Liqin Chai

The vertical deposition self-assembly process and the formation mechanism of poly(styrene-co-methacrylic acid) photonic crystals on polyester fabrics

Three-dimensional (3D) photonic crystals with structural colors were successfully fabricated on soft polyester fabrics through the vertical deposition self-assembly of monodispersed poly(styrene-co-methacrylic acid) (P(St-MAA)) colloidal microspheres. The elaborate process was investigated by digital camera, 3D video microscope, and field emission scanning electron microscopy, and the formation mechanism and the self-assembly mode of photonic crystal on the fabrics were proposed. It was confirmed that during the evaporation of the colloidal dispersion medium, the surface of the dispersion moved down slowly, and the photonic crystal structure was deposited gradually onto the fabrics due to two effects of capillary force, one being from the meniscus between the P(St-MAA) colloidal microspheres and the vertical polyester fabric substrate, and another from the liquid bridges between adjacent P(St-MAA) colloidal microspheres. The array of colloidal microspheres underwent a disorder-to-order transition during the formation stage, generating a series of varying structural colors in the process. Different from those on solid nonporous substrates, the vertical deposition process firstly occurred in the gaps of fibers, then in the fiber surfaces, and eventually formed the ordered photonic crystal structure on polyester fabric substrates.

Study on the formation of three-dimensionally ordered SiO2 photonic crystals on polyester fabrics by vertical deposition self-assembly

In order to form a well-ordered structure of SiO2 photonic crystals on polyester fabrics with fewer defects, a series of influential factors such as particle size and monodispersity of colloidal microspheres, evaporation temperature, relative humidity, mass fraction of colloidal microspheres and solvent in vertical deposition assembly were deeply studied, and the complexities of the self-assembly process of colloidal microspheres on polyester fabric substrates were revealed. In different self-assembly conditions, the quality of SiO2 photonic crystals on polyester fabric substrate was investigated by field emission scanning electron microscopy for the morphology of the crystal structures and by spectrometer measurements for their stop band intensities. Under the conditions of suitable sizes and monodispersity (PDI ≤ 0.08) of colloidal microspheres, the high-quality SiO2 photonic crystals with face centered cubic (fcc) array on polyester fabrics were produced at a low evaporation rate by adopting relative humidity of about 60% with a medium mass fraction of 1.0–1.5% SiO2 microspheres at 25℃ with ethanol as the solvent.

Interface–gravity joint self-assembly behaviors of P(St-MAA) colloidal microspheres on polyester fabric substrates

AbstractP(St-MAA) photonic crystals of face-centered cubic structure in bright structural colors were fabricated on polyester fabrics by interface–gravity joint self-assembly. The elaborate self-assembly process was investigated by digital camera, 3D video microscope, and field emission scanning electron microscopy, and the possible interface–gravity joint self-assembly and crystallization mechanisms of the colloidal microspheres on polyester fabric substrates were proposed. It was confirmed that the interface–gravity joint self-assembly on polyester fabrics was composed of two different self-assembly processes simultaneously, in which the rate of interfacial self-assembly driven by capillary force and convection effect is much faster than the gravitational sedimentation self-assembly under the gravity. With the evaporation of solvent, an ordered colloidal crystal structure was gradually formed in the interfacial self-assembly on the air–liquid interface with a disorder-to-order transition during crystallization stage and covered on the polyester fabric substrate filled with colloidal microspheres in gaps between yarns and fibers during gravitational sedimentation self-assembly.

Study on the binding strength of polystyrene photonic crystals on polyester fabrics

Four different polystyrene colloidal microspheres were used to fabricate the photonic crystals on polyester fabrics via vertical deposition self-assembly. The binding strength of the resultant photonic crystals was evaluated by designing and performing the bending and folding test and the washing test. The differences in binding strength among the resultant photonic crystals on polyester fabrics were thoroughly investigated by means of digital camera, three-dimensional video microscope, field-emission scanning electron microscopy, and transmission electron microscopy, and the related mechanisms were profoundly analyzed. It was confirmed that the binding strength of the resultant polystyrene photonic crystals on fabrics is closely linked to their own compactness and the adhesive property between the microspheres and the fabric substrates. In general, the microspheres with softer polymer shell could easily adhere to the yarns, fibers, and their own adjacent microspheres to improve the binding strength between the photonic crystals and the fabrics. Moreover, the softer microspheres can more easily form the compact photonic crystal structure, and the array of the colloidal microspheres with more compactness in photonic crystals could possess better binding strength. However, too compact a photonic crystal structure might make the surrounding medium among colloidal array disappear and form a transparent film with uniform refractive index on fabric surface, leading to the lack of photonic band gap and the related optical properties.

Study on the stability of the photonic crystals under different application environments and the possible mechanisms

Abstract P(St-MAA) and SiO2 photonic crystals on polyester fabrics were put in the different application environments such as water, oil, acid, alkali, high temperature, and ultraviolet radiation. The related changes of the morphology and the structural colors were characterized by 3D video microscope and field-emission scanning electron microscopy (FESEM) and the possible mechanisms were deeply investigated. It is found that aqueous medium have little influence on P(St-MAA) and SiO2 photonic crystals, however, oil medium restrains the photonic crystals from regaining the original structure. Even though in aqueous medium, strong acid and alkali conditions could easily destroy the photonic crystal structure to great extent even degrade the microspheres. Different from the good stability of P(St-MAA) and SiO2 photonic crystals at conventional high temperatures, under the ultraviolet irradiation P(St-MAA) are severely destroyed due to the drastic thermal depolymerization, but SiO2 photonic crystals keep favorable morphology and structural color.