Kunlin Chen

Facile preparation of self-healing waterborne superhydrophobic coatings based on fluoroalkyl silane-loaded microcapsules

Superhydrophobic surfaces have attracted tremendous attraction because of their novel aspects of surface physics and important applications ranging from self-cleaning materials to microfluidic devices. However, most artificial superhydrophobic surfaces easily lose their superhydrophobicity under natural sunlight irradiation, physical rubbing or organic contamination. Here, fluoroalkyl silane (FAS)-loaded microcapsules, photocatalytic TiO2 nanoparticles and FAS modified SiO2 nanoparticles were mixed with waterborne polysiloxane resins to obtain waterborne self-healing superhydrophobic coatings. Superhydrophobic surfaces were formed by casting the coatings on the substrates after UV-irradiation and could sustain their superhydrophobicity even after 360 h accelerated weathering test. Meanwhile, the coating was durable enough to withstand water blasting and the attacks of strong acid or basic solutions without apparently changing its superhydrophobicity. More importantly, after being mechanically damaged or contaminated with organics, these coatings could restore their superhydrophobicity under UV light. All these characteristics ensure that the coatings have excellent long-term superhydrophobicity for outdoor service.

A new approach for the preparation of durable and reversible color changing polyester fabrics using thermochromic leuco dye-loaded silica nanocapsules

Durable, reversible color changing polyester fabrics were successfully fabricated via a new approach of dyeing with thermochromic leuco dye-loaded silica nanocapsules (TLD@SiO2). TLD@SiO2 was prepared via tetraethyl orthosilicate hydrolyzation and condensation on the surfaces of emulsified thermochromic leuco dye (TLD) nano-droplets by a sol–gel method. The TLD@SiO2 was about 20 nm in size, and its shell could provide protection for TLD. The color of TLD@SiO2 changed from dark blue (25 °C) to light blue (45 °C) and white (80 °C), reversibly. The thermochromic mechanism originated from the conjugation structure conversion of the crystal violet lactone which was confirmed by density functional theory calculations. The shell materials (Si–O–Si) of TLD@SiO2 could be hydrated in water with temperature increase and produced hydrophilic hydroxyl groups for further treating polyester fabrics. These resulting polyester fabrics exhibited excellent thermochromic performance with a color transition temperature of 45 °C. Their color reversibly changed from dark blue (K/S = 12) to light blue (K/S = 2) at 610 nm for more than 50 times. Meanwhile, thermochromic polyester fabrics dyed at 130 °C displayed good color fastness. The washing, dry rubbing and wet rubbing fastness of the thermochromic polyester fabrics all reached above 4 grades, and the thermochromic polyester fabrics showed good solvent resistance.

Improvement of ink-jet printing performances using β-cyclodextrin forming inclusion complex on cotton fabric

Cotton fabric was modified with β-cyclodextrin (β-CD) forming inclusion complex to yield color strength, pattern sharpness, and color fastness for ink-jet printing. The modified cotton fabric was confirmed with the presence of new strong absorption peaks around 1713 cm-1 and 1243 cm-1 in FT-IR. β-CD had been covalently grafted on cotton fabric via the esterification reaction of citric acid (CTR) with cellulose and β-CD. The results indicated that printing performances of the ink-jet printed fabric were enhanced through β-CD modification. The K/S value was enhanced from 4.21 to 6.72, the width of printed line was decreased from 1.48 mm to 1.25 mm, and the color fastness was improved to 3-4 level. These improvements were due to the truncated cone structure of β-CD, which can form inclusions with water-based pigment. Meanwhile, the crease recovery performance was also improved with the aid of CTR. A comparison between the unmodified and modified cotton fabric suggested that the crease recovery angle of β-CD modified cotton fabric was increased by 25.0 % in the warp direction. Therefore, printing performance and crease recovery performance of β-CD modified and water-based pigment printed cotton fabric were enhanced remarkably.

Synthesis of photo-responsive azobenzene molecules with different hydrophobic chain length for controlling foam stability

To obtain an aqueous foam photo-switch, azobenzene molecules [4-hydroxy-4′-oxoalkyl azobenzene (HCnAzo) n = 4, 8, and 12] were synthesized. The hydrophobic chain length affected both photo-responsive properties and foam stability controllability. trans → cis isomerization of HCnAzo occurred by exposing to UV light for 1 s and the cis → trans process for HC4Azo, HC8Azo and HC12Azo was carried out by visible light irradiation for 12 min, 13 min and 14 min, respectively. The reversible isomerization was repeatable, maintaining high sensitivity. Due to the small steric effect and isomerization barrier, photo-isomerization of HC4Azo was more rapid than HC8Azo and HC12Azo. With the increase of the hydrophobic chain length, the decrease of thermal isomerization barrier resulted in less cis isomer and more trans isomer in photo-stationary state via UV and visible light irradiation, respectively. The combination of visible light and heat can accelerate the cis → trans isomerization speed. trans HC4Azo, HC8Azo and HC12Azo increased foam life from 6.67 min to 10.38, 9.91 and 7.74 min, respectively, resulting from the absorption on the air–water interface and a high affinity. cis HC4Azo, HC8Azo and HC12Azo decreased foam life from 6.67 min to 5.12, 5.49 and 6.02 min, respectively, attributed to the interfacial desorption and increase of surface tension. HC4Azo with sensitive photo-isomerization and effective foam stability controllability was the best choice for an aqueous foam photo-switch.

Controllable synthesis of raspberry-like PS–SiO2 nanocomposite particles via Pickering emulsion polymerization

This paper presents a simple and controllable method for the synthesis of monodisperse nanometer-sized organic–inorganic raspberry-like polystyrene (PS)–SiO2 nanocomposite particles (NCPs) via Pickering emulsion polymerization, by simply using a silane coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MPS), as an auxiliary monomer and controlling its hydrolysis/condensation processes and amount. In this method, when MPS was stirred in acidic water with styrene (St) for a period of time, and then a basic silica solution added, raspberry-like PS–SiO2 NCPs were directly obtained after the polymerization. The whole process needs neither surface treatment for the silica particles nor additional surfactants or stabilizers. We propose that a silica-stabilized Pickering emulsion is formed through Si–OH reaction between the hydrolysis/condensation products of MPS distributed on the St droplets surface and the silica particles.