Self-assembly Structures of Block Copolymers in Selective Solvents and of Polysaccharide- Surfactant Mixtures

Transcription

1 Self-assembly Structures of Block Copolymers in Selective Solvents and of Polysaccharide- Surfactant Mixtures Björn Lindman, Physical Chemistry, Lund University, Sweden Center of Excellence Contributions from Lennart Piculell, Tommy Nylander, Per Linse, Paschalis Alexandridis, Ulf Olsson and other colleagues

2 Hydrophilic Hydrophobic

3 Amphiphilic molecules ionic and non-ionic surfactants and lipids block- and graft-copolymers (polysaccharides and proteins), DNA Self-Organize at Interfaces and in Solution modify interfacial properties enhance compatibility compartmentalization Form the basis of life Biological membranes Find widespread use in industry Pharmaceuticals, plastics, foods, detergents, cosmetics, minerals, paper, oil, remediations, etc.

4 SDS CH 3 (CH 2 ) SO - 4 Na + CTAB CH 3 (CH 2 ) 15 N + (CH 3 ) 3 Br - C 12 E 8 CH 3 (CH 2 ) 11 (OCH 2 CH 2 ) 8 OH

5 Surfactant self-assembly Spherical Micelle Reversed Micelle Lamellar phase Bicontinuous Structure Cylindrical Micelle Vesicle

6 Amphiphilic Lipophilic and Hydrophilic Combine the properties of polar solutes like salts with those of hydrocarbons Ambivalence leads to (in aqueous systems) Adsorption at interfaces (water/air, water/hydrocarbon, water/solid, water/macromolecule) And / or Self-assembly (alone or with low molecular or macromolecular cosolutes)

7 Amphiphilic copolymers

8 Amphiphilic Block Copolymers EO n -PO m -EO n EO n -BO m -EO n PO n -EO m -PO n EO : ethylene oxide -(CH 2 -CH 2 -O)- PO : propylene oxide -(CH 2 -CH(CH 3 )-O)- BO : butylene oxide -(CH 2 -CH(CH 2 CH 3 )-O)- Commercially available (BASF, ICI, Dow, Hoechst) Molecular weight range: EO composition range: % (per weight) Composition, molecular weight and architecture can be tailored to meet specific needs (control over amphiphilicity)

9 Surface tension of EO 37 PO 56 EO Pluronic P105 γ / (mn m-1) C 25 C log [C polymer /(kg dm-1)] The arrows denote the location of the cmc:s obtained from dye solubilization.

10 CMCs of EO block copolymers decrease strongly with T

11 Block-copolymer opolymer self-assembly CH 3 HO(CH 2 CH 2 O) n (CHCH 2 O) m (CH 2 CH 2 O) n H PEO PPO PEO

12 Block copolymers: thermal gel is cubic phase

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14 Phase behavior of amphiphilic block copolymer in water temperature cloud point L 1 I 1 H 1 V 1 L α water polymer L 1 I 1 H 1 V 1 L α lamellar increasing amphiphile concentration

15 Tailoring the molecular packing Molecular packing imposes the topology of the structural elements Packing depends on molecular characteristics of amphiphile (block sequence and architecture, block molecular volume ratio), but can be adjusted by solvent quality (modify relative swelling of blocks) cross-linking of self-assemblies (adsorb preferentially to the different blocks)

16 Tailoring the Molecular Packing solvent quality (modify swelling) worsen solvent for red block worsen solvent for blue block Change curvature cosolutes (adsorb preferentially) + Change curvature

17 Phase diagram polymer wt% water % 50% - 60 wt% polymer water 20% wt% oil oil

18 4 cubic,, 2 hexagonal, & 1 lamellar liquid crystalline phase + 2 isotropic solution phases in a ternary (isothermal) copolymer water oil system V 1 V 2 H 1 H 2 I 1 I 2 L 1 L 2 L α

19 L 44 EO 10 PO 23 EO 10 M w = 2200 L 64 EO 13 PO 30 EO 13 M w = 2900 P 84 EO 19 PO 43 EO 19 M w = 4200 P 104 EO 27 PO 61 EO 27 M w = 5900

