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Combining Rheology and Raman Spectroscopy Shear Rate Effects

Combining rheology and Raman spectroscopy provides a way to track shear-rate-dependent influences on molecules and supramolecular structures in real-time. In this report, the effect of shear rate on the molecules of the liquid crystal system N-(4-Methoxybenzylidene)-4-butylaniline (MBBA) is shown.

Introduction

The combination of Raman spectroscopy with a rheological setup offers unique advantages allowing the possibility to probe shear rate effects along with temperature effects on the sample.

In this fashion, the study of liquid crystals offers a simple way to demonstrate this shear rate dependence on Raman spectra.

MBBA (N-(4-Methoxybenzylidene)-4-butylaniline) is a widely used liquid crystal, especially in rheo-optical measurements, since the application of shear rate changes the crystal orientation from a polycrystalline (multiple domains of orientation, signified by a cloudy appearance due to light scattering along the domain walls) to a unilaterally directed state (clear appearance).

Due to the lack of a chemical change in this effect, it is easy to demonstrate the influence of shear rate on the system and track it by the intensity evolution of the crystallinity peak at low wavenumbers while leaving the rest of the spectrum identical in both chemical shifts as well as intensity.

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