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Hardening of Portland cement-based materials in vicinity of electrically conductive surfaces, especially when the surfaces are electrically or galvanically polarized, can lead to both morphological and chemical changes in cement close to the surfaces due to combined electrochemical and electrophysical processes. Cement hydration products close to graphite and steel surfaces being positively (anode) and negatively (cathode) electrically polarized (direct current) were studied. Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy were used to compare structure and atomic composition of cement hydration products on cathode, anode and a reference surface with no electrical polarization. The application of direct current (DC) potential in aqueous Portland G cement dispersion significantly affects cement hydration products close to cathode and anode and different products were found at the anode compared to the cathode surfaces. At the graphite anode, calcium sulphate crystals along with calcium hydroxide were most abundant, while the graphite cathode was mainly covered with calcium hydroxide. The calcium hydroxide carbonated upon exposure to air during drying. When steel electrodes where used, the most significant adsorption occurred at the anode, in contrast to graphite where the largest amount of the adsorbed material was found on the cathode. The observed differences were explained in view of electrophysical (electrophoresis, electroosmosis) and electrochemical (reduction and oxidation) processes occurring at electrode surfaces upon application of DC current. The knowledge gained in this work is important for engineering of electrically conductive cement nano-composites where typically the contact surface of an electrically conductive filler and a cementitious matrix is high.

Cement degradation caused by CO2 exposure is an increasingly important environmental challenge that must be understood, for example, if former oil reservoirs are to be used for CO2 storage. When exposed to CO2-saturated brine, cement undergoes a chemically complex carbonation process that influences all the physicochemical properties of the cement. It is known that under favorable conditions, fractures and voids in cement can be occluded, or self-sealed, by precipitation of calcium carbonate. Here, we report a detailed X-ray microcomputed tomography (μ-CT) study on the carbonation of gas pores (macropores) of diameter ∼1 mm in cement. Specifically, cured class G Portland cement with sub-millimeter spherical disconnected macropores was exposed to CO2-saturated brine at high pressure (280 bar) and high temperature (90 °C) for 1 week. High-resolution synchrotron-based μ-CT enabled visualizing the morphology of the precipitates inside the macropores within both unreacted and carbonated regions. Quantitative analysis of the type and amount of material deposited in the macropores during carbonation suggests that the filling of the disconnected macropores involves transport of calcium ions from the cement bulk to the macropore interior. A detailed model describing the chemical processes involved is provided. The present study gives a deeper understanding of cement carbonation by literally shedding light on the complex precipitate structures within the macropores., Crystal Growth & Design, 19 (10), ISSN:1528-7483, ISSN:1528-7505

Chemical reactions with reservoir fluids and geology related in-situ stress changes may cause damages to cement sealing material in plugged and abandoned oil, gas and CO2 wells. To avoid leakages, a legitimate monitoring technique is needed that could allow for early warning in case such damages occur. In this paper, we test the utility of oil and gas well cement with a conductive filler in sensing stress changes. To this end, we have measured the resistance response of Portland G—oil and gas well cement with carbon nanofibers (CNF) to axial load during uniaxial compressive strength test. Simultaneously, the microseismicity data were collected. The resistance of the nanocomposite was measured using two-point method in the direction of loading. The resistance changes were correlated with acoustic emission events. A total of four different material response regions were distinguished and the resistivity and acoustic emission changes in these regions were described. Our results suggest that the two complementary methods, i.e., acoustic emission and resistance measurements, can be used for sensing stress state in materials including well cement/CNF composites. The results suggest that the well cement/CNF composites can be a good candidate material to be used as a transducer sensing changes in stress state in, e.g., well plugs up to material failure.

Asphaltenes are regarded as troublesome components of crude oils as their precipitation and deposition inside production wells and downstream infrastructure often result in a reduction of production capacity and, in critical cases, production shut-in. It has been shown that asphaltene deposition on conductive surfaces can be controlled by the application of an electric field. The electric field has been used to either inhibit or accelerate asphaltene deposition. This paper reviews asphaltene behavior in an electric field. It describes the structure and electric properties of asphaltenes as well as their electrokinetic behavior. State-of-the-art asphaltene electrodeposition and separation from both model and crude oils using electric fields are also discussed. The influence of parameters such as asphaltene chemistry, crude oil composition, pH, electric field strength, and flow conditions on the asphaltene electrodeposition process is addressed, and the effect of asphaltene interactions with themselves and other crude oil components is evaluated. A comprehensive literature survey reported the electrodeposition on both positive and negative electrodes, which suggests the complexity of the process. It has been shown that asphaltene charges can be tailored by changing the process parameters. Because of the high energy efficiency and relatively simple process, asphaltene electrodeposition is currently a key solution for removal of asphaltenes from crude oils. This review also highlights the main challenges and knowledge gaps associated with the asphaltene electrodeposition process.

