Polyacrylamide and its derivatives for oil recovery

Conformation and Size, Swelling Kinetics of Crosslinked PAM Microspheres 
The dry solid polyacrylamide microspheres before swelling were imaged using 
SEM (Figure 4a). The average diameter of the dry microgel particles was 6.9 μm with 
standard deviation of 2.5 μm. Most particles are spherical, which was expected for a 
spherical drop of polar fluid in a non-polar solvent-solvent suspension. Non-uniformity 
of particle size indicated the polymerization was by suspension rather than emulsion 
process. High exothermicity caused by free radical polymerization may the other reason 
for such non-uniformity. During the synthesis process, molten acrylamide monomer 
drops were dispersed within non-polar solvent in the absence of water. Dry microspheres 
were obtained after polymerization. 
The swelling kinetic of particle gels containing one crosslinker has been 
intensively studied.
40-43
and just one stage of expansion had been observed. In this paper, 
the produced microspheres showed different swelling kinetics as a function of 
temperature when dispersed into water. Two swelling stages, corresponding to the 
presence of the two different crosslinkers, were observed. Dry particles were firstly 

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a) 
b) 
Figure 4. 
a). SEM of polyacrylamide dry particles; b). Microscopic image of swelled 
polyacrylamide microgels.
 
put into DI water under 40 º
C for two months and swelling size was equilibrated.
Polymer microgel particles swelled rapidly in first several days, after which the swelling 
speed slowed and became zero. After reaching equilibrium state at 40 º
C, the average 
volume of the swollen microgels divided by the volume of the dry microspheres (V
f
/ V
o
) 
reached about 18 times the size of dry spheres. 
When the temperature of the microgel dispersions were elevated to 80 º
C, the 
microgels experienced a second expansion stage after more than a month at the higher 

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temperature. The particle sizes were measured by microscopic imaging of drop aliquots 
of microgel dispersion taken over time. At 80 º
C, the particles increased (= V
f
/ V
o
) to 
160 times the original size. Throughout the expansion process the polydisperse 
microgels retained a spherical conformation (Figure 4b).
Figure 5. 
Swelling kinetic and diameter change of crosslinked microgels in DI water 
under 40 º
C and 80 º
C. Different types of data are illustrated by different colors: black 
solid lines are swelling ratio and blue dash lines are diameter change. The filled symbols 
are data at 40 º
C and unfilled symbols are data at 80 º
C.
 
Swelling kinetics are illustrated in Figure 5. Two expansion stages were observed 
by change in particle diameter and therefore volume. Under the lower temperature (40 
º
C) swelling of microgel was constrained by both crosslinkers in a more compact 
structure. When the microgel particle dispersion entered the higher temperature stimuli, 
the labile crosslinker (PEGDA) was induced to cleave.
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The secondary expansion 
corresponded to a loosened network upon breakage of PEGDA (Figure 6). 

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