Mechanism of Polyacrylamide Hydrogel Instability on High-Temperature Conditions

Abstract

A gel system composed of acrylamide (AM), N , N ′-methylenebisAM (BIS), and ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) was developed and applied extensively in reservoirs to reduce water cut and increase oil production in mature fields. However, this gel system suffers from thermal stability loss and syneresis at high temperatures that reduces its ability to control water flow. It has been widely accepted that the loss of gel thermal stability can be explained via three aspects: the rupture of polymer chains, the breakage of cross-linker chains, and hydrolysis of polymer. The mechanism of hydrogel syneresis through polymer hydrolysis has been investigated extensively in other publications. However, research on the other two mechanisms is quite limited. In this article, we conduct a series of experiments to demonstrate how the rupture of polymer and cross-linker chains leads to the hydrogel instability at high temperatures. Viscosity and energy-dispersive system measurements suggested that polyAM chains were disrupted by the oxidation reactions involving free radicals. The method to measure the cross-linking degree was established and in combination with X-ray photoelectron spectroscopy measurements, the results showed that cross-linker chains were broken as a result of weaker C–N bond resulting from positively charged mesomethylene carbon and hydrolysis of amide groups on the cross-linker. Because of the application of deionized water in the experiments, nuclear magnetic resonance and FTIR measurements showed that the hydrolysis degree of polymer was weak. Hence, our results verified that breakage of polymer and cross-linker chains led to the rupture of the gel network at high temperature. Besides, cross-linker chains may play a more important role in the thermal stability of the gel, which explains some work into high-temperature-resistant gels.

A Multiscale Investigation of Cross-Linked Polymer Gel Injection in Sandstone Gas Reservoirs: Implications for Water Shutoff Treatment

“…We also observed the shear thinning behavior, that is, viscosity decreased with an increasing shear rate (Figure ), which is also consistent with literature data. , The decrease in viscosity with an increasing shear rate is caused by the disruption of the polymer’s carbon–hydrogen bonds and devaluation in the intermolecular interaction between P­(AAM-co-AA)Na and Cr 3+ . , Such shear thinning ensures reduction in the local drag force during polymer injection in the field . However, small augmentations in viscosity at lower shear rates (i.e., 0.01–0.1 s –1 ) are attributed to the resistance offered by the polymeric solution to the deformation and is coherent with recent investigations. , …”

Virus blocking textile for SARS-CoV-2 using human body triboelectric energy harvesting

“…The human body can generate output current when skin (i) repeatedly contacts and separates from contact materials, and a flexible and transparent polyacrylamide (pAAm) hydrogel electrode is on the skin (ii) (see experimental procedures for the fabrication process of pAAm hydrogel electrode). 27 In step 1, skin (i) has triboelectric charges by triboelectrification. 28 As it is separated in step 2, the human body is polarized by electrostatic induction.…”

“…pAAm hydrogel electrode was prepared by sol-gel method and UV curing. 27 2.5 g acrylamide, 3 mg N,N′-methylenebis (acrylamide), and 25 mg ammonium persulfate were dissolved in 20 mL deionized water. After pouring the solution into the Petri dish mold, 20 μL N,N,N′,N'- tetramethyl ethylenediamine was added, and then the solution was cured by exposure of 365-nm UV light for 10 min, and the cured pAAm hydrogel was cut into squares of 3 cm dimension.…”

Polyacrylamide hydrogels prepared by varying water content during polymerization: Material characterization, reswelling ability, and aging resistance

“…For the samples stored in wet state, practically no changes in ESR are observed at low temperatures (7 C and 25 C), whereas a strong increase in ESR is found for the samples stored at 50 C, especially for those with high water contents. However, these undesirable changes in hydrogel morphology caused by hydrolysis [52] during wet storage at a high temperature can be avoided when the samples are dried before their storage.…”

“…The stability of PAAm hydrogels at elevated temperatures was investigated by Xiong et al [52] The hydrogel degradation due to polymer hydrolysis and subsequent ruptures of both polymer and cross-linker chains was indicated. As the degree of hydrolysis depends on hydrogel aging time and temperature, storage conditions of PAAm hydrogels should be carefully considered.…”