Transcript ICC - Paris

Environmentally Benign Deagglomeration and Mixing of Nanoparticles in Supercritical CO2
4
Shen ,
4
Vishnyakov ,
4
Tomassone
Yangyang
Aleksey
M. Silvina
1
Program NIRT; Award: DMI: 0506722; PI: Dr. Rajesh Davé
Co-PIs: R.
R. Pfeffer, S.
3
Sundaresan ,
M. S.
4
Tomassone
Jersey Institute of Technology, Newark, NJ, 2Auburn University, Auburn, AL, 3Princeton University, Princeton, NJ, 4Rutgers University, New Brunswick, NJ
Motivation
Interparticle Forces
 T = 77.4K, pbulk = 1atm
 FCC structured model
(MD)
 Spherical shell model
(GCMC)
Disjoining Pressure
particles at contact
Nex = N  Nbulk
– 276 SiO2 units
– D = 2.2 nm
2  
 R  2   
     
U sf R, h  = 2 s  2    
  
 
 

5 Rh
 h   5  R  h 
 Rh  Rh
10
0.1
10
4
4
large separation



0
-0.05
10
20
40
50
60
70
Hin,
ii. dependence on fluid model
25
0.1
4
CO2 on MCM at 195K -- Morishige vs Bakaev
Peaks correspond to the pore
width when a new layer is
formed and the separation
distance is small
Morishige - MCM41 36A
20
3
 T = 318K, pbulk = 68atm
p, Gpa
10
5
0
0.2
0.4
0.6
0.8
p /p 0
1
Sorption isotherms at 273 K on
amorphous silicas that differ only
by hydroxylation level
Sorption isotherms at 195K at
different amorphous silicas
The attraction is substantially
weaker for dehydroxylated particles
The disjoining force
is repulsive when
nanoparticles are
close, then
becomes attractive,
and finally
diminishes to zero
when the
separation is
sufficiently large.
dumbbell
1.5
bulk
Minima correspond to pore
width with large distance
between adjacent layers
0.5
-0.1
0
5
10
15
Fluid Models (CO2)
 Dumbbell with point quadruple
(Moller & Fischer, 1994 and 1997)
10
 2   sf
  
 5  z
.
p, Gpa

 sf 4

  sf 
  
 

3

 z  30.61  z  
10
6
4
2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
p/p 0
Experiment vs GCMC 195K
303K ~ Critical temperature
1.4
10
1.2
8
1
6
4
GCMC - 10-4-3
0.8
0.4
0.2
0.6
0.8
1
0
20
40
60
80
p, kPa
p /p 0
GCMC and experimental isotherms of
CO2 (Dumbbell model) at 195K
40
50
H in, A
Conclusions
GCMC, dumbbell, rough
0
0.4
30
References
GCMC, LJ 10-4-3
Bakaev's isotherm scaled
0.2
20
experiment, 303K
GCMC, dumbbell, 10-4-3
2
10
0.6
GCMC - rough surface
0
Contact:  Tel.: +1-732-445-2972  Fax: +1-732-445-2421  Email: [email protected]
Here, the influence of
inhomogeneities is negligible
 Both Monte Carlo and Molecular Dynamics approaches were
successfully applied to study the forces between two
spherical silica nanoparticles in a supercritical carbon dioxide
environment at realistic pressures.
 The two models considered (dumbbell and one-center LJ)
with validated parameters, accurately reproduce experimental
data on bulk CO2 and CO2 sorption on silica.
 Particles effectively attract at the lower pressures ranging 68100 atm and they experience repulsive forces for pressures
above 100 atm.
 These conclusions do not depend on the molecular model
considered.
 Energetic inhomogeneities do not significantly affect the
value of the force between the particles.
Point inhomogeneity: distance between the
solute molecule and inhomogeneity vs.
extra energy added to the “base” 10-4-3
0
LJ model: one set of parameters. LJ model does not fit experimental
isotherm at low temperature.
Dumbbell model: different sf to account for hydroxylation
0
4
U inh = 4ff
for r< 0.75
= 8ff r -10ff
for 0.75< r < 1.25
 mol/m2
mo l/m
8
Disjoining pressure for
dumbbell model with smooth
walls (10-4-3 potential) and
inhomogeneous walls at pbulk
=102atm
-0.1
12
2
...
12
rough
smooth
(bulk)
(2)
 Solid-fluid parameters:
fitting sf and sf for a surface in the presence of inhomogeneities
GCM C - strong field
GCM C - m edium field
GCM C - weak field
expt, M CM 41 (M orishige)
reference isotherm
14
60
H in, A
0.05
Attractive: blue; repulsive: red
Here sf and sf parameters are chosen to get the best fit of GCMC and
MD isotherms with the Steele potential to experiment
50
0.1
0

40
iii. dependence on surface roughness
Usf = Usf (z1)  Usf (z2 ) U inh
10
4

 sf 4

  sf 
  
 

