Environmental Scanning Electron Microscopy Observations Research Articles

Mechanical Properties and Microstructure of Highly Flowable Geopolymer Composites with Low-Content Polyvinyl Alcohol Fiber

Geopolymer enhances mechanical properties with polyvinyl alcohol (PVA) fibers, but there has been limited research exploring low PVA fiber dosages for mechanical properties in 3D printing or shotcrete. This study experimentally investigated slag and fly ash-based geopolymer mixtures reinforced with 0.1%, 0.15%, and 0.2% PVA fiber by volume as well as a control group without PVA fibers. These mixtures were prepared using fly ash, quartz sand, slag powder, silica fume, and an aqueous sodium silicate solution as the alkali activator, with the addition of PVA fiber to enhance composite toughness. The mechanical properties of the composites, encompassing dog-bone tensile properties, cubic compressive strength, bending and post-bending compressive strength, and prism compressive properties, were evaluated. Significantly, specimens with 0.15% PVA fibers exhibited optimal performance, revealing a notable 28.57% increase in tensile stress, a 36.45% surge in prism compressive strain, and a 47.59% rise in tensile strain compared to fiber-free specimens. Furthermore, environmental scanning electron microscopy observations were employed to scrutinize the microscopic mechanisms of composites incorporating PVA fibers, slag, and fly ash. In comparison to fiber-free specimens, prism compressive specimens with 0.15% PVA fibers demonstrated a 27.17% increase in post-cracking loading capacity, a 44.07% increase in post-cracking ductility, a 50.00% increase in peak strain energy, and a 76.36% increase in strain energy ratio.

The Micro-Occurrence Mechanisms of Tight Oil: Fluid–Rock Interactions at Microscale Pores, Nanoscale Pores, and Mineral Surfaces

Understanding the micro-occurrence mechanism of tight oil has long been a daunting challenge in the exploration and development of unconventional resources. This article discusses the micro-occurrence mechanism of tight oil through continuous extraction by combining thin casting, fluorescent thin sections, environmental scanning electron microscope observations, physical property testing, and X-ray diffraction experiments. The results indicated that in the tight sandstone of the Chang 8 Formation in the Ordos Basin, the average tight oil content was 35.46% for microscale pores, 35.74% for nanoscale pores, and 28.79% for mineral surfaces. Six types of micro-occurrence states of tight oil were identified: emulsion, cluster, throat, star-like, isolation, and thin film forms. Although clay minerals and heavy components dominate the adsorption of tight oil on mineral surfaces, micro-occurrence is fundamentally an oil–rock interaction process. Hence, oil–rock interactions and occurrence states were combined in this study to identify tight oil’s micro-occurrence mechanism. The van der Waals forces of attraction between asphaltene molecules and a mineral surface play a critical role, and minerals with hydroxyl groups can also combine with carboxyl and hydroxyl groups present in tight oil. As a consequence of the adsorption of heavy components by minerals, tight oil components remain in microscale and nanoscale pores with a higher saturation, increased aromatic hydrocarbon content, and greater fluidity. The heterogeneity of the components due to adsorption influences the physical properties and mineralization framework of tight oil reservoirs. These findings suggest that tight oil occurrence results from the coupling of microscopic occurrence and component heterogeneity in microscale and nanoscale pores.

Insights into the Effect of Micropore Structure and Mineralogy on Adsorbed Tight Oil in the Huaqing Area, Ordos Basin, China

There is great potential for tight oil as an alternative to conventional fossil fuels throughout the world. Adsorption, mineralogy, and pore structure of tight sandstone are very important factors for the efficient development of adsorbed tight oil from tight sandstone oil reservoirs. In this study, the occurrence morphology of tight oil adsorbed to varying pore structures was examined, as well as the relationship between adsorption content and occurrence morphology. X-ray energy dispersive spectra, environmental scanning electron microscope observations, and thin fluorescence sections were used to describe the occurrence morphology of adsorbed tight oil in tight sandstone reservoirs. It was found that adsorbed tight oil can be classified into five types: emulsion, cluster, throat, thin-film, and isolation, with average contents of 34.9%, 14.5%, 3.1%, 42.7%, and 4.7%, respectively. In addition, a Soxhlet extraction was developed with four pore structures to describe the geological effects of adsorbed tight oil in reservoirs. The adsorption content of tight oil ranges from 4.015 mg/g to 16.987 mg/g, with an average of 10.115 mg/g. The order of adsorption content for different occurrence morphologies is as follows: emulsion form > throat form > cluster form > isolation form > thin-film form. It is the size and connectivity of the porous throat that determines the desorption efficiency of tight oil. An important outcome of this study can be the introduction of rational development plans and the improvement of oil recovery efficiency for tight oil reservoirs.

