Cross-linked Polymer Gels Research Articles

Freezing-Induced Mechanoluminescence of Cross-Linked Polymer Gels Based on Mechanocleavable Dynamic Carbon-Carbon Covalent Bonds

Polymer mechanochemistry is a fundamental research field to understand how macroscopic mechanical forces are applied to polymeric materials. As a branch of mechanochemistry, mechanochromism, changing color in response to mechanical stress, has been achieved by various stimuli such as tension, compression, shearing, and sonication. Surprisingly freezing also induces mechanical stress. Previous study of our research group showed freezing-induced mechanochromism (FIM) of polymer gels, where diarylbibenzofuranone (DABBF) derivatives at the cross-linking points acting as the color-changing mechanophores was homolytically cleaved to form blue-colored radical in response to shear force induced by freezing.1 In this study, freezing-induced mechanoluminescence was achieved by the introduction of tetraarylsuccinonitrile (TASN)2 skelton as a yellow light-emitting mechanophore into the cross-linking points of polymer gels (TASN gel, Fig. 1). FIM of TASN gel enhanced capability to see mechanical stress with not only pink coloration but also yellow light emission under UV irradiation. The mechanism and characteristics of FIM were studied with the quantitative evaluation by electron paramagnetic resonance (EPR) measurements, revealing that the network structure3 and solvent affinity with polymer chain had good correlations with the dissociation behavior of TASN in FIM.4 Fig. 1 Freezing-induced mechanoluminescence of TASN gel.4 H. Otsuka et al., Angew. Chem. Int. Ed. 2015,54, 6168-6172.H. Otsuka et al., Chem. Commun. 2017, 53, 11885-11888.H. Otsuka et al., J. Am. Chem. Soc. 2014,136, 11839-11845.S. Kato, K. Ishizuki, D. Aoki, R. Goseki, H. Otsuka, submitted. Figure 1

Synthesis of Single-Walled Carbon Nanotubes Coated with Thiol-Reactive Gel via Emulsion Polymerization.

Single-walled carbon nanotubes (SWNTs) have unique near-infrared absorption and photoemission properties that are attractive for in vivo biological applications such as photothermal cancer treatment and bioimaging. Therefore, a smart functionalization strategy for SWNTs to create biocompatible surfaces and introduce various ligands to target active cancer cells without losing the unique optical properties of the SWNTs is strongly desired. This paper reports the design and synthesis of a SWNT/gel hybrid containing maleimide groups, which react with various thiol compounds through Michael addition reactions. In this hybrid, the method called carbon nanotube micelle polymerization was used to noncovalently modify the surface of SWNTs with a cross-linked polymer gel layer. This method can form an extremely stable gel layer on SWNTs; such stability is essential for in vivo biological applications. The monomer used to form the gel layer contained a maleimide group, which was protected with furan in endo-form. The resulting hybrid was treated in water to induce deprotection via a retro-Diels-Alder reaction and then functionalized with thiol compounds through Michael addition. The functionalization of the hybrid was explored using a thiol-containing fluorescent dye as a model thiol, and the formation of the SWNT-dye conjugate was confirmed by energy transfer from the dye to SWNTs. Our strategy offers a promising SWNT-based platform for biological functionalization for cancer targeting, imaging, and treatment.

Photoinduced reinforcement of supramolecular gels based on a coumarin-containing gelator

The mechanical strength of supramolecular gels is usually low compared to that of cross-linked polymer gels, which sometimes limits practical applications of supramolecular gels. We report here photoinduced reinforcement of supramolecular gel structures using photodimerization of coumarin moieties introduced on a trans-(1R,2R)-1,2-cyclohexanediamine-based gelator. UV irradiation (λ > 300 nm) of toluene gels containing mixtures of trans-(1R,2R)-1,2-cyclohexanediamine-based gelators with and without coumarin moieties induced an enhancement in both the thermal and mechanical stabilities of the gels.

