Supercritical Carbon Dioxide as Solvent for Polymer Thin Films S. K. Satija,Y.-S. Seo STONY BROOKT. Koga, M. H. Rafailovich, J. C. Sokolov K-JIST KOREA K.W. Shin NCNR

NG7 Reflectometer

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. Solid Substrate Question: Any differences in properties and phenomena between bulk and thin films in scCO 2 ? air 2Rg scCO 2 exposure Polymer Thin Films

How do SCFs look like in microscopic scale? P P c T T c SCFs T c : critical temperature P c : critical pressure What is SCFs ? Liquid Vapor Solid H 2 0 NH 3 T c (°C) P c (MPa) CO Substance Key word “density fluctuations” What is SCFs?

Neutrons ii ii Si qzqz (1) Thickness (2) Roughness (3) Density can be obtained Polymer High Pressure Neutron Reflectometry

I P(MPa) 50°C deuterated styrene-butadiene copolymer (d-SBR, Mw=84k, 450 Å thickness) L i n e a r D i l a t i o n Pressure(MPa) 29° C 32°C 36°C 45°C 50°C 20°C Bulk film Pc 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. Both locus and shape for scattering intensity (density fluctuations) are similar to those of swelling !! Isothermal Swelling Behavior

< (          Pressure(MPa) 20°C 29°C 36°C 50°C Density Fluctuations P T ºC “Ridge” Liquid Gas CP Supercritical Anomalous swelling of polymer thin films in CO 2 is associated to the density fluctuation ridge. Density fluctuations can significantly enhance the solvent quality in thin films even when the bulk miscibility with CO 2 is very poor. A locus of maximal points is called as “ridge” Density-Fluctuation-Induced Swelling

Structural Studies of Proteins in Model Cell Membranes

Hybrid Bilayer Membrane Sample Scattering Length Density (SLD) Profile Gold-coated Silicon Substrate Deuterated Phospholipid C 18 Alkanethiol H 2 O/D 2 O Melittin (Ethylene Oxide) 6 Z Incident beam Reflected beam ww 33 22 11 ss   44  (z) Melittin in Hybrid Bilayer Membranes Susan Krueger, Chuck Majkrzak, Joe Dura, Norm Berk, NCNR Curt Meuse, Anne Plant, NIST Biotechnology Div.

Contrast Variation Deuterated Protein Deuterated RNA CD 2 Deuterated Lipid Head Group RNA DNA Water Protein Lipid Head Group CH 2 Contrast (  )

Used gold-coated substrates, chain-deuterated lipid and thin water reservoir to obtain data to high Q value. Q max ~ 0.7 Å -1 ! Hybrid Bilayer Membranes Data

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 Used MD simulations and scattering length density profiles to obtain structural models of biomimetic membranes. with Mounir Tarek, NIST NCNR 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 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. Frank Heinrich, Duncan McGillivray, Mathias Loesche, Carnegie Mellon Univ. Jim Hall, Univ. of California, Irvine

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, sub- membrane space. OUTER LEAFLET: DOPC monolayer.

Neutron Reflectivity Data D 2 O buffer Other measurements made with mixtures of H 2 O and D 2 O buffers are not shown. Used model-dependent fitting technique, simultaneously fitting data obtained using mixtures of H 2 O and D 2 O buffers.

Scattering Length Density Profiles D 2 O 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