Spray-Coated Superhydrophobic Overlayer with Photothermal and Electrothermal Functionalities for All-Weather De/anti-icing Applications.

High-performance de/anti-icing overlayers which can be deposited on diverse surfaces offer great potential in many industrial settings and daily life, yet a versatile overlayer applicable to all-weather conditions (high humidity, low temperature, raining, snowing, etc.) is in high demand for practical applications. This study presents the fabrication and application of a superhydrophobic overlayer with a bioinspired hierarchical surface which additionally possesses photothermal and electrothermal functionalities, so it can operate as a de/anti-icing layer in extreme environments. The overlayer, with a papilla-like microstructure similar to that of a lotus leaf, features polydopamine-decorated layered basic zinc acetate microparticles distributed in the framework of multiwalled carbon nanotubes. Specifically, the overlayer is superhydrophobic, and its capability of suppressing the condensation of water droplets and growth of ice crystals is verified by both in situ environmental scanning electron microscopy observations and freezing experiments. Moreover, the overlayer can be warmed up to 74 and 105 °C under the excitation of sunlight and direct current bias, respectively, which is sufficiently high for deicing in severe weather. It is worth mentioning that the overlayer is produced by a spray-coating technique; therefore, it is suitable for large-scale deployment on arbitrary substrate materials. The findings provide insights into a new strategy for engineering multifunctional overlayers and can lead to expanding applications of composite coatings.

ESEM observation and rheological analysis of rejuvenated SBS modified bitumen

Observing the microstructure of bituminous binders with an environmental scanning electron microscope (ESEM) can contribute significantly to reveal the underlying rejuvenation mechanism. In this study, three rejuvenators were selected to regenerate the aged SBS modified binders at five dosages, and their rheology was evaluated using a dynamic shear rheometer. ESEM was employed to examine the microstructure of binders as well, and a series of microstructure parameters were quantified with image analysis. The results demonstrated that the chemical composition changes correspond to the evolution of microstructure morphological and rheological properties. Moreover, the rheological and microstructure characteristics were analyzed with Principal Component Analysis (PCA) and regression analysis. Based on PCA results, the microstructure of rejuvenated binders has shown a good correlation with stiffness after combining various principal components. According to regression analysis, the distance between adjacent fibrils exhibited a significant correlation with Jnr3.2 and the complex modulus index. Overall, the results of this study strengthen the hypothesis that the ESEM microstructure is intimately correlated with chemical composition and rheological properties, rather than with irrelevant surface phenomena.Bitumen, polymer modified bitumen, rejuvenator, microstructure, rheology, environmental scanning electron microscopy.

Effect of Thermal Stresses Formed during Air Annealing of Amorphous Lanthanum Cuprate Thin Films Deposited on Silicon Substrate

Amorphous thin films of La–Cu–O deposited by magnetron sputtering have been annealed at different temperatures and in situ analyzed by X-ray diffraction. These experiments were useful to determine the crystallization temperature and to follow the crystallization process of the film. The in situ annealing X-ray diffraction analyses have been also used to determine the thermal expansion coefficient of La2CuO4 thin film. The estimated value is close to that obtained for a commercial powder. The thermal expansion coefficient value with additional environmental scanning electron microscopy observations explains the delamination origin that occurs during the annealing before the crystallization step. The buckling and delamination of the film observed is caused by the thermal expansion coefficient mismatch of the film and the substrate. During the heating step, the mismatch generates compressive stress at the film/substrate interface, causing the film to lift off and crack in the typical way.

Oxidation as an Early Stage in the Multistep Thermal Decomposition of Uranium(IV) Oxalate into U3O8.