Cement-steel interfacial strength is an important measure for estimating the robustness and hydraulic sealing ability of wells. In this paper, laboratory experiments were performed in which small steel pipes (10 mm in diameter) were cemented in place within a Portland cement slurry under application of constant electrical potential difference between the pipes. The objective was to investigate whether there might be an observable difference between push-out strengths obtained with the pipes of different polarity (anode vs. cathode vs. reference nonpolarized pipe). The duration of the potential application and the magnitude of the potential difference were varied between the tests. The experiments demonstrated that at the higher potential difference (4 V), the duration of potential application had a noticeable effect on interfacial bonding. Application of 4 V for 24 h resulted in loss of bonding at cement-cathode interface, which could be attributed to massive water transportation to the cathode region by small radii cations. At the lower applied potential difference (1 V), there is an improvement in push-out strength at anode at short duration of potential application. This could be due to pore filling by precipitation of expansive minerals in pores and cement particles migration toward anode. The effect of potential on push-out strength in a hardened cement suggests that low potential difference applied for a short period of time might improve cement-steel interfacial strength.

Depleted oil reservoirs are considered a viable solution to the global challenge of CO2 storage. A key concern is whether the wells can be suitably sealed with cement to hinder the escape of CO2. Under reservoir conditions, CO2 is in its supercritical state, and the high pressures and temperatures involved make real-time microscopic observations of cement degradation experimentally challenging. Here, we present an in situ 3D dynamic X-ray micro computed tomography (μ-CT) study of well cement carbonation at realistic reservoir stress, pore-pressure, and temperature conditions. The high-resolution time-lapse 3D images allow monitoring the progress of reaction fronts in Portland cement, including density changes, sample deformation, and mineral precipitation and dissolution. By switching between flow and nonflow conditions of CO2-saturated water through cement, we were able to delineate regimes dominated by calcium carbonate precipitation and dissolution. For the first time, we demonstrate experimentally the impact of the flow history on CO2 leakage risk for cement plugging. In-situ μ-CT experiments combined with geochemical modeling provide unique insight into the interactions between CO2 and cement, potentially helping in assessing the risks of CO2 storage in geological reservoirs.

Cement nanocomposites with carbon nanofibers (CNFs) are electrically conductive and sensitive to mechanical loads. These features make them useful for sensing applications. The conductive and load sensing properties are well known to be dependent on carbon nanofiber content, however, much less is known about how the conductivity of hybrid cement&ndash, CNF depend on other parameters (e.g., water to cement ratio (w/c), water saturation of pore spaces and temperatures above ambient temperature). In this paper we fill-in these knowledge gaps by: (1) determining a relationship between the cement&ndash, CNF bulk resistivity and w/c ratio, (2) determining the effect of water present in the pores on bulk resistivity, (3) describing the resistivity changes upon temperature changes up to 180 &deg, C. Our results show that the increase in the water to cement ratio results in increased bulk resistivity. The decrease in nanocomposite resistivity upon a stepwise temperature increase up to 180 &deg, C was found to be related to free water release from cement pores and the dry materials were relatively insensitive to temperature changes. The re-saturation of pores with water was not reversible with respect to electrical resistivity. The results also suggest that the change in the type of electrical connection can lead to two orders of magnitude different bulk resistivity results for the same material. It is expected that the findings from this paper will contribute to application of cement&ndash, CNF-based sensors at temperatures higher than ambient temperature.

Electrically induced or coupled transport processes including electrophoresis, electroosmosis and electromigration in solutions and porous media under an external electric field have been extensively studied and employed in many disciplines. For protection and rehabilitation of concrete structures, cathodic protection, electrochemical realkalization, and chloride extraction are extensively used. Other electrokinetic techniques are developed for the concrete industry, but have not been widely used so far, including electrokinetic treatment processes, for corrosion mitigation, recovery from sulfate attack, crack healing, and porosity and permeability reduction. These processes can improve the microstructure of the cement-based systems resulting in an improved performance in long-term and can be applied to repair failed structures. Application of electrokinetic processes are rapidly extended in well construction due to the increased interest in techniques enabling manipulation of micro- and nanosized particles. The techniques could be beneficial in building a robust cement sheath in oil and gas wells. Additionally, electrokinetic remediation techniques can possibly be introduced for repairing damaged structures in oil and gas wells. This review provides an overview of electrokinetic-based techniques, which has been introduced to cement-based materials, mainly reinforced concrete. The potential application of these techniques in oil well construction is discussed.

