Self-assembly and phase behaviorpcsp/2017/PCSP-2017-3... · 2017-10-11 · oSurface tension of a...
Transcript of Self-assembly and phase behaviorpcsp/2017/PCSP-2017-3... · 2017-10-11 · oSurface tension of a...
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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
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o Surface tension of a liquid = a measure of the cohesive forces betweenthe molecules at a surface liquid/air
-Molecules inside the liquid
Amphiphiles and surface tension
0==∑ iFF
-Molecules at the surface of the liquid
0≠=∑ iFF
γ mN /072.0=γ
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o Surface tension of a film = the increase in free energy/area (A)
Amphiphiles and surface tension
y
F
ydx
Fdx
dA
dw ===γ Fy
xxw = work done to increase the area Ax-y = rectangular frame to create a thin
film of fluid
o Surfactants: decrease the surface tension when they localize at thesurface → monolayer of surfactants
Application of the surfactants:
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Amphiphiles and surface tension
o low c(surfactant) → surfactants molecules at the surface (surface excess,Γ) + surfactants molecules inside the liquid
Γ−= RTcd
d
ln
γ
o c(surfactant) Γ monolayer of surfactant
o c(surfactant) micelles
Gibbs isotherm:
c = concentration of surfactant
R = ideal gas constant
T = temperature
Γ = surface excess of surfactant
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Amphiphiles and surface tension
Γ−= RTcd
d
ln
γGibbs isotherm:
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 o Surface excess depends on the affinity of the surfactant molecules for the surface
Langmuir equation:ck
cka
ad
ad
+=Γ
10
c = concentration of surfactant
kad = rate constant for surfactant
adsorption to the interface
Γ= surface excess of surfactant
( ) 00
1ln γγ ++−= cka
RTad
=0γ surface tension of the
solvent
=0a Surfactant head group area
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o Lyotropic phases = phases that are formed when the concentration ofthe amphiphilic molecules is increasing
Lyotropic phases change their architecture as function of the amphiphilicconcentration
Lyotropic phases
Lyotropic phases:
-Micelles
-Lattice-like arrangements
-Lamellar phases
-Inverse phases
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Micelles
o Micelles = supramolecular assembly (normally spherical as shape) basedon surfactants/amphiphilic molecules that are formed above a certainconcetration of the surfactant/amphiphilic molecules
o Micelle architecture: a core of the hydrophobic chains of thesurfactant/amphiphilic molecuels surrounded by the hydrophilic headgroups/corrona of the hydrophilic chains:
Micelles form at a low concentration of the surfactant/amphiphilic molecules
TEM image of PEG-SS-PLA-SS-PEI micelles
C. He, et al, Polym. Chem, 2016, 7, 4352-4366
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Micelles
o Critical micellar concentration, CMC = concentration of thesurfactants/amphiphilic molecules where a transition from a disperse of thesurfactant/amphiphilic moleculea to a mielle phase occurs.
c < CMC c > CMC
� Micelle solution is highly dynamic > molecules leave/rejoin micellearchitecture
� Micelle dynamics = f (T)
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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) in the neighborhood of the CMC
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Various methods to detemine CMC use the change of the macroscopic propertyx, x = f(c ) : CMC is the discontinuity point/region
CMC importance
Example. Changes in surface tension
serve for the determination of the
CMC
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CMC importanceExample. sodium dodecyl sulfate (SDS)
Electric conductivity
TurbidityTurbidity
Surface tension
In most cases there is a small range of concentration where changes inmacroscopic properties appear: CMC range !
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CMC examples
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CMC examples
Types of surfactants/amphiphiles:- Ionic- Cationic- Non-ionic- Zwitterionic
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Micelles: Aggregation number
o Aggregation number, Nagg = number of surfactant molecules/micelle
o Nagg ranges from 50 up to 100 for spherical micelles, depending on thesurfactant type.
surfact
micelle
surfact
micelleagg A
A
V
VN ==
surfactsurfact AV
� Nagg when CMC
Nagg of non-ionic polyethylene oxide amphiphiles.
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� Nagg when CMC
Micelles: Aggregation number
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Key parameters for micellisation
o CMC = f (length of the hydrocarbon chains)
o CMC = f (head groups charge)
� CMC when chain length
o CMC = f (addition of salts in the solution)
o CMC = f (T) – complex behavior
� CMC for anionic/cationicamphiphilic molecules
� CMC by addition of counterions
CMC decreases with increasing
the chain length of the
hydrophobic tail, more
pronounced for non-ionic
surfactants/amphiphiles.
