Fourier-Transform-Rheology on linear polystyrene melts

Abstract

Large amplitude oscillatory shear (LAOS) was applied to a linear polymer melt in order to study the mechanical harmonic generation in the nonlinear regime. In the nonlinear regime mechanical harmonics at 3w1, 5w1, etc. are generated under oscillatory shear with a shear frequency w1. These higher harmonics can be analysed with respect to frequencies, amplitudes and phase if the time data of the torque is Fourier transformed. This experimental method (FT-Rheology) permits therefore to quantify the mechanical nonlinearities if sinusoidal shear rates are applied. This article describes the basic idea of this experimental method as well as the application to different anionically polymerized polystyrene melts. The dependence of the nonlinear, rheological properties with respect to the molecular weight Mn, the applied strain g0, the frequency w1 and the temperature was investigated. In addition to simple nonlinear theories we could also observe even harmonics at 2w1, 4w1, etc. in the FT-rheology spectra. The appearance of even harmonics was correlated with the appearance of a more complex nonlinear behaviour.

Fourier-Transform Rheology

“…Pipkin diagram together with three simple experimental possibilities to explore the non-linear regime using FTrheology. [75] Strain, frequency or both can be used to investigate the non-linear regime. at all.…”

“…[73] The polystyrene melts were first characterized in the linear regime via the time-temperature superposition (TTS) principle and the data were found to be in agreement with G 9, G 99 master curves in the literature. [4,5,74,75] All melts were measured at T 0 = 453 K with a shear frequency of x 1 /2p = 0.1 Hz. The results are shown in Figure 9 as a function of shear amplitude.…”

Distinguishing Linear from Star‐Branched Polystyrene Solutions with Fourier‐Transform Rheology

“…[7][8][9][10] Recently, an extremely sensitive detection system in combination with a specific FT algorithm on commonly available rotational rheometers has been introduced. [11][12][13][14] Several modifications have led to an overall improvement by a factor 100-1 000 in the signal-to-noise ratio so that much smaller differences were detectable and quantifiable. [15,16] A detailed introduction to high sensitivity FT rheology can be found in recent publications.…”

“…An extended version of this work will be published shortly. [18] Experimental Part Setup A Rheometric Scientific ARES rheometer equipped with a 2KFRTN1 torque transducer was used to obtain data. Raw time data were externally digitised using a 16-bit analog-to-digital converter (ADC) card (PCI-MIO-16XE; National Instruments) which allowed the measurement and averaging (''oversampling'') of the shear strain and the shear torque on the fly.…”

Analysing the large amplitude oscillatory shear of the Cross and Cross–Maxwell models with the aid of Fourier transform rheology using the example of a solvent-borne alkyd primer

“…Parameter m in equation (21) can be determined with the aid of the higher harmonic contribution ( [16], [19]) delivered by normalised intensities I k I 1 .…”