Environmental Scanning Electron Microscopy Research Articles

Exploring the microstructure of hydrated collagen hydrogels under scanning electron microscopy.

Collagen hydrogels are a rapidly expanding platform in bioengineering and soft materials engineering for novel applications focused on medical therapeutics, medical devices and biosensors. Observations linking microstructure to material properties and function enables rational design strategies to control this space. Visualisation of the microscale organisation of these soft hydrated materials presents unique technical challenges due to the relationship between hydration and the molecular organisation of a collagen gel. Scanning electron microscopy is a robust tool widely employed to visualise and explore materials on the microscale. However, investigation of collagen gel microstructure is difficult without imparting structural changes during preparation and/or observation. Electrons are poorly propagated within liquid-phase materials, limiting the ability of electron microscopy to interrogate hydrated gels. Sample preparation techniques to remove water induce artefactual changes in material microstructure particularly in complex materials such as collagen, highlighting a critical need to develop robust material handling protocols for the imaging of collagen hydrogels. Here a collagen hydrogel is fabricated, and the gel state explored under high-vacuum (10-6 Pa) and low-vacuum (80-120Pa) conditions, and in an environmental SEM chamber. Visualisation of collagen fibres is found to be dependent on the degree of sample hydration, with higher imaging chamber pressures and humidity resulting in decreased feature fidelity. Reduction of imaging chamber pressure is used to induce evaporation of gel water content, revealing collagen fibres of significantly larger diameter than observed in samples dehydrated prior to imaging. Rapid freezing and cryogenic handling of the gel material is found to retain a porous 3D structure following sublimation of the gel water content. Comparative analysis of collagen hydrogel materials demonstrates the care needed when preparing hydrogel samples for electron microscopy.

Autogenous deformation induced- stress evolution in high-volume GGBFS concrete: Macro-scale behavior and micro-scale origin

This study aims to experimentally investigate the autogenous deformation and the stress evolution in restrained high-volume ground granulated blast furnace slag (GGBFS) concrete. The Temperature Stress Testing Machine (TSTM) and Autogenous Deformation Testing Machine (ADTM) were used to study the macro-scale autogenous deformation and stress evolution of high-volume GGBFS concrete with w/b ratios of 0.35, 0.42, and 0.50. The early-age cracking (EAC) risk (quantified by stress-strength ratio) and stress relaxation were analyzed extensively based on ADTM and TSTM results. Furthermore, Environmental Scanning Electron Microscopy (ESEM), X-ray Diffraction (XRD), and Mercury Intrusion Porosimetry (MIP) were conducted to explore the micro-scale origin of the autogenous deformation of high-volume GGBFS concrete, which supports the observations on the macroscale measurement of TSTM/ ADTM tests. This study finds that the ettringite formation in the first two days results in autogenous expansion, which can delay the appearance of tensile stress. The magnitude of autogenous expansion depends on the compatibility of ettringite content and pore size. The w/b ratio of 0.42 turns out to be optimal because it produces the highest amount of ettringite and results in the highest autogenous expansion. In comparison, the w/b ratio of 0.35 introduces significant autogenous shrinkage after the expansion peak and therefore corresponds to a high early-age cracking risk.

Synthesis and characterization of a novel active polymer for enhanced oil recovery

AbstractA new type of quaternary ammonium surface‐active polymer for enhanced oil‐recovery application was synthesized through the free‐radical polymerization of a functional monomer (DMCA) with acrylic acid (AA) and acrylamide (AM) and denoted as AM/AMPS/DMCA. The optimum polymerization conditions of AM/AMPS/DMCA were explored, and its chemical structure was characterized by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The molecular weight of AM/AMPS/DMCA was determined by gel‐permeation chromatography. Its thickening ability, oil–water interfacial tension, and emulsifying property were investigated. Results showed that AM/AMPS/DMCA had superior thickening ability and lower interfacial tension than the binary polymer AM/AMPS, as well as good emulsifying properties. AM/AMPS/DMCA also yielded 26.00% oil recovery, higher than the 20.57% of AM/AMPS, as determined using polymer‐flooding tests. The oil‐displacement mechanisms of this surface‐active polymer at pore level were also explored. Analysis of microscopic displacement characteristics through a visual micromodel revealed that AM/AMPS/DMCA solution improved sweep efficiency and reduced residual‐oil saturation due to its bulk viscosity and surface activation. All these findings indicated the excellent potential of AM/AMPS/DMCA in oil displacement.