Study on rheology and microstructure of phenolic resin cross-linked nonionic polyacrylamide (NPAM) gel for profile control and water shutoff treatments

Phenolic resin cross-linked polymer gel as a plugging agent for profile control and water shutoff has wide industrial applications. There have been many studies on the gel, but research on the rheology and microstructure has not been systematic. In this study, the rheological properties and microstructure of phenolic resin gel were measured by using a Haake Mars 60 rheometer and a Carl Zeiss Jena cryo-etching electron microscope. Viscosity and viscoelastic moduli of the gel rose constantly and the structure became denser during the gelation process. An increasing polymer or cross-linker concentration increased the viscosity and viscoelastic moduli of the gel. This increase is attributed to a higher polymer concentration contributing to form a stronger membrane structure and a higher cross-linker concentration making the density of the spherical particles higher. The addition of salt and acid affected the stability of the gel. As salinity increased or pH decreased, both the viscosity and viscoelastic moduli of the gel decreased. Combined with the microstructures of the gel systems, this outcome confirmed that salt and acid made the structure of the gel fragile and easily dehydrated. The results showed that phenolic resin gel (gelation temperature: 95 °C; aging time: 8 h) can maintain good stability under a salinity of less than 30,000 mg/L or alkaline conditions with pH > 7. This study can help to understand the gelation mechanism of phenolic resin gel and the impact mechanism of various factors.

Mesoscopic Heterogeneity in Pore Size of Supramolecular Networks.

There has been a considerable interest in developing new types of gels based on a network of fibrous aggregate composed of low molecular weight gelators, also known as supramolecular gels (SMGs). Unlike conventional polymer gels with chemical cross-linking, the network formation in SMGs does not involve any covalent bonds. Thus, the network in SMGs has been often regarded as homogenous or less heterogeneous in comparison with that in chemically cross-linked polymer gels. In this study, we have experimentally verified the existence of the network heterogeneity even in SMGs. The thermal motion of probe particles in SMGs, which were prepared from aqueous dispersions of gelators having a different number of peptide residues, PalGH, PalG2H, and PalG3H, was tracked. The gels were spatially heterogeneous in terms of the network pore size, as evidenced by the variation in the particle motion depending on the location, at which a particle existed. With varying particle size, it was found that the characteristic length scale of the heterogeneity was in the order of (sub)micrometers and was smaller in the order of the PalG2H, PalG3H, and PalGH gels.

Microencapsulation of 2,2′-Azobis(2-methylpropionamide) dihydrochloride initiator using acrylonitrile butadiene styrene as shell for application in lost-circulation control

Gel sealants are often used to recover lost circulation, a problem that plagues drilling engineers throughout many oil and gas development project. Organic cross-linked polymer gel such as cross-linked polyacrylamide gel is one of the most popular and available gel sealant materials. It is of strong sealing ability, but the gelation time is too short to control and ensure safe drilling operation. Initiator used to supply free radical can prolong polyacrylamide gelation time, but the gelation time will dramatically decline with the increase of temperature. Microencapsulation of initiator can increase the gelation time because the concentration of initiator is controlled effectively by microcapsules. This paper proposes microcapsules of an initiator, 2,2′-Azobis(2-methylpropionamide) dihydrochloride (AIBA) encapsulated by Acrylonitrile Butadiene Styrene, prolonging the gelation time of cross-linked polyacrylamide gel. It was prepared via coacervation induced by polydimethylsiloxane (PDMS). The gelation time was prolonged to be eight times greater than that initiated by free AIBA initiator. Fourier transform infrared spectroscopy, thermogravimetric analysis, Ultraviolet-visible spectroscopy, specific surface area analysis, and scanning electron microscopy were used to observe the properties of microcapsules. The results indicated that AIBA was successfully microencapsulated and there were nano-sized pores in the outer surfaces of the microcapsules which serve to control the release of AIBA, and viscosity of PDMS and core/shell ration affected the content of AIBA loaded in the microcapsules. Moreover, it is microencapsulation that makes the concentration of AIBA in water increase stable as a function of time for prolonging the gelation time of sealant system. Computerized tomography (CT) scans revealed that the cross-linked polymer gel system significantly reduces the number of pores inside the cores and enhances pressure-bearing ability. Cross-linked polyacrylamide gel initiated by encapsulated AIBA shows notable potential for recovering lost circulation.

