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Polymer hydrogels are a promising category of materials for conformance control of oil reservoirs. One of the main difficulties of this application is the severe temperature and salinity of many reservoirs. Nanotechnology is an alternative to improve the performance of gels, by enabling the insertion of reinforcement fillers in their composition, enhancing rheological properties, e.g., tan(delta) measurements. This study evaluated the properties of hydrogels based on partially hydrolyzed polyacrylamide (HPAM), with different molar masses, crosslinked with polyethyleneimine (PEI), with or without aluminum or zinc oxide. For simulation of one real reservoir characteristic, gelling systems were prepared with synthetic brine containing 29.940 mg/L of total dissolved solids (TDS) and aged at a temperature of 70 °C. The concentrations of 5000 mg/L of HPAM and 2200 mg/L of PEI were chosen to obtain nanocomposite hydrogels containing 50, 100, or 200 mg/L of oxides. The hydrogels were evaluated by means of the gel strength code, rheological tests, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results indicated that the best rheological properties were obtained by the nanocomposite hydrogels when compared to conventional hydrogels when aged at 70 °C. The viscous modulus/elastic modulus ratio (G″/G′) and tan(delta) factor indicated that the decrease of the elastic component began after 7 days for the conventional hydrogels and after 15 days for the nanocomposite hydrogels. The best filler concentration was 200 mg/L according to the tan(delta) values. The micrographs confirmed the presence of metal oxide particles in the polymer matrix, which possibly contributed to strengthening the structure of these materials. [ABSTRACT FROM AUTHOR]

Tetra-PEG gels, near-ideal polymer networks prepared by cross-end-coupling of A and B tetra-functional poly(ethylene glycol) (PEG) prepolymers having complementary end groups, were first fabricated in 2008. Comparisons of the mechanical properties with those of theoretical predictions indicate negligible fractions of defects and/or entanglements. Small-angle neutron scattering profiles of Tetra-PEG gels are very similar to those of the corresponding polymer solutions, suggesting negligible inhomogeneities originated from cross-linking. Due to the remarkable mechanical properties, extremely low structural inhomogeneities, and biocompatibility, tetra-PEG gels have gathered much attention since its discovery. The number of citation of Tetra-PEG gels is now over 2700 and is still growing rapidly. Chemical reaction kinetic studies also show a high degree of cross-linking reaction and its tunability, which leads to an idea of cross-linking probability tuned (p-tuned) networks. Versatility of the cross-coupling reactions allows us to prepare not only hydrogels but also organogels and ion gels, copolymer gels, non-stoichiometric gels, and so on. A decade history of the Tetra-PEG gels is reviewed with a variety of potential applications encompassing multiresponsive systems.ᅟ [ABSTRACT FROM AUTHOR]

We developed a pH-responsive, hydrogel based on poly(ethylene glycol) (PEG) covalently cross-linked with acrylic acid and N′,N′-dimethylacrylamide along with acid-labile groups. In the hydrogel, PEG plays a role as the key constituent. If its chains break, the polymer networks are destroyed. The pharmacological potential of these hydrogels were demonstrated by determining their water transport profile, modulus of elasticity, and cytotoxicity assay. The hydrogels showed a pseudo-Fickian behavior, a transport mechanism that occurs when the diffusion coefficient changes with the time and the swelling equilibrium is never fully reached. At pH 2, the PEG-richer hydrogels degraded and the scanning electron microscopy (SEM) images illustrated less-defined shapes than at pH 7 and 10. This morphological characteristic results of the hydrogel deconstruction owing to cleavage of ether bonds of the PEG chains unmaking its 3D polymer network. The proposed hydrogels were shown to be compatible to cells, indicating acceptable biocompatibility and an appropriate level of security for use in the biological environments. Furthermore, they showed structural changes in their polymer network in response to pH, which is an important characteristic for stimuli-triggered release of guest molecules. [ABSTRACT FROM AUTHOR]

a novel biomimetic polymer gel, we have been studying polymer gel with an autonomous self-oscillating function since it was firstly reported in 1996. For developing the polymer gels, we utilized an oscillating chemical reaction, called the Belousov-Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer gel is composed of a poly( N-isopropylacrylamide) network in which the metal catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous swelling-deswelling changes (in the case of gel) or cyclic soluble-insoluble changes (in the case of uncross-linked polymer) without any on-off switching of external stimuli. Several kinds of functional material systems utilizing the self-oscillating polymer and gel such as biomimetic actuators, mass transport surface, etc. are expected. Here, these recent progress on the self-oscillating polymer and gels and the design of functional material systems are summarized. [ABSTRACT FROM AUTHOR]

Covalently immobilized pore-surface gel phases were prepared in a functionalized macroporous ultra-high-molecular-weight polyethylene by covalent coupling of lightly cross-linked polymer colloid particles [50% styrene, 49.8% (chloromethyl)stryrene, 0.2% divinylbenzene] to the interstitial pore surfaces. Swelling the covalently coupled colloid particles in a good solvent followed by chemical derivitization resulted in an immobilized pore-surface gel phase rich in primary amine groups. The macromolecular reactivity and molecular size-exclusion characteristics of the aminated pore-surface gel phase were then determined using monofunctional, amine-reactive, poly (ethylene glycol)s (PEG). Pegylated pore-surface gel phases that ranged from 71% (10,000 molecular weight PEG) to 56% (40,000 molecular weight PEG) PEG by weight resulted from reaction of the aminated gel phase with the PEG probe molecules. The number of PEG molecules reacting with the aminated pore-surface gel phase depends only on the Flory radius (or radius of gyration) of the PEG molecule to the negative 2.49th power i.e., 1/ Rf 2.49, corresponding to a M−1.48 dependence. The immobilized and pegylated polymer colloid particles swell by a factor of 16–25 times the diameter of the original polymer colloid particles in water, thereby demonstrating that pegylation occurred though a substantial fraction of the volume of the immobilized colloid particles. [ABSTRACT FROM AUTHOR]

We report synthesis and characterization of a macroporous polymeric material containing a covalently immobilized pore-surface phase of well-defined thickness, gel-phase porosity and organic functional group content. The pore surfaces of otherwise inert macroporous (32 μm mean pore size) ultrahigh-molecular-weight polyethylene (UHMWPE) are aminated throughout using a low-pressure flowing-discharge process to enable covalent immobilization of lightly cross-linked polymer colloid particles on all pore surfaces in the monolith. Solvent swelling and chemical derivitization of the covalently immobilized polymer colloid particles produce a pore-surface gel phase of well-defined thickness, organic amine content, and gel-phase porosity. The low degree of cross-linking in the polymer colloid particles prevents dissolution of the immobilized colloid in good solvents and enables the formation of pore-surface gel phases having high gel porosity on swelling in good solvents. The pore-surface amination introduced by the flowing discharge process varies by less than 17% through 5-mm thickness of the macroporous UHMWPE material. The properties of the pore-surface gel phase also vary by less than 17% through the cross section. The pore-surface immobilized polymer colloid particles swell by a factor of 10 in water and tetrahydrofuran after derivitization with polyethylene glycol. [ABSTRACT FROM AUTHOR]