The thermal decomposition of actinide oxalates is greatly dependent on the oxidation state of the cation, the gas involved, and the physical characteristics of the precursor. In the actinides series, uranium(IV) oxalate U(C2O4)2·6H2O can be viewed as a peculiar case, as its sensibility toward oxidation leads to a specific series of reactions when heating under an oxygen atmosphere. In order to clarify the disagreements existing in the literature, particularly concerning potential carbonate intermediates and the possible transitory existence of UO3, we show here an extended characterization of the different intermediates through a combination of X-ray diffraction, vibrational spectroscopies and X-ray absorption near-edge spectroscopy. In this frame, uranium oxidation was found to occur at low temperature (200 °C) concomitantly to the onset of oxalate groups decomposition, leading to an amorphous oxo-oxalato compound. Pursuing the thermal conversion up to 350 °C led to complete oxidation of U(IV) into U(VI), then to the formation of amorphous UO3 still bearing adsorbed carbonates. The first pure oxide formed during the thermal conversion was further identified to substoichiometric UO3-δ after heating at 550 °C. Finally, U3O8 was obtained as the final stable phase after heating above 660 °C. The mechanism of thermal conversion of uranium(IV) oxalate into oxide under oxygen is then driven by a complex interplay between redox reactions and decomposition of the organic fractions. Such chemical reactions were also found to significantly modify the morphology of the powder through high-temperature environmental scanning electron microscopy observations: decomposition led to a 20% reduction in the size of the aggregates, while uranium oxidation clearly promoted growth within the agglomerates.

Preparation and study of Polyvinyl Alcohol/Attapulgite nanocomposite fibers with high strength and high Young’s modulus by gel spinning

Polyvinyl alcohol (PVA)/Attapulgite (ATT) nanocomposite fibers with high strength and high Young’s modulus were prepared via gel spinning. The structures and properties of PVA/ATT nanocomposite fibers were investigated with Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimeter (DSC), thermo gravimetric analysis (TGA), x-ray diffraction (XRD), Environmental scanning electron microscope (ESEM), and mechanical testing. The results showed that ATT had a great influence on the structures and properties of PVA/ATT nanocomposite fibers. The melting temperatures, crystallinities, initial decomposition temperatures and maximum decomposition temperatures of PVA/ATT nanocomposite fibers increased firstly when ATT content was increased from zero to 3 wt%, however, they were then dropped when ATT contents were 5 wt% and 7 wt%. The highest melting temperature, crystallinity, initial decomposition temperature and maximum decomposition temperature of PVA/ATT-3 were 240.4 °C, 67.6%, 266.7 °C and 358.6 °C, respectively. Furthermore, ESEM observation indicated that ATT had good adhesion to PVA matrix. Mechanical tests showed that PVA/ATT-3 had the highest breaking tensile and Young’s modulus of 12.6 cN/dtex and 301.9 cN/dtex, respectively.

PH controlled gelation behavior and morphology of gelatin/hydroxypropylmethylcellulose blend in aqueous solution

Studies on unique blends of cool and thermal gels have attracted increasing attention since they both have scientific and commercial importance, such as functional food design and edible packaging materials etc. In this work, the pH dependent gelation behaviors and morphologiesof blends of a cool gel, gelatin (GA), and a thermal gel,hydroxypropylmethylcellulose (HPMC), in aqueous solution were investigated by rheometer, UV spectrophotometer, fluorescence microscope (FM) and environmental scanning electron microscopy (ESEM). It was found that when pH < 4.75, HPMC was the continuous phase, while GA was the separated phase distributed in HPMC matrix as small spherical domains. Phase transition occurred at pH 5.00, in which GA became the continuous phase, while HPMC appeared as separated droplets dispersed in GA matrix. At lower pH values, GA and HPMC were compatible based on UV detection, ESEM observation, as well as phase separation kinetics. Near the isoelectric point (pI) of gelatin (pH 7.0–9.0), a maximum viscoelastic module (G') was detected. It was noticed that there were many interphasic regions in the blend systems. Each phase was not pure: GA phase contained some HPMC and vice versa at all pH values, which means that GA and HPMC are partly miscible or compatible to a certain degree.

