Sabine Kosmella

Structural studies of ionic liquid-modified microemulsions

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.

BaSO4 nanorods produced in polymer-modified bicontinuous microemulsions

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.

Polymers in lyotropic liquid crystals

Abstract 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.

Polymers in lyotropic liquid crystalline systems

Abstract 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.

Polymer-Modified Bicontinuous Microemulsions Used as a Template for the Formation of Nanorods

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.

Polyelectrolyte-induced structural changes in the isotropic phase of the sulfobetaine/ pentanol/toluene/water system

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.

Interactions of polyelectrolytes with the lyotropic liquid crystalline system hexadecyltrimethylammonium bromide/decanol/water

Abstract 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.

Change in size, morphology and stability of DNA polyplexes with hyperbranched poly(ethyleneimines) containing bulky maltose units

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 (μ-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 °C to 76 °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.

Nano-porous calcium phosphate balls

By dropping a NaH2PO4·H2O precursor solution to a CaCl2 solution at 90°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°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.

Formation of rod-like CdS nanoparticles in SDS/decanol based multilamellar vesicles

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.