http://hdl.handle.net/2117/3814 Tue, 21 May 2013 07:20:27 GMT 2013-05-21T07:20:27Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/14679 Title: Liquid-crystalline hybrid materials based on (60) fullerene and bent-core structures Authors: Martín, Nazario; Sánchez, Luis; Vergara, Jorge; Barberá, Joaquín; Serrano, José Luis; Ros, M. Blanca; Sebastián, Nerea; de la Fuente, Rosario; López Pérez, David Orencio; Fernández, Gustavo Abstract: What a core-ker! By the appropriate combination of promesogenic bent-core structures and the C60 unit, lamellar polar liquid-crystal phases were induced (see scheme). The supramolecular organization of the functional fullerene-based assemblies, the temperature range of the soft phase, the stabilization of the mesophase-like order at room temperature, and the molecular switching under an electric field can be tuned, depending on the molecular structure Thu, 19 Jan 2012 13:12:51 GMT http://hdl.handle.net/2117/14679 2012-01-19T13:12:51Z Martín, Nazario; Sánchez, Luis; Vergara, Jorge; Barberá, Joaquín; Serrano, José Luis; Ros, M. Blanca; Sebastián, Nerea; de la Fuente, Rosario; López Pérez, David Orencio; Fernández, Gustavo no What a core-ker! By the appropriate combination of promesogenic bent-core structures and the C60 unit, lamellar polar liquid-crystal phases were induced (see scheme). The supramolecular organization of the functional fullerene-based assemblies, the temperature range of the soft phase, the stabilization of the mesophase-like order at room temperature, and the molecular switching under an electric field can be tuned, depending on the molecular structure http://hdl.handle.net/2117/14443 Title: Self-assembly of Fmoc-tetrapeptides based on the RGDS cell adhesion motif Authors: Alemán Llansó, Carlos; Castelletto, V.; Moulton, C.M.; Cheng, G.; Hamley, I. W.; Hicks, Mathew R.; Rodger, Alison; López Pérez, David Orencio; Revilla López, Guillermo Abstract: Self-assembly in aqueous solution has been investigated for two Fmoc [Fmoc = N-(fluorenyl)-9-methoxycarbonyl] tetrapeptides comprising the RGDS cell adhesion motif from fibronectin or the scrambled sequence GRDS. The hydrophobic Fmoc unit confers amphiphilicity on the molecules, and introduces aromatic stacking interactions. Circular dichroism and FTIR spectroscopy show that the self-assembly of both peptides at low concentration is dominated by interactions among Fmoc units, although Fmoc-GRDS shows β-sheet features, at lower concentration than Fmoc-RGDS. Fibre X-ray diffraction indicates β-sheet formation by both peptides at sufficiently high concentration. Strong alignment effects are revealed by linear dichroism experiments for Fmoc-GRDS. Cryo-TEM and small-angle X-ray scattering (SAXS) reveal that both samples form fibrils with a diameter of approximately 10 nm. Both Fmoc-tetrapeptides form self-supporting hydrogels at sufficiently high concentration. Dynamic shear rheometry enabled measurements of the moduli for the Fmoc-GRDS hydrogel, however syneresis was observed for the Fmoc-RGDS hydrogel which was significantly less stable to shear. Molecular dynamics computer simulations were carried out considering parallel and antiparallel β-sheet configurations of systems containing 7 and 21 molecules of Fmoc-RGDS or Fmoc-GRDS, the results being analyzed in terms of both intermolecular structural parameters and energy contributions. Tue, 10 Jan 2012 10:48:23 GMT http://hdl.handle.net/2117/14443 2012-01-10T10:48:23Z Alemán Llansó, Carlos; Castelletto, V.; Moulton, C.M.; Cheng, G.; Hamley, I. W.; Hicks, Mathew R.; Rodger, Alison; López Pérez, David Orencio; Revilla López, Guillermo no Self-assembly in aqueous solution has been investigated for two Fmoc [Fmoc = N-(fluorenyl)-9-methoxycarbonyl] tetrapeptides comprising the RGDS cell adhesion motif from fibronectin or the scrambled sequence GRDS. The hydrophobic Fmoc unit confers amphiphilicity on the molecules, and introduces aromatic stacking interactions. Circular dichroism and FTIR spectroscopy show that the self-assembly of both peptides at low concentration is dominated by interactions among Fmoc units, although Fmoc-GRDS shows β-sheet features, at lower concentration than Fmoc-RGDS. Fibre X-ray diffraction indicates β-sheet formation by both peptides at sufficiently high concentration. Strong alignment effects are revealed by linear dichroism experiments for Fmoc-GRDS. Cryo-TEM and small-angle X-ray scattering (SAXS) reveal that both samples form fibrils with a diameter of approximately 10 nm. Both Fmoc-tetrapeptides form self-supporting hydrogels at sufficiently high concentration. Dynamic shear rheometry enabled measurements of the moduli for the Fmoc-GRDS hydrogel, however syneresis was observed for the Fmoc-RGDS hydrogel which was significantly less stable to shear. Molecular dynamics computer simulations were carried out considering parallel and antiparallel β-sheet configurations of systems containing 7 and 21 molecules of Fmoc-RGDS or Fmoc-GRDS, the results being analyzed in terms of both intermolecular structural parameters and energy contributions. http://hdl.handle.net/2117/8874 Title: Cylindrical sub-micrometer confinement results for the