Bentonite microstructure and saturation evolution in wetting–drying cycles evaluated using ESEM, MIP and WRC measurements

In this paper, the microstructure of the Czech bentonite B75 was investigated by three methods: water retention curve (WRC) measurements, mercury intrusion porosimetry (MIP) measurements and environmental scanning electron microscopy (ESEM) investigation. The experiments were performed on samples at various compaction levels (between 1·27 and 1·90 g/cm3) and at various suctions (between 3·3 and 290 MPa) along both drying and wetting hydraulic paths. In the ESEM observations, target relative humidities (and thus total suctions) were imposed directly in the ESEM chamber to observe the effect of the hydraulic path on the microstructure. Apart from the inter-lamellar pores, which are not accessible to the adopted experimental techniques, two pore families were identified: micropores and macropores. The transition pore size between the micropores and macropores was found to be suction dependent. The microporosity was practically insensitive to compaction and only the largest micropores were sensitive to suction. Smaller macropores were sensitive to compaction only, whereas larger macropores were sensitive to both compaction and suction. It was observed that, during wetting from the as-compacted state, the macropores remained completely dry up to very low values of suction, whereas the micropores were found to be unsaturated up to the suctions between 10 to 60 MPa. Both macropores and micropores contributed to sample volume changes during drying and wetting. Although the microstructural volume change appeared to be reversible, the macrostructure exhibited permanent deformation.

Cinaciguat in combination with insulin induces a favorable effect on implant osseointegration in type 2 diabetic rats

The osseointegration process of implant is seriously impaired in type 2 diabetes mellitus (T2DM) that causes high failure rate, and insufficiency exists in current insulin therapy, creating a demand for new bone-synergistic agent. Cinaciguat, a novel type of soluble guanylate cyclase (sGC) activator, plays a vital role in glucose metabolism, inflammation control and bone regeneration. We hypothesized that the combined application of cinaciguat and insulin could reverse poor implant osseointegration in diabetes. To test this hypothesis, streptozotocin-induced diabetic rats were placed implants in the femur, and divided into five groups: control, T2DM, cinaciguat-treated T2DM (7 μg/kg), insulin-treated T2DM (12 IU/kg), cinaciguat plus insulin combination-treated T2DM (7 μg/kg and 12 IU/kg respectively), according to different treatment received. The weight and glucose levels of rats were evaluated at fixed times, and plasma level of cyclic guanosine monophosphate (cGMP) was determined before euthanasia. Three months after therapy, the femurs were isolated for pull-out test, environmental scanning electron microscope observation, microscopic computerized tomography evaluation and various histology analysis. Results revealed that diabetic rats showed the highest blood glucose level and lowest cGMP content, which led to the worst structural damage and least osseointegration. Combined treatment could attenuate the diabetes induced hyperglycemia to be normal, restore the cGMP content, protein kinase G II (PKG II) expression, phosphodiesterase-5 (PDE5) activity and ameliorate the mechanical strength, the impaired bone microarchitecture and osseointegration to the highest level. Meanwhile, monotreatment (insulin or cinaciguat) also showed restorative effect, but less. Our findings demonstrated that the cGMP/PKG II signaling pathway activated by cinaciguat mediated the favorable effects of the combined application on improving implant fixation under T2DM condition.

In situ observations for growth kinetics of water droplets on Bambusa multiplex leaves

The wetting of material surfaces is an important topic and is now being intensively investigated toward various practical applications, yet most previous studies have adopted postmortem methods. Fortunately, the recent development of environmental scanning electron microscopy (ESEM) means that hydrated samples can be observed in their native state, as well as dynamic surface reactions. Here, we use in situ ESEM observation to explore the microscopic growth dynamics of water droplets on adaxial and abaxial surfaces of Bambusa multiplex leaf (BML) during wetting. Our results show that, due to the dramatic structural differences between adaxial and abaxial surfaces, the growth of water droplets on the two sides is quite different. Furthermore, the growth kinetics of water droplets on different BML surfaces are quantitatively discussed. This conceptual study demonstrates a straightforward pathway to understanding the wetting behavior, and the results may pave the way for further research on bio-inspired materials.

