Search Results (33)

Cementitious materials are multiscale and multiphase composites whose frost resistance at the macroscale is closely governed by microstructural characteristics. However, the interfacial transition zone (ITZ) between clinker and hydrates, recognized as the weakest solid phase, plays a decisive role in the initiation and propagation of microcracks under freezing conditions. Understanding the frost damage mechanism of ITZ is therefore essential for improving the durability of concrete in cold regions. The motivation of this study lies in revealing how freezing affects the mechanical integrity and microstructure of ITZ in its early ages, which remains insufficiently understood in existing research. To address this, a nanoscratch technique was employed for its ability to quantify local fracture properties and interfacial adhesion at the submicronscale, providing a direct and high-resolution assessment of ITZ behavior under freeze–thaw action. The ITZ thickness and fracture properties were characterized in unfrozen cement paste and in cement paste frozen at 1 and 7 days of age to elucidate the microscale frost damage mechanism. Moreover, the enhancement effect of nano-silica modification on frozen ITZ was investigated through the combined use of nanoscratch and mercury intrusion porosimetry (MIP). The correlations among clinker particle size, ITZ thickness, and ITZ fracture properties were further established using nanoscratch coupled with scanning electron microscopy (SEM). This study provides a novel micromechanical insight into the frost deterioration of ITZ and demonstrates the innovative application of nanoscratch technology in characterizing freeze-induced damage in cementitious materials, offering theoretical guidance for designing durable concrete for cold environments. Full article

Polymer-modified bitumen is difficult to produce and often separates during storage and transport. In contrast, granular bitumen modifiers offer wide applicability, construction flexibility, and ease of transport and storage. This study involved preparing a multipolymer granulated bitumen modifier with a styrene–butadiene–styrene block copolymer, polyethylene, and aromatic oil. To elucidate the modification mechanism of a multipolymer granulated bitumen modifier on bitumen, the elemental composition of bitumen A and B, the micro-morphology of the modifiers, the changes in functional groups, and the distribution state of the polymers in the bitumen were investigated using an elemental analyzer, a scanning electron microscope, Fourier-transform infrared spectroscopy, and fluorescence microscopy. The effects of the multipolymer granulated bitumen modifier on the physical, rheological, and viscoelastic properties of two types of base bituminous binders were investigated at various dosages. The test results show that the Z_H/C ratio of base bitumen A is smaller than that of base bitumen B and that the cross-linking effect with the polymer is optimal. Therefore, the direct-feed modified asphalt of A performs better than the direct-feed modified asphalt of B under the same multipolymer granulated bitumen modifier content. The loose, porous surface structure of styrene–butadiene–styrene block copolymer promotes the adsorption of light components in bitumen, and the microstructure of the multipolymer granulated bitumen modifier is highly coherent. When the multipolymer granulated bitumen modifier content is 20%, the physical, rheological, and viscoelastic properties of the direct-feed modified asphalt of A/direct-feed modified asphalt of B and the commodity styrene–butadiene–styrene block copolymer are essentially identical. While the multipolymer granulated bitumen modifier did not significantly improve the performance of bitumen A/B at contents greater than 20%, the mass loss rate of the direct-feed modified asphalt of A to aggregate stabilized, and the adhesion effect reached stability. Image processing determined the optimum mixing temperature and time for multipolymer granulated bitumen modifier and aggregate to be 185–195 °C and 80–100 s, respectively, at which point the dispersion homogeneity of the multipolymer granulated bitumen modifier in the mixture was at its best. The dynamic stability, fracture energy, freeze–thaw splitting strength ratio, and immersion residual stability of bitumen mixtures were similar to those of commodity styrene–butadiene–styrene block copolymers with a 20% multipolymer granulated bitumen modifier mixing amount, which was equivalent to the wet method. The styrene–butadiene–styrene block copolymer bitumen mixture reached the same technical level. Full article