20 Experimental PEO-PPO-PEO Theoretical A-B from Matsen et al Macromolecules 1996, 29, 1091 Experimental PI-PS from Khandpur et al Macromolecules 1995, 28, 8796

21 Block symmetry Approximately symmetric - (EO) 19 (PO) 43 (EO) 19 Unsymmetric 80 wt% PEO - (EO) 43 (PO) 16 (EO) 43 Unsymmetric 10 wt% PEO - (EO) 5 (PO) 68 (EO) 5

22 80% PEO 40% PEO 10% PEO

23 Effect of copolymer architecture on self-assembly EO 13 PO 30 EO 13 (L64) PO 19 EO 33 PO 19 (25R4)

24 3 cubic,, 2 hexagonal, & 1 lamellar liquid crystalline phases + 2 isotropic solution phases in a ternary (isothermal) block copolymer water oil system L α V 2 H 1 H 2 I 1 I 2 L 1 L 2

25 Amphiphilic graft copolymer self-assembly

26 Hydrophobically modified water soluble polymers: HM-P Polymer backbone Hydrophobic group Features: can form inter- and intrachain hydrophobic aggregates exhibit unique rheological properties have strong tendency to associate with surfactants and other polymers Applications: Rheology modifiers and thickeners in paint formulations cosmetics/skin care products, detergents, oil recovery Drug delivery systems Dispersing/stabilizing agents

27 The associative (hydrophobically modified) water-soluble polymers Hydrophobe Polymer chain grafted end-capped

28 Associated structures in aqueous solutions of hydrophobically modified polymers (HMPs)

29 Hydrophobically modified water soluble polymers (HMP) Polymer modified surfactant

30 A Slightly Hydrophobic Cellulose Derivative The degree of ethyl and hydroxyethyl substitution determines the hydrophobicity of polymers in the EHEC family.

31 Hydrophobic modification of a water-soluble polymer increases viscosity Viscosity /Pa.s

32 Cross-links in HM-EHEC entanglements of polymer chains physical bonds of associating hydrophobic tails physical bonds of associating segments of the EHEC backbone

33 Surfactant like behavior polar head hydrophobic tail surfactant micelle polymer aggregate

34 Reversible inter-chain association Hydrophobe Polymer chain Crosslink transient network viscosity

35 O H C H C O O H O H C H C C H C O H H H H Hydrophobic cavity Cyclodextrin O O O O O O OH O O O O O HO O O O O O H OH O O O HO O O O HO OH O O Hydrophilic exterior

36 Hydrophobic molecules can hide inside the cavity of a CD water molecule

37 CD breaks the hydrophobic associations

38 c CD η/η0 η/η

39 Too large hydrophobe

40 Surfactant-polymer systems. General aspects

41 Polymer-Surfactant Association: pearl-necklace model

42 Polymer-Surfactant Interaction Cooperativity Surfactant micellization induced by polymer

43 Polymer-Surfactant Complexes micelle mixed micelle alginate + C 12 TAB Nonic cellulose derivative + SDS hydrophobically modified cellulosics + SDS

44 When do surfactants bind to polymers? Ionic Surfactants Oppositely charged polymers Non-ionic polymers self-assembly induced by polymer All Surfactants Hydrophobically modified polymers mixed micellization Hydrophobic association is always essential to the interaction

45 The structure of Associative Polymers Hydrophobic group Water soluble backbone

46 Hydrophobic modification of a water-soluble polymer increases viscosity Viscosity /Pa.s

47 The influence of surfactant concentration on viscosity Viscosity log c Surfactant

48 Hydrophobically modified polymer Polymer

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50 Viscosity and hydrophobic microdomains Addition of: hydrophobically modified 1% w/w EHEC Na + Cl - DoTA + Cl - Increase micelles size Increase viscosity

51 -Broaden the area of high viscosity Screening electrolyte (NaCl) Oppositely charged surfactant (DoTAC) Decrease in viscosity depends on the stoichiometry between polymer hydrophobic side-chains and mixed micelles. One way to alter the stoichiometry is to: Decrease the number of micelles by increasing their size.