Depleted oil reservoirs are considered a viable solution to the global challenge of CO2 storage. A key concern is whether the wells can be suitably sealed with cement to hinder the escape of CO2. Under reservoir conditions, CO2 is in its supercritical state, and the high pressures and temperatures involved make real-time microscopic observations of cement degradation experimentally challenging. Here, we present an in situ 3D dynamic X-ray micro computed tomography (μ-CT) study of well cement carbonation at realistic reservoir stress, pore-pressure, and temperature conditions. The high-resolution time-lapse 3D images allow monitoring the progress of reaction fronts in Portland cement, including density changes, sample deformation, and mineral precipitation and dissolution. By switching between flow and nonflow conditions of CO2-saturated water through cement, we were able to delineate regimes dominated by calcium carbonate precipitation and dissolution. For the first time, we demonstrate experimentally the impact of the flow history on CO2 leakage risk for cement plugging. In-situ μ-CT experiments combined with geochemical modeling provide unique insight into the interactions between CO2 and cement, potentially helping in assessing the risks of CO2 storage in geological reservoirs. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

In carbon storage activities, and in shale oil and gas extraction (SOGE) with carbon dioxide (CO2) as stimulation fluid, CO2 comes into contact with shale rock and its pore fluid. As a reactive fluid, the injected CO2 displays a large potential to modify the shale’s chemical, physical, and mechanical properties, which need to be well studied and documented. The state of the art on shale−CO2 interactions published in several review articles does not exhaust all aspects of these interactions, such as changes in the mechanical, petrophysical, or petrochemical properties of shales. This review paper presents a characterization of shale rocks and reviews their possible interaction mechanisms with different phases of CO2. The effects of these interactions on petrophysical, chemical and mechanical properties are highlighted. In addition, a novel experimental approach is presented, developed and used by our team to investigate mechanical properties by exposing shale to different saturation fluids under controlled temperatures and pressures, without modifying the test exposure conditions prior to mechanical and acoustic measurements. This paper also underlines the major knowledge gaps that need to be filled in order to improve the safety and efficiency of SOGE and CO2 storage.

Applying positive potential to a steel electrode immersed into a cement changes the packing of cement particles in the vicinity of the electrode surface. The electrophoresis-induced packing enhancement at anode has promising applications in oil & gas and CO2 storage industries since it could be used to improve the mechanical and hydraulic cement-casing bonding in wells and thereby improve the well integrity, both in short and long term. In this experimental study, we use synchrotron radiation microtomography (µ-CT) and X-ray diffraction (XRD) analyses of the interfacial transition zone (ITZ, a 20–100 µm wide near-wall zone depleted of large particles) to find out what structural changes are responsible for different cement-steel adhesion at anode and cathode. Particle size distribution analysis reveals that the ITZ is enriched with large (equivalent diameter > 10 µm) cement particles near anode. On the contrary, near cathode, cement is depleted of large particles, which results in poor adhesion to the electrode. XRD analysis reveals that cement near anode is enriched with tricalcium silicate (Ca3SiO5). These findings suggest that electrophoresis-enhanced cement-steel adhesion is due to large (>10 µm) negatively-charged tricalcium silicate particles being attracted to anode.

Calcium carbonate (CaCO3) is one of the most widespread scaling minerals and has been a long-standing problem within many industrial sectors. Scaling of calcium carbonate on conductive surfaces can be prevented electrochemically by anodic polarization. Anodic polarization, however, cannot be applied directly to metal surfaces like e.g., steel that will suffer from corrosion when polarized anodically in an aqueous environment. Thus, in this paper it is proposed to apply a conductive coating to a metal surface to allow anodic polarization and inhibit surface scaling, without corrosion of the underlying metal surface taking place. To this end an epoxy/carbon nanofiber conductive coating was developed and deposited at steel surfaces. The coating showed good adhesion to the surface and the bulk and surface resistivities were in the order of 52.80 kΩcm and 31.87 kΩ/cm2, respectively. The anti-scaling performance of the coating without- and under anodic polarization was tested upon exposure to 1.5 wt% CaCl2 solution being in contact with CO2. The coating has been tested at several different potentials to find optimal conditions for scale inhibition. Potentials above +3 VOCP caused a degradation of the coating due to oxygen evolution at the anode, as well as evolution of chlorine gas. At +1.5 and + 2 VOCP the coating remained intact and the precipitation of CaCO3 was limited. On the other hand, cathodic polarization of the coating surface enhanced scaling and no coating degradation was observed at cathodic polarization even at potentials as high as −5 VOCP. The coating has thus proven a good solution to control surface scale deposition. Both anodic scale inhibition and cathodic scale acceleration have been achieved at the coating surfaces.

