Refine
Has Fulltext
- no (41)
Year of publication
Document Type
- Article (38)
- Monograph/Edited Volume (1)
- Other (1)
- Review (1)
Is part of the Bibliography
- yes (41)
Keywords
- Maltose-modified poly(ethyleneimine) (2)
- Ring tensiometry (2)
- gold nanoparticles (2)
- microemulsion (2)
- mu-DSC (2)
- polyelectrolyte (2)
- Bentonite clay (1)
- Biomineralization (1)
- Bone repair material (1)
- Calcium phosphates (1)
Institute
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. (c) 2004 Elsevier Inc. All rights reserved
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 H-1-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 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/surfactantrich phase occurs. By incoporating 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.