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25. Investigation of the Relationship between Hydrogen Bonds and Macroscopic Properties in Hybrid Core-Shell gamma-Fe2O3-P(NIPAM-AAS) Microgels

Author

Rubio-Retama, J., Zafeiropoulos, N. E., Frick, B., Seydel, T., and Lopez-Cabarcos, E.

Subjects
poly(n-isopropylacrylamide), thermal-degradation, nanocrystals, nanoparticles, photoluminescence, gels
Abstract

We investigate in a hybrid material the interactions existing between magnetic nanoparticles of gamma-Fe2O3 and the polymer matrix constituted by core-shell poly(N-isopropylacrylamide-sodium acrylate) microgels. These interactions provoke the shifting of the microgel volume phase transition to higher temperatures when the amount of gamma-Fe2O3 increases, The study was performed using different techniques such as incoherent quasi-elastic neutron scattering (IQNS), infrared spectroscopy (FTIR-ATR), and dynamic light scattering (DLS). Below the low critical solution temperature (LCST) of the polymer, the IQNS data confirm that the presence of inorganic nanoparticles affects the PNIPA M chain motions. Thus, in the swollen state both the mean-square displacement of the polymer segments and the diffusive motion of the polymer chains decrease as the iron oxide content increases. The FTIR-ATR study indicates that the reduction of vibrational and diffusional motions of the polymer chains is due to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles. The creation of this hybrid complex would explain the reduction of the swelling capacity with increasing the iron content in the microgels. Furthermore, this interaction could also explain the shift of the polymer LCST to higher temperatures is due to the extra energy required by the system to break the hydrogen bonds prior to the PNIPAM collapse. Langmuir

Published
2010

26. Synthesis and Chemical Modification of Magnetic Nanoparticles Covalently Bound to Polystyrene-SiCl2-Poly(2-vinylpyridine)

Author

Serrano-Ruiz, D., Rangou, S., Avgeropoulos, A., Zafeiropoulos, N. E., Lopez-Cabarcos, E., and Rubio-Retama, J.

Subjects
microgels, magnetic nanoparticles, fe3o4 nanoparticles, hybrid materials, transfer radical polymerization, temperature, cancer, nanoparticles, diblock copolymers, brushes, size, hyper-branched, polymers
Abstract

The present article offers a new approach to create a multifunctional material based on magnetic nanoparticles, which can be dispersed in aqueous and organic media. The preparation of this material was performed by binding covalently polymer chains based on a reactive diblock-copolymer of the polystyrene-SiCl2-poly(2-vinylpyridine) type, with average molecular weight per number (M-n) equal to 14,700 g/mol and a polydispersity index (PDI) less than 1.1, onto the surface of gamma-Fe2O3 magnetic nanoparticles. The dichlorosilane moiety of the diblock-copolymer reacted with the OH groups of the magnetic nanoparticles immobilizing the polymer chain onto its surface. This reaction was monitored by FTIR and the polymer grafting density was determined by TGA and BET. Dynamic light scattering revealed that the hydrodynamic diameter of the nanoparticles increased after immobilizing the polymer. Contact angle measurements demonstrated the ability of the hybrid material to interact with organic and aqueous media allowing its dispersion in solvents with different polarities. This property was used to prepare a magnetically active emulsion. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1668-1675, 2010 Journal of Polymer Science Part B-Polymer Physics

Published
2010

42. Restricted Dynamics in Poly(ether ether ketone) As Revealed by Incoherent Quasielastic Neutron Scattering and Broad-Band Dielectric Spectroscopy

Author

Nogales, A., Ezquerra, T. A., Batallan, F., Frick, B., Lopez-Cabarcos, E., and Balta-Calleja, F. J.

Abstract

The molecular dynamics of semicrystalline poly(ether ether ketone) (PEEK) was studied over a broad dynamic range from 10-1 to 109 Hz by combining dielectric spectroscopy (DS) and incoherent quasielastic neutron scattering (IQNS). This allowed us to characterize the polymer dynamics in the glassy, semicrystalline, and molten states. By performing dielectric and neutron-scattering measurements in a comparable frequency range, we proved that the quasielastic broadening observed in IQNS experiments corresponds to the dielectric α relaxation without invoking any kind of low-frequency dielectric data extrapolation. IQNS measurements indicate that the segmental chain motion observed at temperatures higher than the glass transition temperature possesses an elastic and a quasielastic contribution. A model which considers a confined-jump diffusive motion allows a quantitative description of the IQNS spectra. This model provides dimensions of jump length, residence time, available space, and number of scatterers involved in the process. Results indicate that both the size of the restricted volume and the amount of protons involved in the α process increase with temperature and are smaller than the calculated values based on the crystallinity estimates from calorimetric and X-ray diffraction experiments. Both effects indicate for semicrystalline PEEK the existence of a confined amorphous phase with regions of different degrees of mobility. The present experiments provide a quantitative dynamical and spatial description of the heterogeneous amorphous phase of semicrystalline PEEK.

Published
1999

47. Magnetic-core microgels

Author

Contreras-Caceres, R., Laurenti, M., Perez-Juste, J., Jorge Rubio-Retama, Lopez-Cabarcos, E., and Fernandez-Barbero, A.

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