Role of molybdenum on the structure and properties of A2O-P2O5−MoO3 (A = Na, Ag, Rb, Cs) glasses

Molybdenum phosphate glasses are materials of interest for nuclear waste storage and solid-state electrolytes, amongst others. Thermal and electrical properties of vitreous molybdophosphates are highly dependent on molybdenum local environment while for example the coordination of this transition metal is still a matter of discussion. The structure of glasses of following composition, xMoO3-(100-x)APO3 (with A = Ag, Na, Rb and Cs) was investigated by means of 31P and 95Mo Nuclear Magnetic Resonance spectroscopy. The structural information was used to better understand the evolution of thermal properties as a function of the molar fraction of MoO3. Particular attention was paid to the crystallization mechanism, studied by X-ray Diffraction, High Temperature Environmental Scanning Electronic Microscopy and Kissinger model, highlighting the formation of a molybdate network (Mo-O-Mo bonds).

Study on the Profile Control and Oil Displacement Mechanism of a Polymer Nano-microsphere for Oilfield

In this study, the mechanism of migration/plugging and the main performance of polymer nano-microspheres (HQ) were investigated using environmental scanning electron microscopy (ESEM), swelling hydration experiments, sand-filling pipe flooding experiments, and microscopic displacement experiments. Results show that the swelling ratio of HQ in salt solution first increases and then reaches equilibrium with the increase in swelling time. The expansion ratio of HQ increases rapidly at the initial stage of swelling and reaches its maximum value after swelling for 7 days. The maximum value of the expansion ratio was 15. In addition, the higher the salinity, the smaller the particle size of the studied microspheres. The particle size of the microspheres increases with increasing temperature. According to the visualized microscopic experiments, the migration and blocking mechanism of microspheres in the pore throat were discovered. When the particle size is 1/3–1/7 times the pore throat diameter, the microsphere particles can enter the interior of the pores. The microspheres aggregate together, and bridge plugging occurs due to the mechanical trapping of pore throats. In this case, the pore throats are blocked by the produced inner filter cake. The pressure at each point fluctuates up and down in a zigzag pattern during the displacement experiment, revealing the “migrated-plugged-breakthrough-replugged” mechanism for HQ. It can be seen from the oil displacement experiment that the final cumulative recovery and the enhanced oil recovery were 65.71 and 17.31%, respectively. Thus, the studied nano-microspheres have excellent oil displacement performance.

Effects of Sucrose Replacement by Polyols on the Dough-Biscuit Transition: Understanding by Model Systems.

This study investigated the impacts of the complete substitution of sucrose by maltitol and/or sorbitol on the dough-crumb transition in biscuits. To this end, the phenomena of starch gelatinization/melting were studied at different moisture contents, both in the biscuit dough and model systems, by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and by environmental scanning electron microscopy (ESEM). Observation of doughs in ESEM revealed sorbitol had a structure very different from sucrose and maltitol crystals. After forming the dough pieces, it could be seen that at least some sugar and maltitol crystals were still present while sorbitol flakes were solubilized. At a limiting real water content (~20% dry basis), adding sweeteners to the mixture increased the gelatinization temperature, more markedly for sucrose and maltitol, as well as increasing the enthalpy. These results were confirmed by the model systems analyses. The calorimetric study with mixing batch cells revealed that sorbitol dissolved completely while maltitol and sucrose competed with the flour constituents to capture water. The proportion of water available for the sorption of the starch grain and its gelatinization was therefore different according to the affinity of the sweetener for water, and might influence the degree and temperature of starch gelatinization/melting.

