Instrumentation
Laba Dennis in Rheological Proper ties of Cosmetics and Toiletries, 2017
The basic rheological properties and flow behavior of materials were discussed in Chapter 2. In this chapter we describe how these properties are measured and the various instruments available for these measurements. Rheometers are used to characterize the rheological properties of various systems in quality control, processing, applications, and research and development. As pointed out in Chapter 2, it is necessary to characterize a system by measuring a range of properties, as the system may “see” different application conditions in very short periods of time. An example is a paint being sprayed on a vertical wall. The paint is subjected to very high shear rates in a matter of seconds after it was at rest, and its leveling and sag resistance properties depend on its ability to recover its viscosity and elasticity after the external stress has been removed. Ideally, a rheometer should detect changes in the rheological properties of a system in situations similar to its behavior in real-life applications. The geometry of the testing device is very important and should be similar to the one described in Chapter 2, Fig. 1: The material should ideally be tested between two parallel plates, one stationary and the other movable. Many devices, ranging from very simple and inaccurate to very sophisticated and accurate, have been designed to measure the rheological properties of various systems (1-6). Following are descriptions of most of the instruments used to date to measure rheological properties.
Spinning of Dialysis Grade Membranes
Sirshendu De, Anirban Roy in Hemodialysis Membranes, 2017
Standard rheometers that are used to measure viscosity and its variations due to applied shear stress, shear rates, temperature, and so on are available. These are also known as rotational viscometers. There are two types of rheometers: constant shear and constant rate. A typical rheometer machine (Figure 5.5a) has an air bearing–supported DC motor whose rotor is equipped with permanent magnets, whereas in the stator coils have opposite polarity, producing magnetic poles. The magnets in the rotor and the stator interact with each other and produce a flux of current that provides frictionless synchronous movement of the rotor. The torque produced by the motor is varied by varying the input current to the stator coil and, hence, can be measured. This torque is then used to measure shear rates, and the shear stress is measured using displacement of the upper measuring plate; thus, a curve between shear stress and shear rate yields viscosity of the sample. There are two types of arrangements to measure viscosity. These are the parallel plate and cone and plate (Figure 5.5a). Each has its own set of functionalities; the cone and plate are used for applying constant shear rate while the plate type is used for temperature-dependent tests. A typical rheometer is depicted in Figure 5.5b.
Contribution to the rheological testing of pharmaceutical semisolids
Published in Pharmaceutical Development and Technology, 2019
B. Siska, E. Snejdrova, I. Machac, P. Dolecek, J. Martiska
Semisolid pharmaceutical excipients and preparations are structured materials, and the changes at loading result in shear thinning flow behaviour with a yield stress. The determination of yield stress as a true material constant is difficult as the measured values are affected by the testing and evaluating method employed and the testing conditions in a large extent. Consequently, there is no universal method for determination of yield stress and there exists a number of evaluation approaches. The concept of a true yield stress is still a topic of lively debate (Barnes 1999; Castro et al. 2010). There are several methods available for use with a rotational rheometer including model fitting, stress ramp, stress growth, oscillatory techniques, and creep. The fitting models to the measured flow curves represent the traditional method of obtaining yield stress. Various models are employed, e.g. Power law, Herschel-Bulkley, Cross, Casson, Carreau, etc. (Mezger 2011). This testing gives a dynamic yield stress defined as the minimum stress required for maintaining flow. Another approach is to start with the sample in its at-rest state (zero shear) and incrementally increase the stress until the sample starts to flow. The stress initiating flow is called a static yield stress. It is usually considerably higher than its dynamic counterpart. Static yield stress seems to be more suitable characteristic of pharmaceutical semisolids as it can reflect many processes during manufacturing and application.
Newly developed nano-biocomposite embedded hydrogel to enhance drug loading and modulated release of anti-inflammatory drug
Published in Pharmaceutical Development and Technology, 2023
Sophia Varghese, Jai Prakash Chaudhary, Prachi Thareja, Chinmay Ghoroi
The material characterizations for different formulations CA, β-CD CA, Fe-CNB β-CD CA, and Fe-CNB CA were carried out after drug loading. The surface morphology and the elemental analysis were determined using field emission scanning electron microscopy (FE-SEM) along with EDS. The samples were coated with platinum before image analysis. The experiments were performed using (FE-SEM, JEOL JSM 7600 F, USA) at a working distance of 7–9 mm and 5–10 kV voltage. To study the interactions between drug-ibuprofen and hydrogel matrix fourier transform infrared spectroscopy (FTIR) (Perkin Elmer Spectrum GX-FTIR, USA) using the ATR method from wavenumber 4000–400 cm−1 was carried out. The crystalline nature of the material was investigated using powder X-ray diffraction (P-XRD). P-XRD measurements were performed using (Bruker D8 Discover) Cu-Kα, operating at 40 kV and 30 mA with a scan speed of 0.2 s/step and step size 0.02 and scanning range (2θ) from 5–90. Drug loading and release experiments were performed using a UV-vis spectrophotometer (Analytical Jena, Germany) at the wavelength (λ = 264 nm). Surface charge measurements were performed using a zeta sizer Nano ZS 90 (Malvern Instruments, UK). Rheological properties were measured with stress and strain-controlled modular compact rheometer (MCR 302, Anton Paar GmbH, Germany). All rheological tests were conducted at 25 °C.
Design and characterization of an organogel system containing ascorbic acid microparticles produced with propolis by-product
Published in Pharmaceutical Development and Technology, 2020
Lizziane Maria Belloto de Francisco, Diana Pinto, Hélen Cássia Rosseto, Lucas de Alcântara Sica de Toledo, Rafaela Said dos Santos, Paulo Jorge Cardoso da Costa, M. Beatriz P. P. Oliveira, Bruno Sarmento, Francisca Rodrigues, Marcos Luciano Bruschi
Using the same rheometer and geometry, the oscillatory oscillator analyses were performed at 25 and 37 °C. The linear viscoelastic region (LVR) was investigated by increasing the torque sweep at a fixed frequency for each sample. It was identified as the region where stress and strain are directly proportional and the storage modulus (G′) remained constant. Stress within the LVR was selected for subsequent frequency sweep analyzes. Formulations were carefully applied to the bottom plate of the rheometer, ensuring the minimum shear of the formulation and allowing a time of rest (relaxation of the tension introduced before the analysis) of five minutes before each determination (Bruschi et al. 2007; Jones et al. 2009). In a frequency range of 0.1–10.0 Hz, at least three replicates of each sample were analyzed. The elastic modulus (G′), the loss modulus (G″), the dynamic viscosity (η′) and the loss tangent (tan δ) were determined using the software RheoWin 4.10.0000 (Haake). Three replicates were determined for each sample.
Related Knowledge Centers
- Viscometer
- Suspension
- Acoustic Rheometer