Study on the Performance of a Surface with Coupled Wettability Difference and Convex-Stripe Array for Improved Air Layer Stability

The existence of an air layer reduces friction drag on superhydrophobic surfaces. Therefore, improving the air layer stability of superhydrophobic surfaces holds immense significance in reducing both energy consumption and environmental pollution caused by friction drag. Based on the properties of mathematical discretization and the contact angle hysteresis generated by the wettability difference, a surface coupled with a wettability difference treatment and a convex-stripe array is developed by laser engraving and fluorine modification, and its performance in improving the air layer stability is experimentally studied in a von Kármán swirling flow field. The results show that the destabilization of the air layer is mainly caused by the Kelvin–Helmholtz instability, which is triggered by the density difference between gas and liquid, as well as the tangential velocity difference between gas and liquid. When the air layer is relatively thin, tangential wave destabilization occurs, whereas for larger thicknesses, the destabilization mode is coupled wave destabilization. The maximum Reynolds number that keeps the air layer fully covering the surface of the rotating disk (with drag reduction performance) during the disk rotation process is defined as the critical Reynolds number (Rec), which is 1.62 × 105 for the uniform superhydrophobic surface and 3.24 × 105 for the superhydrophobic surface with a convex stripe on the outermost ring (SCSSP). Individual treatments of wettability difference and a convex-stripe array on the SCSSP further improve the air layer stability, but Rec remains at 3.24 × 105. Finally, the coupling of the wettability difference treatment with a convex-stripe array significantly improves the air layer stability, resulting in an increase of Rec to 4.05 × 105, and the drag reduction rate stably maintained around 30%

Additional file 5 of Transcriptome analysis of sweet potato responses to potassium deficiency

Additional file 5. The sequence of all unigenes

Additional file 4 of Transcriptome analysis of sweet potato responses to potassium deficiency

Additional file 4: Supplement Table 10. The top 20 KEGG pathways of DEGs under low-K+ strss and high potassium condition

Additional file 1 of Transcriptome analysis of sweet potato responses to potassium deficiency

Additional file 1: Fig. S1. Phenotypic and quantitative data of sweet potato under normal and K+-deficient conditions. a. Phenotype of the root. b. Fresh weight of the shoot and root. c. The dry weight of the shoot and root. d. The content of carotenoids in root under low-K+ stress. e. Chlorophyll content of shoot. Sweet potato stems were cut into 5 cm fragments and growth in plot full with vermiculite to two leaf stage. Seedlings were then treated with HK (1 mM K) and LK (0 mM K) Hoagland solution for 14 days, and then the weight, carotenoids and chlorophyll content were detected. Data are shown as means ± SE (n = 4). Student’s t test (*P < 0.05) was used to analyze statistical significance, HK-S: sufficient potassium shoot, HK-R: sufficient potassium root, LK-S: low potassium shoot, LK-R: low potassium root, bar=5 cm. Fig. S2. The numbers of different unigenes length and venn diagrams of different annotation database. a. Distribution of the numbers of different length unigenes. b. Venn diagrams of transcriptions in each annotation database. Fig. S3. Transcription factor ERF binds to IbHAK5 promoter. a. Diagram of the IbHAK5 promoter. The adenine residue of the translational start codon ATG was assigned position +1, and the two ERF binding motif were showed in different color. Relative positions of the two motif were indicated by red and green lines. The scale length is 200 bp. b. Transient expression of the ProIbHAK5:lacZ fusion together with IbERF in yeast. AD together with ProIbHAK5:lacZ was taken as negative control. Observe the color and then photoes were taken. Fig. S4. Amino acid sequence alignment of AtHAK5 and IbHAK5. Table S1. Summary of RNA-seq quality information. Table S2. Unigenes statistical table. Table S3. Statistical table of unigenes annotation. Table S4. primers used in this study. Table S5. Differently expressed unigenes in KEGG

Additional file 3 of Transcriptome analysis of sweet potato responses to potassium deficiency

Additional file 3: Supplement Table 7. Biological process of genes based on the gene ontology. Supplement Table 8. Cellular component of genes based on the gene ontology. Supplement Table 9. Molecular function of genes based on gene ontology

Additional file 2 of Transcriptome analysis of sweet potato responses to potassium deficiency

Additional file 2: Supplement Table 6. The raw expression data and annotation of all DEGs under low-K+ strss and high potassium condition