The conductivity of cement/carbon nanofiber (CNF) composite materials has previously been shown to be affected by parameters such as e.g. CNF content or water to cement (w/c) ratios, water saturation and temperature. However, whether and to what extent chemical processes like cement carbonation can affect the electrical conductivity of cement/CNF materials remains unexplored. To investigate this the resistivity changes upon carbonation of Portland G cement/CNF composites were followed for more than 4 months. An increase in resistivity was observed within the first weeks of carbonation followed by a plateau and a subsequent decrease after 4 months. The changes in resistivity were correlated with the progress of the carbonation front followed using X-ray tomography. The magnitude of the resistivity changes was found to be related to w/c ratio. Volumetric changes affecting the connectivity between the CNFs can explain the resistivity changes.

Tensile strength of cement-steel and cement-rock interfaces is an important input parameter when predicting well integrity failure in petroleum industry as well as during underground CO 2 storage. Laboratory tests of interface strength (e.g. the so-called pushout test) often provide estimates of shear rather than tensile strength. In this work, three-point bending test of bi-material beams was used to study tensile failure at cement-steel, cement-cement, and cement-sandstone interfaces. The tests revealed that cement-steel interfaces were the weakest ones, while cement-cement interfaces were the second weakest. Cement-sandstone interfaces were apparently quite strong: both tested cement-sandstone beams broke inside the cement, ca . 2–3 cm off the interface. This surprising result, i.e. the interface being stronger than the hardened cement, was attributed to water suction from cement into the dry sandstone during setting, which was corroborated by the observed very uneven fracture surface. All bi-material beams had lower flexural strength than monolith cement beams.

Wellbore integrity is critical to long term carbon storage. During CO2 injection, changes in temperature may result in large stress variations that can damage the well, threatening its integrity. The different materials comprising the wellbore and near-wellbore environment (namely the casing, cement and surrounding rock) possess different thermal properties. Consequently, there can be considerable variations in both material properties and thermal gradients across these layers, resulting in different amounts of contraction and expansion of these materials. This may generate sufficient thermal stresses to lead to fracture within the cement and/or host rock, or delamination of the cement/casing or cement/rock interfaces. Downsized wellbore samples have been used in laboratory studies to investigate the failure modes and failure criteria during thermal cycling operations. However, it is not clear to what extent such results can be reliably used to predict well failure at field scale conditions. In this work, we conduct a parameter study involving the size and material properties of the wellbore samples subjected to different rates of thermal loading, with the objective of predicting how these parameters can affect the thermal stress in field scale well conditions. A state-of-the-art parallel multiscale, multiphysics code named GEOS, developed at Lawrence Livermore National Laboratory, was used to study the thermal response of wellbore materials. A finite element solver considering linear elastic materials was coupled with a finite volume heat equation solver to simulate the wellbore deformation and fracture during thermal cycling. To understand the effect of wellbore size on thermal fracturing, simulations were conducted at different height to diameter ratios. The wellbore sample size was systematically varied from the lab scale to field scale with several intermediate scales. The change in thermal stresses were compared for different scales. Additionally, the effect of elastic modulus and cooling rates were studied.

Injection of CO2 into saline storage aquifers is often accompanied by drying of the formation water and salt precipitation. Subsequent salt clogging of a well bore and the near wellbore rock matrix may lead to injectivity impairment. In this paper we present medium-scale experiments on salt precipitation in the near-well region during a dry CO2 injection. In an effort to better simulate the geometry and the flow conditions in the field situation our purpose-designed experimental setup enables (1) realistic radial geometry of CO2 flow, and (2) opened boundary conditions for brine inflow allowing capillary and diffusive flux of brine components from and to practically infinite source of formation water. During the course of injection, no significant pressure build-up was observed across the rock specimen, indicating that permeable flow paths were not completely clogged. Post-test analysis of the specimen included X-ray computed tomography, powder X-ray diffraction and scanning electron microscopy in order to quantify fluid saturation, brine salinity and halite precipitation. The analysis provided indication of the most probable flow patterns of supercritical CO2 and CO2 rich brine in the system. The resulting drying and precipitation is discussed in light of the different drying regimes created under the present flow conditions. This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. You are not required to obtain permission to reuse this article. To request permission for a type of use not listed, please contact Elsevier Global Rights Department.

