An analysis of the thermodynamic conditions for solid powder particles spreading over liquid surface

Abstract

The spreading of solid powder over a liquid surface is a prevalent phenomenon encountered in many industrial processes such as food and pharmaceutical processes.The driving force for powder spreading over a liquid surface is not clearly understood.The Marangoni effect due to a temperature gradient and the spreading coefficient for solid powder over liquid ( S/L ) have both been proposed as causes for powder spreading over liquids. The proposed  S/L was based on the same form of the spreading coefficient for a liquid over a solid surface ( L/S ). Whereas  L/S has a clear thermodynamic definition, the spreading coefficient of solid powder over liquid,  S/L , which was defined by simply interchanging the subscripts of the interfacial energy terms, has not been thoroughly analysed. Our experimental results showed that the spreading behaviour of solid powders over liquids cannot be explained or predicted by  S/L . In this study we focus on problems associated with the  S/L . Through a thermodynamic analysis we conclude that the existing parameter  S/L is unable to predict the spreading behaviour of solid powder on liquid surface, since the interfacial energy approach does not capture the actual physical process of powder spreading over liquid surface. A closer examination of the powder spreading process reveals the *Manuscript Click here to view linked References

Liquid marbles: Physics and applications

“…The permeability of the liquid marble shell, thanks to the porous nature of the microparticulate covering on the liquid marble surface, has led to a number of interesting applications in gas sensing as shown by Nguyen et al (2010) and Tian et al (2010). pH sensing is an important application in the area of liquid marbles as demonstrated by Fujii et al (2010).…”

“…In summary, liquid marbles hold potential for several applications owing to their versatile physical and chemical characteristics. Nguyen et al (2010) performed many studies upon the methodology of the manufacture of liquid marbles and the energy transport associated with it. Comparisons were made between marbles manufactured in the traditional rolling process and those manufactured by the dropping of water droplets onto a bed of superhydrophobic particles.…”

Liquid marble formation: Spreading coefficients or kinetic energy?

“…Therefore SL λ , which is a comparison of liquid-solid adhesion and solid "cohesion", does not reflect the physical process of powder spreading correctly. This is an area of ongoing research effort [20].…”

“…Literature surface tension data of PVP(6%) and HPMC(2%) solutions [9] show that these polymers quite significantly influence the surface tension of water (Table 2) particles do not increase their surface area as they spread. Instead, powder aggregates merely disintegrate when they expand their coverage over the liquid surface [20]. In this process, inter-particle attraction forces must be overcome in order for powder particles to spread over a liquid surface.…”

“…In this process, inter-particle attraction forces must be overcome in order for powder particles to spread over a liquid surface. However, the inter-particle attraction forces cannot be equated to the work of cohesion of the solid surface [20]. Therefore SL λ , which is a comparison of liquid-solid adhesion and solid "cohesion", does not reflect the physical process of powder spreading correctly.…”