Search

We analyze microstructured multilayer films of poly(ethyleneimine) (PEI) and DNA by employing Raman and surface enhanced Raman spectroscopy (SERS). The microstructuring of the samples allows a simultaneous measurement of signal and reference in a single analytic process. Silver nanoparticles are implemented in the microstructured multilayers for SERS measurements. The recorded SERS spectra of PEI/DNA are dominated by the Raman bands of the DNA bases which show a larger mean enhancement than bands belonging to DNA backbone vibrations. Our results show that the combination of SERS and microstructured multilayer films provides an adapted way to characterize the polyelectrolytes as well as to measure the enhancement factor and the distance dependence for the SERS active silver nanoparticles. Furthermore, microstructured polyelectrolyte films containing SERS active nanoparticles are used for sensing molecules.

Static light scattering measurements reveal two levels of organization, i.e., two static correlation lengths, in poly(N-isopropylacrylamide)/clay nanocomposite hydrogels prepared by polymerizing the monomer in an aqueous suspension of uniformly dispersed exfoliated clay particles. One characteristic correlation length is in the range of 200−250 nm irrespective of the preparation conditions. It is assumed to arise from a kinetically controlled rearrangement of the clay particles during the formation of the gels. The other correlation length of several tens of nanometers is in the same order of magnitude as that observed in chemically cross-linked gels and shows a similar dependence on the preparation conditions. The shear modulus of the gels rises with increasing the clay concentration and the monomer concentration. The results infer that clay particles act as multifunctional cross-links with an average effective functionality around 50. Measurements of the equilibrium swelling ratio are in agreement with ...

Static light scattering measurements performed on poly(N-isopropylacrylamide) hydrogels having a polymer volume fraction around 0.05−0.09 reveal that spatial inhomogeneities grow stronger with rising preparation temperature of the gels, increasing cross-linker concentration, and decreasing monomer concentration. Quantitative analysis of the angular dependence of the excess scattering intensity via the Debye−Bueche method results in correlation lengths of several 10 nm. Relative mean-square concentration fluctuations on this length scale are around 15−35% depending on preparation conditions. The cross-linking efficiency as determined by shear modulus measurements declines when the degree of inhomogeneity is enhanced. Comparison of the experimental results with Panyukov−Rabin (PR) theory indicates that the general trends are well predicted and that thermal concentration fluctuations can be calculated almost quantitatively. However, the theory significantly underestimates the static spatial concentration flu...

The title complex was prepared by reaction of succinatomanganese(II) with imidazole in water-ethanol. The complex crystallizes in orthorhombic space group Pna 2 1 with a = 7.9990(15), b = 14.8690(15), c = 11.028(2) A. The metal assumes a distorted octahedral coordination. In the crystal, each succinate dianion bridges three Mn(II) atoms to form a polymer with a layered structure.

The title complex [Mn(bipy)2Cl2]·0.5bipy·2.5H2O, where bipy = 2,2'-bipyridine, has been prepared and its crystal structure has been determined by X-ray diffraction methods. The complex crystallizes in the triclinic space group P-1, with a = 8.814(2), b = 11.335(2), c = 13.347(3) A, α = 76.85(2), β = 89.55(2), γ = 86.52(2)°. Two chloride and two bipy ligands cis-coordinate to a Mn(II) atom with a distorted octahedral geometry. The crystal consists of Mn(II) complex, free bipy and crystalline water. The complex crystalline water link to each other by H-bonding to form supra-molecular chains, and free bipy molecules locate between parallel chains with a van der Waals contact distance of 3.58(1) A. A π-π interaction is also observed between adjacent bipy rings. The chelating bipy and free bipy showed different IR absorptions.

The title complex [Cu2(C4H2O4)2(bipy)2(H2O)3] · 3H2O (bipy = 2,2'-bipyridine) was prepared and its crystal structure determined by X-ray diffraction methods. Both Cu(II) atoms of the binuclear complex assume square pyramidal coordination. The fumarate groups display different coordination modes. One fumarate group bridges two Cu(II) ions to form a binuclear complex while another fumarate group terminally coordinates to a Cu(II) atom with one carboxyl group free from coordination. The terminally coordinated fumarate showed unusual disorder, which may be due to an intermolecular H-bonding interaction. Close stacking of bipy rings is observed as verified by the distance of 3.46 A between parallel ring planes. IR spectra were assigned based on the molecular structure.

