Mesostructured Surfactant Templated Films at the Air- Solution Interface

Transcription

1 Mesostructured Surfactant Templated Films at the Air- Solution Interface Karen J Edler, James A Holdaway, Robben Jaber, Matthew J Wasbrough, Bin Yang Department of Chemistry University of Bath

2 Surfactant-Templating Silicate source 1. Templating 2. Co-precipitation Silicate source

3 Motivation Free-standing polymer membranes useful for: sensors actuators filtration nanoscale organisation of other species coatings Previous work showed: Surfactant + silica formed films with nanoscale ordering at air-solution interface mechanism suggested silica acted as polyelectrolyte during process Can polymer films form via same route?

4 Polyelectrolyte-Surfactant Solution & Surface Interactions in solution: Surfactant aggregates form on the polymer at the surface: Polymer adsorption beneath surfactant monolayer Films are generally thin

5 Polyethylenimine:CTAB Films (CH 2 -CH 2 -NH 2 ) n branched, positively charged polyelectrolyte cm 1cm Surfactant Polymer O Driscoll et al Macromol. (2005) 38(21) 8785

6 Polyelectrolyte-Surfactant Films Polyethylenimine (PEI) ~3% charged at ph 9 MWs ~750,000 (long) & ~2000 (short) [PEI monomer] = 60g/L g/L (1.393M M) CTAB: C 16 H 33 N + (CH 3 ) 3 Br - [C 16 TAB] = M above CMC, below sphere/rod transition Other cationic surfactants also form films Use: CTAB: 60 L-PEI

7 PEI:C 16 TAB Films MW ~ MW ~ µm intensity (arb. units) Neutron reflectivity h-c 16 TAB/PEI on D 2 O MW ~ 2000 MW ~ Q (Å -1 ) Edler et al, Chem Commun, (2003) 1724.

8 Grazing Incidence X-ray Diffraction In-plane film structure, spacing between micelle centres: 0.30 ~68Å 3.75g/L PEI/C 16 TAB 0.30 ~64Å 3.75g/L short PEI/C 16 TAB Q z (Å -1 ) Q z (Å -1 ) Q xy (Å -1 ) Q xy (Å -1 )

9 Intensity (arb. units) Final Structure of Film Orientation of channels within film causes some diffraction peaks to be absent in specular reflectivity Å Q (Å -1 ) 2D hexagonal silica-surfactant powder Å Å Å Å 0.5 reflectivity g/L short PEI C 16 TAB 0.2 Q (Å -1 )

10 SANS on PEI:C 16 TAB Solutions intensity (cm -1 ) L-PEI + CTAB 100% D 2 O [CTAB] 0.037M M M M M no CTAB intensity (cm -1 ) L-PEI + CTAB 100% D 2 O [PEI] 60 g/l 30 g/l 15 g/l 7.5 g/l no PEI Q (A -1 ) Q (A -1 ) Elliptical micelles elongate with increasing PEI concentration No evidence for ordered mesophase in solution O Driscoll et al Macromol. (2005) 38(21) 8785

11 Summary from SANS Fitting C 14 TAB & C 16 TAB: elliptical micelles elongate with increasing PEI concentration No evidence for ordered mesophase in solution C 12 TAB/S-PEI solutions contain micelles disk-shaped or spherical micelles Micelle Diameter / Å PEI Concentation / a.u. C 16 TAB Long PEI C 16 TAB Short PEI C 14 TAB Long PEI 1.0 O Driscoll et al Macromol. (2005) 38(21) 8785

12 Structure Summary No ordered structure in subphase In films peak spacing increases with increasing surfactant chain length Film spacings larger than width of micelles in solution by ~10-20 Å Trend towards smaller micelle widths in solution and smaller d-spacings in films with increasing PEI concentration Film mesostructure can be controlled by surfactant packing parameter

13 Factors Affecting Films Salt ph Micelle charge Reflectivity (arb. units) CTAB: 60 S-PEI no NaBr 0.01M NaBr 0.05M NaBr 0.075M NaBr 0.1M NaBr Reflectivity MW ~ 2000 CTAB: 60 S-PEI 0.1M NaOH 0.05M NaOH 0.01M NaOH no NaOH Q (Å -1 ) MW ~ m Q (Å -1 ) O Driscoll et al J. Phys. Chem. B (11); 5330

