Polyacrylamide and its derivatives for oil recovery

Characterization 
Fourier transform infrared (FTIR) spectroscopy 
FTIR spectra of the powder samples were recorded on a Nexus 470 FT-IR 
(Thermo Electron Corp.). Particle gels were vacuum dried overnight at 60 °C and 
10mmHg. Dried particle hydrogels samples were diluted by mixing dry polyacrylamide 
microspheres with KBr at about 1:100 (wt/wt) ratio. Spectra were collected at 2 cm
-
1
resolution in mid-IR region (4000–400) cm
−1
. 

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Scanning electron microscopy (SEM) study
SEM was performed using a Helios Nanolab 600 FIB scanning electron 
microscope. Swelled hydrogels were cut into small pieces and freeze-dried to keep their 
original network structures. The dried hydrogel-networks were directly mounted using 
conductive tape to a stainless steel SEM stub, and sputter coated with Au/Pd. SEM 
imaging was conducted using a field emission source at a 5kV accelerating voltage and 
43 pA current at a working distance of 3 to 6 mm with an Everhart-Thornley detector.
 
Swelling properties of PVA/PAM IPN hydrogels 
Dried crude hydrogel was cut into particles of size 20 to 30 mesh (0.60 to 0.84 
mm). These particles were placed into a conical graduate cylinder with volumetric scale. 
Dry particles’ volume was measured and immersed into brine of a specific salt 
concentration to absorb water and swell. The swollen volume of the PVA/PAM IPN was 
measured under room temperature (25 º
C). The same procedure was repeated for the 
solutions of different pH values (2 to 7), which was adjusted by aqueous HCl and NaOH 
solutions. The swelling ratio (SR) was calculated by the following equation: 
SR=V
s
/V
d
Equation 1
where 
V
s
and 
V
d
are the measured volumes in their swollen and dry states, respectively.
Rheological and mechanical properties of PVA/PAM IPN hydrogels 
Rheological measurements were carried out with Haake Marsi II Rheometer 
(Germany) with a parallel-plate system PP35-Ti under ambient temperature (25 º
C) with 
‘gel disc’ model. Detailed procedures follow the method of Bai, et al.[49] In this study, 
two predominating methods were involved, dynamic rheological measurement (DRM), 
focused on oscillatory shear, and static rheological measurement (SRM) featuring 

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unidirectional, constant rotational shear. Samples were prepared by cutting the swollen 
bulk gels into 8 x 8 x 3mm cubes.