Rheometry

The rheology of filled polymer systems is an ever expanding field in the polymer industry today. Using a concise, practical and simple format this comprehensive work explains the concepts behind filled polymer systems and the rheological techniques involved in studying their behaviour. Aware that the readers of the book may come from differing background, the first three chapters familiarize the reader with the basics about polymers, fillers and physicochemical interactions between them, rheology and rheometry. Covering such topics as preparation of filled polymer systems, steady shear viscous properties and extentional flow properties, this book covers the areas of importance from an introductory level through to more complex issues.

Review
`Rheology of Filled Polymer Systems will be of most interest to those involved in injection molding and similar processes. [...]if you are interested in molding processes, and especially in the theoretical background, then this book is for you. [...]The main feature which distinguishes this book from others on polymer rheology is its focus on filled systems. The addition of fillers (particles, fibers, flakes, etc.) makes such systems behave much differently than unfilled polymers. [...]the writing is quite good [...] Shenoy does a good job of presenting data for a variety of systems, explaining the trends intuitively, and then showing how it all fits in with the theories developed earlier in the book.'
Barry Berenberg in Composite.About.com

Demon3 on November 22, 2000Format: Hardcover
Book Review - Rheology of Filled Polymer Systems Aroon V. Shenoy

Kluwer Academic Publishers ISBN 0-412-83100-7

As a researcher in the area of particulate-filled composites I am continually looking for good books on this subject. Such books are hard to find, possibly because the topic is so multi-disciplinary that few authors manage to bring together the knowledge from polymer science (processing, stability, mechanical properties), surface science (dispersion, wetting, surface-treatment) and rheology (compounding and processing).

One area where it is especially difficult to find good information is that of filled polymer rheology. This topic is vital to understanding the behaviour of a filled polymer melt. For example, extruder throughput and mould filling during injection moulding are critical factors that must be understood when formulating a good particulate-filled polymer composite. I have found it hard to understand most texts on filled polymer rheology and therefore I was relieved when I read this book. The author must be congratulated on having presented such a complex field in a focussed and interesting way. All aspects of rheological measurement techniques are covered. First of all is an introduction to the rheological behaviour of un-filled polymers. Basic rheological concepts are presented followed by a comparison of the different measurement techniques. Steady shear and unsteady shear are both treated in detail where the author highlights the trends such as the influence of particle size, shape, distribution, concentration and surface treatment. Another chapter discusses the different types of polymer processing equipment and their relative merits and drawbacks for preparing polymer composites.

One especially intriguing section shows that even MFI data, which is simple and inexpensive to obtain, can be used as a powerful tool for estimating the rheological response of a filled polymer melt. The author shows that just by knowing the MFI and the Tg of the polymer, it is possible to calculate an approximate rheological response of the filled polymer melt. This estimation has sufficient accuracy to be of use in predicting the flow behaviour of the filled polymer melt during processing. Thus, even the humble MFI technique is shown to be a powerful tool and I expect that Shenoy's Unification approach will prove useful for many people, including myself.

I highly recommend this book to anyone interested in filled polymers. It is clearly written by someone with an excellent grasp of the subject. The text is concise and easy to read whilst the content is well organized and interesting.

A programme of research is outlined which considers the foaming performance and foam behaviour of surfactant systems commonly encountered in hand-wash laundry detergent applications. An experimental study of the physical chemistry of foam generation indicates that precipitation of a typical anionic surfactant with calcium forms mesophase particles and causes a marked reduction in the rate of transport of surfactant to air–water surfaces and a concomitant reduction in foaming. Oily soil antifoam effects are however insensitive to the presence of calcium, being equally effective regardless of pH and calcium content. They may be reproduced by a simple particle–oil mixture of a saturated and an unsaturated triglyceride (e.g. tristearin and triolein respectively). A detailed foam rheometry study is performed using foam flowing through a constriction. Bubble shapes are used to deduce the normal and shear stresses across the foam flow field. Broad agreement between the experimental stress field and that obtained from quasistatic simulations is demonstrated. As foam flow-rate increases, a different model, which takes explicit account of viscous dissipative forces within the foam flow field is required. The dissipative foam flow model predicts differential shrinkage and stretch rates of foam films. Coupled to a model for surfactant transport, this shows the extent to which surfactant concentration accumulates in shrinking films and is depleted in stretching films. In addition to film stretching, it is also important to know about film bursting or failure rates. Here failure rates are estimated using capillary suction pressures exerted on the films by Plateau border channels around film edges. The failure rates can then be employed to predict the evolution of bubble size at various spatial locations in a foam: reasonable agreement with experimental bubble size distributions is obtained.

