SOFT NANOSTRUCTURE SYSTEMS AND THEIR MODELING BY MOLECULAR THERMODYNAMICS

1
SOFT NANOSTRUCTURE SYSTEMS AND THEIR MODELING BY
MOLECULAR THERMODYNAMICS
Natalia Smirnova and Alexey Victorov
Department of Chemistry St.Petersburg State
University, Russia
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Materials engineered in a controlled or tailored
manner

• 19-th century iron and steel
• 20-th century new inorganic materials,
  semiconductors, polymers
• 21-th century nanomaterials (solid and soft)
• - In our new millennium it seems safe to
  predict the continued importance of soft
  materials, engineered in ways we can as yet only
  dream of
• I.W.Hamley. Introduction to Soft Matter.
  2002
• Soft matter systems with nanoscale
  supramolecular ordering
• Micellar and Vesicular Solutions, Liquid
  Crystals, Polymer gels, Membranes, etc.

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Systems Containing Amphiphiles Rich Mesoscale
Morphology
Polar head
Nonpolar tail
Micelles
vesicles
Reverse micelles
Vesicles
C and Cs concentration of surfactant and salt
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Applications

• Self-assembly phenomena amphiphiles are greatly
  affected by the changes of concentration, pH,
  temperature, by the presence of other components.

• Biomedical (controlled drug delivery, tissue
  implants, etc.)
• Fabrication of nanoporous materials
• Nanoreactor engineering
• Fuel cells
• Separation technologies
• Design of smart materials with desired
  properties/response

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Example nanoscale morphology of a block
copolymer material determines high performance
Performance of contact lense Oxygen
permeability Water permeability
Gel structure on mesocsale
hydrogel phase
siloxane phase
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Goals

• Find formulations with desired properties/response
  
• Better understand self-assembly and response of
  soft nanostructures by combining experiment,
  theory and computer simulation
• Develop predictive molecular thermodynamic models
  for practical applications

7
Topics of our studies

• Aggregation, rheology and phase behavior of
  surfactant solutions
• Aggregation in ionic liquids (IL) ILclassical
  surfactants
• pH-sensitive nanostructures formed by weak
  polyelectrolytes
• Mesostructure and ion exchange in NAFION
  membranes
• Morphology and swelling of block copolymer gels
• Aggregation of asphaltenes and resins in crude oil

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Viscosity of Aqueous Surfactant Solutions with
Additives
Viscosity vs. CTAB and NaBenz mass.
NaBenz, NaBr, ? CCTAB0.35 M
Viscosity ( ) and hydrodynamic radius ( ) vs.
CTAB conc. C add0.83 mol/l
3
1
2
i-PrOH (1), NaBenz (2), NaBenz i-PrOH11 (3)
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CMC and the enthalpy of micellization for aqueous
CTAB NaBenz and CTAB-iPrOH from titration
calorimetry
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Phase Behavior and Viscosity of the mixture
AO-NaDS-HCl-H2O
AO H AOH AOH DS- AOHDS-
Ion-ion, ion-dipole interactions, hydrogen
bonding Strong pH-effects
Precipitation temperature
Isotropic solution-liquid crystal boundary
Viscosity
x?HCl 0.0 (1) 0.2 (2) 0.33 (3)
1
308?,
2
323?
3
2
3
xtotalxAO xNaDS 0.001. x?AOxAO/(xAOxNADS)
x?HCl xHCl/(xHClxAO)
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Aggregate size and viscosity inSDS-C12AO-H2O
8 wt. , T308
15 wt., T308
Freeze-Fracture Transmission Electron
Microscopy 8 wt., wSDS0.22
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Molecular Thermodynamic Approach the Gibbs
energy of aggregation
ggtr gint gdef gst gmix gel
formation of the aggregate core-water interface
hydrophobic tail transfer
head group steric interactions
electrostatic interactions
mixing
deformation of the surfactant tail
Molecular parameters nci carbon number of the
hydrophobic tail api effective cross-section
area of the surfactant head ?i effective
length of the surfactant head

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Effect of pH on CMC forSDS-C12AO-HCl
Cationic AOH
Anioninc SDS
Nonionic Anionic AO SDS aeff0.50nm2,
aeff0.17nm2 ddip0.3nm, d0.545nm
aeff0.30nm2 d0.3nm
aeff0.17nm2 d0.54nm
Catanionic complex AOHDS-
pH7-8 pH2 CMC (11)0.65mM CMC (11)
0.003 mM
Experimental (x, ) Calculated ()
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Nanoscale structures in ionic liquids (ILs)
Cations
Anions

bmimPF6

• Green Chemistry
• nonvolatile
• good solvents, reaction media
• nontoxic and nonflammable
• environmentally benign substances

