Dielectric Aging and Dielectric Degradation (Breakdown) of Polymer Films in AC Electric Fields

This dissertation describes the use of continuous-scan and step-scan Fourier transform infrared (FT-IR) spectroscopic techniques to study the dynamics of the response of polymer films and liquid crystals to external perturbations. The investigation of liquid crystals includes both nematic and chiral smectic C examples. In these studies the dynamic infrared absorbance is used to explore the submolecular (functional group) contributions to the reorientation dynamics of the liquid crystal director in response to both pulsed (DC) and modulated (AC) electric fields. Continuous-scan stroboscopic FT-IR and step-scan impulse-response FT-IR were used to analyze the rise dynamics of reorientation resulting from pulsed DC perturbations; whereas step-scan FT-IR was used to monitor both rise and decay processes in response to synchronously modulated (AC) electric fields. In the step-scan measurements this sub-molecular view of the dynamics of liquid crystal director reorientation was enhanced by frequency correlation analysis, to yield 2D FT-IR spectra. For the nematic liquid crystal 4-pentyl-4$\sp\prime$-cyanobiphenyl (5CB) the data suggest a different rate of response of the rigid and floppy parts of the LC molecules. The second application of dynamic step-scan FT-IR reported is the study of the response of various polymer films to sinusoidally modulated tensile strain. The main advantage of the technique is that it can provide valuable information at the molecular level that can be used to interpret the macroscopic properties of the polymeric material under investigation. Examples of application to different types of polymer films are presented. Results for several heterogeneous polymers including semicrystalline high density/low density polyethylene blends, the micro-phase separated copolymer Kraton$\sp\circler$ and a homogeneous polymer blend of polystyrene/polydimethylphenylene oxide are presented. Finally, the modification of a research-grade FT-IR spectrometer (Nicolet Instruments, System 800) for step-scan operation is described. Some applications of the instrument to photoacoustic spectroscopy (PAS) are presented.

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Fabrication of ZrO 2 /rGO nanocomposites by flash sintering under AC electric fields

Journal of the American Ceramic Society ◽

10.1111/jace.17991 ◽

2021 ◽

Author(s):

Xinghua Su ◽

Mengying Fu ◽

Gai An ◽

Zhihua Jiao ◽

Qiang Tian ◽

...

Keyword(s):

Electric Fields ◽

Ac Electric Fields ◽

Flash Sintering

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Directed Assembly of Janus Particles under High Frequency ac-Electric Fields: Effects of Medium Conductivity and Colloidal Surface Chemistry

Langmuir ◽

10.1021/la302725v ◽

2012 ◽

Vol 28 (37) ◽

pp. 13201-13207 ◽

Cited By ~ 29

Author(s):

Lu Zhang ◽

Yingxi Zhu

Keyword(s):

Surface Chemistry ◽

Electric Fields ◽

High Frequency ◽

Directed Assembly ◽

Janus Particles ◽

Ac Electric Fields ◽

High Frequency Ac ◽

Medium Conductivity

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AC Electrokinetics for Biosensors

Fluids Engineering ◽

10.1115/imece2004-62013 ◽

2004 ◽

Author(s):

M. Sigurdson ◽

C. Meinhart ◽

D. Wang

Keyword(s):

Electric Fields ◽

Dna Hybridization ◽

Fluid Motion ◽

Diffusive Transport ◽

Analyte Concentration ◽

Ac Electrokinetics ◽

Ac Electric Fields ◽

Binding Rate ◽

Electrothermal Flow ◽

Biosensor Device

We develop here tools for speeding up binding in a biosensor device through augmenting diffusive transport, applicable to immunoassays as well as DNA hybridization, and to a variety of formats, from microfluidic to microarray. AC electric fields generate the fluid motion through the well documented but unexploited phenomenon, Electrothermal Flow, where the circulating flow redirects or stirs the fluid, providing more binding opportunities between suspended and wall-immobilized molecules. Numerical simulations predict a factor of up to 8 increase in binding rate for an immunoassay under reasonable conditions. Preliminary experiments show qualitatively higher binding after 15 minutes. In certain applications, dielectrophoretic capture of passing molecules, when combined with electrothermal flow, can increase local analyte concentration and further enhance binding.

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