Preparation And Properties Of Fluorine-free PDMS-based Superhydrophobic Cotton Fabric

Superhydrophobic textiles are famous for their extreme water repellency and are widely used in household,apparel,self-cleaning and oil-water separation fields by virtue of their excellent hydrophobic properties.However,the current preparation of superhydrophobic textiles faces disadvantages such as tedious and time-consuming fabrication process,complicated instrumentation,poor durability and often use of toxic fluorinated reagents,which limit their practical application potential.Therefore,in this study,we use dip-coating combined with in situ growth technique to introduce environmentally friendly fluorine-free micro-nanomaterials on the surface of cotton fabrics to build roughness,optimize the preparation process of rough structures,and then hydrophobically modify the surface of rough cotton fabrics to prepare functionalized cotton fabrics with superhydrophobicity,and conduct characterization and performance tests.Research content includes:(1)Wrinkled fibrous nano silica(WFNS)was prepared through a bi-phase stratification approach using cetyltrimethylammonium bromide(CTAB)as a template and hydrophobically modified with polydimethylsiloxane(PDMS)to prepare WFNS-PDMS mixed dispersion,and WFNS-PDMS superhydrophobic cotton fabric was prepared in one step by treating the fabric with dip-coating-high temperature curing method.The effects of the mass ratio of WFNS to PDMS and dipping time on the hydrophobic properties of cotton fabrics were investigated by single-factor method,and the chemical composition and surface morphology of the superhydrophobic cotton fabric were studied by FT-IR and SEM tests.The results showed that the prepared coated fabrics had the best surface roughness and superhydrophobicity with a static water contact angle of 157.2°and a sliding angle of 3.5°when the mass ratio of WFNS to PDMS was 2:3 and the dipping time was 10 min.After 10 washing cycles and 25 wear cycles,the cotton fabric still maintained superhydrophobicity and had excellent chemical stability.In addition,WFNS-PDMS superhydrophobic cotton fabric has good self-cleaning effect and demonstrated high separation efficiency and certain reusability in the oil-water separation test.(2)To further improve the durability of superhydrophobic fabrics,three submicron silica particles(m Si O₂)with an average particle size of about 100,200 and 400 nm were prepared by a modified Sto?ber method.A uniform hierarchical protrusion structure was successfully constructed by regulating the content of the three m Si O₂ particles,and then PDMS hydrophobic modification was performed on the surface of the rough fabric.The m Si O₂-PDMS superhydrophobic cotton fabric was prepared by forming strong covalent bonds between the coating and the fabric through cross-linking reactions during the high temperature curing process.The effect of each experimental variable on the hydrophobic properties of the cotton fabric was investigated by the single-factor method,and the optimal process was determined:the mass ratio of three m Si O₂ particles was 1:1:1,the total concentration was 2 wt%,the m Si O₂soaking time was 1 min,the PDMS concentration was 2 wt%,and the PDMS soaking time was2 min.The prepared cotton fabric reached a static water contact angle of 161.3°and a low sliding angle of 2.4°.The SEM and AFM test results showed that the modified cotton fabric surface had a graded protrusion structure similar to the surface of lotus leaf,and the roughness of the fabric surface increased significantly,with the root mean square roughness value of RMS reaching 56.3 nm,which was 4.4 times higher than that of the original cotton fabric.The durability test results show that the functionalized cotton fabric has excellent durability and chemical stability with a water contact angle greater than 150°after 40 washing cycles and 130wear cycles.At the same time,the superhydrophobic cotton fabric has excellent self-cleaning performance and oil-water separation performance,high separation efficiency and high recyclability.(3)Based on the previous study,the metal-organic framework structure ZIF-8 was introduced on the surface of cotton fabric to construct the micro-nano structure.The fabric surface was modified by using the strong adhesion property of polydopamine,and ZIF-8particles were generated on the fabric surface by in situ growth method to construct a rough structure with micro-nanoscale cross-sheet morphology.The PDA/ZIF-8/PDMS superhydrophobic cotton fabric was prepared by hydrophobizing the rough fabric with PDMS solution.The effect of the molar ratio of zinc nitrate to 2-methylimidazole on the hydrophobic properties of the cotton fabric during in situ growth was investigated,and the optimal process was explored:the molar ratio of zinc nitrate to 2-methylimidazole was 1:8,the in situ growth time was 15 min,and the PDMS concentration was 2.4 wt%.The prepared cotton fabrics reached a static water contact angle of 156.4°and a sliding angle of 3.8°.EDS and XRD tests confirmed the successful formation of ZIF-8 and PDMS on the fabric surface.The durability test results showed that the superhydrophobic cotton fabrics maintained their superhydrophobic properties after 20 washes,500 cm of sandpaper abrasion and 72 h of light exposure.Meanwhile,the superhydrophobic cotton fabric has excellent self-cleaning and anti-fouling properties,and can effectively separate a variety of oil and water mixtures in the oil-water separation test,the separation efficiency is above 97%.