The role of interfacial morphology in multilayers based on high T c YBa2Cu3O7-x

The interfacial microstructures in CaTiO₃/YBa₂Cu₃O_7-x /SrTiO₃/LaAlO₃/CaRuO₃ multilayers grown on (001) LaAlO₃ substrates has been characterized using transmission electron microscopy in combination with scanning electron microscopy. The morphology of films grown on both flat surfaces and on stepped surfaces patterned by ion beam milling were interpreted in terms of effects that influence epitaxial orientation relationships, nucleation of Y₂O₃ particles, and pinhole formation. The general conclusions are that a-axis oriented YBa₂Cu₃O_7-x particles should be avoided in multilayer structures. The particles give rise to cracking and pinhole formation. Local surface roughness, which may be due to ion beam milling or to the growth mechanism of YBCO, induces Y₂O₃ particle nucleation and pinhole formation. Very steep surface slopes cause the formation of a-axis YBa₂CU₃O_7-x particles. A critical size effect of the Y₂O₃ particles is suggested.     

Hollow capsules prepared from all block copolymer micelle multilayers

We introduce a novel and versatile approach for preparing hollow multilayer capsules containing functional hydrophobic components. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films onto polystyrene (PS) colloids. After removing the PS colloids, the stabilities of the formed BCM hollow capsules were found to be strongly dependent on the charge density of the hydrophilic corona segments (i.e., P4VP and PAA block segments) as well as the relative molecular weight ratio of hydrophobic core (i.e., PS segments) blocks and hydrophilic corona shells. Furthermore, in the case of incorporating hydrophobic fluorescent dyes into the PS core blocks of micelles, the hairy/hairy BCM multilayers showed well-defined fluorescent images after colloidal template removal process. These phenomena are mainly caused by the relatively high degree of electrostatic interdigitation between the protonated and anionic corona block shells.     

Synthesis and Assembly of Dipolar Heterostructured Tetrapods: Colloidal Polymers with “Giant tert‐butyl” Groups

We report on the first synthesis of a heterostructured semiconductor tetrapod from CdSe@CdS that carries a single dipolar nanoparticle tip from a core–shell colloid of Au@Co. A four‐step colloidal total synthesis was developed, where the key step in the synthesis was the selective deposition of a single AuNP tip onto a CdSe@CdS tetrapod under UV‐irradiation. Synthetic accessibility to this dipolar heterostructured tetrapod enabled the use of these as colloidal monomers to form colloidal polymers that carry the semiconductor tetrapod as a side chain group attached to the CoNP colloidal polymer main chain. The current report details a number of novel discoveries on the selective synthesis of an asymmetric heterostructured tetrapod that is capable of 1D dipolar assembly into colloidal polymers that carry tetrapods as side chain groups that mimic “giant tert‐butyl groups”.     

Template-free uniform-sized hollow hydrogel capsules with controlled shell permeation and optical responsiveness

This study has established a robust and straightforward method for the fabrication of uniform poly(vinylamine) hydrogel capsules without using templates that combines the dispersion polymerization and the sequential hydrolysis/cross-linking. The particle sizes are determined by the degree of cross-linking as well as by the cross-linking reaction time, while the shell thickness is independent of these variables. Diffusion-limited reactions occur at the periphery of the particles, leading to the formation of hydrogel shells with a constant thickness. The treatment of the surfaces of hollow hydrogel capsules with oppositely charged biopolymers limits the permeability through the shell of species even with low molecular weights less than 400 g/mol. Furthermore, we demonstrated that the hydrogel shell phase decorated with Au nanoparticles can be optically ruptured by exposure to laser pulse, a feature that has potential uses in optically responsive drug delivery.     

Mold design rules for residual layer-free patterning in thermal imprint lithography

We present the mold design rules for assuring residual layer-free patterning in thermal imprint processes. Using simple relations for mass balance, structural stability, and work of adhesion, we derive the conditions with respect to the given single or multigeometrical feature of the mold, which are compared with simple thermal imprint experiments using soft imprint molds. Our analysis could serve as a guideline for designing the optimum mold geometry and selecting mold material in residual layer-free thermal imprint processes.     

In-situ polymer blends via chain transfer living polymerization (CTLP)

In-situ polymer blends of polystyrene (PS)/poly(methyl methacrylate) (PMMA) with controlled and variable different compositions and molecular weights were found to be successfully synthesized by “chain transfer living polymerization (CTLP)” methodology by a combination of size-exclusion chromatographic analysis, differential scanning calorimetry (DSC), UV/Vis and H NMR spectroscopy, and optical microscopic analysis. The PMMAs prepared in tetrahydrofuran (THF) in the presence of polystyrene exhibit highly syndiotactic stereoregularity (over 70 mol-%) and a glass transition temperature over 120°C. A dispersed morphology was found even for blends with over 31 vol.-% of the weight fraction of one component due to the discrepancy in the molecular weights of two components in the PS/PMMA blends. A ternary polymer blend system having PS/PMMA/PS -block- PMMA can be generated by control of the concentration of fluorene as the chain transfer agent in the CTLP.