Self-assembly and phase behavior

Transcription

1 Self-assembly and phase behavior Amphiphiles and surface tension Lyotropic phases Micelles Key parameters for micellisation Critical packing parameter Other lyotropic phases Special lyotropic phases: vesicles

2 o Surface tension of a liquid = a measure of the cohesive forces between the molecules at a surface liquid/air -Molecules inside the liquid Amphiphiles and surface tension F = Fi = 0 -Molecules at the surface of the liquid F = Fi 0 γ γ = N / m

3 Amphiphiles and surface tension o Surface tension of a film = the increase in free energy/area (A) γ = dw da = Fdx ydx = F y y F w= work done to increase the area A x-y= rectangular frame to create a thin film of fluid x o Surfactants: decrease the surface tension when they localize at the surface monolayer of surfactants Application of the surfactants:

4 Amphiphiles and surface tension o low c(surfactant) surfactants molecules at the surface (surface excess, Γ) + surfactants molecules inside the liquid o c(surfactant) Γ monolayer of surfactant o c(surfactant) micelles Gibbs isotherm: dγ d ln c = RTΓ c = concentration of surfactant R= ideal gas constant T= temperature Γ = surface excess of surfactant

5 Amphiphiles and surface tension Gibbs isotherm: dγ d ln c = RTΓ c = concentration of surfactant R= ideal gas constant T= temperature Γ = surface excess of surfactant o Surface excess depends on the affinity of the surfactant molecules for the surface k c Langmuir equation: a Γ c = concentration of surfactant ad 0 = k ad = rate constant for surfactant 1 + kadc adsorption to the interface a0 = Surfactant head group area RT γ = ln c + a 0 ( 1+ kad ) γ 0 γ Γ= surface excess of surfactant 0 = surface tension of the solvent

6 Lyotropic phases o Lyotropic phases = phases that are formed when the concentration of the amphiphilic molecules is increasing Lyotropic phases concentration change their architecture as function of the amphiphilic Lyotropic phases: -Micelles -Lattice-like arrangements -Lamellar phases -Inverse phases

7 Micelles o Micelles = supramolecular assembly (normally spherical as shape) based on surfactants/amphiphilic molecules that are formed above a certain concetration of the surfactant/amphiphilic molecules o Micelle architecture: a core of the hydrophobic chains of the surfactant/amphiphilic molecuels surrounded by the hydrophilic head groups/corrona of the hydrophilic chains: TEM image of PEG-SS- PLA-SS-PEI micelles C. He, et al, Polym. Chem, 2016, 7, Micelles form at a low concentration of the surfactant/amphiphilic molecules

8 Micelles o Critical micellar concentration, CMC = concentration of the surfactants/amphiphilic molecules where a transition from a disperse of the surfactant/amphiphilic moleculea to a mielle phase occurs. c < CMC c > CMC Micelle solution is highly dynamic architecture > molecules leave/rejoin micelle Micelle dynamics = f (T)

9 Micelles: CMC o Various macroscoppic properties = f (CMC) : - Surface tension - Viscosity - Optical scattering properties Example: Changes in some physical properties for an aqueous solution of sodium dodecyl sulfate (SDS)intheneighborhoodoftheCMC

10 CMC importance Various methods to detemine CMC use the change of the macroscopic property x, x = f(c ) : CMC is the discontinuity point/region Example. Changes in surface tension serve for the determination of the CMC

11 CMC importance Example. sodium dodecyl sulfate (SDS) Electric conductivity Turbidity Surface tension In most cases there is a small range of concentration where changes in macroscopic properties appear: CMC range!

12 CMC examples

13 CMC examples Types of surfactants/amphiphiles: - Ionic - Cationic - Non-ionic - Zwitterionic

14 Micelles: Aggregation number o Aggregation number, N agg = number of surfactant molecules/micelle o N agg ranges from 50 up to 100 for spherical micelles, depending on the surfactant type. V Amicelle V surfact A surfact micelle N agg = = N agg when CMC N agg of non-ionic polyethylene oxide amphiphiles.

15 Micelles: Aggregation number N agg when CMC

16 Key parameters for micellisation o CMC = f (length of the hydrocarbon chains) CMC when chain length o CMC = f (head groups charge) CMC for anionic/cationic amphiphilic molecules o CMC = f (addition of salts in the solution) CMC by addition of counterions o CMC = f (T) complex behavior CMC decreases with increasing the chain length of the hydrophobic tail, more pronounced for non-ionic surfactants/amphiphiles.