14 Phase Separation & Drying Visible phase separation seen in solutions containing dye. Humidity - Films disperse in closed containers Regrowth follows same behaviour as initial growth DDAB DDAB:15SPEI DDAB:15LPEI 5 min 30 min CTAB: 60 S-PEI Covered 2 hours 5 min 30 min reflectivity (arb. units) C 16 TAB: 15 SPEI RH 67% RH 73% RH 75% RH 21% RH 21% 100 m Q (Å -1 )

15 Steady State Film Formation Considering a 2 component system: At open liquid surface, water evaporates Interface moves downwards at steady rate, so concentration gradient develops at interface: Possibility of phase change at interface (especially if bulk solution conc. close to phase boundary) Thickness of layer dependent on %RH Åberg, Sparr, Edler, Wennerström Langmuir (2009) 25 (20), 12177

16 Phase Diagram Dilute Solutions 1,2 100 m 1,0 CAC Tensiometry CMC* Conductivity [PEI] (%) 0,8 0,6 0,4 I II III 0.01% PEI, 0.5 mmol L -1 CTAB 1% PEI : 0.2 mmol L -1 CTAB 0,2 0,0 0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40 [CTAB] /mmol L -1 Comas-Rojas et al Soft Matter (2007) 2, 747

17 Film Growth & Collapse For very dilute solutions: films form, then dissipate Films exist for time concentration Film Thickness - Ellipsometry 1mM CTAB Neutron reflectivity 1mM CTAB, 0.5wt% LPEI LPEI concentrations (A) 0.025wt%, (B) 0.05wt%, (C) 0.1wt% (D) 0.2wt% Campbell & Edler Soft Matter 2011, 7(23), 11125

18 Film Growth & Collapse 1mM CTAB, 0.5wt% LPEI thickness /nm peak area / 10-6 Å time /min 200 d-spacing / Å FWHM / Å time /mins 200

19 Cross-linked PEI-CTAB Films PEI can be cross-linked with ethylene glycol diglycidyl ether reflectivity before crosslinking after crosslinking film weight (g) x10-3 EGDGE Conc (mol dm -3 ) CTAB: 60 S-PEI 0.1M NaOH Intensity (arb. units) O Driscoll et al Langmuir, (2007) 23(8) Q (Å -1 ) Q / Å -1

20 So what can we use these films for?

21 Hydrophobes in PEI Films oil Decane, cyclohexane, cyclohexanol, benzene Nile Red

22 Encapsulation in PEI/C 16 TAB Films Including hydrophobic material in micelles improves film structure for low MW PEI films Alters film structure if hydrophobe changes micelle shape intensity (arb units) no cyclohexanol 10% cyclohexanol 20% cyclohexanol 30% cyclohexanol PEI, MW ~ Q Z / Å Q XY / Å -1 Decane: swells micelles cubic phase Q (Å -1 ) O Driscoll et al JCIS (2008)

23 Film Structures Micelle structures: CTEABr DDAB:20CTAB DDAB:2CTAB DDAB Grazing incidence X-ray diffraction shows film structures reflect solution structures

24 Encapsulation in Solution

25 Encapsulation in Films DDAB/PEI films on D 2 O Neutron reflectivity

26 Release Studies Film split into 5 pieces, each left in 20ml water Nile Red extracted into chloroform Fluorescence to quantify amount released

27 Conclusions Early work on silica-surfactant film formation mechanisms suggests analogy between silica & polyelectrolyte behaviour Solid films can be prepared from many different polymersurfactant solutions by spontaneous self-assembly Positive charge crucial for film formation Film formation is a steady state related to evaporation and solution concentration Applications in encapsulation & responsive sensor supports

28 Wish List Simultaneous techniques with NRR ellipsometry, BAM XRR Higher flux for kinetic experiments off-specular scattering Better techniques for handling rougher interfaces Non-flat interfaces Small samples

29 Bath: Dr Ben O Driscoll (now Reading) Arach Goldar (now CEA) Matthew Wasbrough Jim Holdaway Bin Yang Dr Stephen Roser Lund: Dr Emma Sparr Christoffer Åberg Acknowledgements Diamond, I07: Chris Nicklin, Tom Arnold ESRF, ID10B (Tröika II): Oleg Konovalov, Leide Cavalcanti, Alexei Vorobiev ILL, FIGARO: Richard Campbell, Anna Angus- Smyth ISIS, LOQ: Richard Heenan, Steve King Ann Terry, Sarah Rodgers ISIS, SURF: Stephen Holt, Arwel Hughes ISIS, CRISP: Rob Dalgliesh, John Webster, Christy Kinane The SANS Group, NIST ( The Royal Society (International Joint Project) ESF EUROCORES SONS (SPENSA) EPSRC

