Preparation And Properties Of Superhydrophobic Magnetic Cellulose-based Liquid Marble

As a natural organic polymer materials existing in a large number of green plants and marine life on Earth,cellulose has a wide prospect for development and utilization.The rich hydroxyl groups on cellulose can be modified into novel cellulose-based functional material with special properties.The development of new cellulose-based functional materials is one of the effective ways to utilize cellulose and widen the application of cellulose.Liquid marble is a liquid coated with particles,which exhibits unique properties for potential applications in microreactors,drug delivery,microfluidics and biomedicine filed.In this thesis,novel magnetic superhydrophobic cellulose-based particles were fabricated using a DOPA-containing fluorinated copolymer poly?DOPAm-co-PFOEA?,which provide remarkable stability to liquid marbles with various liquids for liquid droplet transportation and manipulation.Poly?DOPAm-co-PFOEA?with low surface energy was copolymerized.The morphology and properties of liquid marble was studied,which provide theoretical basis for the application of cellulose.The carbon-carbon double bond was introduced into DOPA hydrochloride through amidation reaction.Then poly?DOPAm-co-PFOEA?was prepared by free-radical copolymerization of N-?3,4-dihydroxyphenethyl?acrylamide?DOPAm?and 2-?perfluorooctyl?ethyl acrylate?PFOEA?.The influence of the content of fluorine-containing monomer on the hydrophobicity and surface energy of the copolymer was discussed.The chemical structure and components of the copolymer were analyzed by infrared spectroscopy?FTIR?,nuclear magnetic resonance spectroscopy?NMR?and X-ray photoelectron spectroscopy?XPS?.The poly?DOPAm-co-PFOEA?is superhydrophobic and has low surface energy.The higher content of the fluoro-containing monomer,the better hydrophobicity and lower surface energy.When the fluorine content was 48.5%,the contact angle of copolymer was 151.1°,and the surface energy of polymer was 15.1 m N/m.Using bamboo dissolving pulp as raw material,cellulose microspheres were prepared using inverse emulsification method.Fe₃O₄ nanoparticles were introduced into the microspheres by in-situ synthesis to prepare magnetic cellulose microspheres.Poly?DOPAm-co-PFOEA?was used to modify the magnetic cellulose microspheres to make the microspheres superhydrophobic.XRD,XPS and contact angle analyzer were used to characterize the morphology and properties of cellulose microspheres before and after modification,and the effect of DOPA-containing copolymer on the hydrophobic properties of cellulose microspheres was studied.The DOPAm moieties containing 1,2-dihydroxybenzene?catechol?groups anchor onto the Fe₃O₄ nanoparticle surface due to its stronger chelating ability with iron.The PFOEA moieties containing fluorinated units cover the outmost surface of the cellulose-based microspheres.Thermogravimetric results showed that the content of magnetic nanoparticles was ca.20%.The modified magnetic cellulose particles showed superhydrophobicity with a contact angle exceeding 150°.For the superhydrophobic magnetic nanocellulose with Fe₃O₄ content of 17.8%,the contact angle reached 152.9°.The fabrication and morphology of liquid marbles using superhydrophobic magnetic cellulose microspheres and superhydrophobic magnetic nanocellulose particles were investigated.The effects of the surface energy of the encapsulated droplets and the volume of the droplets on the morphology of the liquid marbles were discussed.The magnetic properties of liquid marbles were discussed,and the floatability,stability,and bouncing properties of liquid marbles prepared using two cellulose-based particles were studied.The results show that superhydrophobic magnetic cellulose particles can coat various droplets to form liquid marbles,such as water,ethanol,toluene,N,N-dimethylformamide.The surface energy of liquid droplets has a great influence on the stability of liquid marbles.The surface energy of the droplets is higher,the shape of prepared liquid marble tends to be spherical,the line of contact with the solid surface is shorter,and the liquid marbles become more stable.The liquid marble can bounce on a solid surface when it falls from a certain height,exhibiting high stability on impact.The maximum falling height of liquid marble was 2.5 cm and the bounce height was 0.5 cm.The prepared liquid marbles have magnetic properties and can be manipulated under the magnetic field,moving vertically or horizontally.Moreover,liquid marbles could float on the surface of the water.The marbles prepared using high surface energy droplets can sustain for a longer period of time,and that by low surface droplets are prone to rupture.Compared liquid marbles prepared with superhydrophobic magnetic cellulose microspheres,liquid marbles prepared with nanocellulose existed on the water surface for a longer period of time,and the marbles exhibited better stability,whose maximum height is 2.8 cm before rupture and bouncing height is 0.7 cm.The influence of water evaporation/absorption on the stability of glycerol–water marbles were studied.Liquid marbles were formed by encapsulating glycerol aqueous solution with superhydrophobic magnetic cellulose nanocrystals.The effect of volatilization time on the distribution of hydrophobic particles on the surface of liquid marbles was observed.The morphological changes of liquid marbles during volatilization was investigated.The influence of glycerol concentration and relative humidity?RH?on the liquid marble's volatilization rate and the evaporation resistance were studied.Conditions for liquid marbles maintaining long-term stability have been determined.The results showed that the distribution of hydrophobic particles in liquid marbles was random,and the pores was exist between particles.As the liquid volatilize,the particles move to each other and the pore area decreased.Through the movement between hydrophobic particles,the area percentage of interparticle gaps decreased from 18.6%to 4.9%within 40min.When the glycerol marbles absorbed water,the area percentage of the interparticle gaps increased from 20.3%to 26.2%.During the volatilization process,the shape of the liquid marbles deformed and the volume changed,or even collapsed.However,the volume of liquid marbles increased during the absorption process and eventually rupture.The volatilization rate of liquid marble decreased with increasing glycerol concentration and humidity,but the absorption rate increased.When the volatilization rate and the absorption rate reached equilibrium,the liquid marble maintain long-term stability.The absorption rate of the pure glycerol marbles was lower than that of the pure glycerol droplets.This is because the multilayered nanoparticles prevented the water molecules from passing through the liquid/air interface.The formation of underoil particle-stabilized droplets and removal of tiny water droplets from oil using superhydrophobic magnetic CNC nanoparticles were studied.Superhydrophobic magnetic nanocellulose particles were used to encapsulate water droplets in n-hexane solution to prepare magnetic liquid marbles.When the Petri dish containing n-hexane was covered by a layer of superhydrophobic CNC-based nanoparticles,the water droplet balled up on the powder of CNC-based nanoparticles.By shaking the Petri dish,the CNC-based nanoparticles were transferred to the water/oil interface,and an under oil liquid marble was formed.The thickness of the coating was estimated by the gravimetric contrast before and after the formation of a liquid marble to be 20±6 mm,which is much larger than the size of the CNC-based nanoparticles.CNC-based nanoparticles on the surface of the water droplet formed a multilayered shell.The liquid marble in n-hexane solution could even be cut into two small liquid marbles by a blade,showing these particle-stabilized droplets can self-heal upon damage by an external force.Because the solid/liquid interfaces of the particle-stabilized droplet are flexible;upon deforming by cutting with a blade,the CNC-based nano-particles on the shell can move quickly to heal the freshly exposed interface.The particle-stabilized droplets can be collected and moved by a magnetic force,and thus may have wide applications in various fields.