Simeon D. Stoyanov Unilever R&D Vlaardingen, The Netherlands

Transcription

1 Simeon D. Stoyanov Unilever R&D Vlaardingen, The Netherlands Laboratory of Physical Chemistry and Colloid Science, Wageningen University, NL Department of Mechanical Engineering, University College London, UK

2 Introduction / Why Saponis are relevant Natural surfactants found in more than 500 plant species (can reach»10-15 % of the dry mass) -> natural /sustainable sourcing feasible Molecules consist of hydrophobic part (triterpenoid or steroid aglycone) and hydrophilic oligosaccharide chains (1 3). Aglycone Quillaja Saponin: Triterpenoid aglycone. 2 sugar chains (2 5 residues). One of oldest detergents (x00 years of usage in America/Asia) In1890 saponins by Lord Rayleigh to clarify the origin of interfacial viscosity and address the dispute between Maragoni & Plateau

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4 Studied saponins Horse Chestnut (Aesculus hippocastanum) Sapindus Mukurossi Camellia Oleifera Abel Panax Ginseng Quillaja Saponaria Molina Acacia concinna Sapindus Trifoliatus Tribulus Terrestris Yucca Schidigera Trigonella foenum graecum Licorice

5 Mono/Bidesmosidics Horse Chestnut (HC/ES) (Aesculus hippocastanum) Sapindus Mukurossi (BSC (Berry Saponin) Camellia Oleifera Abel (TS) (Tea seed saponin) Panax Ginseng (GS) Triterpenoid aglycone Quillaja Saponaria Molina (QD) Oligosaccharide chains Monodesmosidic saponins Bidesmosidic saponins

6 Purity of Studied saponins How we can make science out of the mess? Type of aglycone Trade Name Abbreviation Saponins in extract % Horse chestnut extract HC 20 Escin ES ³ 95 Tea Saponin TS 96.2 Berry Saponin BSC 53 Concentrate Triterpenoid Sapindin SAP 50 Quillaja Dry 100 QD 26 Ginsenosides GS 80 Ayurvedic Saponin Concentrate ASC 30 Tribulus terrestris TT 45 extract Steroid Foamation Dry 50 FD 9 Fenusterols Ò FEN 50

7 Surface tension, mn/m Surface tension isotherms b = 5.4 b = 0 Gibbs Escin concentration, mm Escin ph = natural s = s G k B TG + bg G - G CMC Volmer adsorption isotherm se s 0 kt KC Van der Waals adsorption isotherm G æ G 2bG ö KC = exp ç - G - G è G - G kt ø Gibbs adsorption isotherm ds =-G dµ =-G dµ =-ktgdln( C) s b ds e = -kt G d lnc 2 d s kt dg =- 2 dln( c) c dc G = - G G -G G æ G ö = exp G ç -G èg -Gø ( r ) U æ - ö kbt b = - πk BT ç ò 1 - e rdr» -πòu ç r0 è ø r0 ( r)rdr

8 Surface tension, mn/m Area per molecule at CMC = 0.54 nm 2 Tea Saponin Mw = 1000 g/mol Volmer isotherm K = 1088 m 3 /mol G inf = 3.9 µmol/m 2 G CMC = 3.1 µmol/m Saponin concentration, mm

9 Surface tension isotherms for ASC, BSC and Sapindin Surface tension, mn/m ASC Surface tension, mn/m Berry saponin Saponin concentration, wt % Saponin concentration, wt % Surface tension, mn/m 80 Saponidin Saponin concentration, wt % Positive Curvature!!!! For these saponins we cannot determine the characteristics of adsorption layer (slope of the curves contradicts Gibbs isotherm) Mixture of components and presence of aggregates?!

10 Molecular packing mono vs bi desmosides A» nm 2 A» nm 2 Is there a link between molecular packing & surface modulus Shear

11 Surface Rheology Interactions between the molecules Kinetics of adsorption / desorption tg ( ), tg& ( )

12 Surface Shear Rheology: bicone tool Lateral view Top view M, q Shear stress: ( 2 t = М / 2pR ) 1 Shear deformation: [ ] g = q( R + R)/ 2( R -R)

13 The Boussinesq number Bo surface viscous drag hs = = bulk viscous drag h. L B At Bo < 200: Surface and sub-surface flows coupling. Numerical procedure needed to calculate the surface viscosity. Surfactant layer regarded as a 2D body at Bo > 200.

14 Oscillatory Amplitude sweep (t A = 30 min) Elastic modulus, mn/m 10 3 GS ESC TS BSC QD Viscous modulus, mn/m 10 3 GS ESC TS BSC QD Strain amplitude, % Strain amplitude, % The bidesmosidic saponins have lower elastic and viscous modulus.