In situ observation of dewetting-induced deformation of vertically aligned single-walled carbon nanotubes

We investigated dynamical processes of capillary-mediated deformation of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) via in situ observation of their wetting and dewetting behaviors using an environmental scanning electron microscope (ESEM). Three types of wetting behaviors on a VA-SWCNT sample were confirmed, including conical shaped water aggregates, spherical droplets on tips of conical shaped water aggregates, and extensively distributed water layers. While the former two types both resulted in dimples on the VA-SWCNT surface and failed to induce large-scale deformation of VA-SWCNTs, the latter caused the formation of wall-like structures and crack propagation in the VA-SWCNT film during the dewetting process due to directional retraction of vapor-liquid interfaces. This dewetting-induced large-scale deformation that was confirmed by the in situ ESEM observation for the first time represented initial stages of capillary processes, leading to the self-organization of VA-SWCNTs reported in recent literatures. Compared to the previous studies based on ex situ observations of dried samples, our in situ observation successfully captured temporal evolution of the dewetting-induced deformation, facilitating the more precise construction of predictive models of final morphologies of VA-SWCNT films after capillary-mediated densification.

Research on water retention and microstructure characteristics of compacted GMZ bentonite under free swelling conditions

In this study, water retention tests under free swelling conditions were performed to investigate the water intake (or loss) behaviour of compacted GMZ bentonite. First, the water retention characteristics were investigated, and then the microscopic pore structure was observed by environmental scanning electron microscope (ESEM). The results indicate that GMZ bentonite has a strong swelling (or a limited shrinkage ability) due to water intake (loss). The suction behaviour of GMZ bentonite is similar to MX80 bentonite and FEBEX bentonite. We also find that the confinement conditions can affect the suction behaviour of the material, especially at high relative humidity (RH). Additionally, a mathematic model can fit the mass change data very well. Microscopic tests show that the granular sensation of GMZ bentonite is obvious for a sample at low RH. With the increase in RH, the surface of GMZ bentonite becomes more smooth. The differences in the porosities calculated by the macroscopic and microscopic tests can be attributed to image resolution. The inter-laminar pores and intra-aggregate pores cannot be observed by the ESEM method. In addition, ESEM observation can provide an intuitive basis for the further research of the seepage property of GMZ bentonite.

Influence of carboxylated styrene–butadiene copolymer on tetracalcium aluminoferrite hydration in the presence of gypsum

In mixes with gypsum and hydrated lime, the influence of carboxylated styrene–butadiene (SB) copolymer at dosages of 0 to 20% on the hydration of tetracalcium aluminoferrite (C4AF) curing from 12 h to 28 d was investigated through X-ray diffraction (XRD) analysis coupled with environmental scanning electron microscopy (ESEM). The XRD results revealed that the addition of SB copolymer accelerated C4AF hydration, favouring the formation of AFt and AFm at the early hydration stage, but leading to a decrease in crystallised AFm content at the late hydration stage. With an increase in SB copolymer dosage, the content of unhydrated C4AF showed an inflection point after 12 h of hydration and tended to decrease after 1 to 7 d of curing. A dormant period was found to exist between 12 and 24 h for SB copolymer dosages of less than 10%. The ESEM observations complemented the XRD findings and also revealed a morphological change in the hydrates with the addition of SB copolymer.

Functionalization of a nanostructured hydroxyapatite with Cu(II) compounds as a pesticide: in situ transmission electron microscopy and environmental scanning electron microscopy observations of treated Vitis vinifera L. leaves.

The present study evaluated a biocompatible material for plant protection with the aim of reducing the amount of active substance applied. We used a synthetic hydroxyapatite (HA) that has been studied extensively as a consequence of its bioactivity and biocompatibility. An aggregation between HA nanoparticles and four Cu(II) compounds applied to Vitis vinifera L. leaves as a pesticide was studied. Formulations were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS) and electron microscopy and applied in planta to verify particle aggregation and efficiency in controlling the pathogen Plasmopara viticola. The XRD patterns showed different crystalline phases dependig on the Cu(II) compound formulated with HA particles, DLS showed that nanostructured particles are stable as aggregates out of the nanometer range and, in all formulations, transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM) microscopy showed large aggregates which were partially nanostructured and were recognized as stable in their micrometric dimensions. Such particles did not show phytotoxic effects after their application in planta. A formulation based on HA and a soluble Cu(II) compound showed promising results in the control of the fungal pathogen, confirming the potential role of HA as an innovative delivery system of Cu(II) ions. The present work indicates the possibility of improving the biological activity of a bioactive substance by modifying its structure through an achievable formulation with a biocompatible material. © 2018 Society of Chemical Industry.