A monolithic column based on covalent cross-linked polymer gels for online extraction and analysis of trace aflatoxins in food sample

Aflatoxins are highly toxic mycotoxin contamination, which pose serious food safety incidents. It is very important to precisely and rapidly determine trace aflatoxins in food. In this study, we designed porous monolithic column based on covalent cross-linked polymer gels for online extraction and analysis of trace aflatoxins in food samples with complicated matrices coupled with high-performance liquid chromatography-ultraviolet detector (HPLC-UV). The prepared monolithic column showed excellent enrichment performance due to its good permeability, good reproducibility and long life span. The study of adsorption mechanism suggested that the excellent enrichment performance of this monolithic column was attributed to the multiple effect of π-π stacking interaction, hydrophobic effect and steric effect. When the online analytical method was applied for the determine of trace aflatoxins in real food samples, aflatoxins G1 and aflatoxins B1 could be actually found in one positive bean sauce sample and quantified to be 32.8 and 26.4 μg/kg, respectively. Aflatoxins G1 in one bean sample could be also found and quantified to be 25.9 μg/kg. The low detection limits of the developed method were achieved in range of 0.08-0.2 μg/kg. And the recoveries for spiked samples were in range from 76.1 to 113% with RSDs of 1.1-9.6%. The developed method was proved to be a promising method for online enrichment and analysis of trace aflatoxins in complicated food samples.

Cross-linked AIE supramolecular polymer gels with multiple stimuli-responsive behaviours constructed by hierarchical self-assembly

Cross-linked AIE supramolecular polymer gels were successfully constructed by hierarchical self-assembly.

Concentration-dependent swelling and structure of ionic microgels: simulation and theory of a coarse-grained model.

We study swelling and structural properties of ionic microgel suspensions within a comprehensive coarse-grained model that combines the polymeric and colloidal natures of microgels as permeable, compressible, charged spheres governed by effective interparticle interactions. The model synthesizes the Flory-Rehner theory of cross-linked polymer gels, the Hertz continuum theory of effective elastic interactions, and a theory of density-dependent effective electrostatic interactions. Implementing the model using Monte Carlo simulation and thermodynamic perturbation theory, we compute equilibrium particle size distributions, swelling ratios, volume fractions, net valences, radial distribution functions, and static structure factors as functions of concentration. Trial Monte Carlo moves comprising particle displacements and size variations are accepted or rejected based on the total change in elastic and electrostatic energies. The theory combines first-order thermodynamic perturbation and variational free energy approximations. For illustrative system parameters, theory and simulation agree closely at concentrations ranging from dilute to beyond particle overlap. With increasing concentration, as microgels deswell, we predict a decrease in the net valence and an unusual saturation of pair correlations. Comparison with experimental data for deionized, aqueous suspensions of PNIPAM particles demonstrates the capacity of the coarse-grained model to predict and interpret measured swelling behavior.

Polymer Gel Systems for Water Management in High-Temperature Petroleum Reservoirs: A Chemical Review

Polymer gel systems as water management materials have been widely used in recent years for enhanced oil recovery applications. However, most polymer gel systems are limited in their ability to withstand the harsh environments of high temperature and high salinity. Those polymer gel systems that can handle high-temperature excessive water treatments are reviewed in this paper and categorized into three major types: in situ cross-linked polymer gels, preformed gels, and foamed gels. Future directions for the development of polymer gel systems for high-temperature conditions are recommended. For excessive water management with temperatures from 80 to 120 °C, current polymer systems are substantially adequate. Polymer gel systems composed of partially hydrolyzed polyacrylamide (HPAM)/chromium can be combined with nanoparticle technology to elongate their gelation time and reduce the adsorption of chromium ions in the formation. Phenolic resin cross-linker systems have reasonable gelation times and gel streng...

