adding an anionic polyelectrolyte, i.e., sodium polyacrylate, the area of the optically clear phase is drastically decreased. The incorporation of the neutral polymer poly(ethylene glycol) (PEG), and the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) induces the formation of an isotropic narrow phase channel in the area of the origin L2 phase. The cationic poly(ethyleneimine) can be incorporated much better up to polymer concentrations of 5 wt%. From 1H NMR self-diffusion experiments one can conclude that the isotropic phase is indeed a reverse micellar microemulsion. Rheological experiments show a non-Newtonian flow behavior of the microemulsions. By means of differential scanning calorimetry (DSC) bulk water can be detected in the reverse w/o droplets. In comparison to the natural soybean lecithin, a pure phosphatidylcholine (>95%), modified with sodium dodecylsulfate, and/or PDADMAC was investigated. The reverse microemulsion droplets were used as a template phase for the synthesis of BaSO4 nanoparticles. The polymers involved in the redispersion process, influence the size, and supramolecular arrangement of the nanoparticle composites formed.

The influence of polyelectrolytes on structure formation in liquid crystalline Na-dodecylsulfate/decanol/water systems was investigated by means of small angle X-ray diffraction, rheology, NMR spectroscopy, and microscopy. By adding Na-polyacrylate (PAA) into the mesophase, the one-phase region is left and phenomena of phase separation into a solvent-rich and a polymer/surfactant-rich phase occurs. By incorporating an anionic and cationic polyelectrolyte step by step the tendency of phase separation is increased drastically. The self-organization process can be regulated directly by varying the water content of the system. However, at a water content of 30% the properties of the resulting liquid crystal were changed drastically. X-ray diffraction shows a multitude of Bragg peaks, NMR shows a peak-splitting, and rheology shows a change from non-Newtonian to Newtonian-flow behavior. On the basis of the experimental results an ordered multilayer associate structure can be assumed.