Efficient control of the bulk and surface rheological properties by using C8-C18 fatty acids as co-surfactants

Transcription

1 Efficient control of the bulk and surface rheological properties by using C8-C18 fatty acids as co-surfactants Zlatina Mitrinova, 1* Zhulieta Popova, 1 Slavka Tcholakova, 1 Nikolai Denkov, 1 Bivash R. Dasgupta 2 and K.P. Ananthapadmanabhan 2 1 Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University, Bulgaria 2 UNILEVER R&D, Trumbull, USA

2 Content 1.Introduction. 2.Aim of the study 3.Materials and methods. 4.Experimental results. 5.Conclusions.

3 Introduction

4 Surfactant adsorption and surface modulus A 0, Γ 0, σ 0 A 0 +δa 0 Γ < Γ 0 σ > σ 0 A 0 Γ > Γ 0 σ < σ 0 A 0 -δa 0 Γ > Γ 0 σ < σ 0 ( ) = 0 +δ sin ( ω ) At A A t Surface modulus G * δσ = δ ln A ( t) 0 sin( t) σ =σ +δσ ϕ+ω

5 Oscillating drop Surface properties 10 3 Golemanov et al., Langmuir 24, 2008 Golemanov et al., Langmuir 24, 2008 SLES+CAPB+MAc G LS, mn/m SLES+CAPB+LAc SLES+CAPB 2 2 ( ) 12 G = G + G D ST LS δa/a 0, % Significant effect of FAc on SLES+CAPB surface rheological properties Surface condensed layer formation

6 Foam rheology V Ca µγ& R = σ % τ = V τv σ R n τγ (&) = τ + k & γ τ 0 yield stress k consistency n power law index n < 1 (concentrated foams) 0 Dimensionless viscous stress 10 0 SLES+Betaine +LAc Soap MAc τ% +PAc V Ca n n=0.2 n= Capillary Canumber, Ca Value of n <=> Viscous friction mechanism SLES+Betaine 1 mpa.s, 290 µm +Akypo 4 mpa.s, 150 µm +LADA +NaCIT 4 mpa.s, 200 µm 10 mpa.s,110 µm Denkov et al., 2008; Tcholakova et al., 2008; Denkov et al., 2009.

7 Mechanism of energy dissipation in sheared foam A 0 Inside film friction A 0 + δa A 0 Surface dissipation τ% Ca VF 0.5 % τ G Ca VS LS 0.2 Denkov et al., 2008; Tcholakova et al., 2008

8 Bubble break-up during inside foam friction Golemanov et al.,, 2008 BS+LAc, R µm R µm τ 1 ~ n R Shear stress, Pa BS+LAc BS 1 γ=100 & s Time, s G 100 mn/m G 3 mn/m BS, R µm Much smaller bubbles are formed in presence of long-chain FAc as co-surfactant

9 Aim of the study To clarify the effect of fatty acid on foam and bulk rheological properties Studied factors: Ø Fatty acid chain length Ø Fatty acid concentration Ø ph

10 Materials Sodium laureth sulfate-sles-1eo Fatty acids (FAc): C8Ac - C18Ac Cocoamidopropyl betaine-capb Basic solution (BS): (300 mm = 10 wt %) SLES + CAPB Concentrated solution: (300 mm = 10 wt %) SLES + CAPB = 2:1 + FAc Diluted solution: (15 mm = 0.5 wt %) SLES + CAPB = 2:1 + FAc

11 Methods for systems characterization Oscillating drop Tensiometer 2 2 ( ) 12 G = G + G D ST LS Rheometer P. Garrett et al., 1993

12 Effect of fatty acids on solution rheology η 0, Pa.s Apparent viscosity, Pa.s wt % BS + 1 wt % C8Ac 300 mm BS + C8Ac wt % C8Ac wt % C8Ac+ C10Ac wt % C8Ac wt % C8Ac + C12Ac 10 wt % BS wt % C8Ac 10 wt % BS only + C14Ac FAc Shear concentration, rate, s -1 mm C8Ac-C10Ac C12Ac-C18Ac Entangled wormlike micelles Elongated micelles Formation of wormlike micelles in presence of C8Ac and C10Ac, while longer FAc lead to formation of cylindrical micelles. (Mitrinova et al. Langmuir, 2013)