3

 z  30.61  z  
30
Nature of force oscillations on the width differs in narrow pores. Pronounced oscillation
periodicity when LJ model is used. However, in general the results are consistent
 Interaction potential (with FCC structured nanoparticle)
 2   sf
2
U sf z  = 2 s  sf  sf   
 5  z
20
-0.05
(1)

10
Disjoining pressure for LJ and dumbbell models with smooth walls (10-4-3 potential
only) at pbulk =68atm
 Solid-fluid potential:
Steele’s potential + point inhomogeneities
U sf z  = 2 s  sf  sf
0
20
H in, A
Larger Particles and
Surface Inhomogeneity
2
-0.02
-0.08
 Interaction potential (with spherical shell nanoparticle)
This potential
reduces to the
10-4 form of
Steele potential
when R
approaching
infinity, which
represents a
flat surface.
0
-0.06
-0.5
The attraction is most prominent
for strongly hydroxylated particles
Solid-Fluid Interaction
0.02
-0.04
0
Interactions strongly depend on surface hydroxylation: Surface hydroxylation
increases => more energetic adsorption sites => adsorption is intensified
 2   10 2   10    4    4 
2 R 
U sf R, h  = 2 s     
  
 
 
 
h
5
R

h
5
R

h
R

h
R

h
  





 
 
0.04
LJ
2
1
0
LJ
dumbbell
bulk
0.06
2.5
.
Bakaev - dehydroxylated glass
15
0.08
.
Bakaev -hydroxylated glassglass
Reduction of pressure causes evaporation of the supercritical solvent -->
supersaturation of drug and subsequent precipitation
The fluid model must exactly reproduce the phase diagram and thermodynamic
properties of the bulk fluid in the given range of temperature and pressure.
30
Experimental Sorption Isotherms
 The drug is dissolved in the supercritical fluid
 The drug containing supercritical fluid is passed through an
expansion valve
 The nanoparticles are collected when the particles settle on a
collection plate
 = 3.68 Å
/kB = 286.2 K
Disjoining pressure for LJ model
at T=318K and different pbulk.
Long-range repulsion at pbulk
=102 and 200 atm, not observed
at 68 atm
68atm
102atm
200atm
68 atm (bulk)
102 atm (bulk)
200 atm (bulk)
0
 RESS: Rapid Expansion in Supercritical
Solvents
 One-center effective
Lennard-Jones particle
i=1
-0.1
Tc = 31.1 °C
Pc = 7.38 MPa
Low toxicity
High stability
 = 3.033 Å
/kB = 125.57 K
l = 0.699 Å
Q2/5 = 3.0255
i
 Fw2
  Pbulk
0.05
 Supercritical CO2




i
w1

adsorption micromole/square meter .
 Liquid-like density and solubility
 Gas-like diffusivity and viscosity
 An ideal medium for the purpose of deagglomerating
nanoparticles, because it can penetrate the pores within the
nano-agglomerates, and upon rapid depressurization, can
cause separation of the nanoparticles
F
LJ model influence of bulk
pressure
micromole /s qua re me te r .
 Supercritical fluids:
N
i. dependence on bulk pressure
3.5
Background
1
Pdisjoining =
A
derived form the Derjaguen approximation
p, Gpa
 Nanoparticles (NP) and nanocomposites have great potential
to improve performance of drugs, biomaterials, catalysts and
other high-value-added materials. They offer unique properties
that arise from their small size and large surface area.
 A major problem in utilizing nanoparticles is that they often lose
their high surface area due to grain growth or unavailability of
the high surface area where it matters. It is difficult to produce
forces required to deagglomerate the nanoparticles at a
sufficiently small length scale.
 The addition of nanoparticles to polymer composites has been
shown to significantly influence the mechanical, optical, and
electrical properties. However when nanoparticles aggregate,
they lose their nanoscale size and corresponding properties.
 The breakup of nanoagglomerates, driven by the tensile
stresses generated by depressurization, has not been studied
previously for nanoparticles and there is a paucity of published
analysis on this subject.
Nanoparticle Models (SiO2)
p, Gpa
1New
2
Gupta ,
GCMC and experimental isotherms of
CO2 (Dumbbell and LJ models) at 303K
100
Bakaev, V. A., W. A. Steele, et al. (1999). Journal of Chem. Phys. 111(21): 9813-9821.
Katoh, M., K. Sakamoto, et al. (2000). PCCP 2(19): 4471-4474.
Morishige, K., H. Fujii, et al. (1997). Langmuir 13(13): 3494-3498.
Möller, D. and J. Fischer (1994). Fluid Phase Equilibria 100: 35-61.
Span, R. and W. Wagner (1996). J. of Phys. and Chem. Refer. Data 25(6): 1509-1596.
Funding from NSF – NIRT (Award # 0506722) and IGERT (Award # 050497) is acknowledged.