EMA 4121 Interfacial Engineeering Chapter 3 spring 2011

EMA 4121 Interfacial Engineeering Chapter 3 spring 2011 - 1...

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Unformatted text preview: 1 Chapter 3: General Properties of Systems Containing Liquids Chapter 3: General Properties of Systems Containing Liquids KEY CONCEPTS KEY CONCEPTS (Note the application of key concepts from previous chapters (Note the application of key concepts from previous chapters in the present discussion) in the present discussion) • What are major differences between gas/liquid/solid systems? What are major differences between gas/liquid/solid systems? • What are the molecular origins of surface/interfacial tension/en What are the molecular origins of surface/interfacial tension/en ergy ergy . . (surface tension, interaction energy parameter W)? • What is the relationship between surface tension, work of cohesi What is the relationship between surface tension, work of cohesi on/ adhesion on/ adhesion and spreading of liquids? What is spreading coefficient ( and spreading of liquids? What is spreading coefficient ( Young’s equation) ? • What is the relationship between surface curvature and pressure What is the relationship between surface curvature and pressure difference difference across the interface across the interface (Young-Laplace equation, capillary rise) ? • What interfacial phenomena describe What interfacial phenomena describe vapor condensation vapor condensation (Kelvin equation, homogeneous and heterogenious nucleation, capillary condensation, role of surface morphology/roughness)? • How to characterize a fluid How to characterize a fluid-fluid interface fluid interface (Surface excess, Gibbs equation)? • How to measure adsorption in fluid systems How to measure adsorption in fluid systems (Langmuir isotherm, Quartz Crystal Microbalance) ? ? 2 Chapter 3 General Properties of Systems Containing Liquids Much of the chapter is presented in terms of fluids . Fluids will comprise liquids and gases . In general, they will differ from solids in that: • They cannot support a shear strength • Viscosity, diffusivity and thermal conductivity exhibit a different temperature dependence • Fluids possess a measurable free volume- including Liquids • Equilibrium, related to mobility, is achieved on a much more rapid time scale. • Fluids can deal with thin film 3 The alternative to the previous statement is that interfacial phenomena, driven by the minimization of free energy, involve changes in shape and composition. i i i dG dA dn σ σ σ γ μ = + ∑ The free energy of an interfacial system can be described in terms of its area and composition. 4 3.1 Surface Tension is the Key Concept in Characterizing Fluid Interfaces Surface tension ( γ ) can be conceptualized in terms of either: • A two-dimensional pressure • Increase in Gibbs energy per unit increase in surface area 2 F l γ = , T P G A γ ∂ = ∂ 2 dw Fdx ldx dA γ γ = = = 5 3.1.1 Molecular Origins of Surface and Interfacial Tension can be Understood in terms of Differences in Interaction between Molecules in the Bulk and those at the Interface.those at the Interface....
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This note was uploaded on 11/16/2011 for the course EMA 4121 taught by Professor Moudgil during the Spring '11 term at University of Florida.

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EMA 4121 Interfacial Engineeering Chapter 3 spring 2011 - 1...

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