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Radek Pivokonsky, Petr Filip, Jana Zelenkova
Visualization of elongation measurements using an SER universal testing platform

Appl. Rheol. 25:1 (2015) 13636 (8 pages)

A Sentmanat Extension Rheometer represents one out of a few experimental devices for the measurement of elongational viscosity of polymer melts. However, the appropriateness of this technique for individual polymer materials is not sufficiently apparent and in some case is disregarded or ignored. The proposed visualization technique is based on imprinting painted pattern from the inner surface of the studied polymer samples onto the counter-rotating drums. Digitization of the imprinted pattern gives a possibility to evaluate a degree of sagging, incorrect fixing of rectangular polymer samples to the drums, possible appearance of sample inhomogeneity (variance in thickness, bubbles, etc.). The presented visualization technique is demonstrated using branched LDPE Escorene. Two various imprinted patterns are applied. First, the upper and lower contours are charted on a prepared sample with the aim to determine the sample shapes during stretching and to compare them with the theoretical ones. Second, the inclined rectangular grid pattern is charted for evaluating possible inhomogeneity of the sample.

Cite this publication as follows:
Pivokonsky R, Filip P, Zelenkova J: Visualization of elongation measurements using an SER universal testing platform, Appl. Rheol. 25 (2015) 13636.

Petra Peer, Martin Stenicka, Petr Filip, Vladimir Pavlinek
Comparison of Electrorheological Measurements Based on Different Methods of Electric Field Generation

Appl. Rheol. 24:4 (2014) 42875 (4 pages)

Electrorheological measurements represent a key approach in characterizing the efficiency of electrorheological fluids. The rotational rheometers, the Physica MCR 501 (Anton Paar) equipped with an electrorheological cell and the Bohlin Gemini CVOR 150 (Malvern Instruments) modified for electrorheological experiments generate an electric field in two completely different ways. Each of the two generations has a specific influence on electrorheological measurements. The experimental data were obtained and compared for a suspension of polyaniline powders mixed (10 wt%) in silicone oil. For a concentric-cylinders arrangement, it was shown that the data are fully comparable for both rheometers. However, for a parallel-plate arrangement, the data using the Physica MCR 501 provide higher values in comparison with both the corresponding plateplate data obtained with the Bohlin Gemini CVOR 150 and with the mutually comparable concentric cylinders data.

Cite this publication as follows:
Peer P, Stenicka M, Filip P, Pavlinek V: Comparison of Electrorheological Measurements Based on Different Methods of Electric Field Generation, Appl. Rheol. 24 (2014) 42875.

J. David, P. Filip, A.A. Kharlamov
Back extrusion of Vocadlo-type fluids

Appl. Rheol. 23:4 (2013) 45366 (8 pages)

Back extrusion represents one of the cheapest experimental methods to determine rheological characteristics of studied fluids, and simultaneously minimise their disruption in comparison with conventional rotational rheometers. This method is based on plunging a circular rod into an axisymmetrically located circular cup containing the experimental sample. Formerly this method has, among other uses, been successfully applied to determinations of parameters appearing in power-law, Bingham and Herschel-Bulkley fluids. The aim of this contribution is to present a sufficiently simple user-friendly procedure for determining individual rheological parameters appearing in the Vocadlo model (sometimes called the Robertson-Stiff model) - yield stress, consistency parameter and flow behaviour index.

Cite this publication as follows:
David J, Filip P, Kharlamov A: Back extrusion of Vocadlo-type fluids, Appl. Rheol. 23 (2013) 45366.

Petr Filip, Petra Svrcinova
Measurement of elongational viscosity of polymer melts using SER Universal Testing Platform

Appl. Rheol. 22:1 (2012) 14776 (5 pages)

The measurement of elongational viscosity still evokes a series of problems in comparison with the relatively well-established measurement of shear viscosity. Recently new techniques have appeared enabling measurement of elongational viscosity with the samples for which the aspect ratios of their geometrical shapes (i.e. length vs. width (diameter)) can attain moderate values, i.e. not necessarily of a longitudinal character as in the case of earlier techniques. The aim of this contribution is to experimentally demonstrate the invariantness of transient uniaxial elongational viscosity measured with respect to a rectangular shape and thickness of LDPE samples using a SER Universal Testing Platform fixed in an Anton Paar MCR 501 host system. The width of the samples was varied within the range 2.1-12.7 mm and thickness altered within 0.1-1 mm. An advantage of fixing polymer samples directly to both drums (if possible) over the application of clamps is documented.

Cite this publication as follows:
Filip P, Svrcinova P: Measurement of elongational viscosity of polymer melts using SER Universal Testing Platform, Appl. Rheol. 22 (2012) 14776.

J. David, P. Filip
Phenomenological Modelling of Non-Monotonous Shear Viscosity Functions

Appl. Rheol. 14:2 (2004) 82-88

The aim of this paper is to present a new phenomenological rheological model suitable for the description of a wide class of viscoelastic fluids. Classical phenomenological models predict the relation shear viscosity vs. shear rate (or shear stress) for shear-thinning (or thickening) materials exhibiting smooth monotonous passage from the first - upper (lower) - Newtonian plateau to the second - lower (upper) - one. However, present state of non- Newtonian materials used in practice (ranging from aqueous surfactant solutions, bituminous materials, associative polymers, polymer thickeners, lacquers and gels, to some special disperse systems, etc.) evokes the need to describe this - for many materials non-monotonous - relation in the corresponding way, i.e. through the sufficiently simple phenomenological model with a moderate number of parameters. A six-parameter model enabling description of not only monotonous but also non-monotonous course of shear viscosity function against shear rate (stress) is proposed including physical characterisation of the parameters. This model describes not only extreme points (maximum or minimum) but also a possible appearance of intermediate Newtonian plateau or its indication. The meaning and influence of the individual six parameters is documented on the experimental data published in the literature. There is a good agreement of the model proposed with many different experimental data representing different rheological behaviour. The applicability of this model for a wide class of viscoelastic materials is its principal advantage over the hitherto published phenomenological models.

Cite this publication as follows:
David J, Filip P: Phenomenological Modelling of Non-Monotonous Shear Viscosity Functions, Appl. Rheol. 14 (2004) 82.

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