Microscopic Observations of Polyacrylamide Structures
Authors: Ferrer Jose G. 
Published: December 2007

Polyacrylamide solutions have been used recently in Polyacrylamide solutions have been used recently in secondary recovery processes as mobility control agents. The literature presents several papers dealing with the behavior of these solutions in porous media and viscometers. Various investigators have presented theories describing the shapes and sizes of presented theories describing the shapes and sizes of polyacrylamides in water; however most of these polyacrylamides in water; however most of these investigators have based their conclusions on the measurement of apparent viscosities and resistance factors. But no one has made direct microscopic observations. This note is based upon results of microscopic studies' regarding the shape and size of Pusher 500* and Pusher 700* polyacrylamide polymer solutions after water had been evaporated. It was observed that the structures of these polymers are not linear but rather branched, and their shape and size can be modified by changing the pH or the NaCl concentration, or both. The structures observed have distances between their extremes several times greater than 0.45u; however, they can pass through filters of 0.45u. Fig. 1 shows portions of drops of Pusher 500 water-evaporated solutions as photographed through a conventional microscope. The pH of the solutions was 3.6, 8.0, and 10.8, reading from left to right. As can be seen from this figure, the shape of the polymer structures varies with the pH of the solution. The structures present more branches at an intermediate pH and larger, degraded structures at a low pH. This pH and larger, degraded structures at a low pH. This behavior explains the effect of pH on the apparent viscosities of polyacrylamide solutions as presented by Patton. Patton indicated that these solutions exhibit maximum apparent viscosities at intermediate pH. As we stated earlier, however, the structures of pH. As we stated earlier, however, the structures of polyacrylamides observed are more branched at this polyacrylamides observed are more branched at this pH. Consequently, the probability of interference pH. Consequently, the probability of interference between structures is greater, hence there is more resistance to flow. A photograph of a drop of Pusher 500 water-evaporated solution is shown in Fig. 2a. The pH of the solution was increased from an initial value of 3.6 to 10.6. It can be seen that branches regenerate; however, they seem to be larger than those shown in Fig. 1c, where the final pH was 10.6 but the initial pH was 8. This suggests that there is no permanent pH was 8. This suggests that there is no permanent change of structure of the Pusher 500 upon changing the Ph and that the original shapes can be nearly restored by changing the pH to its original value. The effect of NaCl in polyacrylamide solutions can be deduced from Fig. 2b. This figure shows a portion of a drop of 500 ppm water-evaporated solution of Pusher 500 with 0.1 percent NaCl and a pH of 8.0. Pusher 500 with 0.1 percent NaCl and a pH of 8.0. The structure shown in Fig. 2b is comparable with that of the low-ph pusher solution shown in Fig. la. This explains the behavior of ionizable polymers when there is an increase in NaCl concentration as reported by Mungan et al. The effect of filtration of polyacrylamide Pusher 500 solutions was studied by polyacrylamide Pusher 500 solutions was studied by passing the solution through filters of 0.45u. It was passing the solution through filters of 0.45u. It was observed that polymers having, certain structures were able to pass through these filters. Figs. lb and 2c are photographs of solutions of the same NaCl photographs of solutions of the same NaCl concentration and pH, before and after filtration, respectively. The structures are markedly similar. This suggest that they are highly flexible because they can pass through filters of 0.45u even when the maximum pass through filters of 0.45u even when the maximum distance between the extremes is several times greater than the openings in these filters. Microscopic observations on some nonionizable polymers indicate that their structures look like polymers indicate that their structures look like poly-acrylamides in the presence of NaCl or when the pH poly-acrylamides in the presence of NaCl or when the pH is low.

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