ABSTRACT: A rheometric characterization of the functional Polyurethane (PU) foam composite with and without solid additives (aluminum flakes) were experimentally derived using a computer controlled mechanical spectrometer (rheometer) ARES-G2. It is determined that PU composite exhibits a strong time thickening and shear thinning behavior. The rheological behavior of this composite can be described with the power-law generalized non-Newtonian fluid model. The rheometric tests showed that the PU/Al mixture exhibits thermal thickening and shear thinning behavior with the yield stress. The system can be described with the power-law generalized non-Newtonian fluid (Ostwald-de-Waele) model. The effective viscosity of PU composite increases with both the testing time (exponentially) and the solid content (polynomial) in the mixture.

The curing reaction of stoichiometric and off-stoichiometric diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylene diamine (m-PDA) mixtures was studied by differential scanning calorimetry, thermogravimetric analysis and rheological measurements. In order to highlight the side reactions such as etherification and homopolymerization, the neat DGEBA and DGEBA/DMBA (N,N-dimethylbenzylamine) mixture were examined. The classical model-fitting and the advanced isoconversional methods were used to determine the activation energy of the different reactions. The advanced isoconversional method leads to a good agreement between isothermal, nonisothermal and rheological results. The effective activation energies of primary amine epoxy reaction, etherification and homopolymerization were estimated to about 55–60, 104 and 170 kJ mol−1, respectively.

Treatments for Parkinson’s disease face significant challenges in delivery to the due to the presence of blood brain barrier (BBB). The aim of this study was to develop and characterise an in-situ thermoresponsive polymer based gel system for possible exploitation of the intranasal olfactory route where the BBB is absent. Reaching the olfactory region in the nasal cavity and mucociliary clearance are the main hurdles from formulation point of view. Thermo-sensitive and pH sensitive polymers seem to be the answer to these problems. Formulation made with these polymers along with mucoadhesives will be liquid at room temperature and will turn into a viscous gel when comes in contact with the body either due to change in pH or temperature. We have successfully prepared the gels using cold method using amantadine, with Pluronic F127 as a thermoreversible polymer and carboxymethylcelluose (CMS) as a mucoadhesive polymer. Rheological characterisation confirmed the sol-to-gel phenomenon at desired temperatures. CMC increased the gelation temperature with increase in concentration, whereas amantadine lowered the gelation temperature with increase in concentration. After preliminary studies, 16 % of Pluronic F127 found to be a suitable concentration for the formulation to change from sol-to-gel at ambient nasal temperatures. Molecular, gene expression and drug transport studies using the nasal epithelial cell lines RPMI 2650 are also under investigation along with the development of an in-vitro olfactory-epithelial cell culture model to study axonal transport. Unlike the animal studies this model will be faster to use, efficient and also better representation of human olfactory system.

Microfluidic rheometry is considered to be a potential alternative to conventional rheometry for the rheological characterization of viscoelastic solutions having relatively low viscoelastic properties. None of the microfluidic platforms introduced so far, however, can be used for the measurements of multiple rheological properties in the same device. In this work, I present the first microfluidic platform, named the "μrheometer," which allows for the simultaneous measurement of zero-shear viscosity η 0 and longest shear relaxation time λ. This is achieved by transforming the original "flow rate controlled" platform presented by Del Giudice et al., "Rheometry-on-a-chip: Measuring the relaxation time of a viscoelastic liquid through particle migration in microchannel flows," Lab Chip 15, 783-792 (2015) into a "pressure drop controlled" microfluidic device, by replacing a syringe pump with a pressure pump. The novel device has been tested by measuring both η 0 and λ for a number of polyethylene oxide solutions in glycerol-water 25 wt. % and pure water, respectively. Its effectiveness has been corroborated by means of a direct comparison with a conventional rotational rheometer.

A water-soluble azide-functionalised chitosan was crosslinked with propiolic acid ester-functional poly-(ethylene glycol) using copper-free click chemistry. The resultant hydrogel materials were formed within 5–60 min at 37 °C and resulted in mechanically robust materials with tuneable properties such as swelling, mechanical strength and degradation. Importantly, the hydrogels supported mesenchymal stem cell attachment and proliferation and were also non-toxic to encapsulated cells. As such these studies indicate that the hydrogels have potential to be used as injectable biomaterials for tissue engineering.

In most conventional rheometers, notably the coaxial cylinders and capillary viscometers, the food specimen is pressed into a narrow gap and its structure is altered by uncontrolled shear. Also, most semiliquid foods exhibit slip, and consequently the measurements do not always reflect their true rheological properties. A feasible solution to these two problems is squeezing flow viscometry where the specimen, practically intact and with or without suspended particles, is squeezed between parallel plates. The outward flow pattern mainly depends on the friction between the fluid and plates or its absence ("lubricated squeezing flow"). Among the possible test geometries, the one of constant area and changing volume is the most practical for foods. The test can be performed at a constant displacement rate using common Universal Testing Machines or under constant loads (creep array). The tests output is in the form of a force-height, force-time, or height-time relationship, from which several rheological parameters can be derived. With the current state of the art, the method can only be applied at small displacement rates. Despite the method's crudeness, its results are remarkably reproducible and sensitive to textural differences among semiliquid food products. The flow patterns observed in foods do not always follow the predictions of rheological models originally developed for polymer melts because of the foods' unique microstructures. The implications of these discrepancies and the role that artifacts may play are evaluated in light of theoretical and practical considerations. The use of squeezing flow viscometry to quantify rheological changes that occur during a product's handling and to determine whether they are perceived sensorily is suggested.