odd-symmetric dimer alpha,omega-Bis[(4-cyanobiphenyl)-4 '-yloxy]undecane (BCB.O11) Authors: Fuente, M.R. de la; López Pérez, David Orencio; Pérez Jubindo, M.A.; Dunmur, D.A.; Díez Berart, Sergio; Salud Puig, Josep Abstract: Broadband dielectric spectroscopy (102 Hz to 1.9 × 109 Hz) and specific heat measurements have been performed on the odd-symmetric dimer R,ω-bis[(4-cyanobiphenyl)-4′-yloxy]undecane (BCB.O11) in the isotropic (I) and nematic (N) phases confined to 200 nm diameter parallel cylindrical pores of Anopore membranes. Unlike previous studies on liquid crystal monomers, untreated and hexadecyltrimethylammonium bromide-treated membranes give rise to radial and axial confinements, respectively. An attempt is made to explain these unexpected results by means of a qualitative model for the dimer arrangement on alumina substrates. The model suggests that the population of conformers, which follow the bulk-like dynamics, is modified by confinement. Such a fact seems to be consistent with other distinctive features attributed to confinement, as for example, the increasing of the entropy change at the N-to-I phase transition for both axial and radial confinements. Specific-heat measurements have shown how confinement affects the N-to-I phase transition by a downward shift in transition temperature as well as by broadened and rounded specific-heat peaks. However, these modifications are revealed to be substantially different from what has been found previously in similar studies on liquid crystal monomers. Dynamic dielectric measurements have probed the different molecular motions in both confinements and how these motions are developed in a way similar to the bulk-dimer. Dielectric results have also proved that the surface-pinned molecular layer (where molecular motions are very restricted) adjacent to the pore-wall is temperature-dependent as already found previously for liquid crystal monomers. Wed, 15 Sep 2010 10:53:01 GMT http://hdl.handle.net/2117/8874 2010-09-15T10:53:01Z Fuente, M.R. de la; López Pérez, David Orencio; Pérez Jubindo, M.A.; Dunmur, D.A.; Díez Berart, Sergio; Salud Puig, Josep no Broadband dielectric spectroscopy (102 Hz to 1.9 × 109 Hz) and specific heat measurements have been performed on the odd-symmetric dimer R,ω-bis[(4-cyanobiphenyl)-4′-yloxy]undecane (BCB.O11) in the isotropic (I) and nematic (N) phases confined to 200 nm diameter parallel cylindrical pores of Anopore membranes. Unlike previous studies on liquid crystal monomers, untreated and hexadecyltrimethylammonium bromide-treated membranes give rise to radial and axial confinements, respectively. An attempt is made to explain these unexpected results by means of a qualitative model for the dimer arrangement on alumina substrates. The model suggests that the population of conformers, which follow the bulk-like dynamics, is modified by confinement. Such a fact seems to be consistent with other distinctive features attributed to confinement, as for example, the increasing of the entropy change at the N-to-I phase transition for both axial and radial confinements. Specific-heat measurements have shown how confinement affects the N-to-I phase transition by a downward shift in transition temperature as well as by broadened and rounded specific-heat peaks. However, these modifications are revealed to be substantially different from what has been found previously in similar studies on liquid crystal monomers. Dynamic dielectric measurements have probed the different molecular motions in both confinements and how these motions are developed in a way similar to the bulk-dimer. Dielectric results have also proved that the surface-pinned molecular layer (where molecular motions are very restricted) adjacent to the pore-wall is temperature-dependent as already found previously for liquid crystal monomers. http://hdl.handle.net/2117/7353 Title: Dynamics of orientationally disordered mixed crystal sharing Cl-adamantane and CN-adamantane Authors: Martínez García, Julio Cesar; Capaccioli, Simon; Díez Berart, Sergio; Tamarit Mur, José Luis; Barrio Casado, María del; Veglio, Néstor Raúl; Pardo Soto, Luis Carlos Abstract: Orientationally disordered (OD) mixed crystals formed between cyanoadamantane (CN-A) and chloroadamantane (Cl-A) have been thermodynamically characterized by means of thermal analysis and X-ray diffraction. The dynamics of these OD mixed crystals has been studied by means of broad band dielectric spectroscopy. Results evidence that dynamics of the α-relaxation process associated with the overall molecular tumbling slows down when molecules of CN-A are substituted by molecules of Cl-A. Fri, 21 May 2010 10:25:57 GMT http://hdl.handle.net/2117/7353 2010-05-21T10:25:57Z Martínez García, Julio Cesar; Capaccioli, Simon; Díez Berart, Sergio; Tamarit Mur, José Luis; Barrio Casado, María del; Veglio, Néstor Raúl; Pardo Soto, Luis Carlos no Orientationally disordered (OD) mixed crystals formed between cyanoadamantane (CN-A) and chloroadamantane (Cl-A) have been thermodynamically characterized by means of thermal analysis and X-ray diffraction. The dynamics of these OD mixed crystals has been studied by means of broad band