Surface Tension of Liquids. A short presentation

Transcription

1 Surface Tension of Liquids A short presentation

2 Liquids Static Methods Du Noüy Ring Method The traditional method used to measure surface or interfacial tension. Wetting properties of the surface or interface have little influence on this measuring technique. Maximum pull exerted on the ring by the surface is measured. Wilhelmy Plate Method A universal method especially suited to check surface tension over long time intervals. A vertical plate of known perimeter is attached to a balance, and the force due to wetting is measured. Spinning Drop Method This technique is ideal for measuring low interfacial tensions. The diameter of a drop within a heavy phase is measured, while both are rotated. Pendant Drop Method Surface and interfacial tension can be measured by this technique, even at elevated temperatures and pressures. Geometry of a drop is analysed optically.

3 Liquids Dynamic Methods Bubble Pressure Method A measurement technique for determining surface tension at short surface ages. Maximum pressure of each bubble is measured. Drop Volume Method A method for determining interfacial tension as a function of interface age. Liquid of one density is pumped into a second liquid of a different density and time between drops produced is measured.

4 Solids Sessile Drop Method This optical contact angle method is used to estimate wetting properties of a localised region on a solid surface. Angle between the baseline of the drop and the tangent at the drop boundary is measured. Dynamic Wilhelmy Method A method for calculating average advancing and receding contact angles on solids of uniform geometry. Wetting force on the solid is measured as the solid is immersed in or withdrawn from a liquid of known surface tension. Single Fibre Wilhelmy Method Dynamic Wilhelmy method applied to single fibres to measure advancing and receding contact angles. Powder Contact Angle Method Enables measurement of average contact angle and sorption speed for powders and other porous materials. Change of weight as a function of time is measured.

5 Surface Tension of Liquids σ = σ P + σ D σ P = Polar Parts of Surface Tension Dipole-Dipole-Interaction Hydrogen bonding Lewis Acid-Base-Interaction σ D = Disperse Parts of Surface Tension Van der Waals-Interaction

6 Short Excerpt of Liquid Database

7 Liquid Name Surface Tension Disperse Part Polar Part N,N-dimethyl-Formamid n-decane n-heptane n-hexane n-octane n-tetradecane nitro-ethane (Schultz) nitro-methane (Schultz) Phthalic-acid-diethylester 22 sym-tetrabromo-ethane (Ström) sym-tetrachloro-ethane (Ström) tetrachloro-methane (Schultz) Toluene (Schultz) Tricresyl-phosphate (Fowkes) Water Water (Busscher) Water (Rabel) 22 Water (Ström) 20 α-bromo-naphthalene (Busscher) α-brom-naphthalene (Ström)

8 Forces Between Molecules in the Bulk and at the Interface Phase 1 Phase 2 Interface

9 Methods to Determine Surface Tension and Interfacial Tension of Liquids

10 Du Noüy Ring Method

11 F = Force Air Ring made of Pt-lr L = Wetted Length θ = contact angle Liquid

12 Forces During Ring Measurement F 1 F max F 3 θ = 0 at F = Fmax

13 10 Force During Ring Measurement F 3 F max Force (mn) 5 F 1 Lamella Breaks Water at 20 C Distance, d, of ring above surface (mm)

14 Ring σι = F max F V L cosθ σl = Liquid Surface Tension L = Wetted Length cos θ =1 FV = Force Due to Liquid Weight Fmax = Total Force

15 Wilhelmy Plate Method Plate made of roughened Pt Air F = Force, mn L = Wetted Length, mm Liquid θ =0 o Liquid Plate σ = F L cos θ

16 Wilhelmy Plate Method σ = L FW cosθ FW = Wetting Force L = Wetted Length of the Platinum Plate cos θ = 1

17 Ring σ = F max F V L cosθ Plate σ = L F cosθ

18 Time Dependence of Surface Tension 35 mn/m stirring 72 mn/m 55 mn/m 35 mn/m

19 Surface-Tension [mn/m] Gold Plating Solution Containing Fluorosurfactants Plate Method Surface Tension versus Time Data Low Surfactant Concentration High Surfactant Concentration Time [sec]

20 Micelle Formation

21 75 Determination of Critical Micelle Concentration 70 Surfactant Molecule Hydrophobic Portion Hydrophilic Portion Surfactant in Water at 20 C Surface Tension(mN/m) Critical Micelle Concentration (CMC) Air Surfactant at Surface Surface Saturated Micelles Formed 35 Surface 30 Water ,000 Log Concentration (mg/l)

22 A Spherical Micelle

23 Surfactant Bilayer

24 50 Critical Micelle Concentration Determination Surface Tension (mn/m) CMC = 33 mg/l (CHCH) 2 2 Sample: Nonylphenol Ethoxylate CH3 (CH) 2 8 O Solvent: Water Temperature: 24.2 ± 0.4 C Method: Plate Analysis Time: 92 minutes 9.5 OH Concentration (mg/l)