Penaeus monodon (black tiger shrimp) is one of the important shrimp species in aquaculture. Cryopreserving its sperm not only provides technical support for breeding but also effectively prevents the decline of genetic resources, promoting the sustainable development of its aquaculture industry. This study screened different types of diluents, cryoprotectants, and concentrations and explored equilibration time, cooling protocols, and thawing conditions, ultimately determining the optimal cryopreservation protocol for P. monodon sperm. The results showed that the optimal cryopreservation protocol involved using natural seawater as the diluent with 10% dimethyl sulfoxide (DMSO) as the cryoprotectant, in which the sperm suspension and cryoprotectant were mixed at a 1:1 (v/v) ratio and equilibrated at 4 °C for 30 min. Subsequently, cooling was performed using a programmable controlled-rate freezer: the temperature was reduced to −20 °C at −5 °C/min and held for 5 min; then cooled to −80 °C at −10 °C/min and held for 5 min; finally, the temperature was reduced to −180 °C at −20 °C/min. After cooling, the sperm samples were transferred to liquid nitrogen for long-term storage. The results demonstrated that thawing in a 37 °C water bath achieved the highest sperm motility compared to conditions at 27 °C, 32 °C, 42 °C, and 60 °C. After 15 days of liquid nitrogen storage, the sperm survival rate was 53.33 ± 9.18%. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that the sperm structure was intact before freezing, with a rounded head, a distinct acrosomal spike anterior to the head, a concentrated nucleus in the head, dense chromatin, and a smooth cell membrane surface. However, after freezing and thawing, the acrosomal spikes of some sperm were fractured, and the membrane structure was damaged. Enzyme activity analysis showed that during liquid nitrogen storage from 0 to 15 days, the enzyme activity of alkaline phosphatase (AKP) and acid phosphatase (ACP) in sperm gradually increased with significant differences observed compared to day 0 (p < 0.05). The activity of malondialdehyde (MDA) showed a gradual increase at 0, 5, and 10 days, but then decreased at day 15. The enzyme activity of catalase (CAT) showed no significant changes from 0 to 10 days (p > 0.05) but significantly increased on day 15 (p < 0.05). The activity of total superoxide dismutase (T-SOD) showed no significant changes from 0 to 5 days (p > 0.05) but significantly increased from days 10 to 15 (p < 0.05). These findings provide valuable insights into the cryopreservation of P. monodon sperm and will guide the optimization of cryoprotectant combinations and freezing protocols aimed at improving sperm survival rates. Full article

The human pineal gland is the largest producer of the hormone melatonin. Pineal acervuli (brain sand), calcified concretions in the pineal gland, have long been studied because of their association with ageing, melatonin production, and neurological disorders. The solid inorganic matter of the hydroxyapatite crystals often renders sample sectioning impossible, to the extent that the sections lose value. Technically, freeze-fracturing has revealed the detailed structure and cell relationships without tissue damage. In our electron microscopic study, samples of the human pineal gland were obtained during autopsy from 20 donors with mean age 69 years. Samples underwent freeze-fracturing and standard histological procedures, and were analysed by scanning electron microscopy (SEM) in high vacuum. Based on our results, freeze-fracturing enabled identification of a mulberry-like acervulus topography. The acervuli were situated in specific “nest-like” structures, which were surrounded by pinealocytes, interstitial cells, and nerve fibres. A fractured surface of the intrapineal acervuli exhibited a regular lamellar structure. Freeze-fracturing the pineal gland and imaging by SEM enabled complex structural analysis. This approach permits viewing the surface acervuli spherical and internal lamellar architecture. Our results confirmed that the parenchyma of this small but important gland contains two types of acervuli, depending on their size: non-aggregated and aggregated. We propose to include these forms of acervuli in the new edition of the Terminologica Histologica. In conclusion, pineal gland freeze-fracturing by SEM is suitable for complex structural analysis. Our description of our methods can be a guide for other scientists who want to study the pineal gland with electron microscopy methods. Full article

In order to investigate freeze–thawed red sandstone failure processes under cyclic loading and unloading conditions, real-time acoustic emission (AE) and scanning electron microscopy (SEM) techniques were used to reveal the fracture process of the saturated red sandstone after cyclic loading and unloading tests using uniaxial compression. The results show that the stress–strain curves of the freeze–thawed sandstones show signs of hysteresis and exhibit a two-stage evolution of “sparse → dense”. In the cyclic loading and unloading process, the modulus of elasticity in the loading process is always larger than that in the unloading process, while the Poisson’s ratio is the opposite, and the radial irreversible strain and cumulative irreversible strain are larger than those in the axial direction. As the number of freeze–thaw cycles increases, the rock specimens need more cycles of loading and unloading to make the crack volume compressive strain $\Delta {\epsilon }_{cv}^{+}$ reach the maximum value and tend to stabilize, while the crack volume extensional strain $\Delta {\epsilon }_{cv}^{-}$ tends to decrease gradually. This study also shows that the growth phase of the cyclic loading and unloading process has more ringing counts and a shorter duration, while the slow degradation phase has more ringing counts with loading and less with unloading. In addition, the F-T cycle gradually changes the internal microcracks of the red sandstone from shear damage, which is dominated by shear cracks, to tensile damage, which is dominated by tensile cracks. This study’s findings contribute to our knowledge of the mechanical characteristics and sandstone’s degradation process following F-T treatment, and also serve as a guide for engineering stability analyses conducted in the presence of multiphysical field coupling. Full article

