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Our primary studies are centered on the properties of thin films and interfacial effects, especially the influence of spectroscopic properties.  We use a variety of spectroscopic tools in our investigations including UV-vis-NIR, FTIR, Raman, and fluorescence spectroscopies. Two problems are currently of interest: controlling the surface structure of polymer thin films and exploiting the piezoelectric properties of poly(vinyidene difluoride) (PVDF) to influence chemical reactivity.

Spin casting is a common method for creating smooth polymer films with thicknesses from hundreds of nanometers to tens of microns. Under certain circumstances, a spin-cast film can result in a structured surface that has the form of periodic wrinkles. We have found that the wrinkles have wavelengths on the order of tens of microns and amplitudes of tens of nanometers. The wrinkle pattern is influenced by the concentration of the polymer solution used in spin-casting, the angular velocity used, and the polymer molecular weight. The surface structure, especially the possibility of introducing quantum confinement, can be used to influence the spectroscopic properties of surface deposited species such as dyes. We investigate the morphological properties of the polymer surfaces using optical profilometry, which has a resolution in the 10s of nm without introducing possible surface damage.

Our probe of choice are xanthene dyes, a class of fluorescent materials that are readily available and commonly used as laser dyes. These compounds have strong absorbance in the visible region of the spectrum and are highly emissive, with many having quantum yields in solution approaching 1. When cast as thin films the properties of these dyes change, with a typical response being a significant quenching of the fluorescent when the films are more than a few nm thick. Further, the underlying substrate can also influence the photophysics of the dye. Depending on the nature of the substrate, the wavelength maximum, the absorbance or emission intensity, or the quantum yield can all be modulated.

PVDF (-[CH₂CF₂]_n-) has interesting electrostatic properties because of the polarity of the C-F bonds. Depending on the dihedral angle of the -C-C-C-C- bonds, three

different phases are commonly found. The α-phase is nonpolar, the β-phase is polar and ferroelectric, and the γ-phase is polar and piezoelectric. Attaining the β-phase is relatively difficult but we reported many years ago that addition of metal salts to PVDF thin films leads to a significantly  increased fraction of the β- and γ-phases. In addition to influencing the photophysics of surface chromophores, the piezoelectric properties can influence chemical reactivity. When a metal ion doped PVDF film is inserted into a solution of rhodamine B (RhB), the dye absorbs onto the surface without decomposition. However, when PVDF film is placed in an ultrasonic field, the piezoelectric effect induces decomposition of the RhB. We are investigating the mechanism of this effect and the extent of applications that can be envisioned.