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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
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
Metal ion induced self-assembly of the rigid ligand 1,4-bis(2,2':6',2 ''-terpyridine- 4'-yl) benzene (1) with Fe(II), Co(II), Ni(II) and Zn(II) acetate in aqueous solution results in extended, rigid- rod like metallosupramolecular coordination polyelectrolytes (MEPE-1). Under the current experimental conditions the molar masses range from 1000 g mol(-1) up to 500 000 g mol(-1). The molar mass depends on concentration, stoichiometry, metal-ion and time. In addition, we present viscosity measurements, small angle neutron scattering and AFM data. We introduce a protocol to precisely control the stoichiometry during self-assembly using conductometry. The protocol can be used with different terpyridine ligands and the above-mentioned metal ions and is of paramount importance to obtain meaningful and reproducible results. As a control experiment we studied the mononuclear 4'- (phenyl)2,2':6',2 ''-terpyridine (3) complex with Ni(II) and Zn(II) and the flexible ligand 1,3- bis[4'-oxa(2,2': 6',2 ''-terpyridinyl)] propane (2) with Ni(II) acetate (Ni-MEPE-2). This ligand does not form extended macroassemblies but likely ring-like structures with 3 to 4 repeat units. Through spin- coating of Ni-MEPE-1 on a solid surface we can image the MEPEs in real space by AFM. SANS measurements of Fe-MEPE-1 verify the extended rigid-rod type structure of the MEPEs in aqueous solution.
Metal-ion-induced self-assembly in aqueous solution of the rigid ligand 1,4-bis(2,2':6',2 ''-terpyridine-4'-yl)benzene (1) with Fe(OAc)(2) and Ni(OAc)(2) is investigated with viscosimetry, SANS, and AFM. Ligand 1 forms extended, rigid-rod like metallo-supramolecular coordination polyeectrolytes (MEPEs) with a molar mass of up to 200 000 g mol(-1) under the Current experimental conditions. The molar mass depends oil concentration, stoichiometry, and time. By spin-coating MEPEs oil a solid surface, we call image the MEPEs in real space by AFM. Both AFM and SANS confirm the extended rigid-rod-type structure of the MEPEs. As a control experiment, we also studied the flexible ligand 1,3-bis[4'-oxa(2,2':6',2 ''-terpyridinyl)]propane (2). Ligand 2 does not form extended macro-assemblies but likely ringlike structures with three 10 four repeat units. Finally, we present it protocol to control the stoichiometry during self-assembly using conductometry, which is of paramount importance to obtain meaningful and reproducible results.
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
As an engineering material derived from renewable resources, wood possesses excellent mechanical properties in view of its light weight but also has some disadvantages such as low dimensional stability upon moisture changes and low durability against biological attack. Polymerization of hydrophobic monomers in the cell wall is one of the potential approaches to improve the dimensional stability of wood. A major challenge is to insert hydrophobic monomers into the hydrophilic environment of the cell walls, without increasing the bulk density of the material due to lumen filling. Here, we report on an innovative and simple method to insert styrene monomers into tosylated cell walls (i.e. –OH groups from natural wood polymers are reacted with tosyl chloride) and carry out free radical polymerization under relatively mild conditions, generating low wood weight gains. In-depth SEM and confocal Raman microscopy analysis are applied to reveal the distribution of the polystyrene in the cell walls and the lumen. The embedding of polystyrene in wood results in reduced water uptake by the wood cell walls, a significant increase in dimensional stability, as well as slightly improved mechanical properties measured by nanoindentation.
This paper is focused on the temperature dependent synthesis of gold nanotriangles in a vesicular template phase, containing phosphatidylcholin and AOT, by adding the strongly alternating polyampholyte PalPhBisCarb.
UV-vis absorption spectra in combination with TEM micrographs show that flat gold nanoplatelets are formed predominantly in presence of the polyampholyte at 45 °C. The formation of triangular and hexagonal nanoplatelets can be directly influenced by the kinetic approach, i.e., by varying the polyampholyte dosage rate at 45 °C. Corresponding zeta potential measurements indicate that a temperature dependent adsorption of the polyampholyte on the {111} faces will induce the symmetry breaking effect, which is responsible for the kinetically controlled hindered vertical and preferred lateral growth of the nanoplatelets.
Materials derived from renewable resources are highly desirable in view of more sustainable manufacturing. Among the available natural materials, wood is one of the key candidates, because of its excellent mechanical properties. However, wood and wood-based materials in engineering applications suffer from various restraints, such as dimensional instability upon humidity changes. Several wood modification treatments increase water repellence, but the insertion of hydrophobic polymers can result in a composite material which cannot be considered as renewable anymore. In this study, we report on the grafting of the fully biodegradable poly(ε-caprolactone) (PCL) inside the wood cell walls by Sn(Oct)2 catalysed ring-opening polymerization (ROP). The presence of polyester chains within the wood cell wall structure is monitored by confocal Raman imaging and spectroscopy as well as scanning electron microscopy. Physical tests reveal that the modified wood is more hydrophobic due to the bulking of the cell wall structure with the polyester chains, which results in a novel fully biodegradable wood material with improved dimensional stability.