The combination of lyotropic liquid crystals (LLCs) and low-molecular-weight gelators (LMWGs) for the formation of lyotropic liquid crystal gels (LLC gels) leads to a versatile and complex material combining properties of both parent systems. We gelled the calamitic nematic N_C phases of a binary and ternary system using the LMWG 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). This binary system consists of the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water, whereas the ternary system consists of the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C₁₄TAB), the cosurfactant n-decanol, and water. Though containing similar surfactants, the gelled N_C phases of the binary and ternary systems show differences in their visual and gel properties. The gelled N_C phase of the binary system remains clear for several days after preparation, whereas the gelled N_C phase of the ternary system turns turbid within 24 h. We investigated the time evolution of the gel strength with oscillation rheology measurements (a) within the first 24 h and (b) up to two weeks after gel formation. The shape of the fibers was investigated over different time scales with freeze fracture electron microscopy (FFEM). We demonstrate that despite their similarities, the two LLC gels also have distinct differences. Full article

To improve the long-term performance of concrete engineering in high-altitude areas, waste tire rubber was added to a concrete mix, and freeze–thaw and impact tests were conducted. The effects of waste tire rubber with different particle sizes (10, 20, 30 mesh) and freeze–thaw cycles (0, 25, 50, 75, 100, 125) on the dynamic mechanical properties of concrete materials were studied. The stress–strain curves, peak stress, and fracture morphology of the specimens were analyzed. The microstructure changes of the specimens were also analyzed using scanning electron microscopy (SEM). The results showed the following: (1) Both macroscopic and microscopic analysis results showed that the internal damage of rubber concrete specimens was smaller after freeze–thawing, and the integrity was better after impact, maintaining a loose but not scattered state. The addition of waste tire rubber significantly improved the material’s impact resistance to a certain extent. (2) As the impact pressure increased, the strain rate of the specimens increased linearly, and the dynamic peak stress was linearly positively correlated with the strain rate. (3) After 125 freeze–thaw cycles, the peak stress of the specimens with 30-mesh added rubber decreased significantly less than that of ordinary concrete under 0.3, 0.45, and 0.6 MPa impact pressure. The dynamic peak stress was higher than that of specimens with 10-mesh and 20-mesh added rubber, and the addition of 30-mesh rubber significantly improved the frost resistance and impact resistance of concrete materials. This study can provide new ideas for the engineering application of rubber concrete. Full article

In this study, we employed a straightforward flame synthesis process to produce carbon soot containing carbon nano onions (CNOs) using easily accessible ghee oil as a precursor. The ghee oil, with a molecular composition rich in more than 50 carbon atoms, served as an effective source for generating CNOs. The synthesized CNO particles underwent comprehensive characterization through high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses, providing a detailed account of their physicochemical properties. In addition, we explored the direct deposition of CNOs on carbon fiber (CF) surfaces for 5 and 10 min via a soot deposition process. The resulting freeze–fracture images obtained from scanning electron microscope (SEM) offered insights into the morphology of the CNO-deposited CF. Our study aims to shed light on the potential applications of CNOs, focusing on their characterization and the possible benefits they may offer in diverse fields, including but not limited to enhancing interfacial bonding in thermoplastic composites. Full article

Analysis of secondary plant compounds for the development of novel therapies is a common focus of experimental biomedicine. Currently, multiple health-supporting properties of plant-derived molecules are known but still information on many mechanisms is scarce. Cinnamic acid and caffeic acid are two of the most abundant polyphenols in human dietary fruits and vegetables. In this study, we investigated cinnamic acid and caffeic acid effects on the gastric barrier, which is primarily provided by members of the transmembrane tight junction protein family of claudins. The Xenopus laevis oocyte has been established, in recent years, as a heterologous expression system for analysis of transmembrane tight junction protein interactions, by performing paired oocyte experiments to identify an effect on protein–protein interactions, in vitro. In our current study, human gastric claudin-4, -5, and -18.2. were expressed and detected in the oocyte plasma membrane by freeze fracture electron microscopy and immunoblotting. Oocytes were paired and incubated with 100 µM or 200 µM cinnamic acid or caffeic acid, or Ringer’s solution, respectively. Caffeic acid showed no effect on the contact area strength of paired oocytes but led to an increased contact area size. In contrast, cinnamic acid-incubated paired oocytes revealed a reduced contact area and a strengthening effect on the contact area was identified. These results may indicate that caffeic acid and cinnamic acid both show an effect on gastric barrier integrity via direct effects on tight junction proteins. Full article

