# Presentation: 532466

## Supercritical Carbon Dioxide as Solvent  for Polymer Thin Films

- S. K. Satija,

- Y.-S. Seo

- STONY BROOK

- T . Koga, M. H. Rafailovich,  J. C. Sokolov

- K-JIST KOREA         K.W. Shin

- NCNR

## NG7 Reflectometer

**NG7 Reflectometer**

## Polymer Thin Films

**	**_**Question**_:
- 	Any differences in properties and phenomena between bulk and thin films in scCO2 ?

- air

- 2Rg

**Polymer Thin Films**

## What is SCFs?

- P

- P

- c

- T

- T

- c

- SCFs

- Tc: critical temperature
- Pc: critical pressure

- <Schematic view of molecular distribution>

- Liquid

- Vapor

- Solid

- Key word
- “density fluctuations”

**What is SCFs?**

## High Pressure Neutron Reflectometry

- <Reflectivity geometry>

- qz

- (1) Thickness
- (2) Roughness
- (3) Density
- can be obtained

- Polymer

**High Pressure Neutron Reflectometry**

## Slide 6

## Isothermal Swelling Behavior

- <Scattering intensity from pure CO2>

- deuterated styrene-butadiene copolymer
- (d-SBR, Mw=84k, 450 Å thickness)

- 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.

**Isothermal Swelling Behavior**

## Density-Fluctuation-Induced Swelling

- 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.

- A locus of maximal points is called as “ridge”

**Density-Fluctuation-Induced Swelling**

## Structural Studies of Proteins in Model Cell Membranes

## Melittin in Hybrid Bilayer Membranes

- Hybrid Bilayer
- Membrane Sample

- Scattering Length
- Density (SLD) Profile

**Gold-coated**
**Silicon Substrate**

******(z)**

**Melittin in Hybrid Bilayer Membranes**

- Susan Krueger, Chuck Majkrzak, Joe Dura, Norm Berk, NCNR
- Curt Meuse, Anne Plant, NIST Biotechnology Div.

## Contrast Variation

**Contrast (********)**

## 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**

## 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

**Neutron Reflectivity Data**

**D****2****O buffer**

- Other measurements made with mixtures of H2O and D2O buffers are not shown.

- Used model-dependent fitting technique, simultaneously fitting data obtained using mixtures of H2O and D2O 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**