A novel Mn(II) complex bridged by 1,3-benzenedicarboxylate (BDC) has been synthesized by the diffusion method. The complex crystallizes in space group P21/c with a = 8.345(2), b = 10.427(1), c = 18.756(2) A, β = 100.19(1)°. Each BDC bridges three Mn(II) atoms through two carboxyl groups with different coordination modes to form a complex polymeric chain. The coordination geometry around the Mn(II) atom is seriously distorted from the normal octahedron. Large deviations of the donor atoms out of the coordination planes and unexpected bond angles around Mn(II) and donor O atoms suggest the existence of an electrostatic interaction between Mn(II) and donor atoms in the complex. Close stacking of aromatic rings is observed in the complex, the distance between the neighboring phen planes being 3.2085 A.

The complex [Cu2(μ-cis-oxpn)(phen)(NO3)2], where oxpn = N,N′ -bis(3-aminopropyl) oxamidato and phen = 1,10-phenanthroline, has been synthesized and its crystal structure determined by X-ray methods. The structure consists of binuclear copper (II) molecules in which the Cu(II) atoms are bridged by oxamidato group in the cis conformation, the Cu—Cu distance being 5.205(10) A. The coordination geometry around Cu (II) atoms is square pyramidal; the apex is occupied by a more weakly bonded O atom from a nitrate group. Electron delocalization is observed in the bridging oxamide moiety. The co-planarity of bridge ligand and basal plane around Cu (II) atoms may benefit spin super-exchange between two Cu (II) atoms. IR spectra of the binuclear complex are discussed.

By utilizing the hydrolysis and condensation of the methoxysilyl groups, thermo-sensitive organic/inorganic hybrid poly[ N-isopropylacrylamide- co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm- co-TMSPMA)] microgels were successfully prepared via two different methods without addition of any surfactant. First, the microgels were obtained by a two-step method; that is, the linear copolymer P(NIPAm- co-TMSPMA) was first synthesized by free radical copolymerization, and the aqueous solution of the copolymer was then heated above its low critical solution temperature (LCST) to give colloid particles, which were subsequently cross-linked via the hydrolysis and condensation of the methoxysilyl groups to form the microgels. Second, the microgels were also prepared via conventional surfactant-free emulsion polymerization (SFEP) of the monomers NIPAm and TMSPMA. TMSPMA can act as the cross-linkable monomer. No surfactant was involved in the preparation of the hybrid microgels. The obtained microgels were rather spherical and exhibited reversible thermo-sensitive behavior. The size, morphology, swellability, and phase transition behavior of the microgels were dependent on the initial copolymer or monomer concentration, preparation temperature, and the content of TMSPMA. The size of microgels obtained by SFEP was found to be more uniform than that by the two-step method. The hybrid microgels obtained by these two methods had more homogeneous microstructures than those prepared via conventional emulsion polymerization with chemical cross-linker N, N'-methylene-bisacrylamide.

The contributions of the dynamic fluctuations and the frozen-in inhomogeneities to the total light scattering intensity observed in poly(N-isopropylacrylamide)/clay nanocomposite hydrogels were analyzed by applying the nonergodic method proposed by Pusey and van Megen. Approximately 90% of the total scattering intensity corresponds to the frozen-in component. The scattering intensity of the fluctuating component is smaller by far than that of a pure clay suspension, indicating that the thermal fluctuations of the clay particles are largely suppressed upon network formation. Accordingly, the fluctuating component consists of two contributions: one due to the polymer chains and the other, smaller one representing the residual mobility of the clay particles. The latter depends on how tightly the clay particles are fixed in the network. The dynamic features of the nanocomposite hydrogels are described by two relaxation modes. The fast one is purely diffusive and can be related to a dynamic correlation length of 6-8 nm, which is similar to that of a corresponding polymer solution. The relaxation time of the slow mode varies appreciably with sample position even though the data had been treated with the nonergodic method.