Research on engineered cementitious composites was carried out using recycled micronized powder from waste construction waste as a substitute for cement. Consequently, this paper focuses on the investigation of recycled micronized powder (RMP) as the subject of study. Using RMP-PP-ECCA0 as the control group, we explored the impact of polypropylene fiber content (0.5%, 1%, 1.5%, 2%) and the substitution rate of RMP (10%, 20%, 30%, 40%) on the mechanical properties, resistance to chloride ion penetration, and freeze–thaw durability of recycled micronized powder polypropylene-fiber-engineered cementitious composites (RMP-PP-ECCs). It was found that, with the increase in RMP substitution rate and fiber content, the mechanical, chloride ion permeation, and freeze–thaw resistance of recycled micronized powder polypropylene-fiber-engineered cementitious composites showed a trend of increasing and then decreasing when the RMP substitution rate was 10%, and the fiber content was 1.5%; the compressive, tensile, chloride ion permeation, and freeze–thaw resistance of recycled micronized powder polypropylene-fiber-engineered cementitious composites were most obviously improved. Compressive strength performance increased by 18.8%, tensile strength performance increased by 80.8%, maximum tensile strain increased by 314%, and electrical flux decreased by 56.3%. Meanwhile, when the recycled micronized powder substitution rate was 10%, the fiber content was 1%, with the most obvious improvement in flexural and freeze–thaw cycle resistance, compared with the control group 28 d flexural strength increased by 22%, after 150 freeze–thaw cycles, the mass-loss rate was reduced by 26%, and the relative dynamic elastic modulus was improved by 4%. In addition, the chemical composition of the regenerated microfractions and the defects in the matrix of the fracture surface of the tensile specimens, the distribution of polypropylene fibers, the surface morphology, and the failure mode were analyzed by X-ray diffraction and scanning electron microscopy. Full article

This article relates personal recollections and starts with the origin of electron microscopy in the sixties of the previous century at the University of Amsterdam. Novel fixation and embedding techniques marked the discovery of the internal bacterial structures not visible by light microscopy. A special status became reserved for the freeze-fracture technique. By freeze-fracturing chemically fixed cells, it proved possible to examine the morphological effects of fixation. From there on, the focus switched from bacterial structure as such to their cell cycle. This invoked bacterial physiology and steady-state growth combined with electron microscopy. Electron-microscopic autoradiography with pulses of [³H] Dap revealed that segregation of replicating DNA cannot proceed according to a model of zonal growth (with envelope-attached DNA). This stimulated us to further investigate the sacculus, the peptidoglycan macromolecule. In particular, we focused on the involvement of penicillin-binding proteins such as PBP2 and PBP3, and their role in division. Adding aztreonam (an inhibitor of PBP3) blocked ongoing divisions but not the initiation of new ones. A PBP3-independent peptidoglycan synthesis (PIPS) appeared to precede a PBP3-dependent step. The possible chemical nature of PIPS is discussed. Full article

In the 1960s, electron microscopy did not provide a clear answer regarding the compact or dispersed organization of the bacterial nucleoid. This was due to the necessary preparation steps of fixation and dehydration (for embedding) and freezing (for freeze-fracturing). Nevertheless, it was possible to measure the lengths of nucleoids in thin sections of slow-growing Escherichia coli cells, showing their gradual increase along with cell elongation. Later, through application of the so-called agar filtration method for electron microscopy, we were able to perform accurate measurements of cell size and shape. The introduction of confocal and fluorescence light microscopy enabled measurements of size and position of the bacterial nucleoid in living cells, inducing the concepts of “nucleoid occlusion” for localizing cell division and of “transertion” for the final step of nucleoid segregation. The question of why the DNA does not spread throughout the cytoplasm was approached by applying polymer-physical concepts of interactions between DNA and proteins. This gave a mechanistic insight in the depletion of proteins from the nucleoid, in accordance with its low refractive index observed by phase-contrast microscopy. Although in most bacterial species, the widely conserved proteins of the ParABS-system play a role in directing the segregation of newly replicated DNA strands, the basis for the separation and opposing movement of the chromosome arms was proposed to lie in preventing intermingling of nascent daughter strands already in the early replication bubble. E. coli, lacking the ParABS system, may be suitable for investigating this basic mechanism of DNA strand separation and segregation. Full article

