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Bae, Sung Chul
Multiscale Optical Imaging Lab
Research Interests
  • Multiscale optical imaging, laser spectroscopy, laser microscopy, laser sensing, soft matter physics, surface and interfacial science, laser Matter Interaction

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Chemical imaging in a surface forces apparatus: Confocal Raman spectroscopy of confined poly(dimethylsiloxane)

Cited 45 times inthomson ciCited 9 times inthomson ci
Title
Chemical imaging in a surface forces apparatus: Confocal Raman spectroscopy of confined poly(dimethylsiloxane)
Author
Bae, SCLee, HLin, ZQGranick, S
Keywords
Contact area; Dilute solution; Polymer films; Surface forces apparatus
Issue Date
200506
Publisher
AMER CHEMICAL SOC
Citation
LANGMUIR, v.21, no.13, pp.5685 - 5688
Abstract
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.
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DOI
http://dx.doi.org/10.1021/la050233+
ISSN
0743-7463
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