52 The Viscosity and the Mixed micelles Concentration in Mixtures of 1 w/w% HMHEC and 30 mm surfactant (SDS+DoTAC) versus the molar ratio of DoTAC

53 The viscosity can increase with addition of a surfactant that changes the shape of the micelles DoTAC

54 Polymer-modified surfactant mixed micelles

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56 Oil droplet

57 Polymer-surfactant systems. Phase separation

58 Segregating Polymer/Surfactant mixtures

59 Mixtures of oppositely charged polyelectrolyte + surfactant: Associative phase separation

60 In a mixed solution Interactions between cosolutes are: Repulsive (most common) or Attractive (electrostatic, hydrophobic) Depending on interaction Segregation Association, or Miscibility

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62 POLYELECTROLYTE EFFECTS A polyelectrolyte in aqueous solution dissociates into 1 polyion and n counterions; typically n >> 1 a large no. of particles: large S mix If the counterions mix into a phase, the polyion has to follow (condition of electroneutrality)

63 POLYELECTROLYTE EFFECTS Dissociating counterions on one of the polymers increases miscibility tremendously Added salt facilitates demixing in both cases.

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66 Polymer Surfactant Phase Diagrams

67 SEGREGATING POLYMER/SURFACTANT MIXTURES In general (i.e,. in absence of electrostatic or hydrophobic attractions), effective repulsion between a polymer and a surfactant micelle is expected Since a surfactant micelle is effectively a polymer, repulsion should lead to a segregative phase separation, as for mixtures of dissimilar polymers

68 Nonionic polymer + nonionic surfactant Segregation

69 MIXTURES OF OPPOSITELY CHARGED POLYELECTROLYTE + SURFACTANT: ASSOCIATIVE PHASE SEPARATION For intrinsically hydrophilic polyions, the association is driven only by electrostatic interactions Close analogy to polyelectrolyte complexes

70 Association Anionic polysaccharide + Cationic surfactant Nature of conc phase: conc soln/gel, liq crystal, solid crystal

71 Effect of salt on polyelectrolyte + ionic surfactant Low salt Association Intermediate salt Miscibility High salt Segregation

72 Problem with conventional approach Concentrated phase generally contains 4 ions in unknown proportions => complex system!

73 OPPOSITELY CHARGED MIXTURES: TWO ALTERNATIVE REPRESENTATIONS Left hand diagram conventional mixing plane Right hand diagram alternative mixing plane Stoichiometric mixtures belong to both mixing planes

74 Segregation in a P - S - systems 40 C NaHy M w = NaHy SDS H 2 O 1M NaBr NaHy SDS H 2 O

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76 Network formation and gelation A gel contains at least two components, one solid-like and one liquid-like, where both are continuous throughout the gel.

77 What are polyelectrolyte gels? Polymer network with charged groups

78 Gel Swelling Experiment: How & Why Make gel pieces of cross-linked polymer Immerse gel pieces in series of solutions with increasing conc of additive water water + additive water + more additive => Potential responsive gels (drug delivery, water retention ) => Info on interactions between gel & additive

79 General Swelling Isotherm for Weakly Hydrophobic Nonionic Gel with Ionic Surfactant V/V cac C f,sds

80 Gel Swelling Experiments Detect Surfactant Binding V / m (ml/g) CMC: SHS STS SDS SDeS SOS HEC gels swollen in alkyl sulfate solutions Sjöström & Piculell Langmuir 17(2001)3836 => HEC binds alkyl sulfates with > 8 carbon tails c (mm)

81 Cat-HEC Gels + Different Anionic Surfactants V / m (ml/g) CMC: STS SDS SD(EO) 2 S Sjöström & Piculell Colloids Surf A (2001) 429 Collapse & redissolution Two CAC:s!? c (mm) Both correlate with CMC => both reflect surfactant self-assembly

