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Biomedical subjects

Unyong Jeong

Publications and source records attributed to Unyong Jeong.

6 recordsLinked to original sources
PubMed2006

An optical waveguide study on the nanopore formation in block copolymer/homopolymer thin films by selective solvent swelling.

Thin films of mixtures of asymmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) diblock copolymers and PMMA homopolymers with cylindrical PMMA microdomains oriented normal to the substrate surface were used to couple optical modes in the Kretschmann configuration, and their optical properties were investigated by optical waveguide spectroscopy (OWS). The nanopore formation in the block copolymer (BCP) waveguide layer via selective solvent swelling and subsequent reannealing was monitored in terms of shifts in the coupling mode angles. The sequential swelling/reannealing of the initial mixture film resulted in a number of discrete or partially interconnected pores instead of cylindrical pores with a high aspect ratio. The simultaneous processes occurring inside and on top of the BCP waveguide layer were discerned independently with high selectivity for p- and s-polarization.

Membranes, Artificial↗
PubMed2005

Polymer hollow particles with controllable holes in their surfaces.

Colloidal particles with hollow interiors play important roles in microencapsulation-a process that has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments or chemical reagents; protection of biologically active species; and removal of pollutants. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates by means of calcination or chemical etching. This simple and straightforward approach works for a variety of materials that include polymers, ceramics, composites and metals. For polymers, methods such as emulsion polymerization, phase separation, crosslinking of micelles and self-assembly have also been demonstrated for generating hollow structures. However, diffusion through these closed shells with pores <10 nm is often a slow process. To solve this problem, macroporous capsules have been fabricated by organizing colloids around liquid droplets to form colloidosomes or by controlling the mixing of liquid droplets. Here we report the preparation of another class of macroporous capsules-polymer shells with controllable holes in their surfaces. After loading of functional materials, the holes can be closed by means of thermal annealing or solvent treatment.

Biocompatible Materials↗
PubMed2005

Amorphous Se: a new platform for synthesizing superparamagnetic colloids with controllable surfaces.

We have successfully incorporated iron oxide nanoparticles into monodispersed amorphous selenium (a-Se) colloids by regulating the reaction temperature during the synthesis of a-Se. The surfaces of these a-Se colloids could be coated with conformal and smooth shells made of Pt and SiO2. The Se cores could then be removed by etching with hydrazine. The spherical morphology and superparamagnetism were maintained in all these synthetic steps. The presence of Pt and SiO2 on the outer surfaces of these colloidal particles allows one to control their surface functionalities through the formation of alkanethiolate and siloxane monolayers, respectively.

Colloids↗
PubMed2005

Monodispersed spherical colloids of Se@CdSe: synthesis and use as building blocks in fabricating photonic crystals.

Monodispersed spherical core-shell colloids of Se@Ag(2)Se have been exploited as a chemical template to synthesize Se@CdSe core-shell particles using a cation-exchange reaction. A small amount of tributylphosphine could facilitate the replacement of Ag(+) by Cd(2+) in methanol at 50 degrees C to complete the conversion within 150 min. The orthorhombic structure of beta-Ag(2)Se changed to a well-defined wurtzite lattice for CdSe. The CdSe shells could be converted back to beta-Ag(2)Se by reacting with AgNO(3) in methanol at room temperature. Because of the uniformity in size and high refractive index associated with the Se@CdSe core-shell colloids, they could serve as a new class of building blocks to fabricate photonic crystals with wide and strong stop bands.

Cadmium Compounds↗
PubMed2002

Closed-loop phase behaviour in block copolymers.

Closed-loop phase diagrams are known in systems with specific intermolecular interactions. In weakly interacting systems, however, such behaviour has never been observed. Here, diblock copolymers formed from polystyrene covalently linked to poly (n-pentylmethacrylate), P(S-b-nPMA), which have only weak segmental interactions, are shown to exhibit a closed-loop phase behaviour over a narrow range of molecular weight. The endothermic transitions from the disordered to ordered and back to the disordered state, as a function of increasing temperature, are dominantly entropic in origin. The morphology and rheological properties of P(S-b-nPMA) undergo characteristic changes at the transitions. Whereas the disorder-to-order transition temperature increases with decreasing molecular weight, the order-to-disorder transition temperature decreases. At a limiting molecular weight, the closed-loop vanishes and no ordering occurs. These findings provide quantitative insight into an elusive transition in weakly interacting multicomponent systems.

Crystallography, X-Ray↗