Special Wettability Of Surfaces Fabricated By Electrospinning Of Fluorosilicone-containing Block Copolymers

Wettability is one of the important properties of solid surface. Some naturalwetting behaviors have caused people’s interests in special materials which haveexcellent wettability and many studies have been carried out on it. Materials likesuper-hydrophobicity, super-amphiphobicity, intelligent response with specialwettability are widely used in industrial and agricultural activities as well as in dailylife because of its special physical and chemical properties. Incorporation offluorinated polysiloxane blocks into conventional vinyl polymers would form blockcopolymers with different microphase-separated structures and novel properties.Combining the copolymer characteristics with the technology of electrospinning,super-amphiphobic surfaces with stable physical and chemical properties are expectedto obtain.In this work, a series of PMTFPS-b-PS diblock copolymer were synthesizedbased on a combination of the anionic ROP of1,3,5-trimethyl-1,3,5-trifuoropropylcyclotrisiloxane (F3) and atom transfer radical polymerization (ATRP) of St. Then,superhydrophobic and highly oleophobic surfaces were fabricated by anelectrospinning process. Main results obtained are shown as follows:1. Well-architectured PMTFPS-b-PS diblock copolymers were obtained viaATRP of St from the PMTFPS-Br macroinitiators. Then the physical and chemicalproperties of PMTFPS-b-PS diblock copolymers were investigated in this work.(1) A series of PMTFPS-b-PS diblock copolymer were synthesized via atomtransfer radical polymerization (ATRP) of St initiated by PMTFPS-Br,which wassynthesize via a combination of anionic ring-opening polymerization (ROP) of1,3,5-trimethyl-1,3,5-trifluoropropyl)cyclotrisiloxane (F3) and functionalizationreaction of its terminal group.(2) The results of differential scanning calorimetry (DSC) measurementsindicated that the content of PMTFPS blocks would influence the glass transition temperature of PMTFPS-b-PS copolymers. When the degree of PMTFPS was smaller,the glass transition was so weak that it’s difficult to be clearly observed.(3) AFM images showed that the surface of the copolymer films would appear acertain morphology. The films of block copolymers had a certain value of surfaceroughness, which may be attributed to the self-assembly behavior of the blockcopolymers on the surface.(4) Contact angles measurements indicated that the contact angles of water andformamide on the thin films were over100.4°and82.5°, respectively. Moreover, thesurface energies of PMTFPS-b-PS thin films ranged between21.80and25.97mJ/m2.When the weight content of PMTFPS was35.9%, the surface energies ofPS-b-PMTFPS films was close to the value of the pure PMTFPS.(5) XPS data at90°takeoff angle showed that the surface region of the film wascovered with PMTFPS segments, the surface composition changed with the changingcontent of PMTFPS segments2. Surfaces with special wettability of super-hydrophobicity and highlyoleophobicity were fabricated by electrospinning of the block copolymer of PS andPMTFPS.(1) Contact angles data demonstrated that contact angles value of the fibrousfilms with water, glycerol, formamide and diethylene glycol were over146.2°,145.8°,143.4°and141.4°, which endowed the electrospun fiber films with excellent andunique super-hydrophobicity, solvent-repellent efficiency.(2) While adding a little weight content of PMTFPS segments, the contact anglewith various liquids had enhanced sharply. However, when the PMTFPS content waslarge enough as increasing the weight content of PMTFPS from58.9wt%to74.1%, itdid not lead to an obvious increase in the contact angle.(3) With the weight content of PMTFPS block was58.9wt%, the fiber film’scontact angle with water, glycerol, formamide and diethylene glycol were157°,156°,154°,151°, respectively, which suggests the fiber films were superhydrophobic,solvent-resistant and self-cleaning.(4) Comparing to PMTFPS-b-PS copolymer thin film before electrospinning, the contact angle of electrospun fibrous film with water and other liquids hadimproved greatly, which were both over150°(with water). The water roll-off angleson the electrospun films were less than10°for all six samples, which denoting asuper-hydrophobic property for the electrospun films.(5) TEM results indicated the microphase-separated structures have been clearlyformed in the electrospun fibers or electrosprayed particles. Super-hydrophobic andhighly oleophobic surfaces were obtained due to the enrichment of PMTFPSsegments and the surface roughness on the electrospun fibers film.3. The influence of electrospinning processing conditions on the fibrous film’smorphologies and wettability were investigated in detail.(1) SEM results showed that by using DMF as the electrospinning solvent, themicro-morphology of the PMTFPS-b-PS fibrous film transformed from beadsstructure to smooth and continuous fibrous structures when the concentration ofelectrospun copolymer solution increased.(2) Using DMF/THF as the electrospinning solvent, the micro-morphologies ofthe electrospun films transformed from polymeric, irregular micro (nano)-particles touniform, porous beads when the collecting distance between the tip of the syringe andthe collector screen increased. When the collecting distance was15cm, theelectrospun fibrous film exhibited good continuity and good stability.(3) The fiber’s diameter increased with the increasing of molecular weight of thecopolymers. What’s more, within the scope in which fibers can be formed, molecularweight and viscosity of the copolymer solution played an important role on thewettability, fiber diameter and morphology of the fibrous films.(4) The electrospun fiber films appeared a micro-spherical structure as thesyringe’s diameter increased from0.58mm to1mm. What’s more, the fiber’sdiameter slightly increased when increasing the syringe’s diameter.(5) When the ambient humidity increased from38%to67%, the fiber’s diameterdecreased and beads showed up. This prevented the surface from getting wetted bywater, oil or solvents, making the surface prone to hydrophobicity and oleophobicity.The surface wettability of the fiber films was a joint outcome of both its chemical composition and its micro-morphology.