New Hybrid PVC/PVP Polymer Blend Modified with Er2O3 Nanoparticles for Optoelectronic Applications.

Polymer blend hybrid nanocomposites are of great importance for future optoelectronic applications. This paper presents the preparation of new polymer blend hybrid nanocomposites based on PVC/PVP modified with Er2O3 nanoparticles. A low-cost solution casting method has been used to prepare the polymer nanocomposites at 0.0, 0.1, 0.3 and 0.6 wt% of Er2O3. X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, and environmental scanning electron microscopy (ESEM) measurements have all been used to examine the impact of a varying wt% of Er2O3 on the structural and optical characteristics of PVP/PVC polymer blends. The PVC/PVP polymer blend and Er2O3 nanoparticles showed a strong interaction, which was validated by XRD, FTIR, and Raman spectrum investigations. The SEM micrographs showed a remarkable complexation among the components of the polymer nanocomposites. The activation energies for thermal decomposition of PVC/PVP doped with different Er2O3 concentrations were less than that of the pure polymer film. The linear and nonlinear refractive indexes, dispersion energy, optical susceptibility and the energy gap values were found to be Er2O3 concentration-dependent. With an increase in Er2O3 concentration to 0.1 and 0.3 wt%, the dispersion energy and nonlinear refractive index improved, and thereafter decreased when the concentration was further increased to 0.6For the film doped with 0.1 wt% Er2O3, the optical band gap (Eopt) of the composite film enhanced by about 13%. The optical absorption measurements revealed clear improvements with the addition of erbium oxide. Higher refractive index values of PVC/PVP/Er2O3 films qualify the polymer blend as a cladding for electro-optic modulators. Our results indicated that the PVC/PVP/Er2O3 polymer films could be suitable for optoelectronic space applications.

Consolidation and swelling behavior of kaolinite clay containing xanthan gum biopolymer

Recently, microbial biopolymer-based soil treatment (BPST) has gained attention for its application in environmentally friendly soil stabilization, particularly for enhancing the strength and stability of fine-grained soils. However, the effects of BPST on clay’s compressibility (consolidation) and expansion (swelling) behaviors remain unclear. This study used xanthan gum, a microbially produced polysaccharide with anionic charges, to stabilize kaolinite clay. The effect of xanthan gum BPST on the consolidation and swelling behavior of cohesive kaolinite clays was assessed through a series of experimental tests, including one-dimensional consolidation tests with elastic wave measurements, swelling tests, environmental scanning electron microscopy, and unconsolidated-undrained triaxial tests. The formation of xanthan gum hydrogels induces pore-clogging, resulting in a delay in the consolidation process, increased energy dissipation, and compressibility. Furthermore, the interaction between kaolinite and xanthan gum improved the undrained shear strength of kaolinite soils, thereby reducing the consolidation time required for a specific bearing capacity. This study demonstrates the possible application of controlling hydraulic conductivity, seismic stabilization, and rapid surface stabilization. However, additional drainage is necessary for in situ applications.

Physicochemical properties of enzymatic hydrolysis lignin-modified bitumen and its modification mechanism

ABSTRACT Enzymatic hydrolysis lignin (EHL) is a renewable, inexpensive and widely available biomass resource, which has great potentials in improving service performance of bituminous pavement. To develop EHL-modified bitumen and to reveal modification and anti-ageing mechanisms of EHL on bitumen, the impacts of EHL on basic performance, rheological property, micromorphology, chemical compositions, molecular weight distributions and thermal decomposition behaviors of bitumen were studied using basic property tests, dynamic shear rheometer (DSR) test, bending beam rheometer (BBR) test, environmental scanning electron microscope (ESEM) test, Fourier transform infrared spectrometry (FTIR) test, gel permeation chromatography (GPC) test and thermal gravimetric analyzer (TG) test. Results show that bituminous ductility and penetration are decreased, but bituminous viscosity and softening point are increased. Bituminous deformation resistance is improved by EHL. Bituminous cracking resistance is decreased slightly by EHL. Also, the compatibility between EHL and bitumen is satisfactory. Bituminous ageing is delayed owing to abundant phenol hydroxyl groups in EHL, which capture active free radicals produced in bituminous ageing process. Moreover, EHL cross-links with asphaltene to form macromolecular network structures to lower bituminous temperature sensitivity. Finally, EHL dosage of 8% is proposed to prepare EHL-modified bitumen, which effectively reduces energy consumption and increases ecological benefits.

