Responsive Pickering Foam And Emulsion Based On Dynamic Covalent Bonds

Emulsion and foam are multi-phase dispersion systems formed by dispersing one phase(gas phase or liquid phase)into the other phase.They are widely used in the fields of washing,oil extraction,cosmetics and biomedicine,etc.Traditional emulsions and foams are formed by surfactants stabilizing at the oil-water or gas-liquid interface.Pickering foams or emulsions are a type of foam or emulsion stabilized by particles.Compared with traditional surfactants,Pickering foam or emulsion has higher stability and lower toxic and irritating,and has better biocompatibility.In some application areas,it is necessary to prepare long-term stable emulsions and foams,but also need emulsions and foams to break and defoam in a short time.However,the traditional method of adding foaming agents and defoaming agents limits the reuse of emulsions.This requires the preparation of responsive foams and emulsions,that is,under external stimuli(such as pH,CO2,light,magnetic field,etc.),the particles or surfactants that stabilize emulsions and foams can be converted in surface-active and non-surface-active states.Therefore,the preparation of responsive foams and emulsions not only has high stability and low toxicity,but also can realize repeated foaming and defoaming,emulsification and demulsification,and greatly reduce the cost of defoaming and demulsification.Relying on traditional covalent bond and non-covalent bond interaction is a common method to prepare responsive particles,but traditional covalent bond often requires complex synthesis methods,which are costly and time-consuming.However,with the help of non-covalent interactions,there are disadvantages such as weak interaction and susceptibility to concentration.Dynamic covalent bonds not only have the stability of traditional covalent bonds,but also have the advantage of reversibility of non-covalent interactions.Therefore,they have more advantages in the preparation of responsive particles.In this paper,responsive emulsions and foams based on dynamic covalent bonds are prepared.There is no need to resort to complex synthesis.The responsive granular emulsifier can be prepared only by in-situ reaction and mixing under mild conditions in the water phase.By adjusting the concentration of responsive particles,the ratio of oil to water and pH,responsive foams,liquid marbles,responsive oil-in-water and water-in-oil emulsions can be prepared separately,and the foam stability is further improved by cross-linking the particles.The emulsifying ability of the particles enriches the dynamic covalent bond emulsion and foam system.The specific content of this article is as follows:1.Study on responsive Pickering foam and liquid marbles.By adjusting the ratio of amino-aldehyde groups and pH,Pickering foam and liquid marbles with pH responsiveness were prepared.Under the condition of pH=7.4,according to the amino-aldehyde group ratio of 1:0.2,benzaldehyde(BA)was added to polyallylamine hydrochloric acid(PAH)to prepare a hydrophobic aldehyde-modified PAH-B A particle dispersion,hand or homogenous foam can be foamed under the condition of pH≥7.4,and defoaming under the condition of pH≤2,all foams can be foamed again after three cycles of foaming/defoaming.Both hydrophobic salicylaldehyde and cinnamaldehyde can be used to prepare responsive foam under the same conditions,verifying the versatility of the method.The amino-aldehyde group adjustment ratio is 1:1,hydrophobic powder particles are prepared,and the powder particles are used to prepare responsive liquid marbles.The liquid marbles can be stable at pH=11,and break and disappear at pH=2.0.2.Study on responsive Pickering emulsion.The pH-responsive Pickering oil-in-water and water-in-oil emulsions were prepared by adjusting the amino-aldehyde group ratio and the oil-water ratio.Under the condition of pH=8.0,hydrophobic aldehyde modified PAH-aldehyde particles(amino-aldehyde group ratio is 1:0.4)were prepared.The same as the previous part,the particles are also formed by the self-polymerization of hydrophobically modified polymers.The particles can emulsify and stabilize non-polar oil phase(such as C8-C14 linear alkanes,paraffin oil,etc.)and weakly polar glycerides,etc.,to obtain an oil-in-water emulsion with good responsiveness.By increasing the ratio of amino-aldehyde groups and pH,a responsive water-in-oil emulsion can be prepared under high pH conditions.The obtained oil-in-water or water-in-oil emulsions both have pH responsiveness and demulsify under the condition of pH≤2.0.3.Study on the effect of dynamic covalent crosslinking on the responsive Pickering foam and emulsion.The pH-responsive Pickering toluene emulsion and foam were prepared by cross-linking with o-phthalaldehyde.Because PAH-BA are soluble in strong polar solvents such as toluene and cannot emulsify the strongly polar oil phase,PAH-BA particles are dynamically covalently cross-linked by using o-phthalaldehyde as a cross-linking agent.The cross-linked particles can be emulsified to prepare a toluene emulsion with a particle size of about 200 nm;at the same time,the cross-linked particles have better foaming performance,and a foam with higher stability can be prepared.Foams and emulsions prepared by cross-linked particles also have pH responsiveness.The emulsions and foams can be stable at pH=8.0,and demulsify or defoam at pH=2.0.With the help of dynamic covalent bonds,the preparation process is simplified,and a new method for preparing responsive emulsions and foams is provided.