Self-assembly Of Colloidal Nanoparticles Into Large Scale Colloidal Fiber Through Crack Engineering

Colloidal particles usually refer to particles with the size of less than 10 ?m.Colloidal particles in water or ethanol solvents usually have a size of 1-100 nm.Due to the small size,its gravity is negligible,which presents a relatively stable colloidal suspension.Under certain conditions,the colloidal particles in the suspension can selfassemble into two and three-dimensional colloidal crystals with various shapes,including Janus sphere,colloidal film,stripe and fiber.Among all these shapes,colloidal fiber has attracted widespread attention due to their potential value in photonic devices and surface patterning.In order to obtain colloidal fiber,templates are usually introduced during the fabrication process,and the particles are restricted to a specific area to form desired colloidal fiber.However,during the self-assemble process,due to the weak interaction between particle,the resulted colloidal fiber has small size,which usually in the order of micrometers.And the introducing of templates requires precise operating conditions,which leads to higher preparation cost.Therefore,a template-free strategy for preparing colloidal fiber with large size in urgently needed.When colloidal particles in the suspension self-assemble into colloidal film,cracks usually appear in the drying process due to the tensile stress.Since these cracks will damage the integrity of the film,they are regarded as a negative factor in numerous applications.Most previous efforts are devoted to circumventing them.However,it was demonstrated that regulated crack patterns are useful in applications such as microchannels and photonic sensors since they can provide controllability to the morphology and periodicity for reaching excellent device performance.Based on this,this paper proposed a strategy for self-assembly of particles into regular colloidal fiber by controlling crack propagation.When particles self-assemble into colloidal film,we introduce regular parallel cracks and the film will crack to form regular colloidal fiber.By controlling solvent composition,temperature,particle concentration and other influential factors,we can control the morphology of colloidal fiber,including the length,width,thickness.In addition,high-temperature sintering can increase the interaction force between particles,and the mechanical properties of colloidal film can be improved as a result.As a showcase,these fibers are used as probes for Surface enhanced Raman scattering(SERS)detection making use of their rich nanostructured surface.The probe was used to detect Bisphenol A in water.The experiment results showed that the colloidal fiber probe can detect 10-8 M Bisphenol A.This strategy for colloidal fiber preparation is simple and might be further developed in large-scale,providing new opportunities for many technological fields.