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Zhiqun Lin

Publications and source records attributed to Zhiqun Lin.

6 recordsLinked to original sources
PubMed2006

Self-assembly of gradient concentric rings via solvent evaporation from a capillary bridge.

A drop of solution containing nonvolatile solute is allowed to evaporate from a sphere-on-flat geometry. Left behind is a striking pattern of gradient concentric rings with unprecedented regularity. The center-to-center distance between adjacent rings, lambda(C-C), and the height of the ring, h(d), are strongly affected by the concentration of the solution and the properties of the solvent. The nature of the formation of regular gradient ring patterns during the course of irreversible solvent evaporation is revealed through theoretical calculations based on the mass conservation of the solution.

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PubMed2006

Template-assisted formation of gradient concentric gold rings.

Gradient concentric rings of polymers, including (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(methyl methacrylate) (PMMA), with unprecedented regularity were formed by repeated "stick-slip" motion of the contact line in a sphere-on-flat geometry. Subsequently, polymer rings served as templates to direct the formation of concentric Au rings. Three methods were described. The first two methods made use of either UV (i.e., on MEH-PPV) or thermal treatment (i.e., on PMMA) on Au-sputtered polymer rings, followed by ultrasonication. The last method, however, was much more simple and robust, involving selective removal of Au and polymer (i.e., PMMA) consecutively.

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PubMed2005

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↗
PubMed2005

Patterns formed by droplet evaporation from a restricted geometry.

We show that hundreds of concentric rings, each approximately nanometers high and micrometers wide, form when a drop is allowed to evaporate from a confined geometry, leaving behind a dry, nonvolatile polymer solute. This new preparative strategy offers a simple, versatile, generalizable method to produce patterns of unprecedented high fidelity and regularity, as well as a direction to look to design yet more complex patterns.

Journal Article↗
PubMed2003

Hierarchical structure formation and pattern replication induced by an electric field.

Several techniques based on soft lithography have emerged to replicate micrometre-sized patterns. Similar to most other lithographic methods, these techniques structure a single layer of photo resist. For many applications, however, it is desirable to control the spatial arrangement of more than one component. With traditional methods, this requires an iterative, multistep procedure, making the replication process more complex and less reliable. Here, a replication process is described where multiple materials are processed simultaneously. Using a bilayer formed by two different polymers, electrohydrodynamic instabilities at both polymer surfaces produce a hierarchic lateral structure that exhibits two independent characteristic dimensions. A lateral modulation of the electric field enables replication with a resolution down to 100 nanometres. This approach might provide a simple strategy for large-area, sub-100-nanometre lithography.

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