Biomedical subjects

Hong H Lee

Publications and source records attributed to Hong H Lee.

8 recordsLinked to original sources

PubMed2006

Anisotropic rupture of polymer strips driven by Rayleigh instability.

We demonstrate that the separated polymer strips of micro- and sub-micro-length-scales rupture anisotropically along the strip direction, resulting in the formation of distinctly observable, regularly spaced polymer drops. The wavelength of the polymer drops and the surface tension dependence of the rupture behavior are found to be well represented by a relationship derived on the basis of Rayleigh instability. The period is proportional to the square root of the cross-sectional area of the strip and the proportionality constant depends on the contact angle. The rupture of polymer strips into polymer blocks instead of drops, which result when annealed with physically confining walls in place, is found to be well described by the same relationship.

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PubMed2006

Surface modification of poly(dimethylsiloxane) for retarding swelling in organic solvents.

A method of alleviating swelling problems of poly(dimethysiloxane) (PDMS) molds in organic solvents is developed that allows repeated use of the molds without deleterious solvent effects. The method involves surface modification of PDMS surface with poly(urethaneacrylate) that results in a partially modified PDMS surface. This modification leads to a significant reduction in the rate of solvent absorption into PDMS such that the swelling can be controlled.

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PubMed2006

Formation of regular nanoscale undulations on a thin polymer film imprinted by a soft mold.

We observed the formation of regular nanoscale undulations on a polystyrene film when imprinted by a soft poly(dimethylsiloxane) mold above the polymer's glass transition temperature. The shape of the wave was reminiscent of a buckling wave frequently observed for a metal film supported on an elastomeric substrate. We derived a simple theoretical model based on an anisotropic buckling of the polymer film rigidly bound to a substrate, which agrees well with the experiment.

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PubMed2004

Solvent-driven dewetting and rim instability.

An experimental method suitable for reproducible results has been used to investigate dewetting behavior of thin films of solvent-laden polymer. This solvent-driven dewetting enables one to change spreading coefficient by an order of magnitude that is not readily realizable in thermal dewetting and to study polar interactions that have not been fully exploited experimentally. While the film instability is similar to that found in thermal dewetting, the rim instability is quite different. Two different types of the rim instability have been found. With a polar solvent, the rim instability changes from one type to another with increasing film thickness whereas the unstable rim becomes stable for an apolar solvent.

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PubMed2004

Polymer elasticity-driven wrinkling and coarsening in high temperature buckling of metal-capped polymer thin films.

We report the critical effects the deformational stress from the elastic nature of a confined polymer layer has during the relaxation process on the buckling of thin metal-polymer bilayer systems (less than 100 nm) even above the temperature at which the polymer is in the liquid flow region. In contrast with what is generally believed, the dispersion force does not play a significant role in the buckling. We also find that the final wrinkled waves take on the shape of wormlike islands. The coarsening leading to the island structure is driven by the growth in amplitude of the dominant wave at the expense of less dominant ones.

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PubMed2004

An ultraviolet-curable mold for sub-100-nm lithography.

We describe a novel UV-curable mold that is stiff enough for replicating dense sub-100-nm features even with a high aspect ratio. It also allows for flexibility when the mold is prepared on a flexible support such that large area replication can be accomplished. The composite material of the mold is inert to chemicals and solvents. The surface energy is made low with a small amount of releasing agent such that the mold can be removed easily and cleanly after patterning. In addition, the material allows self-replication of the mold. These unique features of the mold material should make the mold quite useful for various patterning purposes.

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PubMed2004

Sub-100 nm patterning with an amorphous fluoropolymer mold.

A fluoropolymer mold is introduced and used to pattern sub-100 nm features with the characteristics that cause problems in patterning with a mold. The low surface energy and inertness, stiffness, and permeable nature of the mold material make it possible to pattern without surface treatment densely populated very fine features, mixed patterns of small and large features, and features with a high aspect ratio, when the mold is used with a polymer solution for the patterning. The ultraviolet transparency of the mold material also allows for patterning with photocurable pre-polymers.

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PubMed2003

Evolution of a stress-driven pattern in thin bilayer films: spinodal wrinkling.

We report the full spectrum of the evolution of the wrinkle pattern formation in a thin bilayer film of an elastic metal on a viscoelastic polymer. Although the origin is different, the transition of an initial islandlike pattern to a labyrinthine structure without any change in the wavelength (q approximately t(0)) and the overall evolutionary process is strikingly similar to that in the spinodal system but the process is robust and takes place on a long time scale (about 10 days). The change into a mountainous topography in the late stages is accompanied by an increase in the length scale from an initial wavelength to another. This change, due to the relaxation of the confined polymer that results in a transition from elastic- to viscouslike behavior, induces wave coarsening (q approximately t(-1.04+/-0.08)) and macroscopic roughening.

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