Archaeological Evidence for the Dietary Practices and Lifestyle of 18th Century Lisbon, Portugal—Combined Steroidal Biomarker and Microparticle Analysis of the Carbonized Faecal Remains

The study of the urban context in the contemporary center of Portugal’s capital city uncovered traces of daily lives that were abruptly interrupted and utterly transformed by the Great Lisbon Earthquake on the morning of 1 November 1755. Charred organic residue was recovered from a cylindrical vessel excavated from the storage area of the town house at the Rossio square. The archaeological sample was studied through a multi-analytical approach based on microstructural, elemental and biomolecular characterization by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR), variable pressure scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (VP-SEM-EDS), and gas chromatography coupled with mass spectrometry (GC-MS). The residue was identified as human faeces collected in the ceramic vessel for disposal, and further analysis provided additional information about diet and the living conditions in the 18th century.

Investigation of microscopic creep and shrinkage deformations of cement paste assisted by digital image correlation technique

New in-situ microscopic mechanical tests in Environmental SEM (ESEM) and climatic chamber (CC), assisted by Digital Image Correlation (DIC) technique, have been developed. The developed testing frameworks speed up the drying duration at least 200 times compared to classical test methods. We mitigate the risk of cracking to focus on the intrinsic drying creep and shrinkage. Free drying shrinkage is assessed at a micro-scale and exhibits a high correlation with the mass loss for relative humidity above 60% relative humidity (RH). We observe a water cavitation effect between 50–60% (RH). Although the drying conditions in ESEM occur at low pressure compared to ambient air-drying conditions in a climatic chamber, the shrinkage deformations at equilibrium at 20% RH are quite the same. The evolution of desiccation creep with drying shrinkage is bilinear in uniaxial and linear under biaxial compression. The drying creep Poisson’s ratio is negative, between −0.1 and 0.

In situ synchrotron study of sintering of gas-atomized Ti-6Al-4 V powders using concomitant micro-tomography and X-ray diffraction: Effect of particle size and interstitials on densification and phase transformation kinetics

Compared to the well-established powder bed fusion techniques, sinter-based additive manufacturing of titanium alloys remains extremely challenging. This technique involves three steps: (i) shaping of a part composed of metallic powders bound with polymeric binder (ii) debinding (iii) sintering. One main issue is that densification during the solid sintering is promoted by small powder particles whereas the latter have a high propensity to carbon and oxygen uptakes from the binder, which are detrimental to ductility of titanium parts. In this article, we report a unique in-depth characterization of solid sintering of titanium powders using in situ coupled micro-computed tomography (µCT) and X-Ray diffraction under synchrotron radiation at high temperature, combined with in situ environmental scanning electron microscopy (HT-eSEM). Evolution of global porosity, pore size distribution and interconnectivity as well as allotropic titanium phase transformation and precipitation of second-phase precipitates (titanium carbides) were determined, allowing a discussion on the densification/phase transformation relationship. This multi-scale in situ study of solid sintering was used to identify the effect of powder particle size on the contamination / densification trade-off. Carbon/oxygen uptakes clearly increase the α-to-β transus but do not affect significantly the final porosity of the sintered parts, which argues for a secondary role of the β phase on the sintering kinetics of titanium alloys. Reducing the powder particle size has a tremendous effect on both the densification kinetics and the final pores structure.