Changes in physicochemical properties of rice in response to high-temperature fluidized bed drying and tempering

ABSTRACTThe effects of high-temperature fluidized bed drying and tempering on pasting, gelatinization, crystalline and microstructural properties of long-grain Vietnamese rice cultivar A10 were examined. The freshly harvest paddy (33% wet basis) was dried at two drying temperatures (80 and 90°C) and two drying durations (2.5 and 3.0 min) using a custom-made lab-scale batch fluidized bed dryer. The dried rice was immediately tempered in sealed containers at 75 and 86°C for various tempering durations (0, 30, 40, and 60 min), followed by thin-layer drying at 35°C to reduce moisture level to 14% wet basis. Characterization of pasting, gelatinization, crystallinity, and microstructure of the dried rice was undertaken using rapid visco analyzer, differential scanning calorimetry, X-ray diffraction (XRD), and environmental scanning electron microscopy (ESEM), respectively. Pasting properties and gelatinization enthalpy decreased with higher drying temperature and longer tempering time while pasting and gelatinization temperatures increased. Degree of crystallinity changed slightly, however, a shift from A-type to A+V-type XRD pattern was observed. ESEM observation demonstrated some degree of collapse of the rice microstructure. The kernel integrity appeared to be enhanced by the gel network formed during partial gelatinization of starch, corroborating with the changes in pasting and gelatinization properties of the fluidized bed dried and tempered rice.

Microscopic mechanisms of soil moisture related to hydromulching

Abstract Hydromulching is a new mulch product which has positive effects on soil moisture conservation and the inhibition of evaporation. However, current research on its soil moisture conservation effect has mainly adopted the field fixed-point observation method, rather than revealing the soil moisture conservation mechanism from the microstructure of the hydromulching. This paper applied spectrum analysis technology to observe the structure and micromorphological features of hydromulching, which will be able to reveal the mechanism of soil moisture conservation. Three types of hydromulching, based on laboratory preparation, were used to analyze the mechanism of soil moisture, using the infrared spectrometer (FTIR) and environmental scanning electron microscope (ESEM). The results showed that −OH generates intermolecular hydrogen bonds between carboxymethylcellulose sodium (CMC) and polyvinyl alcohol (PVA); the hydrogen bonds were formatted between the molecules of the two components, strengthening their compatibility, which increased the effectiveness of the hydromulching and created a dense mesh structure. ESEM observation results showed that preparation 1's hydromulching coverage had good effects, while preparations 2 and 3 performed poorly. Therefore, we can conclude that hydromulching effectively cements soil particles. Then it can generate the soil membrane structure to reduce evaporation and improve soil moisture conservation function.

In Situ Oxide Growth Characterization of Mn-Containing Ni–25Cr (wt%) Model Alloys at 1050 °C

The oxidation behaviour of four model alloys with the composition Ni–25Cr–xMn (with x = 0, 0.5, 1 and 1.5 wt%) was investigated at 1050 °C in air by thermogravimetry and by in situ observations in an environmental scanning electron microscope (ESEM). The addition of manganese modifies the oxidation rate of Ni–25Cr alloys by (1) increasing the parabolic constant k p compared to that for Ni–25Cr and (2) lowering the short-time oxidation rate. Regardless of the Mn concentration, in situ ESEM observations indicated the formation of spinel crystallites from the very beginning of the oxidation process. The size of the spinel crystallites was directly linked to the initial Mn concentration. The obtained results suggested that the formation of the spinel layer at the top of the chromia oxide scale rather than at the metal–oxide interface as thermodynamically expected must be attributed to the higher diffusion rate of Mn than Cr both in the lattice and at the grain boundary.

Innovative environmental scanning electron microscopy observations of the human semen in the study of male infertility (preliminary data)

Innovative environmental scanning electron microscopy observations of the human semen in the study of male infertility (preliminary data)