br Materials and methods br Results and discussion br

Materials and methods

Results and discussion

The continuous precipitation of glycogen synthase kinase particles was investigated in two CSTRs operated in series for the first time at room temperature (ambient conditions were used with an objective of saving the energy requirements) in the presence and absence of ultrasonic irradiations. The effect of various operating parameters such as Ca(OH)2 concentration, CO2 flow rate and Ca(OH)2 slurry flow rate on the particle size and morphology of CaCO3 was investigated for both the synthesis approaches. It was established that the particle size of CaCO3 in the carbonation reaction was dependent on the operating parameters and also use of ultrasound made a distinct effect on the morphology and the final particle size. Smaller particles of calcium carbonate with a narrower particle size distribution were obtained for the approach based on the use of ultrasound as compared to the conventional approach. For both the approaches, the particle size decreased with an increase in the concentration of Ca(OH)2, CO2 flow rate as well as slurry flow rate. XRD and FTIR analysis confirmed that only calcite phase of CaCO3 was formed for both the synthesis approaches. It was also established that the shape of the crystals varied with the synthesis approach. Rhombohedral calcite particles were formed in the presence of ultrasound while conventional stirring based approach of synthesis resulted in spindle like particles. Overall the current work has clearly established the utility of ultrasound assisted approach with two reactors in series for obtaining lower mean size of particles as compared to the conventional approach of synthesis also giving higher capacity for processing as compared to the single reactor based approach.

Understanding and characterization of the wettability of a surface by a liquid is a process of great scientific as well as industrial importance. The wetting of solid surfaces by liquids is the governing phenomenon in processes such as lubrication, coatings, printing, detergency, separations process, and manufacture of composite materials [1–4].
Wettability is the ability of a liquid to maintain contact with a solid surface, resulting from the molecular interaction of the solid with the liquid. The degree of wettability is determined by the balance of forces of adhesion and cohesion between the surfaces involved in the interface. The greater the wettability the greater are the adhesion forces between the solid and liquid. This proposal, called the force treatment of the wettability process, is supported by several scientists like Extrand [5] and Lichao Gao [6], who proposed that the force per unit length gives a more clear understanding of the wettability phenomena and the hysteresis produced when the advancing and receding contact angle are measured. This last point of view allows the vector sum leading to the well-known Young relationship. It should be noted that a vector sum like that shown in Fig. 1 must be made only if the forces are applied at one point, in this case the point where the three interfaces, solid, liquid, and gas meet. There are other scientists like Wenzel [7] and Cassie [8] who introduce other points of view, suggesting that the balance of surface energies are the governing mechanism describing the wettability phenomena. It is interesting to point out that the controversy between the two points of view is alive until our days. However, the great interest of this controversy will not be treated in this paper because the experimental emphasis of this research leaves it out of its scope.
Numerous methods have been developed to measure the forces involved in the phenomenon of wettability, e.g., Wilhelmy plate and Du Nouy ring [9]. These methods allow measuring the cohesive strength of a liquid and a surface at equilibrium as well as in a dynamic way.
Moreover, each material has a specific energy and expresses different surface adhesion forces when in contact with a liquid, the magnitude of these forces depends not only on the nature of both, but also on the history of wetting, porosity, and chemical properties. This makes it difficult to know all the real surface energies and their balance of forces. In addition, there are other problems with the surface wetting, since there is not a perfectly smooth surface, and regardless of the polishing efforts that are made, a surface will always have some degree of roughness, making it difficult to assess the real dimensions of a wetted surface. For instance, if a solid surface is roughened so that a unit plane geometrical area has an actual surface area σ times that of the “smooth” surface, the measured contact angle obtained from will be termed “apparent contact angle”. This denomination may be considered somewhat arbitrary, however, the surface area of a solid liquid interface is unique and can always be identified with its plane geometrical area [10].