Precision Modification of Monolayer Transition Metal Dichalcogenides via Environmental E-Beam Patterning

Layered Transition Metal Dichalcogenides (TMDs) are an important class of materials that exhibit a wide variety of optoelectronic properties. The ability to spatially tailor their expansive property-space (e.g., conduction behavior, optical emission, surface interactions) is of special interest for applications including, but not limited to, sensing, bioelectronics, and spintronics/valleytronics. Current methods of property modulation focus on the modification of the basal surfaces and edge sites of the TMDs by the introduction of defects, functionalization with organic or inorganic moieties, alloying, heterostructure formation, and phase engineering. A majority of these methods lack the resolution for the development of next-generation nanoscale devices or are limited in the types of functionalities useful for efficient TMD property modification. In this study, we utilize electron-beam patterning on monolayer TMDs (MoSe2, WSe2 and MoS2) in the presence of a pressure-controlled atmosphere of water vapor within an environmental scanning electron microscope (ESEM). A series of parametric studies show local optical and electronic property modification depending on acceleration voltage, beam current, pressure, and electron dose. The ultimate pattern resolution achieved is 67 ± 9 nm. Raman and photoluminescence spectroscopies coupled with Kelvin Probe Force Microscopy reveal electron dose-dependent p-doping in the patterned regions, which we attribute to functionalization from the products of water vapor radiolysis (oxygen and hydroxyl groups). The modulation of the work function through patterning matches well with Density Functional Theory modeling. Finally, post-functionalization of the patterned areas with an organic fluorophore demonstrates a robust method to achieve nanoscale functionalization with high fidelity.

Thermally expanded graphite polyetherimide composite with superior electrical and thermal conductivity

Thermally expanded graphite (EG) polymer composite has high potential for application in the modern thermo-electronic industry due to cost-effectiveness and excellent electrical and thermal properties. In this study, we report electrical and thermal conductivity enhancement of expanded graphite/polyetherimide (EG/PEI) composite fabricated by a simple solution mixing technique. Expanded graphite has the potential to enable larger enhancement in properties relative to graphene nanoplatelets, through the creation of continuous graphitic networks in the composite. Solution casting technique enables preservation of worm structure of expanded graphite in the composite thus enabling the development of continuous graphitic networks throughout the composite, leading to superior property enhancement. Measurements reveal ∼19 orders of magnitude increase in electrical conductivity of composite (yielding values up to 969 Sm-1) through the inclusion of 10 wt% of EG filler, relative to pure polyetherimide (electrical conductivity ∼ 1.2 × 10−17 Sm−1). Theoretical prediction using an effective medium approach reveals the impact of continuous graphitic network on the electrical conductivity of the composites. We also find that composite with 10 wt% EG filler composition exhibits a thermal conductivity (k) value of 7.3 Wm−1K−1, representing a significant enhancement of ∼3070% compared to pure PEI (k ∼ 0.23 Wm−1K−1). Field Emmission Environment Scanning Electron Microscopy (FE-ESEM) reveals the preserved interconnected structure of EG within the composite allowing the development of a conductive interpenetrating network of polymer and filler. Raman spectroscopy, X-ray diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) analysis are further used to characterize the fillers and EG/PEI nanocomposites. Our work identifies the solution casting method as a promising approach for developing high-performance EG/PEI composites in this work.

Artificial weathering of plastics used in oyster farming

With the omnipresence of plastic litter from oyster farming in marine coastal areas, the objective of this work was to better understand the weathering of plastics used in this field, focusing on oyster spat collectors. During their use, around fifteen years, collectors made of polypropylene (PP) undergo numerous degradations, alternatively submerged, emerged in seawater, and stored outdoor until the next cycle. They weaken, crack, break, end up fragmenting and disseminated in the environment as microplastics associated to persistent organic pollutants. In this work, a comparison of 55 months of in situ weathering with five months of artificial weathering in air or in artificial seawater in a homemade UV chamber was conducted to better understand the mechanisms involved. Chemical, thermal and surface characterizations of virgin and weathered samples were conducted using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Environmental Scanning Electron Microscopy (ESEM). After 55 months of in situ weathering, collectors were notably damaged with large fissures and loss of microplastics (MPs) associated with an increase of carbonyl index values and a decrease of melting temperatures and crystallinity rates. Considering only UV irradiation, five months of artificial weathering at 30 °C under continuous irradiation of 6.9 W/m2 under UV lamps (295–400 nm) reproduced approximately 4.4 months of natural sunlight. Artificial weathering confirmed that photooxidation by combined effects of UV rays and oxygen was the main weathering mechanism and was reduced in seawater. These results help to understand the mechanisms involved in the weathering of these collectors in the marine environment and provide valuable information for industrials and professionals. Our study suggests a better storage away from UV rays and a reduction of the duration of use compared to current practices.