Electrochemical and Mechanical Properties of Sodium-Ion Conducting Cross-Linked Polymer Gel Electrolyte

Electrochemical and Mechanical Properties of Sodium-Ion Conducting Cross-Linked Polymer Gel Electrolyte

Swelling kinetics of cross-linked polymer gels based on polystyrene and poly(vinyl alcohol) in aqueous solutions of electrolytes and sucrose

The swelling kinetics of polymer gels has been studied in water and aqueous solutions by optical micrometry. Cross-linked hydrophilic polymers based on polystyrene and poly(vinyl alcohol) have been used as gel-forming materials. The effects of the natures of the matrices and polar groups of the polymers and their cross-linking densities and granule sizes, as well as the properties of external phase, on the swelling kinetics of the polymer gels have been investigated. The experimental results have been processed in terms of a heterophase kinetic model. The applicability of the model to describing the behavior of all studied systems has been shown.

Study on a Novel Cross-Linked Polymer Gel Strengthened with Silica Nanoparticles

This paper studied the strengthening effects of silica nanoparticles on the polyacrylamide (PAM)/hydroquinone (HQ)–hexamethylenetetramine (HMTA) composite gel. Pure PAM/HQ–HMTA gel and PAM/HQ–HMTA gels containing silica nanoparticles up to 0.3 wt % were prepared at 110 °C. Influences of silica nanoparticles on gelation performances were systematically evaluated. By the addition of silica nanoparticles, the gelation time became shorter and the gel strength was improved observably. Rheological measurements showed that silica nanoparticles enhanced both elasticity and viscosity of the gel significantly. Thermal stability of the gel was studied by differential scanning calorimetry (DSC) measurements. The maximum tolerated temperature of the gel was improved from 137.8 to 155.5 °C by the addition of silica nanoparticles with a concentration of 0.3 wt %. Furthermore, to study the strengthening mechanisms of silica nanoparticles to the gel, the microstructure and existing state of water within the gel were inves...

Development of New Supramolecular Lyotropic Liquid Crystals and Their Application as Alignment Media for Organic Compounds.

Most alignment media for the residual dipolar coupling (RDC) based molecular structure determination of small organic compounds consist of rod-like polymers dissolved in organic solvents or of swollen cross-linked polymer gels. Thus far, the synthesis of polymer-based alignment media has been a challenging process, which is often followed by a time-consuming sample preparation. We herein propose the use of non-polymeric alignment media based on benzenetricarboxamides (BTAs), which self-assemble into rod-like supramolecules. Our newly found supramolecular lyotropic liquid crystals (LLCs) are studied in terms of their LLC properties and their suitability as alignment media in NMR spectroscopy. Scalable enantiodifferentiating properties are introduced through a sergeant-and-soldier principle by blending achiral with chiral substituted BTAs.

Mechanism of ion stacking in aqueous partition chromatographic processes.

It has been reported that ion enrichment phenomena are observed in liquid chromatographic processes with an aqueous mobile phase on the columns packed with nonionic materials. However, the mechanism of the ion enrichment is not at all well understood. In this study, we investigated the retention and enrichment behaviors of simple inorganic anions on a C18-bonded silica column and a cross-linked hydroxylated methacrylic polymer gel column with pure aqueous mobile phases containing various electrolytes. We show that the stacking of ionic solutes can successfully be accounted for by the ion partition model, and it takes place due to the effect of the background coion in the eluent and/or sample solution on the distribution of the ions between the bulk water and the water incorporated in the packing material, which acts as the stationary phase. Using the ion exclusion effect of fixed anionic charges on a packing material as well as the ion stacking by partition, we developed a simple and versatile method for effective enrichment of anionic solutes in aqueous solutions. The enrichment factor and the elution time of the stacked ion zone can be predicted by the ion partition model.