17 Key parameters for micellisation

18 Key parameters for micellisation o Condition for an efficient packing into a shperical micelle surface area occupied by the hydrophilic head groups/domains must shield the volume ocupied by the hydrophhobic tails/domains. R = R opt R > R opt R < Ropt

19 Key parameters for micellisation o CMC = f (T) complex behavior but does not vary significantly with T - Ionic surfactants: surfactants C4-Azo-OCnTMAB in pure water CMC when T Exception SDS Temperaturedependent CMC of SDS

20 Key parameters for micellisation - Non-ionic surfactants: CMC when T CMC allows estimation of TD functions: G = RigT ln ( CMC) S H = = R dg dt ig T = R 2 ig T d ln dt d ln( CMC) dt ( CMC) R ig = ideal gas constant T= temperature R ig ln ( CMC)

21 Critical packing parameter Important: - Low concentrations of surfactant spherical micelles - High concentrations of surfactant other phases Critical packing parameter, CPP surfactant defined as : = geometric parameter of a CPP = V surfact a 0 l c V surfact a 0 l c = = = Volume of the tail chain Area of the head group at the head-tail interface Critical length of the tail chain CPP can be used to predict the likely phase of a particular surfactant system

22 Critical packing parameter CPP can be estimated using empirical values for V surfact and l c. V surfact = ( n)m l c = n n = m = Number of Cin the hydrophobic chain Number of hydrocarbon chains Estimation of CPP for spherical micelles MVsurfact = Mα 0 = 4πR 4 π R V surfact α R 0 l c 1 CPP > CPP for other shapes of micelles: 3 R = 1 3 CPP 1 3

23 Critical packing parameter Polybutadiene- block-poly(1-methyl-2-vinyl pyridinium)- block -poly(sodium methacrylate)(bvqmana) micelles with a rather thin corona Anionic/zwitterionicsurfactant solution (SDS/ TPS) in the presence of Ca(NO 3 ) 2 in which viscoelastic wormlike micelles are formed

24 Other lyotropic phases Other lyotropic phases are formed as function of: molecular geometry of the surfactant molecules + concentration of surfactant molecules: Lattice-like arrangement: - Cubic phase micelles packed closely and interacting - Hexagonal phase closely packed arrangement of cylindrical micelles Other architectures can be found in specific conditions (different surfactant concentrations) hollow disks, tubules, vesicles Lamellar phase bilayer sheets Inverse haxagonal phase cylinders of water surrounded by surfactant phase Inverse micelles water spherical domains surrounded by surfactant phase

25 Other lyotropic phases Micelle Inverse micelle Hexagonal phase Lamellar phase Inverse hexagonal phase

26 Critical packing parameter

27 Other lyotropic phases Example: Lipids CPP Shape Structures

28 Special lyotropic phases scale bar = 100 nm) scale bar = nm) Vesicles/polymersomes Giant Unilemellar Nanotubes vesicles(guvs) Complex phases

29 Vesicles: mechanism of formation From disk-like bilayer structures to closed vesicles Line energy Membrane bending energy

30 Minimal vesicle size a c critical scaling parameter (associated with nonlinear elasticity) d thickness of membrane d 0 the length of the hydrophobic core of the membrane

31 Minimal vesicle size membrane stiffness formation of larger vesicles membrane thickness Pure egg lecithin (black) and egg lecithin/cholesterol (red) vesicles Giants formed by PEO-b-PCL-b-PMOXA

32 Thermodynamic stability Most of vesicles are non-equilibrium structures. The molecules are kinetically trapped during preparation. Size regulation by extrusion Vesicle formation with various shapes

33 Vesicles: types and applications Classification based on materials Liposomes (phopholipid) Drug delivery Polymersomes (amphiphilic block copolymers) Artificial organelles Sensors Collioidsome New materials P. Tanner, V. Balasubramanian, C.G. Palivan, Ading Nature s organelles: Artificial peroxisomes play their role, Nano Letters, 2013, 13(6), X. Zhang, M. Lomora, T. Einfalt, W. Meier, N. Klein, D. Schneider, C. G. Palivan, Active surfaces engineered by immobilizing protein-polymer nanoreactors for selectively detecting sugar alcohols, Biomaterials, 2016, 89, J. Liu, V. Postupalenko, S. Lörcher, D. Wu, M. Chami, W. Meier, C. G. Palivan, DNA-mediated self-organization of polymeric nano-compartments leading to interconnected artificial organelles, Nano Letters, 2016, 16,

34 Giant unilamellar vesicles: types and applications giant unilamellar vesicles Artificial cells and synthetic cells Janus giant vesicles multicompartment vesicles synthetic tissues

35 References: G. M. Kontogeorgis, S. Kill, Introduction to applied colloid and surface chemistry, Wiley-VCH, 2016 L.S. Hirt, Fundamentals of soft matter science, CRC Press, D. F. Evans, H. Wennerstrom, The colloidal domain, Wiley- VCH, second edition, M. Antonietti, S. Förster, Vesicles and liposomes: A selfassembly principle beyond lipids, Advanced Materials, 2003, 15, C.G. Palivan, R. Goers, A. Najer, X. Zhang, W. Meier, Bioinspired polymer vesicles and membranes for biological and medical applications, Chem. Soc. Rev, 2016, 45, 377.

36 Self-assembly and phase behavior Amphiphiles and surface tension Lyotropic phases Micelles Key parameters for micellisation Critical packing parameter Other lyotropic phases Special lyotropic phases: vesicles