Acoustic emission of the fracture behaviors of epoxy foam composites reinforced by bamboo fibers

The epoxy foam composites reinforced by unidirectional bamboo fibers were prepared and their mechanical property was examined by tensile test. The fracture morphology was observed by an environmental scanning electron microscopy (ESEM) and the fracture behaviors were quantitatively analyzed based on the acoustic emission (AE). The results indicated that the fiber reinforced foam (FRF) composites displayed much higher strength and toughness that are 131.3% and 223.5% higher than the pristine unfilled epoxy foam (PF), respectively. The mechanical behaviors of FRF during the fracture process were mainly the failure of porous matrix covered on the fiber interface, which took a proportion of 72.2%. The fiber dissociations and fiber breakage took 19.6% and 8.2%, respectively. The structure-property relationships bridged by AE and the fractography were investigated, and the strategies on strengthening and toughening the porous polymer composites were discussed.

Tribological analysis of TiN film during run-in period: An in situ investigation under controlled environment in eSEM

Most of the conventional tribological studies are performed through long duration tests, which therefore often neglect the run-in period. To highlight these early stages of damaging, which may present a predominant role on the global wear, a custom-built dedicated mini-tribometer in a linear reciprocating configuration was designed and is presented in the paper. The tribometer is developed to be implemented into an environmental SEM, in which the atmosphere is controlled. As a proof-of-concept, a well-known model system steel-hard TiN coating is used for two different atmospheres: vacuum and humid environments. The adopted small-scale and in situ approach has led to the validation of the mini-tribometer. Through this combined strategy, some scenarios of materials degradation are suggested in light of the interface nature involved in the contact. In this sense, the role of the environment is pointed out, and explained.

Improvement Mechanism of the Mechanical Properties and Pore Structure of Rubber Lightweight Aggregate Concrete with S95 Slag

This paper used natural pumice from the Inner Mongolia region as coarse aggregate to produce a lightweight concrete mix with a 3% rubber particle (20 mesh) content and dissimilar slag contents (0%, 5%, 10%, 15%, 20%, 25%, and 30%). It measured the compressive strength in five periods (3, 7, 14, 21, and 28 d). It also observed the development of the microstructure and measured the air content and pore distribution of the concrete using environmental scanning electron microscopy and nuclear magnetic resonance. A microtest combined with macroscopic mechanical experiments were used to analyze the influence on the mechanical properties of the rubber lightweight aggregate by the content of the S95 slag. The results showed that slag can improve the microstructure of rubber lightweight aggregate concrete. It hydrated the products, optimized the porous structure, and enhanced the compressive strength of the rubber lightweight aggregate concrete at 28 days, with excellent results regarding the air entraining. The best compressive strength of the rubber powder lightweight aggregate concrete at 28 days was when the content of the slag was 15%. An Atzeni pore-structure–strength model was introduced that contained a cement mass fraction. The results of the fitting indicate that the pore structure located at 0.1~1 μm had a marked influence on the mechanical properties of the rubber powder concrete.

