A Novel Rheological Microscope for Flow Studies of Thermotropic Polymers and Polymer Blends: Droplet Deformation

Mather, Patrick T.; Stüber, H. R.; Chaffee, Kevin P.; Haddad, Timothy S.; Romo-Uribe, A.; Lichtenhan, Joseph D.

doi:10.1557/proc-425-137

Cited by 12 publications

(13 citation statements)

References 5 publications

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“…Recent work has shown Rayleigh instabilities in many experimental systems: lasertweezed cylindrical lipid vesicles [4], liquid crystal tethers embedded in a polymer matrix [5], shrunken polymer gels [6], and columns of viscoelastic fluid [7]. Traditional experiments display an instability developing uniformly along the cylinder [8].…”

mentioning

confidence: 99%

Pearling and Pinching: Propagation of Rayleigh Instabilities

Powers

Goldstein

1997

Phys. Rev. Lett.

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A new category of front propagation problems is proposed in which a spreading instability evolves through a singular configuration before saturating. We examine the nature of this front for the viscous Rayleigh instability of a column of one fluid immersed in another, using the marginal stability criterion to estimate the front velocity, front width, and the selected wavelength in terms of the surface tension and viscosity contrast. Experiments are suggested on systems that may display this phenomenon, including droplets elongated in extensional flows, capillary bridges, liquid crystal tethers, and viscoelastic fluids. The related problem of propagation in Rayleigh-like systems that do not fission is also considered.Comment: Revtex, 7 pages, 4 ps figs, PR

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mentioning

confidence: 99%

Pearling and Pinching: Propagation of Rayleigh Instabilities

Powers

Goldstein

1997

Phys. Rev. Lett.

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“…For this purpose, a custom conductive heating stage 31 was employed, featuring a nitrogen purge and temperature control better than Ϯ1.0°C. The heating stage was mounted on an aus Jena Jenalumar polarizing optical microscope, which was used with the polarizer and analyzer crossed, a Tungsten lamp light source, and a 25ϫ long working distance objective lens.…”

Section: Methodsmentioning

confidence: 99%

“…31 A single powder particle was placed on one cover slip and quickly melted to a clear liquid drop. Subsequent placement of the second coverslip spread the drop to a thin film with a thickness of approximately 5 m. The glass-monomer-glass stack was then quickly quenched to 50°C on another temperature-controlled, cooler surface of the heating stage, at which point spherulites were observed to grow to the point of impingement over a period of five minutes.…”

Section: Thermosetting Arylene Ether Monomersmentioning

confidence: 99%

Synthesis and thermal properties of thermosetting bis-benzocyclobutene-terminated arylene ether monomers

Tan

Venkatasubramanian

Mather

et al. 1998

J. Polym. Sci. A Polym. Chem.

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A series of new bis‐benzocyclobutene‐endcapped arylene ether monomers was prepared and characterized. Whereas 2,6‐bis(4‐benzocyclobutenyloxy)benzonitrile (BCB‐EBN) could be prepared in good yield using the standard procedure (K2CO3/NMP/toluene/Dean–Stark trap/120°C), other bis(benzocyclobutene) (BCB)‐terminated monomers containing ether‐benzophenone (BCB‐EK), ether‐phenylsulfone (BCB‐ES), and ether‐6F‐benzoxazole (BCB‐EBO) moieties were invariably contaminated by mono‐endcapped products under similar reaction conditions. This can be attributed to a much greater activating effect of the nitrile group on the ortho‐fluorides in the aromatic nucleophilic displacement reaction than the carbonyl, sulfonyl, and benzoxazolyl groups. However, the latter monomers could be synthesized (70–80%) from 4‐trimethylsiloxybenzocyclobutene and respective aromatic fluorides in the presence of CsF at 140°C. Similar curing behaviors under N2 (DSC: extrapolated onset and peak temperatures at 227–230° and 260–262°C, respectively) characterized all four monomers. BCB‐EK, BCB‐ES, and BCB‐EBN showed melting transitions at 108, 119, and 146°C, in that order. As BCB‐EBO contained more rigid benzoxazole segments, it only exhibited a glass transition (Tg) at 85°C prior to curing exotherm, after it had been previously heated to 125°C. The following Tgs were observed for the cured materials: BCB‐EK (201°C), BCB‐EBN (224°C), BCB‐ES (264°C), and BCB‐EBO (282°C). The relative thermal stability according to TGA (He) results is: BCB‐ES < BCB‐EBN < BCB‐EK < BCB‐EBO. Finally, the results from thermal analysis, infrared spectroscopic, and variable temperature microscopic studies indicated that the nitrile group plays an important role in the cure chemistry, thermal, and microstructural properties of BCB‐EBN. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2637–2651, 1998

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“…8,10 With this device, a thin polymer film is sheared between heated quartz plates through the use of a stepper motor driving a ball screw. The stepper motor is controlled by a Compumotor™ indexer and drive system as commanded from a PC and the top and bottom disks are independently thermostated with embedded mica heaters and Eurotherm™ PID controllers.…”

Section: Optical Microrheometry (Omr)mentioning

confidence: 99%

“…In those works, it was found that disclination density increases substantially with shear rate, an effect sometimes termed textural refinement, but to a greater extent in the case of 8CB. Also, with a modified rheological microscope, 8 we have studied the influence of shear on the texture of liquid crystalline polymers, revealing quite distinct phenomena, including band formation on flow direction reversal 9 and flow induced isotropic-nematic transition. 10 However, the influence of flow on the disclination density, flow patterns, and molecular orientation through gelation of liquid crystalline thermosets has not been studied.…”

mentioning

confidence: 99%

Optical Rheology of New Liquid Crystalline Thermosets (LCTs): Influence of Shear on Disclination Texture

Qin

Mather

2001

MRS Proc.

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Liquid crystalline thermosets (LCTs) have been under intensive study because of their outstanding mechanical performance and low viscosity during processing. We have successfully synthesized four kinds of nematic bismaleimide thermosets that differ in the nature of a pendant group substitution and that feature a thermally stable nematic phase. Importantly, the pendant groups were found to be efficient in depressing the melting point to a level that allows for flow and cure at reasonably low temperatures. By blending two particular monomers with monofunctional maleimide that we synthesized, N-(4-hydroxyphenyl) maleimide (HPMI), the melting point is depressed and the curing process is postponed to higher temperatures. Such a blend has a processing window amenable to much-needed thermal and rheological characterization, particularly the evolution of disclination density during shear flow as cure progresses. Our previous work on disclination density measurements during shear flow has revealed particular scaling of dimensionless disclination density with dimensionless shear rate. The influence of shearing on the disclination density, flow patterns, and molecular orientation though gelation of thermosetting liquid crystals remains unexplored. In this presentation, we will follow a description of material synthesis with a report on the results of optical rheology experiments applied to the ternary blends containing HPMI and two bismaleimide monomers, detailing the influence of shear on disclination density though gelation.

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A Novel Rheological Microscope for Flow Studies of Thermotropic Polymers and Polymer Blends: Droplet Deformation

Cited by 12 publications

References 5 publications

Pearling and Pinching: Propagation of Rayleigh Instabilities

Pearling and Pinching: Propagation of Rayleigh Instabilities

Synthesis and thermal properties of thermosetting bis-benzocyclobutene-terminated arylene ether monomers

Optical Rheology of New Liquid Crystalline Thermosets (LCTs): Influence of Shear on Disclination Texture

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