Biomedical subjects

Hyong-Jun Kim

Publications and source records attributed to Hyong-Jun Kim.

4 recordsLinked to original sources

PubMed2005

Dynamic sequential layer-by-layer deposition method for fast and region-selective multilayer thin film fabrication.

We present a newly devised technique, the dynamic layer-by-layer (LbL) deposition method, that is designed to take advantage of the LbL deposition method and fluidic devices. Polyelectrolyte solutions are sequentially injected through the fluidic LbL deposition device to quickly build well-defined multilayer films on a selected region with a linear increase in the material deposited. Multilayer film fabrication by this new method on a specific region was proven to be fast and effective. The effects on film quality of the processing parameters such as concentration of polyelectrolytes, flow rate, and contact time were investigated. A half-tethered self-standing film on a substrate was fabricated to demonstrate the effectiveness and the region-selective deposition capability of the devised dynamic LbL deposition method.

Adsorption↗

PubMed2005

Blends of amphiphilic poly(dimethylsiloxane) and nonamphiphilic octaisobutyl-POSS at the air/water interface.

Brewster angle microscopy (BAM) shows that a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS) nanofiller, octaisobutyl-POSS, forms aggregates at all surface concentrations at the air/water interface. When amphiphilic poly(dimethylsiloxane) (PDMS) is blended with the octaisobutyl-POSS (>10 wt % PDMS), the degree of POSS aggregation dramatically decreases. Thermodynamic analyses and morphology studies through surface pressure-area per monomer isotherm data and BAM, respectively, exhibit three distinct composition regimes: (1) Blends with >70 wt % POSS have unstable isotherms whose shapes deviate from those of PDMS and form large rigid domains comparable to but smaller than pure, octaisobutyl-POSS films. (2) At compositions between approximately 40 and 70 wt % POSS, the isotherms' features are qualitatively similar to those of pure PDMS, and extensive nanofiller "networks" are observed by BAM. (3) For compositions < or = approximately 30 wt % POSS, the isotherms are essentially those of pure PDMS with small POSS domains dispersed in the PDMS matrix. These results provide further insight into nanofiller aggregation mechanisms and dispersion that may be present in thicker films and bulk systems.

Journal Article↗

PubMed2005

Blends of amphiphilic trisilanolisobutyl-POSS and phosphine oxide substituted poly(dimethylsiloxane) at the air/water interface.

Mixtures of a polyhedral oligomeric silsesquioxane, trisilanolisobutyl-POSS, and a polar silicone, poly(dimethyl-co-methylvinyl-co-methyl, 2-diphenyl phosphine oxide ethyl) siloxane (PDMS-PO), spread as Langmuir monolayers at the air/water interface are used to examine the surface phase behavior and aggregation of trisilanolisobutyl-POSS as a function of silicone composition. Analyses of the surface pressure-area per monomer (Pi-A) isotherms in terms of the collapse pressures and excess Gibbs free energies of mixing indicate the monolayers form slightly negative deviation mixtures. Direct observations of surface morphology with Brewster angle microscopy in the collapsed regime reveal that the governing factor for aggregation is the collapse Pi of the component with a stronger affinity for water. In trisilanolisobutyl-POSS/PDMS-PO blends, POSS aggregates as discrete domains and does not coalesce into larger aggregates or networklike structures for <80 wt % POSS, a feature that is vastly different from a previous study of POSS blended with regular poly(dimethylsiloxane).

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PubMed2004

Polyhedral oligomeric silsesquioxane amphiphiles: isotherm and brewster angle microscopy studies of trisilanolisobutyl-POSS at the air/water interface.

A trisilanol derivative of polyhedral oligomeric silsesquioxanes (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. Moreover, the trisilanolisobutyl-POSS monolayer undergoes a nonequilibrium structural transition (collapse) around a surface pressure of Rho approximately 18 mN.m(-1). This paper explores the mono- and multilayer properties of POSS molecules at the air/water interface by the Wilhelmy plate technique and Brewster angle microscopy. Surface concentrations are controlled by four mechanisms: (1) compression at a constant rate, (2) stepwise compression followed by surface pressure relaxation to an "equilibrium" value, (3) successive additions of spreading solution followed by relaxation to a stable surface pressure value, and (4) hysteresis loops to test the reversibility of the structural transitions. Results show that both an increasing compression rate and a decreasing temperature lead to an increase in the surface pressure of the structural transition, which is consistent with the formation of solidlike multilayer domains during the collapse process. For the case of compression at a constant rate, small domains initially form and later aggregate to form large solid masses. Cessation of compression allows these large solid masses to relax into equilibrium ringlike structures with a lower surface pressure, Rho approximately 13 mN.m(-1). In contrast, if the film is expanded rapidly, these large solidlike domains relax into "spaghetti" like networks with a residual surface pressure that depends on the initial amount of the solidlike collapsed phase. Finally, successive addition and stepwise compression isotherm experiments lead to different and time-dependent morphologies. Understanding these surface properties of POSS molecules affords an excellent opportunity to design and study POSS/polymer blends for coating applications where POSS molecules with rigid inorganic cores, soft organic coronae, and dimensions comparable to polymeric monolayers can serve as perfectly monodisperse nanofillers.

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