All you need is Neutrons season 2, episode 6 Part 1. PhD Student: Andrea TUMMINO Supervisors: Richard CAMPBELL (ILL); Imre VARGA (ELTE)

Transcription

1 ELTE University Chemistry Department Budapest Institut Laue-Langevin LSS group Grenoble All you need is Neutrons season 2, episode 6 Part 1 PhD Student: Andrea TUMMINO Supervisors: Richard CAMPBELL (ILL); Imre VARGA (ELTE)

2 Outline Polyelectrolytes and surfactants: a bit of chemistry; Some applications: from shampoos to biomedical; Bulk interactions and non-equilibrium effects: tuning surface properties; Aim of the project; Protein and polyelectrolyte/surfactant spread films at the air water interface: In the PSCM labs (surface tensiometry and ellipsometry); On FIGARO: compositional analysis by Neutron Reflectometry. Conclusions and future works

3 POLYELECTROLYTES AND SURFACTANTS Polyelectrolytes: a polymer (macromolecule) containing ionizable functional groups (amine, sulfonic acids, carboxylates ) in aqueous solution. PAA NaPSS NaDS DTAB Surfactants: Class of organic compounds composed of a hydrophilic head group and hydrophobic carbon chain. Their main feature is the ability to adsorb at the air/water interface, lowering the surface tension of the solution.

4 POLYELECTROLYTE/SURFACTANT MIXTURES IN EVERYDAY LIFE Polyelectrolyte-surfactant mixtures are widely used in everyday products 1 (detergents, shampoos etc.) Some biological polyelectrolytes, like proteins and DNA, are vital for life and can be exploited in applications such as drug & gene delivery 2. More work is required to underline the key factors of their interaction at interfaces and to understand the relation between surface and bulk properties.

5 POLYELECTROLYTE/SURFACTANT AGGREGATES: GOOD CANDIDATES FOR DRUG DELIVERY Drugs interaction with surfactant micelles and layers have been quite investigated 3,4. Oppositely charged polyelectrolytes multilayer have been used to improve stability of drug delivery systems 5,6 Oppositely charged polyelectrolyte/surfactant (P/S) aggregates could be used to enhance drug delivery in a trapped film at the air/water interace.

6 POLYELECTROLYTE/SURFACTANT MIXTURES: BULK INTERACTIONS AND NON EQUILIBRIUM EFFECTS 1.Mixing polyelectrolytes and surfactants close to the charge neutralization point results in the formation of aggregates; 2.Precipitation with sedimentation or creaming depletes the surface from active material; 3.Non equilibrium effects are observed: the sample history (the mixing order, redispersion) affects the properties of these systems, both at surfaces and in the bulk 7 ; Fixed polymer concentration: 100 ppm x-axis: surfactant concentration

7 POLYELECTROLYTE/SURFACTANT MIXTURES: BULK INTERACTIONS AND NON EQUILIBRIUM EFFECTS 1.Mixing polyelectrolytes and surfactants close to the charge neutralization point results in the formation of aggregates; O.D Fresh 1 day 1 week 1 month A 2.Precipitation with sedimentation or creaming depletes the surface from active material; DTAB B 3.Non equilibrium effects are observed: the sample history (the mixing order, redispersion) affects the properties of these systems, both at surfaces and in the bulk 7 ; [mn/m] Fresh 1 month 1 10 c SURF [mm] Fixed polymer concentration: 100 ppm x-axis: surfactant concentration

8 POLYELECTROLYTE/SURFACTANT MIXTURES: BULK INTERACTIONS AND NON EQUILIBRIUM EFFECTS 1.Mixing polyelectrolytes and surfactants close to the charge neutralization point results in the formation of aggregates; 2.Precipitation with sedimentation or creaming depletes the surface from active material; 3.Non equilibrium effects are observed: the sample history (the mixing order, redispersion) affects the properties of these systems, both at surfaces and in the bulk 7 ; Fixed polymer concentration: 100 ppm x-axis: surfactant concentration

9 AIM OF THE PROJECT 1) To investigate the penetration of polyelectrolyte-surfactant aggregates at the airwater interface and their spreading; 2) To understand the surface tension behaviour in relation to the changes taking place in the bulk; 3) To see if the surface behaviour can be explained in term of non equilibrium effects; 4) To investigate a surprising range of aggregate structures created; 5) Encapsulation and delivery of functional molecules (such as drugs) at the air/water interface TECHNIQUES Using: Surface Tensiometry; Ellipsometry; Brewster Angle Microscopy (BAM); Electrophoretic Mobility; UV-Vis Spectroscopy; Gravimetric Analysis, Neutron Reflectometry.

