Supercritical Carbon Dioxide as Solvent for Polymer Thin Films
NCNR STONY BROOK K-JIST KOREA S. K. Satija, Y.-S. Seo T . Koga, M. H. Rafailovich, J. C. Sokolov K.W. Shin
NG7 Reflectometer
Polymer Thin Films
Confined geometry causes large differences in properties (glass transition, density, crystallinity, adhesion) as well as phenomena (phase separation/transition, chain dynamics) at surface or interface. air Question:
Solid Substrate scCO2 exposure
Any differences in properties and phenomena between bulk and thin films in scCO2 ?
2Rg
What is SCFs?
P
Liquid
SCFs
How do SCFs look like in microscopic scale?
Inhomogeneous media with high and low-density region
Pc
Solid Vapor
Tc
T
Tc: critical temperature Pc: critical pressure
Substance T (°C) c CO2 H20 NH3 31.3 374.1 132.5 Pc(MPa) 7.38 22.03 11.39
Key word “density fluctuations”
Unique features of both gas and liquid
Gaslike diffusivity,viscosity with liquidlike density
What is SCFs ?
High Pressure Neutron Reflectometry
Neutrons
qz
i
Si (1) Thickness (2) Roughness (3) Density can be obtained
i
Polymer
Isothermal Swelling Behavior
Pc
0.6 Linear Dilation
20°C 29°C 32°C 36°C 45°C 50°C
0.4
All swelling isotherms show the maxima near critical pressure (Pc) while bulk swelling has a plateau (~10%) with no maxima, i.e., very poor solvent.
0.2
I
20 15
50 °C
Bulk film
0.0 0 5 10 Pressure(MPa) 15 20
10 5 0 0 5 10 15 P(MPa) 20 25
deuterated styrene-butadiene copolymer (d-SBR, Mw=84k, 450 Å thickness)
Linear dilation=(L-L0)/L0 L0:Unswollen film thickness L: Unswollen film thickness
Both locus and shape for scattering intensity (density fluctuations) are similar to those of swelling !!
Density-Fluctuation-Induced Swelling
Density Fluctuations
<(DN)2>/=(N/V)
kBT
20
29 32 36
45 50 ºC
P
: Isothermal compressibility kB: Boltzman constant
N: Number of molecules in the corresponding volume V
Supercritical
Liquid
30
29 °C
A locus of maximal points is called as “ridge”
36 °C
<(DN) >/
CP Gas
“Ridge”
T
20
2
10
20 °C 50 °C
0
5
10 Pressure (MPa)
15
20
Anomalous swelling of polymer thin films in CO2 is associated to the density fluctuation ridge. Density fluctuations can significantly enhance the solvent quality in thin films even when the bulk miscibility with CO2 is very poor.
Structural Studies of Proteins in Model Cell Membranes
Melittin in Hybrid Bilayer Membranes
Susan Krueger, Chuck Majkrzak, Joe Dura, Norm Berk, NCNR Curt Meuse, Anne Plant, NIST Biotechnology Div.
Hybrid Bilayer Membrane Sample
H2O/D2O Melittin Deuterated Phospholipid C18 Alkanethiol (Ethylene Oxide)6
Scattering Length Density (SLD) Profile
(z)
w
Z
4 3 2 1
Gold-coated Silicon Substrate Incident beam
s
Reflected beam
Contrast Variation
Deuterated Lipid Head Group CD2
Contrast (D)
Lipid Head Group
CH2
Hybrid Bilayer Membranes Data
Used gold-coated substrates, chain-deuterated lipid and thin water reservoir to obtain data to high Q value.
Qmax~ 0.7 Å-1 !
Hybrid Bilayer Membranes Data Fitting
Used model-independent fitting technique to obtain SLD profile of biomimetic membranes.
SLD Profiles (bilayer region only)
Models of Hybrid Bilayer Membranes
with Mounir Tarek, NIST NCNR
Used MD simulations and scattering length density profiles to obtain structural models of biomimetic membranes.
Roughness
Conclusions
SLD profiles show :
there is no water in the (ethylene oxide)6 layer.
melittin perturbs the headgroup layer significantly, most likely causing the depletion of water in the layer. although melittin lies in the headgroup region, it induces changes in the middle of the alkane region, most likely causing a change in tilt of the alkane chains.
Krueger, S., Meuse, C.W., Majkrzak, C.F., Dura, J.A., Berk, N.F., Tarek, M., Plant A.L. (2001). Langmuir 17, 511.
Amyloid β Peptide – Possible Mechanisms of Alzheimer’s Toxicity
Frank Heinrich, Duncan McGillivray, Mathias Loesche, Carnegie Mellon Univ. Jim Hall, Univ. of California, Irvine
Amyloid β forms ion channels which allow calcium uptake, leading to rapid neuronal degeneration or death.
Amyloid β leads to a disruption (thinning) of the membrane without penetration.
The Biomimetic Membrane System
INNER LEAFLET: Two alkyl tails joined through a glycerol to a thiolated hexa (ethylene oxide) “spacer” (WC14). This spacer supports the membrane above a gold-coated Si solid support, providing a ≈20Å, partly water-filled, submembrane space.
OUTER LEAFLET: DOPC monolayer.
Neutron Reflectivity Data
Used model-dependent fitting technique, simultaneously fitting data obtained using mixtures of H2O and D2O buffers.
D2O buffer
Other measurements made with mixtures of H2O and D2O buffers are not shown.
Scattering Length Density Profiles
D2O buffer
Conclusions
SLD profiles show :
the inner leaflet is not affected by amyloid β. No Channel a significant decrease of the membrane thickness in presence of amyloid β. Membrane Thinning