Enhanced oil recovery in fractured low-permeability reservoirs by a novel gel system prepared by sustained-release crosslinker and water-soluble thixotropic polymer

Polymer gels have been widely used in improving oil recovery and decreasing excessive water production in heterogeneous reservoirs after the long-term water flooding process. However, the high initial viscosity of polymer and the short gelation time still restricts the performance of polymer-based in situ cross-linked gels for in-depth conformance control. Herein, a novel gel system formed by in-situ crosslinking of water-soluble thixotropic polymer (WTP) and sustained-release crosslinker (SRC) was proposed. The WTP was synthesized by acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-[3-(dimethylamino)propyl] methacrylamide. It exhibits low viscosity under high shear rates and becomes thick under low shear rates, which ensures good injectability during the injection process and high gelation strength after cross-linking. The SRC was prepared by coating poly(ethyleneimine) (PEI) into the W/O/W multiple emulsions. The sustained-release mechanisms were well elaborated by confocal laser scanning microscopy (CLSM) observations. Only after the demulsification of multiple emulsions, the PEI would be released from the internal aqueous phase to the external aqueous phase. Therefore, these emulsions can be employed to deliver crosslinkers to specified targets in deep regions and prolong the release of crosslinkers to prevent undesirable crosslinking reactions near the injecting wells. According to the environmental scanning electron microscope (ESEM) observations and viscosity measurements, the low viscosity and an incompact spatial network could be observed in SRC/WTP gel system in the first 17 d, after which the PEI molecules were released to the external aqueous phase and cross-linked with WTP, forming the solid gel with small pores and yielding a high viscosity of 8793 mPa⋅s. Rheology tests have demonstrated that the elastic modules and the liner viscoelastic region of the novel gel system was nearly two times and twenty times than the traditional polymer gel, indicating higher gelation strength and better shear resistance. The core flooding tests showed that the SRC/WTP gel system had good injectability and could effectively plug the millimeter and submillimeter-sized cracks in low-permeability cores. 0.6 pore volume (PV) of SRC/WTP gel system with 3 gel slugs and a low injection rate can yield the best plugging performance in fractured core samples. And the gelation time shortens with the decrease of fracture apertures. Most importantly, the field tests in Ordos Basin verified the desirable EOR performance of the SRC/WTP gel system in fractured low-permeability reservoirs.

Effect of In-Office Bleaching Agents on Three Different Esthetic Restorative Materials: An In Vitro Study

Objective: The purpose of this study was to evaluate the effect of two hydrogen peroxide concentrations, commonly used in In-Office bleaching, on the surface roughness and color change of different esthetic restorative materials. Materials and Methods: Sixty disc samples (10 mm in diameter and 2 mm in thickness) of the different restorative materials used were constructed following the manufacturers’ instructions. Samples were classified into three main groups (n=20) according to the type of restorative material: Group1: Microhybrid composite Filtek P90 Silorane, Group 2: IPS emax Press and Group 3: Vitadur Alpha porcelain. Each of the three groups was divided into two subgroups (n=10) (a and b) according to the type of bleaching agent used (Opalesence Xtra Boost 35% hydrogen peroxide (HP) and Zoom 2 25% HP respectively). Samples of subgroups were further divided into two equal divisions (n=5) according to the type of test performed (Roughness testing and Color assessment). Each sample was assessed for surface roughness and color change before bleaching so that each sample served as its own control. Surface roughness was examined using Environmental scanning electronic microscope (ESEM). Color measurements were made with spectrophotometer using CIELAB color scale. One sample from each subgroup was examined to confirm their crystalline phase before and after bleaching using X-Ray Diffraction. Results were statistically analyzed. Results: Significant differences in Ra values were observed between the unbleached and bleached samples, as well as between subgroups treated with Opalesence Xtra Boost and those treated with Zoom 2. The two bleaching agents had statistically significant effect on the color of restorative materials (P<0.05). Moreover, the color change was found to be significantly higher for the restorative materials treated with Opalesence Xtra Boost compared to Zoom 2, regarding their mean ΔE values. Conclusion: Highly concentrated in-office bleaching systems adversely affected the surface roughness and color of Filtek P90 Silorane, IPS e-max Press and Vitadur Alpha porcelain.