The demixing of immiscible polymers in low gravity is discussed. Applications of knowledge gained in this research will provide a better understanding of the role of phase segregation in determining the properties of polymer blends made from immiscible polymers. Knowledge will also be gained regarding the purification of biological materials by partitioning between the two liquid phases formed by solution of the polymers polyethylene glycol and dextran in water. Testing of new apparatus for space flight, extension of affinity phase partitioning, refinement of polymer chemistry, and demixing of isopycnic polymer phases in a one gravity environment are discussed

Harris, J. Milton

English

NASA Technical Reports Server

N88-11868 
Center: Consortium for Materials Development in Space 
The University of Alabama in Huntsville (UAH) 
Project Name: "Physical Properties of Immiscible Polymers" 
The University of Alabama in Huntsville 
J. Milton Harris 
Annual Report: September 15, 1986 to September 14, 1987 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Introduction 
This project involves investigation of demixing of immiscible polymers in 
low-G and applications of this knowledge to: (a) providing a better understand- 
ing of the role of phase segregation in determining the properties of  polymer 
blends made from immiscible polymers, and (b) purification of biological materi- 
als by partitioning between the two liquid phases formed by solution of the pol- 
ymers polyethylene glycol (PEG) and dextran in water. 
It should be noted that this project has changed directions again in that 
NASA required Celanese to drop out of the Consortium after they were purchased 
by a German firm. 
Work has proceeded in four areas during the past year: 
1. Testing of New Apparatus for Space Flight 
2 .  Extension of Affinity Phase Partitioning 
3 .  Refinement of Polymer Chemistry 
4. Denixing of Isopycnic Polymer Phases in One-G 
Testing of New Apparatus for Space Flight 
F. C. Wessling has worked with us on a redesign o f  the low-G, phase-demixing 
apparatus. The new apparatus, which has been constructed, consists of an alumi- 
72 
https://ntrs.nasa.gov/search.jsp?R=19880002486 2020-03-20T08:40:58+00:00Z
I 
I 
I 
1 
I 
I 
I 
I 
I 
I 
I 
1 
I 
I 
I 
I 
I 
I 
I 
nun block containing two rows of six cavities (for a total of twelve chambers). 
Each cavity will contain a glass cube (1.6 cm3) which in turn will contain a 
polymer two-phase system and a small stirring bar. 
small stirring motors with magnets attached to the shafts. Thus there are six 
motors along the top of the apparatus and six along the bottom. 
design, stirring was done by passing a shaft and paddle through an O-ring into 
the phase system container. 
we should now have a much improved device; leakage and shaft freezing, which 
were problems with the old design, are now eliminated. In addition, the new 
apparatus has heating wires attached to provide heating (necessary in the GAS 
can) and temperature control. We have also purchased a Nikon F3 to be used with 
this apparatus. 
Stirring is provided by 
In our previous 
By eliminating the O-ring and sealing the container 
The apparatus has been flown twice on KC 135 flights, and it performed well. 
We are now making slight modifications for automated flight as a GAS experiment. 
We are considering modifications to make the apparatus suitable for sounding- 
rocket flight. 
Extension of Affinity Phase Partitioning 
A major interest of ours is in developing the technique of affinity phase 
partitioning (with polymer two-phase systems) for eventual use in low-G separa- 
tion of cells of commercial importance. Previous work has shown that gravity- 
driven demixing of the polymer two-phase systems greatly reduces the efficiency 
of phase partitioning on Earth; if this randomizing force were removed from 
affinity phase partitioning, a cell separation procedure of perfect selectivity 
(no undesired cells would be retained) would be provided. Affinity phase 
partitioning, previously developed by us, utilizes an affinity ligand (an 
73 
1 
I 
1 
1 
I 
I 
1 
I 
I 
I 
I 
I 
1 
I 
I 
1 
1 
I 
I 
antibody) attached to PEG to pull cells into the PEG-rich phase (unwanted cells 
remain at the interface between the PEG-rich and dextran-rich phases). 
Previously, we have applied this technique to purifying red blood cells 
using antibodies to the cells as affinity ligands. In the present project we 
have worked on extending this technique by covalently binding protein-A, rather 
than antibody, to PEG. Protein-A is of interest because it binds antibodies. 
Thus if protein-A is covalently attached to PEG, exposure to any antibody will 
provide ready binding, via to the protein-A, of the antibody to PEG. This would 
greatly simplify the technique since it would remove the necessity of covalently 
binding every desired antibody to PEG; a single PEG-protein-A preparation could 
