logging in or signing up 03_gibbs aSGuest123339 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 7 Category: Education License: All Rights Reserved Like it (0) Dislike it (0) Added: January 04, 2012 This Presentation is Public Favorites: 0 Presentation Description gibbs adsorptiom Comments Posting comment... Premium member Presentation Transcript Gibb’s Adsorption Isotherm: Gibb’s Adsorption IsothermSURFACE EXCESS: x 0 Δ A P Area left of x 0 : represents underestimated value of P i Area right of x 0 : represents overestimated value of P i SURFACE EXCESS A Property, P, of system vary across the interface (of thickness S) from that of phase ‘ A ’ and ‘B’ If P i is the value of the Property P at the ideal border of the interface, then: A B x 0 x P A P B Δ B S x A B x 0 x P P B P A Interface P iSURFACE EXCESS (Cont.): SURFACE EXCESS (Cont.) X 0 - may be selected such that two shaded areas are equal -may divide the profiles of other properties differently Property which is least convenient to handle mathematically can be eliminated by selecting its surface excess to be zero. Note - dividing surface only a Reference Level rather than a physical boundary. - Surface excess can be positive or negative.THE GIBBS ADSORBION EQUATION: THE GIBBS ADSORBION EQUATION Amount of surfactant adsorbed per unit area can be calculated from surface or interfacial tension measurements Where, d = change in surface tension i = surface excess concentration of ‘i’ d m i = change in chemical potential of ‘i’ At equilibrium where a i = activity of ‘i’ in bulk phase = mole fraction x activity coefficientTHE GIBBS ADSORBION EQUATION: THE GIBBS ADSORBION EQUATION Therefore For dilute solutions containing one non-dissociating surfactant Where C = molar concentration of surfactant in bulk At constant temperature Surface excess given by slope of plot of g versus log C Knowing , area per molecule at the interface can be calculated.AREA PER MOLECULE AT THE INTERFACE: Important in assessing Degree of packing Orientation of adsorbed molecules a = area per molecule (in Å 2 ) at interface, given by Where N = Avogadro number = Surface excess in moles/m 2 AREA PER MOLECULE AT THE INTERFACE 1 x 10 20 N a =APPLICATION OF GIBBS ADSORPTION: APPLICATION OF GIBBS ADSORPTION Surface tension of aqueous solution of the nonionic surfactant CH 3 (CH 2 ) 9 (OCH 2 CH 2 ) 5 OH at 25 0 C is as given: C (x10 -1 ) mol/m 2 0.1 0.3 1.0 2.0 5.0 8.0 10.0 20.0 30.0 g( mN/m) 63.9 56.2 47.2 41.6 34.0 30.3 29.8 29.6 29.5APPLICATION OF GIBBS ADSORPTION: CMC Surface excess is given by: Average area occupied by each molecule, APPLICATION OF GIBBS ADSORPTION You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
03_gibbs aSGuest123339 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 7 Category: Education License: All Rights Reserved Like it (0) Dislike it (0) Added: January 04, 2012 This Presentation is Public Favorites: 0 Presentation Description gibbs adsorptiom Comments Posting comment... Premium member Presentation Transcript Gibb’s Adsorption Isotherm: Gibb’s Adsorption IsothermSURFACE EXCESS: x 0 Δ A P Area left of x 0 : represents underestimated value of P i Area right of x 0 : represents overestimated value of P i SURFACE EXCESS A Property, P, of system vary across the interface (of thickness S) from that of phase ‘ A ’ and ‘B’ If P i is the value of the Property P at the ideal border of the interface, then: A B x 0 x P A P B Δ B S x A B x 0 x P P B P A Interface P iSURFACE EXCESS (Cont.): SURFACE EXCESS (Cont.) X 0 - may be selected such that two shaded areas are equal -may divide the profiles of other properties differently Property which is least convenient to handle mathematically can be eliminated by selecting its surface excess to be zero. Note - dividing surface only a Reference Level rather than a physical boundary. - Surface excess can be positive or negative.THE GIBBS ADSORBION EQUATION: THE GIBBS ADSORBION EQUATION Amount of surfactant adsorbed per unit area can be calculated from surface or interfacial tension measurements Where, d = change in surface tension i = surface excess concentration of ‘i’ d m i = change in chemical potential of ‘i’ At equilibrium where a i = activity of ‘i’ in bulk phase = mole fraction x activity coefficientTHE GIBBS ADSORBION EQUATION: THE GIBBS ADSORBION EQUATION Therefore For dilute solutions containing one non-dissociating surfactant Where C = molar concentration of surfactant in bulk At constant temperature Surface excess given by slope of plot of g versus log C Knowing , area per molecule at the interface can be calculated.AREA PER MOLECULE AT THE INTERFACE: Important in assessing Degree of packing Orientation of adsorbed molecules a = area per molecule (in Å 2 ) at interface, given by Where N = Avogadro number = Surface excess in moles/m 2 AREA PER MOLECULE AT THE INTERFACE 1 x 10 20 N a =APPLICATION OF GIBBS ADSORPTION: APPLICATION OF GIBBS ADSORPTION Surface tension of aqueous solution of the nonionic surfactant CH 3 (CH 2 ) 9 (OCH 2 CH 2 ) 5 OH at 25 0 C is as given: C (x10 -1 ) mol/m 2 0.1 0.3 1.0 2.0 5.0 8.0 10.0 20.0 30.0 g( mN/m) 63.9 56.2 47.2 41.6 34.0 30.3 29.8 29.6 29.5APPLICATION OF GIBBS ADSORPTION: CMC Surface excess is given by: Average area occupied by each molecule, APPLICATION OF GIBBS ADSORPTION