Nanocellulose-reinforced ionic conductive hydrogels were prepared using cellulose nanofiber (CNF) and polyvinyl alcohol (PVA) as raw materials, and the hydrogels were prepared in a dimethyl sulfoxide (DMSO)/water binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 206%) and firmness (up to 335 KPa). The tensile fracture test shows that the hydrogel has good properties in terms of tensile strength, toughness, and elasticity. The hydrogel as a conductor medium is assembled into a self-powered strain sensor and the open-circuit voltage can reach 0.830 V. It shows good sensitivity in the bend sensing testing, indicating that the hydrogel has good sensing performance. The water retention and anti-freezing performance experiments show that the addition of dimethyl sulfoxide solvents can effectively improve the anti-freezing and water retention properties of hydrogels. Full article

Fiber reinforcement is often used to improve the road performance of cold recycled asphalt mixture (CRAM). The purpose of this research is to evaluate the impact of fiber mixing process on the cracking resistance of CRAM from multiple perspectives. Four kinds of fiber mixing processes, named A, B, C, and D, were designed by changing the order of fiber addition during the mixing process. Then, semicircle bending tests and indirect tensile tests were conducted to characterize the low-temperature cracking behavior of fiber CRAM. Freeze–thaw cycle tests under both dry and water-saturated conditions were performed to investigate the freeze–thaw damage behavior of fiber CRAM. Furthermore, the fiber dispersion in CRAM was observed using scanning electron microscopy (SEM). The results show that the fiber mixing process has a significant effect on the cracking resistance of CRAM. The CRAM specimens prepared by process C have the largest fracture energy, splitting strength, and fracture work, while the specimens made by process D have the smallest value. Specially, the fracture energy of the specimens prepared by process C is 77.23% larger than that of the specimens prepared by process A, while the fracture energy of the specimens prepared by process D is 5.6% smaller than that of the specimens prepared by process A. The reason for this phenomenon is that the fiber is well dispersed in the specimens prepared by process C, which contributes to obtain a better crack resistance. For all CRAM specimens, with the increase of freeze–thaw cycles, splitting strength and fracture work of fiber CRAM decrease. However, there is an obvious difference in the reduction rate of splitting strength and fracture work, especially for the specimens under the water saturation condition. The specimens made by process C have the smallest reduction rate, which indicates a better resistance to freezing and thawing damage. According to the analysis of fiber macro-distribution state in loose CRAM, the fiber dispersion is affected by the humidity conditions in the mixing environment. The best humidity conditions are obtained for fiber dispersion in process C. Based on the SEM observation, the overlapping bridging network structure can be observed in the microstructure of the specimens prepared by process C, allowing the mixture to better transfer and disperse stress. Full article

Ultrafine bubbles (UFBs) in water provide a large amount of gas and a large gas–liquid interfacial area, and can release energy through their collapse. Such features may promote ice nucleation. Here, we examined the nucleation of ice in solutions containing polyphenols and UFBs. To reduce the likelihood of nucleation occurring on the container walls over that in previous studies, we used a much larger sample volume of 1 mL. In our experiments, UFBs (when present) had a number concentration of 10⁸ mL⁻¹. We quantified changes to the nucleation activity by examining the shift in the cumulative freezing (nucleation) probability distribution. Compared to pure water, this freezing curve shifts approximately 0.6 °C higher with the UFBs. Then, to the water, we added three polyphenols (tannic acid TA, tea catechin TC, and oligonol OLG), chosen because they had been reported to reduce the ice-nucleation activity of heterogeneous ice nuclei (e.g., AgI). We found experimentally that, without UFBs, all polyphenols instead shift the pure-water freezing curve to a higher temperature. Then, when UFBs are added, the additional temperature shift in the freezing curve is slightly higher for OLG, essentially unchanged for TA, and slightly lower for TC. To help to explain these differences, we examined the UFB size distributions using dynamic light scattering and freeze-fractured replicas with transmission electron microscopy, finding that OLG and TC alter the UFBs, but that TA does not. Full article