Determination of Orientation in Thermotropic Liquid Crystalline Polymer Films by Spectrographic Measurement of the Birefringence

Beekmans, F.; Boer, A. Posthuma De

doi:10.1021/ma960860t

Cited by 45 publications

(32 citation statements)

References 42 publications

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“…Therefore, we have adopted a spectrographic birefringence technique. 26,27 To the best of our knowledge, spectrographic birefringence has not been previously applied to in-situ measurements on flowing TLCPs, despite the power of this method. The optical train for our spectrographic birefringence setup is shown schematically in Figure 1.…”

Section: Flow Birefringence Measurementmentioning

confidence: 99%

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

2000

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A specially designed flow cell was used to investigate birefringence in transient shear flow, ∆n + (γ ,t), of three semiflexible main-chain thermotropic liquid-crystalline polymers (TLCPs), poly[(x)-pphenylene 1,10-decamethylenebis(4-oxybenzoate)] (PxHQ10) with varying pendant side groups (x ) oxyethyleneethoxy, tert-butyl, or phenylsulfonyl). Also, shear rheometry was used to investigate the growth of shear stress σ + (γ ,t) and first normal stress difference N1 + (γ ,t) during transient shear flow of the same TLCPs. Upon startup of shear flow, ∆n + (γ ,t) initially increases rapidly, follows two minor overshoots, and then levels off to attain a steady-state value ∆n in all three TLCPs. The steady-state value of ∆n for PSHQ10 (PxHQ10 with x ) phenylsulfonyl pendant side group) was found to be greater than that for PEHQ10 (PxHQ10 with x ) ethoxy pendant side group) and PTHQ10 (PxHQ10 with x ) tert-butyl pendant side group). This behavior is strongly correlated to the large van der Waals volume of phenylsulfonyl pendant side groups in PSHQ10 compared to that of ethoxy pendant side groups in PEHQ10 and tertbutyl pendant side groups in PTHQ10. It is also observed that N 1 + (γ ,t) exhibits a very large overshoot followed by an oscillatory decay to attain a steady-state value N1, while σ + (γ ,t) shows a very large overshoot followed by a rapid monotonic decrease to attain a steady-state value, σ. The peak values of N1 + (γ ,t) and σ + (γ ,t) for PSHQ10 were found to be 3-4 times greater than those for both PEHQ10 and PTHQ10, which we again attribute to the bulky phenylsulfonyl pendant side groups in PSHQ10. Only positive values of N1 + (γ ,t) and N1 were observed over the entire range of shear rates investigated. Variations of the ratio N1 + (γ ,t)/σ + (γ ,t) with shear strain (γ t) were found to be very similar to variations of ∆n + (γ ,t) with γ t for all three TLCPs investigated, except for that the ratio N1 + (γ ,t)/σ + (γ ,t) reached a steady state sooner than ∆n + (γ ,t). In steady-state shear flow, it is observed that the ratio N1/σ overlaps ∆n over the entire range of temperatures investigated; specifically, both the ratio N1/σ and ∆n remain constant at temperatures far below the clearing temperature (TNI), decrease gradually as the temperature approaches TNI, and drop precipitously to zero value at and near TNI.

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Section: Flow Birefringence Measurementmentioning

confidence: 99%

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

2000

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“…[33][34][35][36][37][38][39] Birefringence is calculated by using spectral measurement method. [40][41][42][43][44][45][46][47][48][49][50][51][52] A visible wavelength light source is used coupled with a +45 • linear polarizer. The polarized light is reflected through a metallic mirror (no change in the state of polarization) and focused on the sample.…”

Section: A Uniaxial Stretching Machinementioning

confidence: 99%

“…One polarizer is parallel to the original polarization direction (+45 • ) and the other is perpendicular to the original polarization (−45 • ). The light acquired by these fiber optic cables is transmitted to the spectrometer for recording and subsequent retardation calculations (more detailed information is given elsewhere [40][41][42][43][44][45][46][47][48][49][50][51][52]. We calculate the in-plane birefringence by the ratio of the retardation values to the real-time thickness values (Eq.…”

Section: A Uniaxial Stretching Machinementioning

confidence: 99%

Rapid integrated rheo-optical and polarized Fourier-transform infrared spectrometry measurement system for polymer films undergoing chemo-mechanical changes

Ünsal

Nugay

Offenbach

et al. 2013

Review of Scientific Instruments

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The design and performance of a multisensory instrument to track physical and chemical changes of thin polymer films (typically 5 μm < thickness < 100 μm) subjected to thermal and mechanical treatments are described in this paper. For the first time, real-time measurements of spectral birefringence, true stress, true strain, and temperature are integrated together with ultra-rapid-scan polarized FT-IR spectrometer (URS-FT-IR) to investigate the relationships between true mechanical measures and structural features at different length scales. The rheo-optical properties (birefringence-true stress-true strain) are collected at a rate of 10 data points∕s and URS-FT-IR data are collected at a rate of 300 complete spectra∕s. The IR dichroism measurement is performed by exposing the sample to non-polarized IR beam in transmission mode with two mutually perpendicular polarizations, parallel and perpendicular to the stretching direction, received by detector unit. This design allows to analyze both polarizations simultaneously wavenumbers in the range of 500 cm(-1)-4000 cm(-1). Controlled processing parameters include air speed, air temperature, stretching rate, stretching ratio, stretch cycling, and holding times; while simultaneously measuring optical retardation, sample width, temperature, load cell, and both parallel and perpendicular IR spectra. Calibration and performance of this instrument is demonstrated with several film samples. These are: A polystyrene standard, an atactic polystyrene (homo-polymer), a polyurethane (consists of hard and soft segments) for physical changes during uniaxial deformation, and a polyamic acid during imidization reaction. This measurement system is particularly useful in unraveling molecular level details of complex physical and chemical events that take place during very fast deformation schemes (uniaxial stretching, retraction, relaxation, annealing, etc.) relevant to industrial processes. These include specific orientation behavior of each phase, block or filler, crystallization, relaxation and orientation state. It is also suited to track reaction rates and products in polymers undergoing thermal or photo curing.

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“…The system allows simultaneous determination of the mechanical (true stress, true strain) and optical (birefringence) properties of polymers during stretching at desired temperatures. The details of this on-line measurement system were reported earlier [45,46]. In this method white light is used as the light source to get the order number of retardation automatically.…”

Section: Mechano-optical Propertiesmentioning

confidence: 99%

Control of optical anisotropy at large deformations in PMMA/chlorinated-PHB (PHB-Cl) blends: Mechano-optical behavior

Yalcin

Çakmak

Arkin

et al. 2006

Polymer

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Determination of Orientation in Thermotropic Liquid Crystalline Polymer Films by Spectrographic Measurement of the Birefringence

Cited by 45 publications

References 42 publications

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

Rapid integrated rheo-optical and polarized Fourier-transform infrared spectrometry measurement system for polymer films undergoing chemo-mechanical changes

Control of optical anisotropy at large deformations in PMMA/chlorinated-PHB (PHB-Cl) blends: Mechano-optical behavior

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