Cements for well environments with temperatures above 110 °C are typically designed with silica additions. This is the case for many of the wells in the North Sea, which is a region promising for large-scale geological storage of CO2 from European sources. Wells are probable leakage paths in carbon capture and storage (CCS) projects, and it is therefore important to understand how CO2 interacts with cement under downhole conditions. In this study, microstructural changes associated with carbonation of cement with and without silica were followed using micro-computed tomography, X-ray diffraction and scanning electron microscopy. The rims of the cement cores exposed to CO2-saturated brine consisted of a carbonated region and a bicarbonated region. In the silica cement sample, the carbonated region consisted of two distinct layers with a rough interface region containing wormhole-like features. The formation of these two layers in the silica cement is proposed to be due to calcium carbonate dissolution and re-precipitation during exposure to CO2-saturated brine. The results illustrate the importance of the effect of additives for offshore CO2-storage well integrity.

Good shear bonding and hydraulic bonding between cement and steel play a crucial role in well integrity of oil and gas wells. In this experimental study, we investigate the effect that constant electric field may have on the bonding at cement-steel interfaces. Constant voltage (18 V) was applied between two stainless-steel electrodes immersed into a cement slurry. It was found that bonding was significantly improved at the positive electrode, while it was significantly worse at the negative electrode. The effect was due to the negatively-charged cement particles being attracted to the positive electrode. The effect may potentially be used for manipulation and control of casing-cement and reinforcement-concrete bonding strengths in oil & gas and construction industries, respectively. Side-effects that might reduce the applicability of this technology, are gas production at both electrodes (and especially at the negative one) and significant corrosion at the positive electrode due to electrochemical reactions at metal surfaces. Poor bonding at the negative electrode may potentially be used for cleaning of cement equipment, such as cement pumps, pipes, tanks, and mixers used on the rigs to perform well cementing jobs in oil & gas industry.

Calcium carbonate is by far the most widespread scaling material. Its deposition in pipes and flowlines has been a long-standing problem for many industries. Hence, a lot of research is devoted to scale inhibition. One of the calcium carbonate scale management methods relies on removal of calcium ions from scaling solution by electrochemically enhanced deposition. Application of potential between two electrodes may result in oxygen reduction and water electrolysis. Both processes change the local pH in close proximity to the electrodes. Solution close to the anode is becoming acidic while that close to the cathode alkaline. Solubility of calcium carbonate is pH dependent. The alkaline pH in the vicinity of the cathode promotes precipitation of calcium carbonate. On the other hand, the acidic environment near the anode prevents anode from scaling. In this paper we show how the cathodic and anodic processes, respectively, accelerate and prevent scale deposition on graphite electrode surfaces. The growth of calcium carbonate at different calcium ion concentrations and different voltage magnitudes applied were followed using X-ray computed tomography. The morphology of the deposited calcium carbonate was studied using the scanning electron microscopy. The polymorphic forms of calcium carbonate deposited at different voltage magnitudes were identified using X-ray powder diffraction. A strong correlation between the scaling rate, the average crystallite size and the voltage applied was observed. This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The Ketzin pilot site is the longest operating onshore CO2 storage site in Europe. CO2 injection began in June 2008 and ended in August 2013. In total five wells were drilled at the Ketzin pilot site. The Ketzin monitoring well 202 has been abandoned in autumn 2015. During the abandonment, well construction material samples were retrieved. The samples were retrieved from the cementitious plug as well as from the steel casing and the production string at different depths. The samples were analyzed by a set of complementary experimental techniques. The structure and macroporosity of cement samples were studied using X-ray computed tomography (CT) and scanning electron microscopy (SEM). The structural changes associated with hardening of the cementitious material downhole compared to the reference topside sample have been described. Casing and production string samples were studied using light optical microscopy to investigate microstructural changes resulting from CO2 exposure. The relation between corrosion degree and the depth from which the samples were retrieved has been established.

Well integrity is a prerequisite for safe geological storage of CO 2 . Both active and abandoned wells are man-made channels between the storage reservoir and the atmosphere that can become leakage paths over time. The CO 2 injection wells are of special concern, as they are exposed to low temperatures and strong temperature variations. In oil/gas wells this is known to threaten well integrity, and it should therefore be investigated how the sealing ability of well barriers is affected in the temperature range relevant for CO 2 injection wells. This has been the main focus in a research project entitled “Ensuring well integrity during CO 2 injection” carried out in the period 2014-2016. This paper summarizes the major findings obtained within the project, and presents research-based recommendations for construction and operation of CO 2 injection wells.