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Key parameters for micellisation
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Key parameters for micellisation
o Condition for an efficient packing into a shperical micelle → surfacearea occupied by the hydrophilic head groups/domains must shield thevolume ocupied by the hydrophhobic tails/domains.
optRR >optRR = optRR <
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Key parameters for micellisation
o CMC = f (T) – complex behavior butdoes not vary significantly with T
surfactants C4-Azo-OCnTMAB in pure
water
- Ionic surfactants:
Exception SDS
water
� CMC when T
Temperature-
dependent CMC of SDS
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Key parameters for micellisation
� CMC when T
- Non-ionic surfactants:
CMC allows estimation of TD functions:CMC allows estimation of TD functions:
( )CMCTRG ig ln=∆
( )CMCRdT
CMCdTR
dT
dGS igig ln
)ln( −−=−=∆
( )dT
CMCdTRH ig
ln2−=∆
Rig = ideal gas constant
T = temperature
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Critical packing parameter
Important:
- Low concentrations of surfactant → spherical micelles
- High concentrations of surfactant → other phases
Critical packing parameter, CPP = geometric parameter of asurfactant defined as :
c
surfact
la
VCPP
0
=
surfactant defined as :
=surfactV
=0a
=cl
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 surfactantsystem
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Critical packing parameter
CPP can be estimated using empirical values for Vsurfact and lc.
( )mnVsurfact 0269.00274.0 +=
nlc 1265.0154.0 +=
=n
=m
Number of C in the
hydrophobic chain
Number of
hydrocarbon chains
Estimation of CPP for spherical micelles
3
3
4RMVsurfact π=
20 4 RM πα = 3
1
0
=R
Vsurfact
α
Rlc ≥3
1≤CPP
CPP for other shapes of micelles: 3
1>CPP
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Critical packing parameter
Polybutadiene- block -poly(1-methyl-2-vinyl pyridinium)- block
-poly(sodium methacrylate) (BVqMANa) micelles with a rather
thin corona
Anionic/zwitterionic surfactant solution (SDS/ TPS) in
the presence of Ca(NO3)2 in which viscoelastic
wormlike micelles are formed
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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
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Other lyotropic phases
Micelle
Hexagonal
phaseLamellar
phase
Inverse
hexagonal
phase
Inverse
micelle
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Critical packing parameter
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Other lyotropic phases
Example: Lipids CPP Shape Structures
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Special lyotropic phases
scale bar = 100 nm)
scale bar = 10000 nm)
Vesicles/polymersomes Giant Unilemellar NanotubesVesicles/polymersomes Giant Unilemellar
vesicles (GUVs)
Nanotubes
Complex phases
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Vesicles: mechanism of formation
From disk-like bilayer structures to closed vesicles
Line energyLine energy
Membrane bending energy
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Minimal vesicle size
ac → critical scaling parameter
(associated with nonlinear elasticity)
d → thickness of membrane
d0 → the length of the hydrophobic core
of the membraneof the membrane
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Minimal vesicle size
membrane stiffness
membrane thickness
formation of larger vesicles
Giants formed by PEO-b-PCL-b-PMOXAPure egg lecithin (black) and egg
lecithin/cholesterol (red) vesicles
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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
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Vesicles: types and applications
Liposomes (phopholipid)
Polymersomes (amphiphilic block copolymers)
� Drug delivery
� Artificialorganelles
Classification based on materials
Collioidsome
� Sensors
• P. Tanner, V. Balasubramanian, C.G. Palivan, Ading Nature’s organelles: Artificial peroxisomes play their role, Nano Letters, 2013, 13(6), 2875-2883.• 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, 79-88.• 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, 7128-7136.
� New materials
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Giant unilamellar vesicles: types and applications
giant unilamellar vesicles� Artificial cells and synthetic cells
Janus giant vesicles multicompartment vesicles
� synthetic tissues
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� G. M. Kontogeorgis, S. Kill, Introduction to applied colloid andsurface chemistry, Wiley-VCH, 2016
� L.S. Hirt, Fundamentals of soft matter science, CRC Press,2013.
� D. F. Evans, H. Wennerstrom, The colloidal domain, Wiley-
References:
� D. F. Evans, H. Wennerstrom, The colloidal domain, Wiley-VCH, second edition, 2014.
� M. Antonietti, S. Förster, Vesicles and liposomes: A self-assembly principle beyond lipids, Advanced Materials, 2003, 15,1323.
� C.G. Palivan, R. Goers, A. Najer, X. Zhang, W. Meier,Bioinspired polymer vesicles and membranes for biological andmedical applications, Chem. Soc. Rev, 2016, 45, 377.
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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