be used for a large number of affinity separations. 
We have now covalently coupled PEG to protein-A and have shown that this 
material will bind to the antibody to human red blood cells and this complex 
will pull these cells into the top PEG-rich phase. Thus we have greatly simpli- 
fied the general application o f  the phase partitioning technique to cell 
separations. 
Work in the past quarter has dealt with application of this technique to 
purifying megakaryocytes. These are cells which are of interest for future 
space experiments to test the limits of the technique on large cells for which 
gravity-driven sedimentation of the cells themselves is a problem. Preliminary 
results are promising. 
Refinement of Polymer Chemistry 
For the affinity partitioning procedure it is necessary that we have effec- 
tive chemistry for coupling PEG to proteins. An additional chemistry require- 
ment is for coupling PEG and dextran t o  glass to control phase demixing 
74 
~ ~- ~~ 
B 
I 
I 
D 
‘I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
1 
i 
I 
I 
I 
75 
(discussed below). 
required polymer chemistry. 
Thus we have an on-going effort in development of the 
1. PEG-Protein Chemistry 
We have had a long-term effort in evaluating and developing the chemistry 
for attaching PEG to proteins. 
completion. In the last quarter we have completed the bulk of the work neces- 
sary to: (a) show the relationship between coupling method and protein activity: 
(b) understand the effect of organic solvents on protein activity and stability: 
and (c) show the effect of linking proteins to solid supports (glass). We are 
now writing up this work. 
A large segment of this work is now approaching 
2 .  Improvement of Coating Chemistry for Conrol of Wall Wetting 
A key part of this research program lies in controlling the demixing rate of 
immiscible polymers by controlling wall wetting by the immiscible phases. Thus 
we have been examining the effect of covalently bound dextran on the demixing 
rate for the immiscible phases formed from solution in water of dextran and PEG. 
It is obviously critical for this work that the chemistry used to bind dextran 
to the glass containers be effective. In the past we have evaluated our chemis- 
try by wet chemical methods. A great improvement in this evaluation procedure 
results from use of X-ray photelectron spectroscopy (XPS or ESCA) .  With this 
technique it is possible to directly determine the elemental composition of the 
surface with great accuracy. 
I 
I 
I 
1 
I 
1 
I 
B 
1 
I 
4 
1 
I 
1 
1 
I 
1 
I 
I .  
76 
Our method for coupling dextran to surfaces has been to first apply an amine 
sublayer and then to couple the dextran reducing terminus to this amine group. 
During the past quarter we have used XPS to greatly improve (factor of three) 
the thickness of the amine sublayer. 
ing the amine reagents on the glass and heating at 120°C. 
been washing the reagents off before heating under the supposition that the rea- 
gents were held by hydrogen bonding (as published in the literature). 
In the next quarter we will apply the XPS technique to evaluate coupling of 
Basically this improvement came from leav- 
Previously we had 
dextran to the amine sublayer. 
Demixing of Isopycnic Polymer Phases in One-G 
We have been making a major effort to better understand the gravitational 
inputs t o  phase demixing. The question here is: what are the forces which lead 
to separation or dernixing of two stirred but immiscible liquids in the absence 
of gravity-driven sedimentation? To advance work in this area we will quantify 
the phase demixing of isopycnic phase systems. The apparatus for studying this 
process has been assembled (consisting of a Nikon F3 with motor drive and data 
back, and a 2 in. by 2 in. thermostatted cell to contain cuvettes holding two- 
phase systems). 
process as a function of time. Now we are working on automation of the charac- 
terization process (i-e., determination of the growth rate of droplets or 
domains) by use of an Ornnicon Scanner. In addition we are examining the effect 
of polymeric wall coatings (dextran in particular) on the rate of demixing; the 
goal is to control the rate and to control which phase (dextran-rich or 
PEG-rich) goes to the center of the cuvette. Coating effects are observed, but 
it would be premature at this point to attempt quantitative description of these 
effects. 
We have obtained quality photographs of  the phase demixing 
I 
I 
1 
1 
I 
I 
I 
I 
1 
I 
I 
1 
I 
I 
I 
I 
1 
I 
I 
Contact-angle measurements are also being done, as part of another project, 
to aid in understanding the coating effects. 
dextran wall coating will lead to the dextran-rich phase against the wall of the 
cuvette. 
These studies indicate that a 
77 


Physical properties of immiscible polymers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server