82 Adsorption of EHEC CH 3 CH 3 O CH 2 CH 2 O CH 3 O HO OH O CH 2 O HO O CH 2 O CH 2 O HO O CH 2 O n CH 2 O CH 2 HO CH 2 CH 2 O O CH 2 CH 2 O CH 2 CH 2 CH 2 OH CH 3

83 Solvent Polymer Surface Aqueous systems: Adsorption since water interacts unfavorably with polymer (clouding polymer) or surface (hydrophobic surface)

84 Polar/nonpolar surfaces T dependence: Solvency

85 The poorer the solvent the better the adsorption

86 The influence of the solvent Poor solvent Good solvent

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88 Adsorption of EHEC on SiO 2 : Solvency effects due to cosolutes Na 2 SO 4 NaCl 4 3 Increase in adsorption 2 1 NaI NaSCN Concentration (M) 1.0 Decrease in adsorption Decrease in CP NaI NaSCN Increase in CP Na 2 SO 4 NaCl Concentration (M)

89 Interfacial behavior of polymersurfactant mixtures

90 Polymer-Surfactant at Interfaces

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92 General Swelling Isotherm for Weakly Hydrophobic Nonionic Gel with Ionic Surfactant V/V cac C f,sds

93 EHEC/SDS on Hydrophobized Silica Substrate:Silanol groups reacted with dimethyloctylchlorosilane EHEC preadsorbed from 0.01 wt% solution. (Intermediate adsorption) SDS adsorbs on hydrophobized silica; Competitive adsorption!

94 Turbidity of bulk solution 100 ppm cat-heccl (LR30M) + SDS φ Absorbance Absorbance φ 1φ Increase in turbidity due to precipitation in the bulk solution SDS (mm) SDS concentration (mm) polycation and anionic surfactant

95 Polymer-Surfactant applications: Shampoo S P + S - H 2 O H 2 O P P + S H 2 O P +S- - + S -

96 CATIONIC CELLULOSE DERIVATIVES (CH 2 CH 2 O) 2 CH 2 CHCH 2 CH 3 N + R Cl O OH CH 3 CH 2 O HO OH HO OH O O CH 2 OCH 2 CH 2 OH τ 1 τ JR-400: R=CH 3 τ =29mol% Mw = LM-200: R=C 12 H 25 τ =3mol% Mw =100000

97 Thickness [nm] The effect of SDS addition to pre-adsorbed JR-400 layers Adsorbed amount [mg/m2] Φ cac cmc Polar surface mM SDS SDS [mm] >5mM SDS P + -S - stoichiometric complex adsorption - solubility of complex decreases because of charge neutralization - conformation of complex becomes compact, since intramolecular electrostatic repulsion is screened desorption solubility of complex increases because of cooperative SDS binding - complex expands due to the increase of the net negative charge of complex Desorption process was too slow to be followed

98 Rinsing of adsorbed JR-400/SDS layers on silica Effect of rinsing (10mM NaCl) on adsorption Rinsing was started (t=1000) Reference Adsorption of JR-400/SDS complexes from pre-mixed solutions adsorbed amount [mg/m 2 ] mM SDS 10mM SDS 0.06mM SDS 0.006mM SDS adsorbed am ount [m g/m 2 ] SD S [m M ] Rinsing was started after adsorption of the complex from pre-mixed solution reached steady state 2φ time [sec] - For the complexes which were formed in post-precipitation region, the adsorbed amount jumped up by rinsing

99 Effect of rinsing on adsorbed JR-400/SDS layers on hydrophobized silica a b Time [sec.] c The complexes adsorbed from mixed polymer (100 ppm)/surfactant (5 mm) solutions and rinsing was started at t = 1000 sec. (a) adsorption was carried out in water followed by rinsing with water (b) adsorption was carried out in 10 mm NaCl followed by rinsing with water (c) adsorption was carried out in 10 mm NaCl followed by rinsing with 10 mm NaCl.

100 + General trends of co-adsorption of cationic cellulose derivatives with SDS polycation adsorption adsorption phase separation desorption added anionic surfactant rinsing no SDS low SDS high SDS

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