Domain structure of the antiferromagnetic insulating state in Nd₀.₅Sr₀.₅MnO₃

Optical reflectivity studies of the ferromagnetic metal (FMM) to antiferromagnetic insulator (AFI) phase transition are performed on Nd₀.₅Sr₀.₅MnO₃ manganite in a wide temperature and magnetic field range. The formation of a domain structure in the AFI state during the FMM−AFI phase transition is observed. It is shown that the two types of domains observed are energetically equivalent states. On the basis of the experimental results and symmetry analysis we conclude that these domains are crystal twins. The twin domain structure of the AFI state in the Nd₀.₅Sr₀.₅MnO₃ is visible in reflected unpolarized light due to a different tilting of the surface in the domains. The two-phase domain structure FMM+AFI formed in the vicinity of the phase transition is also studied. It is found that a thermodynamically equilibrium two-phase stripe domain structure does not develop. The absence of the magnetic intermediate state is due to the large energy of the interphase wall, which results in the stripe structure period being much larger than the size of the sample

Anisotropic colloids through non-trivial buckling

We present a study on buckling of colloidal particles, including experimental, theoretical and numerical developments. Oil-filled thin shells prepared by emulsion templating show buckling in mixtures of water and ethanol, due to dissolution of the core in the external medium. This leads to conformations with a single depression, either axisymmetric or polygonal depending on the geometrical features of the shells. These conformations could be theoretically and/or numerically reproduced in a model of homogeneous spherical thin shells with bending and stretching elasticity, submitted to an isotropic external pressure.Comment: submitted to EPJ

Deformation and ordering of molecular assemblies in high magnetic fields

Contains fulltext : 32396.pdf (publisher's version ) (Open Access)In this thesis the synthesis and physical properties of polymers of isocyanides containing thiophene and other functional groups are described. Polyisocyanides are ideal frameworks for the incorporation of such groups, because they possess a high degree of structural regularity as a result of the helical arrangement of the polymer backbone. A new type of isocyanide, viz. L-isocyanoalanine(2-thiophen-3-yl-ethyl)amide (IAT), was synthesized and polymerized using Ni(II) catalysts to give the corresponding polymer PIAT. The use of an amino-terminated polystyrene as the initiator in the polymerization of IAT resulted in the formation of a diblock copolymer (PS-PIAT), which displayed amphiphilic character. On dispersal in THF/water, aggregates with morphologies that depended on the ratio between the PS and PIAT block lengths could be obtained. Interestingly, PS-PIAT diblock copolymers also formed well-defined aggregates in organic solvents. In aqueous solution typically polymersomes were obtained, which were found to fuse upon standing, thereby increasing their average diameter by a factor of 20. The thiophene groups present in the polymersomes of PS-PIAT could be polymerized both electrochemically and chemically. Chemical polymerization proved to be the most suitable procedure, because it left the morphology of the polymersomes unaltered, in contrast to electrochemical polymerization, which led to destruction of the aggregates. Nanoreactors were constructed by encapsulating enzymes within the aqueous compartment of the PS-PIAT polymersomes. Three different enzymes, viz. lipase B from Candida antarctica, horseradish peroxidase, and glucose oxidase, were successfully compartmentalized. With the help of enzyme activity assays it was possible to prove that the enzymes inside the polymersomes remained active. Externally added substrates were found to diffuse through the polymersome membrane into the inner aqueous compartment of the nanoreactors where they were converted by the enzymes present. The resulting products were capable of diffusing out of the polymersomes, while the enzymes remained entrapped.RU Radboud Universiteit Nijmegen, 01 februari 2005Promotor : Maan, J.C. Co-promotor : Christianen, P.C.M.118 p

Using magnetic birefringence to determine the molecular arrangement of supramolecular nanostructures

Contains fulltext : 75610.pdf (publisher's version ) (Open Access)6 p

Elastin-based side-chain polymers synthesized by ATRP

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A highly ordered material from magnetically aligned peptide amphiphile nanofiber assemblies

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Magnetic alignment of self-assembled anthracene organogel fibers

High magnetic fields are shown to be remarkably effective to orient self-assembled 2,3-bis-n-decyloxyanthracene (DDOA) fibers during organogel prepn. Magnetic orientation of DDOA results in a highly organized material displaying a fiber-orientation order parameter of 0.85, a large linear birefringence, and fluorescence dichroism. The aligned organogel is stable after removal of the magnetic field at room temp. and consists of fibers oriented perpendicular to the magnetic field direction, as shown by SEM. Models for the mol. organization within the gel fibers are discussed upon quant. anal. of the birefringence. Prospectively, magnetic alignment can be used to improve specific properties of organogel materials

Magnetic alignment of self-assembled anthracene organogel fibers

High magnetic fields are shown to be remarkably effective to orient self-assembled 2,3-bis-n-decyloxyanthracene (DDOA) fibers during organogel prepn. Magnetic orientation of DDOA results in a highly organized material displaying a fiber-orientation order parameter of 0.85, a large linear birefringence, and fluorescence dichroism. The aligned organogel is stable after removal of the magnetic field at room temp. and consists of fibers oriented perpendicular to the magnetic field direction, as shown by SEM. Models for the mol. organization within the gel fibers are discussed upon quant. anal. of the birefringence. Prospectively, magnetic alignment can be used to improve specific properties of organogel materials

Domain structure of the antiferromagnetic insulating state in Nd0.5Sr0.5MnO3

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