Transcript No Slide Title

Department of
Chemical Engineering
NC STATE UNIVERSITY
Our research program is aimed at understanding, at the molecular
level, the behavior of nano-dimensional fluids and solids. The
underlying theme of our work is to develop molecular models that
accurately describe the materials and systems of interest. These
models are then used in molecular simulations and theories to
interpret experimental results, and to predict behavior that is not
accessible to experiment. Experimental studies complement the
molecular simulation work, and comparison of the two frequently
leads to important new insights. Currently our interest is focused on
several systems: (a) Micellar and reverse micellar solutions - their
phase behavior, thermodynamics, surface properties and structure; (b) Nano-porous materials (solid
materials having pores of nanometer dimension), such as templated mesoporous materials (MCM41, SBA-15,etc.), activated carbons, carbon buckytubes, aerogels and xerogels, silicas, etc.; (c)
Chemical reactions in nano-scale systems, where strong intermolecular interactions are important
(porous materials as nano-scale reactors, reactions in supercritical fluids, etc.). Micellar solutions
are important in separations, and in new technologies based on CO2 solvent applications. Nanoporous materials play a prominent role in chemical processing, particularly in separations and as
catalysts and catalyst supports. They can also form the basis of future technologies, involving
energy storage, as nano-reactors, as sensors, fabrication of small devices of molecular dimensions,
etc. Both the yield and rate of chemical reactions are strongly affected by the reduced
dimensionality of nano-scale systems, and experimental studies are very difficult at this scale.
Front Row: (left to right)
Flor Siperstein, Supriyo Bhattachrya, Lauriane Scanu, Gerhard H. Findenegg (visitor)
Keith E. Gubbins, Francisco Hung
Back Row: (left to right)
Jorge Pikunic, Henry Bock, Coray Colina, Alberto Striolo, Erik Santiso
Naresh Chennamsetty
Front Row: (left to right)
Laurel Andersen, Francisco Hung, Keith E. Gubbins, Lauriane Scanu, Supriyo Bhattacharya
Back Row: (left to right)
Coray Colina, Jorge Pikunic, Naresh Chennamsetty, Heath Turner, Martin Lisal,
Flor Siperstein, John Brennan
Current Research
Realistic Molecular Models for Nanoporous Carbons
Jorge Pikunic
Saccharose-based carbon heated
at 400°C
Freezing and Melting Behavior of Fluids Confined in Porous Materials
Francisco R. Hung
Molecular Modeling of Polymer Systems: Prediction of
Phase Behavior and Surfactant Aggregation
Coray M. Colina
Saccharose-based carbon heated
at 1000°C
Molecular Simulation of Surfactant Systems:
Cosurfactant Effects and Adsorption
Naresh Chennamsetty
C copolymer (gr/cm3)
0.1
T=192 K
T=290 K
Freezing of LJ CCl4 confined in multi-walled carbon nanotubes
(carbon walls not shown).
0.01
CMC
two
phases
micelles
0.001
monomers
0.0001
0.00001
0.75
0.8
0.85

0.9
0.95
Micelles formed in CO2 with surfactants consisting of
CO2-philic and CO2-phobic components.
1
3
CO2 (g/cm )
5
Phase diagram for PTAN-b-PVAC in CO2. Symbols are
experimental points. Lines predicted with the SAFT EOS
on this work.
4.5
Nitrogen adsorption at 77 K
(simulation results)
3.5
Probability distribution of chain orientations at
different surfactant concentrations
0.16
T=140 K
3
60% concentration
0.14
Freezing of LJ CCl4 confined in MCM-41 (pore walls in black).
2.5
0.06
2
0.05
1.5
0.004
1
0.003
0.04
1.0E-08
1.0E-06
1.0E-04
1.0E-02
1.0E+00
P/Po
a, K
0
1.0E-10
bridges
loops
0.1
cylindrical phase
0.08
0.06
0.002
0.04
0.001
0.02
-1
0.5
90% concentration
0.12
0.005
Probability
ex (mmol/g)
4
Modeling the Synthesis of Ordered Mesoporous Materials using
Lattice Monte Carlo Simulations
Supriyo Bhattacharya
Water Adsorption and Phase Transitions in Carbon Pores
Alberto Striolo
0.03
0
0
0.02
20
40
60
80
100
lamellar phase
Initial and final configurations in interfacial NVT simulations showing
the surfactant rich and poor regions in equilibrium
120
0
-1
-0.5
0
0.5
1
cos(theta)
0.01
Surfactant-Silica Liquid Crystals as Precursors for
Ordered Mesoporous Materials
Flor R. Siperstein
0
Chemical Reactions in Confined Geometries
Heath Turner
0
20
C
A
gr H2O / gr C
C
B
A
0.4
0.2
80
100
Volume expansivity versus pressure for carbon dioxide
modeled as a two center Lennard-Jones plus point
quadrupole (2CLJQ). Continuous lines predicted by the
Span-Wagner EOS, dashed lines by 2CLJQ EOS and
symbols from NPT Monte Carlo simulations (this work).
1.2
0.6
60
Pressure, MPa
Ammonia synthesis, N2+3H2  2NH3, in a chemically activated carbon
1.0
0.8
40
Addition of silica
0.0
0.1
1.0
10.0
Molecular Modeling of Self-Assembled Nanostructures
on Surfaces and in Narrow Pores
Henry Bock
P / Psat
Pore width determines the pressure at which capillary condensation
occurs.
What is the effect of pore connectivity?
Aqueous Surfactant Solution in the Bulk
B
Ammonia (NH3)
A
C
B
T*
phase boundary
T*
gr H2O / gr C
0.10
0.08
B
0.06
C
cmc
A
0.04
0.02
0.00
0.001
0.010
0.100
1.000
10.000
P / Psat
Ammonia synthesis, N2+3H2  2NH3, in a slit carbon pore
Surfactant removal
evaporation of water
When water is adsorbed in narrow pores there is evidence of a disorderto-order transition at 298K.
Is this a first-order phase transition?
Surfactant Concentration
The phase diagram is obtained from a mean-field
approximation of a modified lattice gas model. Water as
solvent causes a lower critical point and a decrease of the
cmc with increasing temperature at low temperatures.
Surfactant Concentration in the Pore
Active site (-COOH)
Ammonia conversion tends to
increase due to electrostatic
interactions with the COOH
groups on the carbon surface.
Aqueous Surfactant Solution in Confinement
T*=0.29
Synthesis mechanism
Phase behavior of scCO2/surfactant/water systems using
Lattice Monte Carlo simulations*
Lauriane F. Scanu
Molar fraction of surfactant, XS
B
2.5E-03
CMC
2.0E-03
1.5E-03
1.0E-03
5.1E-04
1.0E-05
1.2
Observed structures
T*=0.26
Bulk Surfactant Concentration
Water as solvent causes an inverse temperature behavior
of surfactant adsorption from solution, i.e. the adsorbed
amount increases with increasing temperature.
Observed structures
1.3
1.4
1.5
1.6
1.7
Reduced density, r
1.9
Surfactants contain a CO2-phobic head (red) and a CO2-philic tail (yellow).
They phase separate at low density (rr <1.4). At rr 1.4, they form micelle or are
individually solubilized depending on the density and concentration with respect
to the CMC curve.
* In collaboration with Prof. Carol K. Hall
Silica/Surfactant concentration
1.8