Summary: The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3 g was applied to the epithelium, and the resultant displacement logged at a rate of 1 kHz. Force measurement accuracy was 20 mg and position measurement accuracy was 4 mm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232 Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796 Pa. These data demonstrate that it is pos...

The rheological behaviour of chitosan solutions in 250 mM acetate buffer was studied at different pHs (25° C). The intrinsic viscosity decreased from∼ 17 dL/g to∼ 14 dL/g when the pH increased from 4.7 to 6.0. Concentrated solutions (0.5–3.0% w/w) exhibited a shear-...

The proposed approach consists in studying the behaviour of a concrete starting from four uncoupled suspensions scales: suspending fluid, corresponding to water and the additives, cement paste, mortar and concrete. Rheometric tests using controlled shear rates or shear stresses were carried out on each uncoupled suspension. The experimental data exploitation led us to propose a widened parametric analysis. The influence solid concentration and the particles size on the evolution of the rheological parameters such as the yield stress and the apparent viscosity was identified. In addition, the rheological behaviour of an uncoupled suspension is directly controlled by the behaviour of the uncoupled suspension from size range immediately below.

In this study, a new way of understanding the shear-thickening phenomenon in self-assembled solutions is introduced. The near- and out-of-equilibrium behavior is investigated in four aqueous micellar solutions containing surfactants of the same family: the alkyltrimethylammonium bromide mixed with an ionic salt at equimolar concentration. Thus, the four molecules of surfactants have the same polar head but different aliphatic chain length containing 12, 14, 16, and 18 carbon atoms. In aqueous solutions, the attractive forces between the surfactant molecules depend on the length of the aliphatic chain, thus, varying this parameter will have a definite influence on the aggregation number, the shape and dimension of the micelles. According to our results, the evolution of the low shear viscosity is affected by the chain length. The rheometric measurements performed in steady and time-dependent flows show that the emergence, the range, and the amplitude of the shear thickening also depend on this parameter. However, in the domain of high shear rates, after reaching the maximum of viscosity, all flow curves superimpose irrespective of the chain length. The rheo-optic measurements confirm the apparition of the shear-induced structure (SIS); this new phase is locally oriented and the chain length affects strongly the micelles orientation and the birefringence intensity. These results undoubtedly demonstrate that the chain length plays an important role in the behavior near equilibrium and under shear flow of the micellar systems.

The rheological properties of synovial fluid (SF) are crucial to the performance of joint prostheses. During the development of joint prostheses, wear tests are performed, which simulate joint movements in diluted solutions (usually between 25 and 33% v/v) of bovine serum which has very different rheological properties compared with native SF, where rheology is maintained by hyaluronan. Consequently, there is a need to develop a more suitable artificial SF. In this study, we used rheological techniques to understand SF flow properties which provided an insight into the mechanical behaviour required of a practical SF analogue. Steady-shear viscosity measurements were performed to reveal changes as a function of shear rate. To analyse the viscoelastic properties small deformation oscillatory measurements of storage modulus (G') loss modulus (G″) and complex viscosity (η*) were made. The rheological properties of the SF where compared with those of the polysaccharides sodium alginate, gellan gum and mixtures of both polymers. Initial results revealed classic shear thinning behaviour for the SF with a small Newtonian plateau at low shear rates with a gradual reduction in viscosity with increasing shear rate. Viscoelasticity measurements also showed that at low frequencies of oscillation there was a viscous response with G″ greater than G' and at higher frequencies there was an elastic response. Rheological properties were found to be similar to that of a 50:50 mix of 2% w/v high molecular weight alginate and 0.75% w/v gellan gum. Importantly, the lubricating behaviour of the serum differed significantly from the biopolymer blend over a full range of sliding velocities. The biopolymer blend was shown to lubricate the opposing surfaces more effectively. This difference was attributed to the more rapid alignment of the polysaccharide during shear when compared with the bovine albumin (the most abundant protein in serum), which typically exhibits a globular structure and has a tendency for self-association. These results suggest that polysaccharide solutions with bio-relevant rheology maybe be suitable as lubricants for in vitro orthopaedic prosthetic wear tests.

An experimental micromagnetoflowcell viscometer was fabricated to enable viscosity measurements for microscopic quantities of liquid. The device measures the terminal velocity of superparamagnetic microparticles to determine the fluid properties. The motion of these particles is controlled by the magnetic fields generated from microscopic electromagnetic loops. Initial experiments have been conducted for different fluids, using high speed video microscopy. The results are consistent with viscosity differences and have established proof of principle for the device.