Study On The Assembly Of Nanoparticles At The Oil/water Interfaces Induced By Amine Compounds

Pickering emulsions stabilized by nanoparticles have attracted much attention in recent years.Compared with traditional emulsions stabilized by surfactants,Pickering emulsions have excellent stability and biocompatibility,and are widely used in food science,cosmetics,medicine,transportation of crude oil,textiles,emulsion catalysis,emulsion polymerization and other fields.Amphiphilic nanoparticles play a key role in the preparation and application of Pickering emulsions.The common nanoparticles are usually highly hydrophilic or highly lipophilic.As a result,it is important to prepare nanoparticles with appropriate surface activity.In-situ hydrophobization is a convenient method to prepare amphiphilic nanoparticles.The typical in-situ hydrophobization method is performed by utilizing the electrostatic interactions between the ionic surfactants and the nanoparticles.Amine compounds don’t carry any charges.The ability of amine compounds in stabilizing emulsions is also weak due to their weak surface activities.The amine compounds are thus seldomly used in stabilizing emulsions.In this thesis,stable Pickering emulsions were successfully prepared by using a series of aliphatic amine compounds together with silica nanoparticles and cellulose nanocrystals(CNC).The interactions between amines and nanoparticles were well characterized.Their self-assembly at the oil/water interfaces was revealed.The phase inversions and the stimuli-responsive behavior of the prepared emulsions were also achieved,showing the general principles of the interaction mechanism between the amine compounds and the nanoparticles.The main results are summarized as follows.(1)Stable O/W Pickering emulsions were prepared using hydrophilic silica nanoparticles and aliphatic primary amines.The aliphatic primary amines are adsorbed at the surface of silica nanoparticles through both mutual hydrogen bonding and electrostatic attraction.In the presence of 0.3 wt.% silica nanoparticles,the minimum concentrations required to stabilize the emulsions were 3,0.6,0.3,0.06,and 0.03 m M for n-hexylamine,n-octylamine,n-decylamine,dodecylamine,and tetradecylamine,respectively,decreasing significantly with increasing the alkyl chain length of amines.The mixed emulsifiers are suitable for various oil phases such as alkanes and aromatics.(2)By increasing the amine concentration,the single phase inversion from O/W to W/O type was successfully achieved for the emulsions stabilized by silica nanoparticles together with aliphatic primary amines.The hydrophobicity of silica nanoparticles monotonically increased with the amine concentrations,and the emulsion demulsified after phase inversion.The emulsion phase inversion depends on the overall wettability of silica nanoparticles after amine molecules adsorbed.Different with that of ionic surfactants,the aliphatic amines only form single layers at the surface of silica nanoparticles,leading to very high surface hydrophobicity and the occurrence of phase inversions.(3)The Pickering emulsions stabilized by aliphatic diamines and silica nanoparticles show prompt p H-responsive behavior.In the presence of 0.3 wt.% silica nanoparticles,the minimum concentrations required to stabilize the emulsions were 1,0.6,and 0.3 m M for 1,8-octyldiamine,1,10-decanediamine,and 1,12-diaminododecane,respectively,decreasing significantly with increasing the alkyl chain length.The emulsion can be switched between stable and unstable states more than 10 times upon alternating adding equimolar HCl and Na OH.In addition,the emulsifiers returned to the aqueous phase after demulsification and are fully recoverable and reusable.(4)Stable high internal phase emulsions were successfully prepared using hydrophilic CNC and aliphatic amines.The presence of amine compounds can greatly improve the stability of emulsions stabilized by CNC.The prepared high internal phase emulsions all exhibited elastic behavior,and the mechanical strength of the emulsions could be enhanced by either increasing the concentration of the emulsifier or increasing the volume fraction of the oil phase.The emulsifier can be used to stabilize edible oil emulsions.The system can also be used as a template to prepare porous materials,which have potential applications in the fields of medicine and environmental protection.