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Sung Chul Bae

Publications and source records attributed to Sung Chul Bae.

8 recordsLinked to original sources

Molecular motion at soft and hard interfaces: from phospholipid bilayers to polymers and lubricants.

Spatially resolved and time-resolved understanding of complex fluid situations compose a new frontier in physical chemistry. Here we draw attention to the significance of spatially resolving systems whose ensemble average differs fundamentally from the spatially resolved individual elements. We take examples from the field of fluid phospholipid bilayers, to which macromolecules adsorb; the field of polymer physics, when flexible chains adsorb to the solid-liquid interface; and from the field of lubrication, when two solids are squeezed close together with confined fluid retained between them.

Lipid Bilayers↗

Nanoparticle-assisted surface immobilization of phospholipid liposomes.

Phospholipid liposomes (100-200 nm diameter) are deposited onto solid substrates after stabilizing them against fusion with the solid by allowing charged nanoparticles to adsorb at approximately 25% surface coverage. The immobilized vesicles remain stable over a period of days. Epifluorescence imaging shows that they diffuse freely over surfaces with the same charge but adsorb tightly onto surfaces with opposite charge. Nanoparticle adsorption to surface patterns of opposite charge provides a facile method to create large-scale surface-supported arrays of intact liposomes. This surface attachment method is simple chemically and applies generally for solid surfaces that can be hydrophobic or hydrophilic. Offering routes to localize proteins and other vesicle-contained objects at surfaces in tailored spatial patterns, these immobilized liposome arrays may find diverse applications in the emerging field of nanobiotechnology.

Adsorption↗

Chemical imaging in a surface forces apparatus: confocal raman spectroscopy of confined poly(dimethylsiloxane).

Confocal Raman spectroscopy has been implemented within the molecularly thin films of a surface forces apparatus. Applying this technique to an initial system, we investigate the confinement and shear-induced changes in the Raman spectra of poly(dimethylsiloxane) (PDMS) liquids confined between atomically smooth mica surfaces at thicknesses less than the unperturbed radius of gyration of the polymer. We focus on stretch vibrations of the PDMS methyl group, whose net orientation is perpendicular to the chain backbone. When PDMS was confined to a thickness of approximately the unperturbed radius of gyration (3.5 nm) but no shear, the Raman intensity of the methyl group was anisotropic in the x-y plane, signifying that chains oriented preferentially parallel to the confining surfaces. Relative to the bulk fluid, the relative intensity of the asymmetric to symmetric carbon-hydrogen stretch (2965 and 2907 cm-1, respectively) was enhanced, indicating that asymmetric vibration was enhanced by confinement. Measurements using polarized radiation showed coherent planar anisotropy in the x-y plane whose direction varied stochastically from experiment to experiment. It seems that although coherent in-plane alignment was favored, no preferential alignment direction was favored in the absence of shear. Application of shear caused the time-averaged polymer conformations to become more nearly isotropic in the plane of shear. These measurements are considered to represent the first chemical imaging of chemical species within the contact area of a surface forces apparatus.

Journal Article↗

How confined lubricants diffuse during shear.

The translational diffusion of a fluorescent dye embedded at a dilute concentration in a confined fluid was compared at rest and during shear. The fluid, octamethylcyclotetrasiloxane (OMCTS), was confined between step-free muscovite mica to thickness 3-4 layers. Fluorescence correlation spectroscopy showed that the time scales of intensity-intensity autocorrelation functions were essentially the same during shear and at rest, except they were faster during shear by a factor of 2 to 5. This dynamical probe of how liquids order in molecularly thin films fails to support the hypothesis that shear produced a melting transition.

Journal Article↗

Glenohumeral arthropathy after arthroscopic anterior shoulder stabilization.

PURPOSE: We present 5 cases of iatrogenic arthropathy after arthroscopic Bankart reconstruction using a metallic suture anchor. TYPE OF STUDY: Retrospective case series. METHODS: Five patients with pain and crepitus on motion were referred to our institution for further evaluation of the previous procedure on anterior shoulder instability. Screw-type metallic suture anchors were used in all cases. All patients were men, with an average age of 23 years (range, 21 to 26). Surgical records on previous procedure were reviewed, and the clinical symptoms were evaluated using a visual analogue scale (VAS), the Simple Shoulder Test (SST), and the Rowe scoring system. The secondary surgery for each patient was performed at an average of 12 months (range, 7 to 20) after the initial arthroscopic stabilization, except in one patient who wanted to postpone the revision surgery. RESULTS: Protrusion of the anchor tip was seen in all and chondral defects in the humeral head with some degree of synovitis were also seen. Slight differences between preoperative and postoperative pain were seen, but almost no improvement in function, including range of motion, stability, and average Rowe score were seen after the second procedure. Patients who underwent revision surgery were dissatisfied with the final outcomes. CONCLUSIONS: Careful attention should be paid when using a metallic suture anchor. A secure, buried placement of the anchor is required in arthroscopic Bankart reconstruction. Poorly placed suture anchors may damage the glenohumeral joint, and if these are not corrected either at arthroscopic surgery or shortly after, the results can be suboptimal. If a patient complains of unusual mechanical symptoms after using anchors, radiographs should be performed. This kind of serious complication can be discovered earlier to prevent the severe destruction of the glenohumeral joint. LEVEL OF EVIDENCE: Level IV.

Adult↗

Contrasting friction and diffusion in molecularly thin confined films.

We study, using fluorescence correlation spectroscopy, translational diffusion in molecularly thin liquids confined within a surface forces apparatus. The diffusion coefficient decreases exponentially from the edges towards the center of the Hertzian contact and further suggests the presence of a small number of distinct diffusion processes. This holds alike a crystallizable fluid (OMCTS) and a glass-former (1,2-propane diol), both of which displayed static friction. We conclude that friction, the average of an ensemble of molecules, masked massively heterogeneous molecular mobility.

Journal Article↗