Long-lasting cement plugging of wells is crucial for successful CO2 storage in underground reservoirs. It requires a profoundly improved understanding of the behavior of fractured cement under realistic subsurface conditions including elevated temperature, high pressure and the presence of CO2 saturated brine. Here we report computed X-ray tomography studies on the effects of CO2 on cement. More specifically, we have exposed cured Portland G cement samples with pre-made microchannels mimicking fractures to CO2 saturated brine at elevated pressure (100 bars) and room temperature. The microchannels were observed to get filled with calcite (CaCO3) during the CO2 exposure. The extent of this self-healing was dependent on the diameter of the leakage path, with narrower channels more readily getting clogged. Chemical simulations taking into account the cement composition, CO2 availability, pH, pressure and temperature gave results consistent with our conceptual understanding of how the differences in dissolution/precipitation profiles in the cement may result from the availability of CO2. In particular, the modelling provides an explanation why calcite precipitates preferentially in the channels rather than on the external cement sample surfaces. We conclude that the localized precipitation can be ascribed to higher pH inside the cavities compared to near the external surfaces, owing to long diffusion distances giving a locally limited CO2 supply within the voids. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

For successful CO2 storage in underground reservoirs, the potential problem of CO2 leakage needs to be addressed. A profoundly improved understanding of the behavior of fractured cement under realistic subsurface conditions including elevated temperature, high pressure and the presence of CO2 saturated brine is required. Here, we report in situ X-ray micro computed tomography (μ-CT) studies visualizing the microstructural changes upon exposure of cured Portland cement with an artificially engineered leakage path (cavity) to CO2 saturated brine at high pressure. Carbonation of the bulk cement, self-healing of the leakage path in the cement specimen, and leaching of CaCO3 were thus directly observed. The precipitation of CaCO3, which is of key importance as a possible healing mechanism of fractured cement, was found to be enhanced in confined regions having limited access to CO2. For the first time, the growth kinetics of CaCO3 under more realistic well conditions have thus been estimated quantitatively. Co...

The swelling properties of polyampholytic hydrogels with different charge stoichiometric ratio were characterized by continuous monitoring changes in optical length of 60 μm sized hydrogels with 2 nm resolution using an interferometric readout platform. The hydrogels were synthesized by copolymerizing acrylamide, crosslinker Bis and charged monomers. Anionic–cationic polyampholyte gels consisted of different molar ratio between anionic monomer 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and cationic monomer (3-acrylamidopropyl) trimethylammonium chloride (APTAC). The polyzwitterionic hydrogels consisted of zwitterionic monomer [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBA) with a certain molar of AMPSA or APTAC in addition to the AAM. The observed swelling properties versus the ionic strength in the aqueous immersion solution revealed apparent anti-electrolyte signatures for both types of polyampholytic hydrogels. The swelling kinetics was not affected by charge imbalance within the polyampholyte or polyzwitterionic hydrogels. Polyampholyte hydrogels with balanced charge ratio slightly shrinked and then swelled with the increase of ionic strength, which is at variance with the anionic AMPSA offset hydrogels displaying shrinking in low ionic strength and relatively small swelling at high ionic strength. The swelling properties of imbalanced polyampholyte hydrogels were not equal to simply linear overlap of those of polyampholyte hydrogels with balanced charges, and corresponding polyelectrolyte hydrogels.

A nonionic tri-block copolymer (Pluronic P123) and a cationic polysaccharide (chitosan) were compared as reduction and structure directing agents during in situ synthesis of gold functionalised mesoporous silica materials. The tri-block copolymer syntheses resulted in hexagonally ordered pore structures with cagelike pores present in open-ended tubular pore systems, but provided less control of the growth of gold nanoparticles. The chitosan syntheses, on the other hand, gave better control of the particle growth (i.e. smaller gold particles), but no pore ordering and lower porosity were obtained. Also in this case, however, cagelike pores were present in interconnected pore systems. In both approaches at least some of the gold particles are present in the cagelike pores of the materials. The functionalised structures were characterised using nitrogen physisorption, powder X-ray diffraction, X-ray fluorescence spectroscopy, transmission electron microscopy and UV–Vis spectroscopy.

