Microfluidic Fabrication Of Janus Droplets By Liquid-liquid Phase Separation

Janus particles,which contain two hemispheres with different chemical composition and polarity,refer to a unique class of particles with micron or nanometer size.Due to the fascinating amphiphilic,chemical asymmetric,Janus particles have been extensively used in superparticular assemblies,catalysts,biosensors.Conventional methods of fabricating Janus particles are very hard to control the particle quality between different batches and result in Janus particles not always uniform.Microfluidic emulsification techniques have been developed for fabricating Janus particles with a high mono-dispersity,but there is still no simple approach for fabricating Janus droplets on a large scale.In this thesis,we adopt a existing method,which can fabricate mono phase droplet to fabricate multiple mixture droplets.Janus particles can be produced successfully via liquid–liquid phase separation triggered by the evaporation of cosolvent and temperature variation.It is considered to be a potential route to couple with microfluidic scale-up techniques.1.Fabrication of Janus droplets by evaporation driven liquid-liquid phase separation.Because FC-40 has a high permeability of gas or vapour,volatile cosolvent molecules in ternary droplets evaporate into the air rapidly,triggering phase separation in the ternary droplets.After complete evaporation,the ternary droplets evolve into Janus structures.In this work,the morphologies and chemical properties of separate parts of the Janus droplets can be flexibly regulated by adjusting the liquid compositions and the volume ratio of the ternary mixtures.The established approach is able to construct more complex Janus droplets with even high ordered structures,such as core–shell Janus droplets,ternary Janus droplets and multiple Janus droplets,if the ternary mixture is extended to a four-phase system.Under the irradiation of UV light,microparticles with asymmetric structure,which have semi-spherical configuration and porous semi-spherical configuration were created by Janus,ternary Janus and multiple Janus droplets.By varying the volume ratio of mixtures,particles were produced reliably and regulated flexibly.2.Fabrication of Janus droplets by temperature variation driven liquid–liquid phase separation.We took advantage of binary mixture,which consists of thermosensitivie ionic liquid and water as disperse phase and mineral oils containing 2%(wt)Span 80 as continuous phase.Homogenous binary droplets were generated stably in microfluidic chip.When the temperature of homogeneous binary droplet exceeded the critical phase transition temperature of the ionic liquid by ITO electrode heating,the formed homogeneous binary droplet separated into two phases gradually with the rising temperature,forming Janus droplets.Upon stopping heating,the temperature dropped below critical phase transition temperature of ionic liquid.The Janus droplets were gradually recovered into homogeneous binary droplets.The morphologies of the Janus droplets can be flexibly regulated and precisely controlled by adjusting the volume ratio of the ionic liquid and water.Droplets' configuration reversibly switch between mono phase spherical configuration and Janus configuration,displaying promising potential for intelligent materials.