Gelation Behavior Study of a Resorcinol–Hexamethyleneteramine Crosslinked Polymer Gel for Water Shut-Off Treatment in Low Temperature and High Salinity Reservoirs

Mature oilfields usually encounter the problem of high watercut. It is practical to use chemical methods for water-shutoff in production wells, however conventional water-shutoff agents have problems of long gelation time, low gel strength, and poor stability under low temperature and high salinity conditions. In this work a novel polymer gel for low temperature and high salinity reservoirs was developed. This water-shutoff agent had controllable gelation time, adjustable gel strength and good stability performance. The crosslinking process of this polymer gel was studied by rheological experiments. The process could be divided into an induction period, a fast crosslinking period, and a stable period. Its gelation behaviors were investigated in detail. According to the Gel Strength Code (GSC) and vacuum breakthrough method, the gel strength was displayed in contour maps. The composition of the polymer gel was optimized to 0.25~0.3% YG100 + 0.6~0.9% resorcinol + 0.2~0.4% hexamethylenetetramine (HMTA) + 0.08~0.27% conditioner (oxalic acid). With the concentration increase of the polymer gel and temperature, the decrease of pH, the induction period became shorter and the crosslinking was more efficient, resulting in better stability performance. Various factors of the gelation behavior which have an impact on the crosslinking reaction process were examined. The relationships between each impact factor and the initial crosslinking time were described with mathematical equations.

7. 架橋高分子ゲルの吸湿・脱湿挙動(平成9年度第43回低温生物工学会研究報告)

7. 架橋高分子ゲルの吸湿・脱湿挙動(平成9年度第43回低温生物工学会研究報告)

Elastic Compressible Energy Storage Devices from Ice Templated Polymer Gels treated with Polyphenols

Design and fabrication of rechargeable energy storage devices that are robust to mechanical deformation is essential for wearable electronics. We report the preparation of compressible supercapacitors that retain their specific capacitance after large compression and that recover elastically after at least a hundred compression–expansion cycles. Compressible supercapacitors are prepared using a facile, scalable method that readily yields centimeter-scale macroporous objects. We ice template a solution of polyethylenimine in green tea extract to prepare a macroporous cross-linked polymer gel (PG) whose walls are impregnated with green tea derived polyphenols. As the PG is insulating, we impart conductivity by deposition of gold on it. Gold deposition is done in two steps: first, silver nanoparticles are formed on the PG walls by in situ reduction by polyphenols and then gold films are deposited on these walls. Gold coated PGs (GPGs) were used as electrodes to deposit poly(3,4-ethylenedioxythiophene) as a p...

Blowing agent free generation of nanoporous poly(methylmethacrylate) materials

In this article, we demonstrate a newly developed technique for generation of nanoporous polymer materials. Generally, the production processes of polymeric nanostructured materials require high pressure due to the handling of gaseous blowing agents. Our new approach allows to generate nanoporous polymer materials without blowing agent at ambient conditions. Starting from a crosslinked polymer gel swollen with a mixture of at least two specially selected solvents leads to a nanoporous material by sequential evaporation. We varied the pore size of the generated structures between 80 and 800 nm so that the effect of the pore size on the gaseous thermal conductivity could be analyzed. Decreasing the pore size of the materials, the gaseous thermal conductivity could be reduced considerably. Thus, we developed a blowing agent free technique which allows the generation of nanoporous polymer materials—Knudsen materials—at an ambient pressure.

Investigation on Preparation and Profile Control Mechanisms of the Dispersed Particle Gels (DPG) Formed from Phenol–Formaldehyde Cross-linked Polymer Gel

To achieve in-depth profile control and further improve oil recovery, a new profile control agent, termed a dispersed particle gel (DPG), has been developed and reported. In this paper, the DPG particles with sizes ranging from submicrometer to micrometer are prepared successfully from phenol–formaldehyde cross-linked polymer gel by the high speed shearing method. The preparation method is convenient and easy to scale up for the field application. The microscopic characteristics of the DPG have been investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Parallel sandpack tests and microscopic visualization tests have been conducted to gain insights into the profile control mechanism. Additionally, scanning electron microscope (SEM) has been used to study the distribution of DPG particles in porous media. The results show that the DPG particles can block the high permeability layers by accumulating in large pore spaces or by directly plugging small pore throats. Meanwhil...