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31 Surface Pressure Long PEI surface pressure changes, multiple rates Rate of change related to C n TAB chain length Magnitude related to chain length, PEI concentration Surface Pressure / mn m C 16 TAB: LPEI 60 g/l 30 g/l 15 g/l 7.5 g/l 3.8 g/l no PEI Time / sec

32 Can we control nanostructure? Surfactant chain length: 30g/L PEI solutions: short long C 16 TAB 58.2Å 58.2Å C 14 TAB 58.2Å 50.4Å C 12 TAB 50.2Å 48.8Å reflectivity (arb. units) 30g/L SPEI Q (Å -1 ) 0.20 C 12 TAB C 14 TAB C 16 TAB 0.25 C 16 TAB: 60 LPEI Q Z / Å Q Z / Å C 14 TAB: 60 LPEI Q XY / Å Q XY / Å

33 Can we control nanostructures? CTEABr CTABr Solution structures Intensity (cm -1 ) M DDAB 0.01M DDAB:2CTAB 0.01M DDAB:20CTAB 0.01M CTEAB No Polymer Q (Å -1 ) DDAB Intensity (cm -1 ) M DDAB 0.01M DDAB:2CTAB 0.01M DDAB:20CTAB 0.01M CTEAB With 1.5wt% LPEI Q (Å -1 )

34 Formation of Films [CTAB] monitored by surfactant sensitive electrode equilibrium [CTAB] = 0.71 mmol L -1 at 30 mins matches CMC of CTAB in the presence of polymer at same PEI concentration (CMC* = 0.71 mmol L -1 ) Multiple film formation decreases [CTAB] until film formation ceases CTAB /mmol L CTAB /mmol L :00 1:00 1:35 2:10 2:50 3:30 4:40 t /min:seg CTAB /mmol L -1 1,20 1,00 0,80 0,60 0,40 0.5wt% PEI:1 mmol L -1 CTAB , t /min 0, N o film Comas-Rojas et al, J. Colloid Interface Sci., (2009) 339, 495.

35 Spray Coating - Film Formation SPEI 1wt%, 0.1M SB3-14, 0.1M Ca 2+ 2 nd spray coating 20s frames, 30min total

36 SPEI-SB3-14 Film Final Structure Film transforms: disordered Pm3n 2D hexagonal Pm3n (211) peak becomes (10) 2D hexagonal peak Epitaxial transformation previously seen for dip coated silica-surfactant films as water content decreases Cagnol et al J. Mater. Chem., 2003, 13, 61

37 Biocompatibility? CTAB is toxic No films form with non-ionic surfactants Use zwitterionic surfactant instead? Neutron reflectivity PEI/Ca 2+ /SB m PEI/Ca 2+ No Ca 2+ = no film 100 m

38 Spray Coated PEI/SB3-14 Films Increasing [Ca 2+ ] increases surface curvature Surfactant only PEI/[Ca 2+ ]=0M PEI/[Ca 2+ ]=0.1M LAMELLAR LAMELLAR 2D HEXAGONAL

39 Na Alginate or DNA Films Both form Pm3n micellar cubic structures in spray-coated films with SB3-14 and Ca 2 + DNA Na Alginate Q z (A -1 ) Q z (A -1 ) Q xy (A -1 ) Q xy (A -1 ) Persistence length = 50 nm Unit cell 104 Å Low MW Powder of small crystals Persistence length = 12 nm Unit cell 101Å High MW Large oriented crystals

40 Mineralisation of PEI-CTAB films Silica precursor: Tetramethyl orthosilicate (TMOS) Induction period Silica Film growth at air/water interface Silica Film taken off surface on mesh 10 7 Dried Silica Film 100 Calcined Silica film Intensity(a.u.) 0.15(100) 0.26(110) 0.30(200) 2d hexagonal Intensity(a.u.) A B C D E As prepared calcined TMOS vapour +calcined +washed Q(angstrom) Q(nm -1 ) Yang, Edler, Chem. Mater. (2009) 21(7), 1221

41 Functional Films? Boronic acids bind di-ols used as sugar sensors Polyacrylamide containing phenylboronic acids can form films with CTAB/SDS Mesostructure changes when glucose bound in films Low boronic acid content ph 7 Q z Q z H 2 C Methacrylamide-Nphenylboronic ester O CH 3 NH B O O High boronic acid content ph 7 CH 3 CH Q xy Q xy