10 SURFACE TENSIOMETRY (1) The surface tension (γ) of a system is equal to its surface free energy 8 ; All the phenomena taking place spontaneously on a surface or at an interface (wetting, spreading, adhesion ) are driven by the principle of minimization of energy. Under thermodynamic control, several models can be used to predict the surface tension in relation to surface excess, Г. Those models fail when dealing with out of equilibrium systems.

11 SURFACE TENSIOMETRY (2): Surface pressure-area (π-a) isotherms Surface tension isotherms are useful tools to study adsorption at liquid interfaces. A typical measure system for π-a experiments is a very sensitive scale (tensiometer), a trough and two moving barriers (usually in PTFE). The isotherm is recorded during compression/expansion cycles: compressibility of the adsorbed film, molecular areas, collapse pressure, viscoelastic behaviour (and more) can be investigated through π-a isotherms.

12 Surface pressure (mn/m) Surface pressure (mn/m) DEFATTED HUMAN SERUM ALBUMIN (DFHSA) π-a ISOTHERMS expansion Barrier position (mm) Barrier position (mm) Series1 Series2 Series3 Series4 Series5 compression Series1 Series2 Series3 Series4 Series5 Premixed samples 20 drops DFHSA 0,1 mg/ml in 100 ml pure water; Surface cleaned; 5 compression/expansion cycles: barriers rate set at 8,2 mm/min. Slow adsorption, diffusion Spread samples 10 drops DFHSA 0,1 mg/ml spread on 50 ml pure water (the same concentration!); 5 compression/expansion cycles: barriers rate set at 8,2 mm/min. Film trapped and hysteresis, no collapse!

13 ELLIPSOMETRY In ellipsometry, a polarized monochromatic light beam is reflected from a surface and the change in the polarization of the light is detected. The relative attenuation, Ψ, and the relative phase shift, Δ, depend on the optical properties (dielectric function, ε) of the interface and on the angle of incidence θ. Ψ and Δ are related to the ellipticity coefficient, ρ:

14 Surface pressure (mn/m) COMBINED ELLIPSOMETRY AND π-a ISOTHERMS OF DFHSA FILM Series1 Series2 Series3 Series4 Series Barrier position (mm) The surface excess is periodic. Maxima at full compression and minima when the trough is fully expanded do not vary significantly: No depletion of material, film annealed to a more stable and durable morphology

15 NEUTRON REFLECTOMETRY Specular neutron reflectometry (NR) is a powerful technique that allows us to obtain structural and compositional information of thin films and interfaces (thickness, density, roughness). A reflectivity profile is usually plotted as intensity of the reflected beam/intensity of the direct beam vs. the momentum transfer normal to the interface, Q z D2O 50 nm (SLD=3.5)

16 NEUTRON REFLECTOMETRY ON FIGARO NR in general allows us to obtain different information in the same measurement: 1. Thickness of the adsorbed layer and the surface roughness (specular); 2. Composition of the adsorbed layer (specular); 3. Detailed information about surface structures (specular and off-specular); FIGARO s advantages 9,10,11 : a. Low natural incident angle and maximized flux with versatility from choppers; b. Broad range of Q (relevant for kinetics), scattering investigated through a Time of Flight 2D detector; c. Optimized for liquid interfaces.

17 COMPOSITIONAL ANALISYS BY NEUTRON REFLECTOMETRY ON FIGARO (1) measure in water contrast matched to air (SLD=0) in 2 isotopic contrasts: I. with polymer & deuterated surfactant II. with polymer & surfactant that is contrast matched to the air record data only at low Q to get 2 effective scattering excesses (SLD x d); solve simultaneous equations to calculate directly the surface excesses: (SLD x d) 1 = Na x (Γ surf x SL surf + Γ poly x SL poly ) (SLD x d) 2 = Na x Γ poly x SL poly For a single component DTAB NaPSS

18 NaPSS COMPOSITIONAL ANALISYS BY NEUTRON REFLECTOMETRY ON FIGARO (2) DTAB Only a few hours of beam time on FIGARO were used to study 2 sample histories at 2 ionic strengths in 2 isotopic contrasts. Double surface excess from spreading than adsorption (trapped films direct proof); Interfacial composition is equivalent in both ionic strengths (driven by electrostatics) System Γ surf Γ poly Adsorb/no salt Adsorb/salt Spread/no salt Spread/salt dark green overlapping dark blue: d-dtab, spread (salt and water) brown overlapping dark orange: d-dtab, adsorbed (salt and water) light blue / light green: cm-dtab, spread (salt and water) red overlapping yellow: cm-dtab, adsorbed (salt and water)

