Facile fabrication of superhydrophobic conductive graphite nanoplatelet/vapor-grown carbon fiber/polypropylene composite coatings

The fabrication of superhydrophobic surfaces with mechanical durability is challenging because the surface microstructure is easily damaged. Herein, we report superhydrophobic conductive graphite nanoplatelet (GNP)/vapor-grown carbon fiber (VGCF)/polypropylene (PP) composite coatings with mechanical durability by a hot-pressing method. The as-prepared GNP/VGCF/PP composite coatings showed water contact angle (WCA) above 150° and sliding angle (SA) less than 5°. The superhydrophobicity was improved with the increase of VGCF content in the hybrid GNP and VGCF fillers. The more VGCFs added in the GNP/VGCF/PP composite coating, the higher porosity on the surface was formed. Compared to the GNP/PP and VGCF/PP composite coatings, the GNP and VGCF hybrid fillers exhibited more remarkable synergistic effect on the electrical conductivity of the GNP/VGCF/PP composite coatings. The GNP/VGCF/PP composite coating with GNP:VGCF = 2:1 possessed a sheet resistance of 1 Ω/sq. After abrasion test, the rough microstructure of the GNP/VGCF/PP (2:1) composite coating was mostly restored and the composite coating retained superhydrophobicity, but not for the VGCF/PP composite coating. When the superhydrophobic surface is mechanically damaged with a loss of superhydrophobicity, it can be easily repaired by a simple way with adhesive tapes. Moreover, the oil-fouled composite surface can regenerate superhydrophobicity by wetting the surface with alcohol and subsequently burning off alcohol

Evaluation of the stress sensitivity in tight reservoirs

Abstract: The expressions of three types of stress sensitivity coefficients (S, α, β) are obtained on the basis of analysis of the empirical models and theoretical models on the relationships between permeability and effective stress, and the stress sensitivity evaluation standard is proposed considering experiment data and rock micro-structural features. Then the empirical models and theoretical models were used to fit experiment data of low-permeability and tight sandstones and different types of granites, which promotes the understanding of the empirical models and the physical meanings of the stress sensitivity coefficients. According to the study of the three types of stress sensitivity coefficients and the relationship of effective stress and permeability, it is found that the stress sensitive coefficient S is suitable for evaluating the stress sensitivity (strong stress sensitivity: S>0.40; low stress sensitivity: S<0.25; medium stress sensitivity: 0.25≤S≤0.4). Meanwhile, it is also found that strong-stress-sensitivity cores are more suitable to be characterized by the logarithmic model, while the exponential model (or binomial model) occurred more frequently in low-stress-sensitivity cores, and medium-stress-sensitivity cores are more likely to be described with the power model. Finally, the evaluation standard is discussed based on the micro-structure in the low-permeability and tight sandstones. The results show that the crack-like pores in the strong-stress-sensitivity cores are obvious, but low-stress-sensitivity cores have the characteristics of porous rocks; moreover, the types of cemented clay minerals, the size of rock grain and lithology have impact on stress sensitivity. Key words: tight sandstone, stress sensitivity, stress sensitivity coefficient, effective stress, permeability, micro-structur

Hydrochemical characteristics and genesis analysis of typical aquifer system in karst critical zone of Central Yunnan Plateau

The study of hydrogeochemical processes in the karst critical zone (KCZ) is of great significance for the scientific understanding of their internal evolutionary environment and structural characteristics. Karst groundwater is the main information carrier after water-rock interactions. Quantitative analysis of its hydrochemical characteristics and causes is an effective means to reveal the medium environment and hydrodynamic conditions of the aquifer system in the KCZ. In this paper, three typical karst aquifer systems in the KCZ of the central Yunnan Plateau were taken as the research objects. Through field sampling and laboratory testing of karst springs exposed by different aquifer systems, mathematical statistics analysis, hydrochemical diagram, ion ratio coefficient and hydrogeochemical simulation were comprehensively used to deeply analyze the characteristics of hydrochemical components, genesis and aquifer medium of karst groundwater in each aquifer system; the internal relationship and law between the water cycle and hydrochemistry in the key belt were discussed. The results showed that: ①HCO3- and Ca2+ were the highest and most stable ion components in regional karst groundwater, and Mg2+ was the key factor controlling the alienation of hydrochemical types in each aquifer system; ②The rock weathering and mineral dissolution of carbonate rocks were the main causes of the chemical composition characteristics of karst water in each aquifer system, and karst groundwater dissolution on the aquifer of the Huaning aquifer system was still occurring. The alternation of cation adsorption and the weathering and dissolution of silicate rocks were the main sources of Na+ and K+ in regional karst groundwater; ③The development intensity of regional karst, the exposed condition of karst aquifers and the lithology and connectivity of aquifer media jointly shaped the groundwater chemical characteristics of different aquifer systems in the KCZ of the Central Yunnan Plateau

An Aptamer-Array-Based Sample-to-Answer Biosensor for Ochratoxin A Detection via Fluorescence Resonance Energy Transfer

Food toxins are a hidden threat that can cause cancer and tremendously impact human health. Therefore, the detection of food toxins in a timely manner with high sensitivity is of paramount importance for public health and food safety. However, the current detection methods are relatively time-consuming and not practical for field tests. In the present work, we developed a novel aptamer-chip-based sample-to-answer biosensor (ACSB) for ochratoxin A (OTA) detection via fluorescence resonance energy transfer (FRET). In this system, a cyanine 3 (Cy3)-labeled OTA-specific biotinylated aptamer was immobilized on an epoxy-coated chip via streptavidin-biotin binding. A complementary DNA strand to OTA aptamer at the 3′-end was labeled with a black hole quencher 2 (BHQ2) to quench Cy3 fluorescence when in proximity. In the presence of OTA, the Cy3-labeled OTA aptamer bound specifically to OTA and led to the physical separation of Cy3 and BHQ2, which resulted in an increase of fluorescence signal. The limit of detection (LOD) of this ACSB for OTA was 0.005 ng/mL with a linearity range of 0.01–10 ng/mL. The cross-reactivity of ACSB against other mycotoxins, ochratoxin B (OTB), aflatoxin B1 (AFB1), zearalenone (ZEA), or deoxynilvalenol (DON), was less than 0.01%. In addition, this system could accurately detect OTA in rice samples spiked with OTA, and the mean recovery rate of the spiked-in OTA reached 91%, with a coefficient of variation (CV) of 8.57–9.89%. Collectively, the ACSB may represent a rapid, accurate, and easy-to-use platform for OTA detection with high sensitivity and specificity