Preparation And Properties Of Self-oriented Photonic Crystal Balls

The unique geometrical structure and flexible optical controllability of 1D magnetic photonic crystal balls（PCBs）show promise for applications in various fields such as display,anti-counterfeiting,sensing and optical switch.However,all the previously reported 1D magnetic PCBs in the absence of an external magnetic field（H）hardly control their initial colour and display a uniform colour collectively due to the random orientation of different PCBs.This means that displaying the structural colours must need H,which inevitably consumes energy.Besides,the fixed1D chain-like structure makes the PCBs have single structural color and narrow color range.Based on this,eccentric 1-D magnetic core-shell photonic crystal balls（PCBs）were prepared by using a combined technique of UV-initiated polymerization and micropipet injection in the presence of H.Then,the properties of self-orientation,magnetochromism and wide-angle display of PCBs were investigated.Similarly,self-oriented PC eccentric microspheres,pot-like hemispheres and bowl-like hemispheres with temperature and magnetic dual-responsiveness were prepared by the combination of UV-initiated polymerization with microfluidic technique.Their optical properties and tunability are studied.The main contents are as follows:（1）Eccentric 1-D magnetic core-shell PCBs were fabricated by the combination of micropipet injection technique and UV initiated polymerization method.The cross-sectional SEM images of PCBs show that each of them has a core-shell structure with an off-centered cavity.Futhermore,chain-like periodical structures are collectively embedded in the shell with the same direction,while Fe₃O₄@PVP nanoparticles randomly distributed on the inner wall of the gel shell.（2）The self-orientation performance of PCB is attributed to the geometric centre（O）noncoincident with the mass centre（P）.The heterogeneous region of the whole PCB is similar to that of the tumbler,so we can explain the self-orientation performance of the PCB with the balance principle of the tumbler.（3）The magnetochromism and wide-angle display of PCBs can be controlled by their shell thickness.L₁,L₂,L₃ are defined as the top and bottom shell thickness in the vertical axis direction,and the equal shell thickness in the horizontal axis,respectively.The upper shell thickness L₁ has a strong influence on the visual degree of the structural color from inner liquid cores.PCBs with smaller L₁ show wider shift range ofλ_p.When L₁ approaches to 180μm,PCBs only display the structural color for the PC shells and the color of the liquid core is invisible.Similarly,for the eccentric 1-D magnetic core-shell PCBs,the double orthogonal photonic band-gaps only works at enough small L₃.When L₃ is larger than 330μm,PC ball loses the property of wide-angle display.（4）Self-oriented PC eccentric microspheres,pot-like hemispheres and bowl-like hemispheres with temperature and magnetic dual-responsiveness were obtained by a combination of UV-initiated polymerization and microfluidic method.For PC microspheres,they self-orientated to show uniform structural color,and the color of their dose not be changed with the change of magnetic field intensity.Besides,the optical properties of PC microspheres are dependent on the direction of magnetic field and can be controlled by temperature.（5）For pot-like hemisphere,its opening can be transformed from“on”to“off”through the regulation of external temperature,and the process is reversible.In addition,its directional movement can also be achieved through the application of H.These unique propertyies makes it widely used in the field of sustained-release.For bowl-like hemisphere,the unique geometric and optical structure give it brighter color and wider range of temperature response than PC microshpere.