Deposition of polycations on weakly charged anionic hydrogels and the resulting swelling properties were studied to determine the influence of molecular parameters on the properties of the resulting composite soft materials. The deposition process and swelling properties at various ionic strengths were followed in situ by an interferometric technique allowing continuous monitoring of changes in optical length within the hydrogels with 2 nm resolution. The distributions of the polycations labeled with fluorescent dye Alexa Fluor 488 were additionally monitored employing confocal microscopy. Polyallylamine hydrochloride (PAH) of three different molecular weights and a high molecular weight chitosan were employed as polycations. The high resolution interferometric data revealed the classical ionic hydrogel increase in swelling with decreasing ionic strength that increases with the charge density of the anionic hydrogel. Impregnating the anionic hydrogels with PAH polycation resulted in composite materials where PAH where distributed throughout the original polyanionic hydrogel, and where the changes in swelling at various ionic strengths resembled a polyampholyte hydrogel. Exposure to a chitosan yielded a polycation distribution with a distinct chitosan enriched shell at the surface of the hydrogel, and less penetration within the core of the anionic hydrogels. These materials displayed a typically ionic hydrogel swelling signature on changes in ionic strength. The results here show that tuning of molecular parameters can be used to control transport properties of polycations into polyanionic hydrogels and one can also prepare composite soft hydrogels with polyampholyte properties using such a route.

A simple semi sol-gel method for preparation of stable alumina monoliths is presented. The approach is based on chemical binding of boehmite by hydrolysis products of aluminium nitrate. The crystalline phase of the monoliths depends on the calcination temperature, and the size and shape of the alumina crystallites were determined by transmission electron microscopy and modelling of X-ray diffraction patterns. The monoliths have bimodal pore size distributions with mesopores ranging from 3 to 20 nm and macropores ranging from 10 to 40 μm. Incipient wetness impregnation resulted in gold particles, ranging from 4 to 20 nm, supported on the monoliths. The size of the gold particles depended largely on the crystalline phase of the support, but also on the amount of gold precursor. The catalytic activity of the functionalised materials in liquid-phase oxidation of glucose was higher in continuously stirred batch reactor tests compared to continuous flow fix bed tests. In both cases the activity was improved as the size of gold particles decreased.

Hydrogel-based label-free nucleic acids sensor materials using high resolution interferometric readout of hydrogel swelling changes was prepared and characterized with respect to molecular design parameters. The DNA-sensitive hydrogel comprised sensing (S) and blocking (B) oligonucleotide pairs copolymerized with the network and formed reversible crosslinks in addition to stable covalent ones. Oligonucleotide probes (P) complementary to S with longer complementary regions comparing to B results in competitive replacement of S–B strands. The associated destabilization of DNA crosslinks results in changes of the hydrogel swelling. S–B dioligonucleotidic crosslinkers were designed with 8, 12 and 16 basepairs in complementary regions and were destabilized by probes with matching sequences with 2, 6 and 10 excess basepairs in the so-called “toe-hold” region. The kinetics of hydrogel swelling was tested at room and body temperature for hydrogels with different covalent crosslink densities. In general, the swelling kinetics was faster for longer “toe-holds” and slower for the longer and more stable blocking sequence. An increase of the covalent crosslink density resulted in a decrease of the swelling rate. The swelling of the hydrogel was faster the higher the temperature and closer to the S–B melting point. The following work shows direct correlation between the kinetics of strand displacement reaction and hydrogel swelling rates and provides a direction for further application of DNA-sensitive hydrogels.

Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing materials of other oxides than silica. In this review, we present different synthesis methods for inorganic, non-silica monolithic materials. Some examples of application of the materials are also included.

Selective deposition of polymers at the surface of an ionic hydrogel is conventionally used to tailor properties of the composite material for application in for instance drug release and cell encapsulation. Here we describe a method for determination of the mechanical properties of a thin polymer film deposited on an ionic hydrogel core. The ionic strength-dependent hydrogel swelling is affected by the cross-link density and thickness of the deposited polymer layer. A hemi-ellipsoidal geometry of the hydrogel, corresponding to that employed in proof-of-concept experiments, is used to enforce biaxial deformation of the deposited layer when the ionic hydrogel core is equilibrated at various ionic strengths. The ionic strength dependent equilibrium swelling ratio of the hydrogel with the deposited polymer film is modeled using a finite element approach. The free energy of the hydrogel core includes contributions accounting for polymer mixing, elastic deformation of the network and the Donnan equilibrium. The latter type of contribution is not included in the neutral thin layer in the present study. Adding the polymer multilayer/shell at the surface reveals that the ionic strength-dependent swelling constraint is more pronounced the thicker and stiffer the film is. Combining thickness measurements of the polymer film with high resolution interferometric determination of reduction in swelling capacity of ionic hydrogels, an equivalent elastic property of the polymer layer is obtained using inverse finite element analysis. In the proof-of-concept experiments, analysis of data obtained for chitosan–alginate multilayers composed of four and eight polymer bilayers deposited on an anionic acrylamide-based hydrogel core suggests that these bilayers show an elastic stiffness one order of magnitude larger than that of the hydrogel core. This is the authors' accepted and refereed manuscript to the article.