15 Creep Relaxation Experiments (1) Deformation at constant torque (1 µn.m). (2) Strain relaxation. Visco-elastic (some of triterp/mono) Viscous (main steroidal) Group EV BSC 160x x x10 3 Group LV FD FEN Strain, % TS QD Strain, % 100x x x x10 3 ASC TT 0.05 ESC GS Time, s 20x10 3 LIC Time, s

16 Rheological model (compound Voigt) G 1 G 2 G 0 = 1/J 0 h 0 h 1 h 2 Quillaja saponin. Maxwell + Kelvin (1) + Kelvin (2). 6 parameters (3 viscous and 3 elastic). 2 relaxation times. Compliance, m/n J 0 J Time, sec 0.5 wt % QD 10 mm NaCl 0.1 g/l NaN 3 t = 0.94 mn/m t CR /h 0

17 Molecular interpretation Molecules aggregated in domains. Burger Element: [Maxwell + 1 st Kelvin element] deformation and re-arrangement of domains. 2 nd Kelvin Element re-arrangement of molecules within the domains.

18 Viscoelasticity of triterpenoid saponins Highly elastic surface layer, G`>>G``. G` increases for more than 12 hours of aging of the layer. G`` decreases or stays constant. Saponins with one sugar chain exhibit much higher elasticity. G` ~ 1000 mn/m G` ~ 100 mn/m

19 Oscillatory dilatational deformations Langmuir trough 302LL/D1 (Nima Technology Ltd, UK) Surface pressure, mn/m % deformation s s Surface area, mm 2 Deformation created by the moving barrier(s) in the LM is uniaxial, i.e., it is a superposition of well defined dilatation and shear t = t = t 1 2 = t ^ = ( K + µ ) a + ( z h )! s + s a ( K - µ ) a + ( z -h )a! α=ln(a/a0) - relative dilatation Boundary effects are neglected! s s Time, sec K dilatational elasticity µ shear elasticity z S dilatational viscosity h S shear viscosity (Petkov et al. 2000)

20 Adsorbing system: 0.5 wt % saponins + 10 mm NaCl ta Oscillatory experiments done after equilibration has been reached (>30 min) Expansion 0.5 wt % ES parallel perpendicular Parallel plate t! = s s a a ( K + µ ) + ( z + h ) a From the best fit K+µ = 204 mn/m z S +h S = 163 mn.s/m & aa For expanding Escin layer K = 154 mn/m; µ = 50 mn/m; z s = 127 mn.s/m; h s = 36 mn.s/m Perpendicular plate t! ^ = s s a a ( K - µ ) + ( z -h ) a From the best fit K-µ = 103 mn/m z S -h S = 91 mn.s/m

21 Analysis of experimental data from dilatation 14 stress-relaxation experiments Burger model Surface stress, mn/m E 1 E 2 h 1 h 2 & Time, sec 1 æ E t t ö 1 æ & g ö ç & ç & è ø è ø 1 R1 R1 t t + t = E1 g + tr 1 E2 tr2 tr2 tr 1tR2 tr2 t R1 = h 1 /E 1 t R2 = h 2 /E 2 From the best fit of deformation and relaxation stages we determine E 1, E 2, t R1 and t R2

22 Surface rheological properties, as determined by oscillating drop method Surface moduli, mn/m ASC 40 Storage modulus Loss modulus ± 2 mn/m 11 ± 1 mn/m T = 10 s Deformation, % From this experiment we determine the surface dilatational moduli, as functions of surface deformation.

23 Surface storage modulus GS T = 10 s Storage modulus, mn/m ES TS QD BSC FEN TT SAP FD ASC HC Surface deformation, %

24 Summary saponins & natural ingredients Saponins are large class of natural surfactants with unique architecture and surface properties, with multiple functionalities, which despite of old history of use and long list of functionalities are yet poorly understood (some of the) Saponins show very peculiar surface properties that can our experimental methods - > The origin of interfacial rheology (1890, Rayleigh) is linked with saponins) We can still learn from the old papers and classics The current demand for sustainability (naturalness), cost efficiency and multiple functionality from single molecule are pushing us to go beyond simple model systems and look at nature and its solutions! Working with natural compounds/extracts is difficult as often these are not single component / molecule(s) and there are natural variation(s). In this case one should look for the big (0/1 order effects) and try to combine several methods and materials from different source to build complete picture. From these studies one can not only understand the subject, but can ask & understand why nature made such molecules and structures, get inspiration & new ideas, test methods, theories and be at frontiers of his own field.

25 Contributors Lucy Bialek, Sergey Melnikov Unilever Research Netherlands Grahame Mackenzie, Vesselin Paunov University of Hull, UK Thank You!