Suspensions sedimentation assessment

The colloidal stability of silica Suspensions in the present work was assessed by sediment volumes and from the optical coagulation rate constant. In the first method, 50 mg of silica was dispersed in 5 cm3 polymer solution (concentration 10-2 g cm 3) in a narrow tube and the sediment height found at equilibrium. Coagulation rates of the same systems were found by plotting reciprocal optical densities (500nm, 1cm cell) against time. When unstable dispersions were handled, the coagulation was followed in... 

Most of the cases concerned granules that were suspended in water before the administration. Consequently, the properties of the suspension thus formed were assessed. The parameters that attracted most attention were the relative sediment volume (volume of sediment/total volume) and the redi-spersability. See Chapter 5.3 for details on the suspensions. 

An application of ultrasound that is becoming increasingly popular in the food industry is the determination of creaming and sedimentation profiles in emulsions and suspensions (Basaran et al., 1998). Acoustic techniques can also assess nondestructively the texture of aerated food products such as crackers and wafers. Air cells, which are critical to consumer appreciation of baked product quality, are readily probed due to their inherent compressibility (Elmehdi et al., 2003). Kulmyrzaev et al. (2000) developed an ultrasonic reflectance spectrometer to relate ultrasonic reflectance spectra to bubble characteristics of aerated foods. Experiments were carried out using foams with different bubble concentration and the results showed that ultrasonic reflectance spectrometry is sensitive to changes in bubble size and concentration of aerated foods. 

Sedimentation ratio is often used to assess suspension stability. Byron reported the sedimentation ratios for a 1% sodium fluoresein suspension formulation with different amounts of surfactant (sorbitan trioleate) after standing for 20 days at room temperature. The suspension formulation with the lowest sedimentation ratio had thebest-flocculated system. However, all formulations were easily redispersible one complete revolution of the container was sufficient to produce a homogeneous dispersion. There was no clear difference in the times taken to reach apparent sedimentation equilibrium. Physical stability of the formulation was determined according to ... 

Bulk properties of the suspension. This is particularly important for concentrated systems, and requires measurement of the rate of sedimentation and equilibrium sediment height. More quantitative techniques are based on assessing the rheological properties of the suspension (without disturbing the system that is, without its dilution and measurement under conditions of low deformation) and how these are affected by long-term storage. This subject is discussed in detail in Chapter 20. 

In this chapter, a summary of the methods that can be applied to assess the structure of the solid/Uquid interface will first be provided, followed by details of assessing sedimentation, flocculation, and Ostwald ripening. In the latter cases (flocculation and Oswald ripening), information is needed on the particle size distribution, and several techniques are available to obtain this from diluted systems. It is essential to dilute the concentrated suspension with its own dispersion medium in order not to affect the state of the dispersion during examination. The dispersion medium can be obtained by centrifuging the suspension, when the supernatant liquid will be produced at the top of the centrifuge tube in the case... 

Several physical measurements can be applied to assess sedimentation, and these methods have been described in detail by Kissa [6]. The simplest method is to measure the density of the settling suspension at a known depth, using a hydrometer, but unfortunately this method is highly invasive due to disturbance... 

Suspensions are physically unstable preparations sedimentation occurs at storage. The monograph Unlicensed medicines in the British Pharmacopeia describes how to assess the settling and resuspendability (see Sect. 32.7.2). 

Comparisons are made of the measured and computed cross-shore variations of the mean and standard deviation of the free surface elevation ly, cross-shore velocity U, and longshore velocity V as well as the suspended sediment volume Vg per unit horizontal bottom area. is predicted using Eq. (28.30) with the sediment suspension probability Pg and the bottom slope effect, which were not included previously. These comparisons are assessed in light of those presented by Agarwal et al and Kobayashi et al The degree of agreement is found to be practically the same. The modifications presented in this chapter change the computed results very little. However, the present computation is more efficient and stable because of the... 

The above rheological techniques can be used to assess sedimentation and flocculation of suspensions. This will be discussed in detail below. 

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