-
Increasing hydrophobicity Br-, Cl-lt BF4- lt
PF6-lt NTf2-
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Separation of hydrophilic and hydrophobic regions
in MD simulation
J.C. Lopes, A.Padua, 2006
Liquid ?nmimPF6
?4mimPF6
n2
n4
Polar Nonpolar parts
700 ions ?nmimPF6 in the cell
n6
n12
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Dependence of the CMC on chain length
Aggregation in solutions of ILs
NaDS solutions with added CnmimXXBr, BF4,
PF6
t 298 K
CnmimBr behaves like a typical cationic
surfactant
XILCIL/(CILCNaDS)
Ils are effective modulators of NaDS cmc
N.A.Smirnova et al. J.Coll.Interf.Sci. 2009
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Aggregation in C10mimBr-NaDS solutions from
experiment and theory
T 298.15 K
cmc
cmc
xIL 0.0 0.5 1.0
cmc, mM experiment 8.2 0.16 40 calc, ap 
0.46 nm2 7.7 0.47 45 calc, ap  0.42 nm2
7.7 0.36 40
Composition of micelles (..) and monomer
population ( )
Calculated aggregation numbers
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Local density profiles from MD simulations of
spherical micelles
C12mimBr
b)
C10mimBr
a)
c)
C12mimBr SDS, 11
N R, nm a, A2 a 40 1.55
76 b 60 1.80 68 C 60 1.64
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Modeling of micellar branching and spatial
networks of wormlike micelles
EHAC solution Croce et al., 2003
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Morphology-transition map predicted by
calculating the free energy of aggregation
CTABKBr (350mM CTAB, 308 K)
Narrow interval of bicontinuous structures
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Modeling of nanostructures in diblock copolymer
solutions and gels
A-B diblock
fA fB 1
solvent
Lamellae
2R
2R
Spheres
Cylinders
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Predicted effect of pH and salinity on
nanostructures in solution of diblock copolymer
with one ionic block morphology stability maps
Diblock copolymer molecule NA weak
polyelectrolyte segments (pK5.0) and NB
hydrophobic segments
polystyreneNB - poly(acrylic acid)NA
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AFM-images of polyelectrolyte block copolymer
aggregates of different size and shape
100 mM
no salt
1 M
Förster, Abetz and Müller, Adv.Polym.Sci., 2004
poly(ethylethylene)-poly(styrenesulfonic acid)
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Effect of solution salinity on poly(ethylethylene
)144 poly(styrenesulfonic acid)136 spherical
micelles
Points experiment (Förster, S., et al., 2002),
curves calculation
Aggregation number
Micelle dimensions
hydrodynamic radius
Polymer volume fraction at core-corona interface
core radius
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Predicted domain spacing for sequence of
structures in a nonionic diblock copolymer gel
points spectroscopy data (Hanley et al.,2000)
polysterene(A)-polyisoprene(B) diblock-copolymer,
solvent is good (athermal) for polysterene and
poor for polyisoprene
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Molecular Thermodynamic Model of a Mesoscopic
Ionomer Gel Swollen to Equilibrium in Brine
Salinity in a swollen gel vs salinity of
environment
DFR classical theory of DonnanFlory-Rehner
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Predicted Dissociation of Weak Polyelectrolyte in
Gels of Different Nanoscale Morphology
1mM NaCl
degree of dissociation vs. pH of the environment
for diblock copolymer, pK5, swollen in brine
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NAFION ION-EXCHANGE MEMBRANE
Calculated ion-exchange curves vs. experimental
data
pools of water with mobile counterions in a
hydrophobic polymer matrix
H?K
?(CF2?CF2)n?CF?CF2?m
? O?CF2?CF?O?
CF2?CF2?SO3?M?
?
CF3
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ASPHALTENE NANOPARTICLES IN CRUDE OILS
Predicted asphaltene precipitation curves vs.
experiment for a crude oil
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Conclusions

• Molecular thermodynamic modeling has become an
  important part of soft-matter science models
  on a deeper molecular grounds are under way
• Computer simulations are powerful tool for
  understanding self-assembly phenomena and for
  development of approximate models
• These two approaches provide a guidance in
  experimental studies needed for the design of new
  nanostructured soft materials

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• Research group
• Prof. Alexey Victorov
• Dr. Andrey Vlasov
• Dr. Alexander Vanin
• Dr. Yuri Anufrikov
• Dr. Maria Alexeeva
• Dr. Evgenia Safonova
• Eng. Igor Pukinsky
• PhD Alexey Makarov
• PhD Sonya Koroleva
• PhD Asya Venedictova
• students

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• Acknowledgements
• Russian Foundation for Basic Research
  (07-03-00367),
• Science schools of RF (NS-165.2008.3)

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Polymers used in siloxane hydrogels
Dimethylsiloxane macromonomer
Methacryloxypropyltris(trimethylsiloxy) silane
(TRIS)
OSiMe3
OSiMe3
Dimethylacrylamide (DMA)
OSiMe3
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MD modeling spherical micelles of CnmimBr and
CnmimBr SDS in aqueous solutions

RmimX-
C10mim Br
C12mim Br
SDSRmimX-
conc.
X-
R
temp.
1SDS1C4mim Br 3SDS1C4mim Br
SDSC4mim Br SDSC4mim PF6
3SDS1C4mim Br T 15, 25, 45oC
SDSC4mim Br SDSC12mim Br