A high resolution interferometric technique was used to determine swelling behavior of weakly charged polyacrylamide hydrogels in the presence of oppositely charged surfactants and subsequent exposure to cyclodextrins. Hydrogels of copolymerized acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid (0.22, 0.44, 0.88 mol%) and crosslinked with bisacrylamide (3, 6, 12 mol%) were employed. The equilibrium swelling and swelling kinetics of the hydrogels were determined with 2 nanometer resolution of the optical length and sampled at approximately 1 Hz. These properties were determined for the hydrogels exposed to cationic surfactants dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB) at concentrations from 10-7 up to 2•10-3 M. The distribution of surfactants within AAM-co-AMPSA hydrogel was investigated by confocal laser scanning microscopy imaging of chosen hydrogel equilibrated in CTAB/perylene solution. Hydrogels equilibrated at selected surfactant concentrations were subsequently exposed to cyclodextrins (α-CD, β-CD, methyl-β-CD and γ-CD) forming inclusion complexes with the surfactants. The results show different type of behavior for the two surfactants used, arising from the differences in the length of surfactant hydrophobic tail. The changes in the surfactant induced swelling of the hydrogels are suggested to arise from the net effect of electrostatic screening of sulfonic acid – amide group interactions and surfactant micellization. Hydrogels with the largest charge density and lowest crosslink density yielded the most pronounced changes in swelling properties on exposure to DTAB or CTAB. The hydrogels displayed swelling kinetics on stepwise changes in surfactant concentrations that depended on the surfactant concentration range. The high resolution monitoring of hydrogel swelling associated with supramolecular complex formation in a three-component system hydrogel - amphiphilic molecule - cyclodextrin provide more details in the swelling behavior than previously disclosed. Copyright © 2012 Elsevier Inc. All rights reserved. This is the authors' accepted manuscript to the article.

Hydrogels have found wide application in biosensors due to their versatile nature. This family of materials is applied in biosensing either to increase the loading capacity compared to two-dimensional surfaces, or to support biospecific hydrogel swelling occurring subsequent to specific recognition of an analyte. This review focuses on various principles underpinning the design of biospecific hydrogels acting through various molecular mechanisms in transducing the recognition event of label-free analytes. Towards this end, we describe several promising hydrogel systems that when combined with the appropriate readout platform and quantitative approach could lead to future real-life applications. This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

An oligonucleotide–polymer hybrid hydrogel displaying swelling response in a logical AND and OR fashion depending on specific stimuli by probe oligonucleotides was prepared. The hydrogel acts as a transducer of the specific recognition of DNA sequences into micro- and macroscale mechanics. Input oligonucleotide probes induce hydrogel swelling ratio at two signal levels.

The annular cement is often subject to temperature variations, for example heating during steam injection, or cooling during CO2 injection or hydraulic fracturing. Fractures caused by thermal stresses may create flow paths through the cement sheath thereby jeopardizing the well integrity. The objective of this work was to experimentally and numerically investigate the effect of thermal cycles and harsh cooling on downscaled wellbore sections with a focus on the cement sheath failure. Downscaled wellbore sections were each prepared by cementing a casing section within a hollow cylinder of Berea sandstone. One specimen was subjected to a thermal cycling program that included cooling to −50 °C and heating to 80 °C. Two other specimens (dry and wet) were used in harsh cooling experiments with solid CO2 and liquid nitrogen. CT scanning was performed before the onset of, during and after the completion of the thermal cycling program or harsh cooling experiments. No differences in the distribution of voids and fractures in the cement before and after the thermal cycling were observed. This indicates that the applied temperature range was not sufficient to cause damage in the cement sheath. On the other hand, the harsh cooling experiment using liquid nitrogen resulted in fracturing of both the cement and rock in the water-saturated specimen. Finite-element simulations reproducing the thermal cycling program used in the laboratory experiment were performed. The simulations have shown that thermal radial stresses at cement/casing and cement/sandstone interfaces were relatively low, i.e., from 0.5 to 1.0 MPa, which might explain the lack of thermal-induced damage in CT images. The simulations also suggest that the radial fracture in the water-saturated specimen subject to harsh cooling was caused by a combined effect of tensile hoop stresses and stresses due to water freezing. The fracture was most likely initiated in the sandstone followed by further propagation into the cement. It is likely that well construction materials and the surrounding formation are water-saturated. Thus, cooling well below 0 °C, which may occur during a CO2 blowout, would increase chances for cement and formation failure.