Physical Characterization of a Method for Production of High Stability Suspension

Abstract

Suspensions/Dispersions are encountered in a wide range of applications, e.g., liquid abrasive cleaners, ceramics, medicines, inks, paints....etc. In most cases it is necessary to keep the suspension stable for the product lifetime. A new modified differential sedimentation measuring system is suggested and used to identify physical parameters affecting the sedimentation in suspensions. The technique is discussed in details. It is found that particle sizes as well as viscosity of continuous phase are the most important factors governing the stability of a suspension. Empirical relations are extracted to quantitatively describe the weight effect of each factor. The modified measuring system shows good accuracy enough to detect fluctuations in concentration of suspended particles due to their Brownian diffusion, as well as the particles concentrations in the stable suspension. This study confirmed the fact that particles diameters measured by Zetasizer are much greater than those measured by the transmission electron microscope. This study presents a proposal for new technique for particle size separation based on the differential sedimentation in viscose fluids. This new method is a differential viscosity column. The proposed size separation technique may help to separate engineered nano-particles with higher resolution. International Journal of Science and Engineering Applications Volume 5 Issue 2, 2016, ISSN-2319-7560 (Online) www.ijsea.com 43 Introduction Suspensions/Dispersions are encountered in a wide range of applications, e.g., liquid abrasive cleaners, ceramics, medicines, inks, paints....etc. In most cases it is necessary to keep the suspension stable for the product lifetime [1]. Particle size is one of the most important parameters in materials science and technology as well as many other branches of science and technology, from medicine, pharmacology and biology to ecology, energy technology and the geosciences. Well dispersed stable suspension is one of the most pharmaceutical formats of drugs. Also the stability of suspension is the top feature in paint industry. Therefore this current work aims to describe quantitatively the parameters that are responsible for the stability of a suspension in such a way that one can, initially, right select specifications of the used components before mixing them to produce a high stable suspension at once. Since the particles size (dispersive phase) is the most important parameter, this study will propose a new technique for size separation either in nano scale or micro scale or a mixture of both. a) Sedimentation of Nano-particles Most nano particles have been shown to aggregate once they are hydrated, which has a significant effect on their sedimentation rates. Several studies have addressed the aggregation of different nano particles in simpler aqueous solutions, including the effect of increasing ionic strength (IS) and different pH levels on the size of aggregates [2–5]. It was expressed that nano-fluids would be prepared by suspending solid particles with the size of less than 100 nm inside a base fluid (continuous phase). Terms “synthesis and Characterization “are widely used in literature, describing preparation phase of nano-fluids. In general terms, it could be stated that nanofluids include nanometer sized solid particles, fibres, rods or tubes suspended in different base-fluids [6]. This means that a nano fluid is a solid nano scaled discrete phase suspended in a continuous liquid phase. Accordingly, the stability and durability of the nano-fluid depends on the stability of suspending the solid phase in the host liquid. Hence, the stability of a suspension should depend on the nature of the nano particles (particle`s material density, particles size, particles shape, particles surface charge, ...etc.), nature of the host liquid (liquid density, viscosity, temperature, pH, particles concentration, ...etc.) and the nature of the mixture (aggregation of particles, quality of dispersion, zetapotential, sedimentation rate, Brownian motion ...etc.). Therefore, effects of above factors should be discussed in some details. The equation of motion of a particle in a continuous fluid should clarify the contribution of each of the factors on the stability of the produced suspension. The International Journal of Science and Engineering Applications Volume 5 Issue 2, 2016, ISSN-2319-7560 (Online) www.ijsea.com 44 equation of motion should represent the forces acting on the particle and cause its motion. Let FB is the bouncy force, Fg is the gravitational force, FR is the frictional Stock`s force and Ds is the the Stoke`s diameters correspond to equivalent diameters of hypothetical spheres with the same settling behaviour as the irregular, an isometric particles in question. The particle radius is then R= Ds /2 [7]. Ds may be determined from the measured particle size by the Zetasizer, which is shown later. Hence the equation of motion of the particle moves inside the liquid may be written as: m d2y dt2 = Fg − FB − FR (1) Where dy is the displacement traveled by the particle during time interval dt. Then m d2y dt2 = 4 3 πRρsg − 4 3 πRρlg − 6πηR dy