Solvent-assisted Interface Induced Preparation Of Non-spherical PS Particles And Their Ordered Arrays

Compared with polymer spheres,non-spherical polymer particles exhibit excellent performance in the improvement of optical property,drug carrier efficiency and biological imaging due to their shape anisotropy.Ordered arrays assembled from non-spherical polymer particles show promising applications in novel optical materials and micro/ nanofabrication process due to their shape anisotropy and periodic structures.On the basis of polystyrene(PS)spheres,we have proposed a new strategy called solvent-assisted interface induced principle for controllable preparation of non-spherical PS particles such as raspberry-like and UFO-like particles and ordered arrays.The problems such as the process complexity and the difficulty in control of particle shape have been resolved.We have proposed good solvent-nonsolvent interface phase separation principle and realized the efficient fabrication of raspberry-like polystyrene(PS)particles with stable structure and uniform morphology in one-step process.The influence of PVP adsorption content on shape uniformity of surface nanostructures on raspberry-like PS particles has been systematically studied.Based on Cassie theory on contact angle,the change of particle surface wettability was quantitatively elaborated and it is found that the increase in air gap ratio was the key factor which induced the transformation of particle surface from hydrophilic into hydrophobic state.With the analysis of surface components of raspberry-like PS particles by secondary ion mass spectroscopy,it is further revealed that PVP layer phase separated on particle surface and formed into nanostructures.According to good solvent-assisted interfacial deformation principle,we have successfully achieved the controllable preparation of UFO-like PS particles ranging from micrometer sizes to nanometer sizes.With quantitative study on shape evolution of particles with different sizes,it is found that the change of the aspect ratio showed similar trend and the change rate was higher for particles with smaller initial sizes.Through the in-situ observation of the system,it is identified that Marangoni flow effect played a key role in the formation of UFO-like PS particles.The elasticity anisotropy of UFO-like PS particles was verified based on the characterization of elastic modulus of different positions on particle surface.Based on Johnson-Kendall-Roberts(JKR)contact theory,we have also developed the quantitative dependence of elastic moduli of UFO-like particles on their shapes.It is found that the elastic moduli of particles firstly increased and then exhibited a decrease with the aspect ratio.Two-dimensional non-spherical PS particle arrays with diverse shapes and interstices were prepared at the air/ tetrahydrofuran(THF)aqueous solution interface.Ordered gold nanocap arrays were achieved by employing the non-spherical particle arrays as templates.We have conducted quantitative study of plastic effect of tetrahydrofuran(THF)on PS particles and the force analysis on the mass points of PS particles along the three-phase contact line.It is identified that the stretch forces on PS particles originating from three-phase interfacial tensions played an important role in shape change of the particles.Through the combination of good solvent-assisted interfacial deformation and layer-by-layer assembly technique,we have achieved the generation of three-dimensional gibbous-moon-like and half-moon-like hierarchical PS particle arrays and the hierarchical arrays successfully exhibited an average decrease in the reflection in the near-infrared region(1100 nm-1800 nm)by 9-10 % for silicon substrate.