13 Oscillatory measurements % deformation 10 wt % BS + 1 wt % C8Ac 10 2 G', G", Pa wt % BS + 1 wt % C10Ac t R = 1 ω R /t R 1/t R Full: G' Empty: G" Frequency of oscillation, s -1 t R relaxation time of network restructuring: 5 s for C8Ac and 0.7 s for C10Ac

14 G''/G osc wt % BS 1 wt % C8Ac Cole-Cole plot 10 wt % BS 1 wt % C10Ac Kern et al., 1992 G'/G osc reptation relaxation Combined relaxation time T = ( t. t ) R br rep T = η 1/2 0 R t rep Greptation time; e reaction model ζ stress relaxation modulus ζ = ζ = ( ) 12 br rep t / t 1.23 for C8 Ac ( ) 12 br rep t / t 10.2 for C10 Ac Systems: T R, sec t br, sec t rep, sec BS+ C 8 Ac BS+ C 10 Ac t br breaking time;

15 Effect of FAc on surface rheological properties (Mitrinova et al. Langmuir, 2013) Oscillating drop Surface modulus, mn/m mm BS 1.1 mm FAc 15 mm BS 3.5 mm FAc BS only 2 2 ( ) 12 G = G + G D ST LS C8Ac C10Ac C12Ac C14Ac C16Ac C18Ac C8Ac and C10Ac are unable to increase surface modulus of BS C12Ac-C18Ac increase surface modulus above 100 mn/m

16 Effect of FAc on foam rheology Dimensionless Viscous Stress BS+C12Ac BS+C14Ac BS+C16Ac BS+C18Ac BS only BS+C10Ac BS+C8Ac 15 mm BS Empty: + 1 mm FAc Full: mm FAc Capillary number, Ca (Mitrinova et al. Langmuir, 2013) Foams with G D > 100 mn/m exhibit much higher foam friction, compared to solutions with lower surface modulus

17 Effect of FAc chain length on mean bubble radius Mean bubble size, µ m mm BS 1.1 mm FAc 15 mm BS 3.5 mm FAc 15 mm BS only 120 No C8Ac C10Ac C12Ac C14Ac C16Ac C18Ac C8Ac and C10Ac do not change R 32 for BS system C12Ac-C18Ac lead to much smaller bubbles due to the high G D (Mitrinova et al. Langmuir, 2013)

18 Equilibrium surface tension of diluted solutions Sufrace tension, mn/m C18Ac + C16Ac 15 mm BS only + C8Ac + C10Ac + C12Ac + C14Ac FAc concentration, mm Significant decrease of equilibrium surface tension for all FAc Most effective - C16 and C14Ac, followed by C12Ac (Mitrinova et al. Langmuir, 2013)

19 Effect of ph on surface modulus and foam friction (Mitrinova et al. Colloid and surfaces A, 2013) Surface modulus, mn/m 10 3 υ = 0.2 Hz mm BS 0.88 mm C14Ac ph Dimensionless Viscous Stress 15 mm BS 2.2 mm C14Ac ph=8 ph= ph= ph=9 ph=10 ph=11 BS (no C14Ac) Capillary number, Ca At ph between 3 and 8 surface modulus are high (above 100 mn/m) and there is significant foam friction At ph = 11 G D reaches values for BS and foam friction decrease

20 Effect of ph on BS+C14Ac surafce tension (Mitrinova et al. Colloid and surfaces A, 2013) 34 Surface tension, mn/m mm BS 15 mm BS 0.88 mm C14Ac 15 mm BS+ 2.2 mm C14Ac ph At natural ph σ EQ 6 молекулите is low at ph between FAc molecules 3 and 8 are protonated σ EQ At incerase high ph at significant high ph and molar reaches fraction values of FAc for BS is ionized at ph=11

21 Conclusions Ø In presence of C8Ac and C10Ac : v Apparent viscosity of concentrated solutions significantly increase due to the formation of entangled wormlike micelles; v Foam rheological properties are not affected; Ø In presence of C14Ac, C16Ac, C18Ac: v Apparent viscosity of concentrated solutions is slightly higher than those for BS system due to the presence of cylindrical micelles; v Surface modulus of diluted solution significantly increase; v Foam viscous friction is higher due to additional dissipation in adsorption layer. Ø In presence of C12Ac: v In presence of C12Ac intermediate properties are observed.

22 Thank you for your attention!