25 60 Surface Tension of Aqueous Sodium Dodecyl Sulfate 55 Surface Tension (mn/m) % Pure Purified by passage through HPLC column containing 300 m 2 /g octadecylsilanized silicon gel 35 Sodium Dodecyl Sulfate in water at 25 C Log Concentration (mm)

26 Surface Tension [mn/m] Critical Micelle Concentration Data CH 3 (CH 2 ) 5 CH 2 CH CH 2 (CH 2 ) 5 CH 3 O CH 2 CH 2X OH C 15 E 7 C 15 E 9 C 15 E e3 5e3 1e4 Concentration [mg/l]

27 Polymer / Surfactant Interaction 1 SURFACE TENSION CAC SURFACTANT CONCENTRATION 5 6 CMC

28 Synergistic Effects of Surfactant Mixtures

29 Aqueous CMC Data for SDS / DTAB Solutions 10 5 CMC ( micromolar of total surfactant ) MOLAR RATIO (SDS/Total Surfactant)

30 Spinning Drop Method Heavy Phase, ρ H r ω Light Phase, ρ L Capillary Wall σ i = r 3 ω 2 (ρ H 4 ρ ) L

31 Spinning Drop Tensiometer Diagram Ocular Window Inlet for Heavy Phase Septum Heavy Phase Illumination Droplet of Light Phase

32 Spinning Drop σ i σ i =kr 3 ω 2 (ρ H - ρ L ) = Interfacial Tension k = Constant r = Drop Radius ω = Angular Velocity ρh = Density Heavy Drop ρl = Density Light Phase

33 Pendant Drop Analysis

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35 SUMMARY 4 methods to measure static SFT and IFT Ring Method of DU NOÜY Plate Method of WILHELMY Pendant Drop Techniques Spinning Drop Techniques It is important to split the SFT of a liquid into two or more components The advantages of plate vs. ring method: True static method High stability of plate Fast No correction necessary SFT and IFT-techniques are important for surfactant characterization CMC, Surface excess and synergistic effect are important parameters which can be determined fully automatic

36 Dynamic Methods

37 Dynamic Surface Tension Maximum Bubble Pressure Pressure coming in air or nitrogen 4-6 Bar Tank ( 0 Bar at beginning of measurement) Pressure Sensor PTFE Probe ( Diam. 1.5mm ) Liquid

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39 Diffusion of Surfactants to Bubble Surface P c Tensid >> c CMC

40 Dynamic Behaviour of 2 Surfactants

41 Maximum Bubble Pressure Method σ = P - P r max 0

42 Dynamic Surface Tension [mn/m] Dynamic Data for Nonylphenol Ethoxylate (9.5) in Water mg/l 100 mg/l 30 mg/l 10 mg/l mg/l mg/l ,000 50,000 Surface Age [ms]

43 Drop Volume Technique

44 Light Phase to Heavy Phase Setup Glass Sample Tube Liquid Level Drop LED Photodiode Capillary Capillary Holder Tubing to syringe pump

45 Heavy Phase to Light Phase Setup Tubing to syringe pump Bleed Capillary Holder Capillary LED Photodiode Drop Heavy Phase Glass Sample Tube

46 DROP VOLUME σ i = V drop ρ π d ρ ( H - L) g σ i = Interfacial Tension Vdrop = Drop Volume g = Acceleration Constant ρh = Density Light Phase ρl = Density Light Phase d = Drop Diameter

47 Drop Volume Method Heavy phase, ρ H Balance of Forces at the Tip V (ρ H - ρ L )g = Separation Force Light phase, ρ L d σ i π d = Adherence Force σ i = Vdrop (ρ - ρ)g H L πd

48 Drop Volume Method Tip at Drop Separation Orifice tip thin d 1 = d 2

49 Drop Volume Method Sequence of Drop Detachement Orifice tip too thick d 1 d 2 d 2 d 1 Time

50 Dynamic Interfacial Tension (mn/m) Slow Surfactant Dynamic Interfacial Tension Data for Alcohol Ethoxylate Solutions CMC = 100 mg/l Flow Rates 1 ml/hr 0.75 ml/hr 0.50 ml/hr 0.25 ml/hr 0.10 ml/hr Dense phase: Water withalcohol ethoxylate 3 (density = g/cm) CH CH - O - CH CH - OH Light phase: Canola Oil 3 (density = g/cm) Temperature: 23 ±1 C Method: Drop Volume Concentration (mg/l)

51 SUMMARY Characterization of surfactant dynamics is an important tool for process-near optimization The maximum bubble pressure method is a fast and easy to use technique to characterize fast diffusion of surfactants at the liquid / gas interface The drop volume technique is a method to characterize diffusions of surfactants at liquid / liquid - interface A special capillary tip design increases reproducibility and minimises experimental error