19 Surface pressure (mn/m) Surface pressure (mn/m) Surface pressure (mn/m) Surface pressure (mn/m) NaPSS/DTAB TRAPPED FILM: π-a ISOTHERMS Water 100 ppm PSS + 6 mm DTAB: 500 μl spread on 125 ml subphase NaCl 100 mm Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series Barrier position (mm) expansion compression expansion Barrier position (mm) compression Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series Series1 30 Series Series2 Series3 Series4 Series Series2 Series3 Series4 Series Barrier position (mm) Series6 10 Series7 5 Series Barrier position (mm) Series6 Series7 Series8

20 NaPSS/DTAB MIXTURES π-a ISOTHERMS 100 ppm PSS + 6 mm DTAB: 500 μl spread on 125 ml pure water Large hysteresis after the first cycle; Collapse pressure of 28 mn/m; Behaviour approaching a limiting cycle. Questions 1) Is the large hysteresis related to material loss? 2) Is the film durable? 3) Does the composition of the adsorbed layer change during the consecutive cycles? 4) Can we use NR to answer these questions?

21 REAL TIME, IN SITU COMPOSITIONAL ANALISYS (1) Significant loss of material during the first cycle; After, a limit cycle is reached highlighting the trapped nature of the film; Surfactant/polymer ratio: 1/1 at higher compression, more surfactant when fully expanded; With the new Low Q approach, two minutes scans are enough to obtain the composition (only on FIGARO).

22 REAL TIME, IN SITU COMPOSITIONAL ANALISYS (1) Significant loss of material during the first cycle; After, a limit cycle is reached highlighting the trapped nature of the film; Surfactant/polymer ratio: 1/1 at higher compression, more surfactant when fully expanded; With the new Low Q approach, two minutes scans are enough to obtain the composition (only on FIGARO).

23 CONCLUSIONS Techniques 1. Ellipsometry is an easy, cheap and fast way to obtain the surface excess of single component system; 2. Neutron reflectometry is needed to resolve the interfacial properties of more complex mixtures; 3. Neutrons are the most powerful and most direct probe to quantify the amount of organic material at the air/water interface. HSA I. The surface tension behaviour of HSA spread film can be related to morphological changes of the interface; II. The annealing of the layer produces a more stable and durable film. PSS/DTAB mixtures A. It has been shown that it is possible to tune surface properties by exploiting non equilibrium effects; B. For PSS/DTAB spread films, the ionic strength does not affect the chemical composition of the layer; C. The presence of NaCl does not compromise the film stability under the conditions studied which was a surprise; D. For the first time, it has been possible on FIGARO to follow quantitatively the evolution of a mixed system at the air/water interface in a Langmuir experiment.

24 FOR THE FUTURE a) Explore the behaviour of other polyelectrolyte/surfactant aggregates; b) Investigate the effect of temperature on trapped film and aggregates spreading; c) Investigate further the role of ionic strength on film stability; d) To study the behavior of polyelectrolyte/surfactant aggregates under flowing condition (overflowing cylinder); e) Encapsulation of molecules relevant for biomedical application; f) To exploit aggregates spreading to trigger the delivery of functional molecules, such as drugs and genes, to liquid interfaces. References: [1] Kwak, J. C. T., Ed. Polymer-surfactant systems, Marcel Dekker: New York, 1998, Vol. 77; [2] Donkuru, M.; Badea, I.; Wettig, S.; Verrall, R.; Elsabahy, M.; Foldvari, M. Nanomedicine 2010, 5, 1103; [3] P. Talele, S. Choudhary, N. Kishore, The Journal of Chemical Thermodynamics 2016, 92,182; [4] MF. Nazar et al, Fluid Phase Equilibra 2015, 406, 47; [5] S. Jeon, C. Young Yoo, S. Nam Park, Colloids and Surfaces B: Biointerfaces 2015, 129, 7; [6] M. Adamczack, A. Kupiec, E. Jarek K. Szczepanowicz, P. Warszynski, Colloids and Surfaces A: Physicochemical and Engineering Aspects 2014, 462, 147; [7] Mészáros, R.; Thompson, L.; Bos, M.; Varga, I.; Gilányi, T. Langmuir 2003, 19, 609; [8] S. W. Ip, J. M. Toguri Journal, Of Material Science, 29 (1994) 688; [9] Á. Ábraham, R. A. Campbell & I. Varga, Langmuir, 2013, 29, 11554;.[10] Á. Ábrahám, A. Kardos, A. Mezei, R. A. Campbell & I. Varga,, Langmuir, 2014, 30, 4970; [11] H. Fauser, R. von Klitzing & R. A. Campbell, J. Phys. Chem. B, 2015, 119, 348.

25 THANKS FOR YOUR ATTENTION!