dielectric spectroscopy. Results evidence that dynamics of the α-relaxation process associated with the overall molecular tumbling slows down when molecules of CN-A are substituted by molecules of Cl-A. http://hdl.handle.net/2117/7316 Title: Study of the critical behavior and scaling relationships at the N-to-I phase transition in hexyloxycyanophiphenyl Authors: Salud Puig, Josep; Cusmin, Paul; Fuente, M.R. de la; Pérez Jubindo, M.A.; López Pérez, David Orencio; Díez Berart, Sergio Abstract: An exhaustive analysis of the critical behavior of the nematic to isotropic (N-to-I) phase transition on the liquid crystal hexyloxycyanobiphenyl (6OCB) has been performed. To do so, the accurate evolution of various physical magnitudes (static dielectric permittivity data together with specific heat and volumetric determinations) around the N-to-I transition has been required. The specific heat data with the isobaric thermal expansion coefficient and the derivative of the static dielectric permittivity with temperature have been proven to be related to each other by a scaling relationship. However, some discrepancies have been observed for the dielectric data in relation to such a scaling relationship and the critical behavior of the N-to-I phase transition. All information has been used to get some insight on the strength of the first-order N-to-I phase transition of the 6OCB in relation to the other counterparts in the nOCB series of compounds. Wed, 19 May 2010 10:43:25 GMT http://hdl.handle.net/2117/7316 2010-05-19T10:43:25Z Salud Puig, Josep; Cusmin, Paul; Fuente, M.R. de la; Pérez Jubindo, M.A.; López Pérez, David Orencio; Díez Berart, Sergio no An exhaustive analysis of the critical behavior of the nematic to isotropic (N-to-I) phase transition on the liquid crystal hexyloxycyanobiphenyl (6OCB) has been performed. To do so, the accurate evolution of various physical magnitudes (static dielectric permittivity data together with specific heat and volumetric determinations) around the N-to-I transition has been required. The specific heat data with the isobaric thermal expansion coefficient and the derivative of the static dielectric permittivity with temperature have been proven to be related to each other by a scaling relationship. However, some discrepancies have been observed for the dielectric data in relation to such a scaling relationship and the critical behavior of the N-to-I phase transition. All information has been used to get some insight on the strength of the first-order N-to-I phase transition of the 6OCB in relation to the other counterparts in the nOCB series of compounds. http://hdl.handle.net/2117/7304 Title: Solid phases in cycloheptanol: dynamic disorder and glass transitions Authors: Salud Puig, Josep; López Pérez, David Orencio; Díez Berart, Sergio; Pérez Jubindo, M.A.; Fuente, M.R. de la; Rute Pérez, Maria Ángeles; Puertas, R. Abstract: The stable solid polymorphism of cycloheptanol (C7H14O, for short C7–OH) is revised in the present paper. Four solid stable phases, denoted on cooling from the liquid as phases I, II, III and IV are identified from Xray diffraction measurements. Lattice symmetry of phase III has been unambiguously stated as orthorhombic. Diffraction patterns corresponding to phase IV have been also indexed as orthorhombic, but only in a tentative way. A detailed broadband dielectric spectroscopy study devoted to these phases has been made. Such an experimental technique has no revealed differences between phases III and IV and from specific-heat measurements, the III–IV phase transition has not been observed yet. Dielectric results seem to evidence that the dynamic disorder of phase III and/or IV should be intra-molecular attributed to changes between the possible distinguishable molecular conformations along with possible hydroxyl group rotations. The possibility of C7–OH as conformational glass-forming material is discussed. Tue, 18 May 2010 11:27:59 GMT http://hdl.handle.net/2117/7304 2010-05-18T11:27:59Z Salud Puig, Josep; López Pérez, David Orencio; Díez Berart, Sergio; Pérez Jubindo, M.A.; Fuente, M.R. de la; Rute Pérez, Maria Ángeles; Puertas, R. no The stable solid polymorphism of cycloheptanol (C7H14O, for short C7–OH) is revised in the present paper. Four solid stable phases, denoted on cooling from the liquid as phases I, II, III and IV are identified from Xray diffraction measurements. Lattice symmetry of phase III has been unambiguously stated as orthorhombic. Diffraction patterns corresponding to phase IV have been also indexed as orthorhombic, but only in a tentative way. A detailed broadband dielectric spectroscopy study devoted to these phases has been made. Such an experimental technique has no revealed differences between phases III and IV and from specific-heat measurements, the III–IV phase transition has not been observed yet. Dielectric results seem to evidence that the dynamic disorder of phase III and/or IV should be intra-molecular attributed to changes between the possible distinguishable molecular conformations along with possible hydroxyl group rotations. The possibility of C7–OH as conformational glass-forming material is discussed.