Polycarbonate (PC) nanofibers are prepared using the air blowing-assisted electrospinning process. The effects of air blowing pressure and PC solution concentration on the physical properties of fibers and the filtration performance of the nanofiber web are investigated. The air blowingassisted electrospinning process produces fewer beads and smaller nanofiber diameters compared with those obtained without air blowing. Uniform PC nanofibers with an average fiber diameter of about 0.170 lm are obtained using an applied voltage of 40 kV, an air blowing pressure of 0.3 MPa, a PC solution concentration of 16%, and a tip-to-collection-screen distance (TCD) of 25 cm. The filtration efficiency improvement of the air blowing-assisted electrospun web can be attributed to the narrow distribution of fiber diameter and small mean flow pore size of the electrospun web. Performance results show that the air blowing-assisted electrospinning process can be applied to produce PC nanofiber mats with high-quality filtration.

This study presents a simple approach to the preparation of hollow silica spheres via template-sacrificial techniques. The hard poly(styrene) (PS) template was prepared by soap-free emulsion polymerization in the boiling state for a specified period, followed by introduction of silane into the reaction system to generate the core-shell PS/silicon dioxide (SiO 2 ) spheres without the use of structure-directing agents or surface modification. The SiO 2 shell was constructed by co-hydrolysis/condensation of mixed silane containing various weight ratios of tetraethyl orthosilicate (TEOS) and triethoxymethylsilane. The degree of compatibility between PS and SiO 2 was shown to be affected by the composition of the silane mixture, and increasing the proportion of TEOS in the silane mix enhanced the mechanical robustness of the SiO 2 shell. Based on the residual weight percentage from thermogravimetric analysis, the portion of SiO 2 in the PS/SiO 2 spheres prepared using various compositions of silane was about 10 wt%. Furthermore, hollow SiO 2 spheres were obtained by calcination of the PS/SiO 2 spheres prepared using an appropriate formulation of silane at 400 C. Scanning electron microscopy analysis indicated that the size of the hollow spheres was about 200 nm, and the spheres displayed a high degree of monodispersity. Observation of certain cavities on the surface of the spheres also demonstrated the hollow structure of the SiO 2 spheres.

Monodisperse core-shell poly(styrene) (poly(St))/poly(styrene-co-butyl methacrylate) spheres were fabricated from styrene (St) and butyl methacrylate (BMA) monomers by a two-step, soap-free emulsion polymerization process at the boiling point. The two-step process involves initial polymerization for a fixed period of time, followed by the addition of BMA monomer to generate the core-shell structure microsphere. Formation of the shell portion increased as the initial polymerization time period was decreased. Differential scanning calorimetric analysis showed that the core-shell microsphere exhibited glass transition temperatures (T g s), when the monomer conversion during the initial St polymerization step was higher than 40%. The T g s of the core and shell occurred at 107 C and 41.9-56.7 C, respectively. These core-shell structure spheres were used to fabricate a colloidal crystal film, the photonic band gap of which could be shifted from 455-631 nm by employing core-shell spheres of various sizes. These films having photonic band gaps in the visible region were obtained by self-assembly of the core-shell spheres at 30, 50, and 80 C. The pencil hardness of the films prepared using the core-shell spheres could be increased from 5B to HB by increasing the preparation temperature, whereas the hardness of the film prepared using simple poly(St) spheres was lower than 6B.

Photonic crystals were fabricated using self-assembled polystyrene (PS) submicrospheres with different content of nanospheres with different glass transition temperatures (T g : 100 to À54 C) and their opalescent and mechanical properties were investigated. PS spheres (185.4 nm) and nanospheres were prepared by soap-free emulsion polymerization. Nanospheres were prepared using one or two types of monomers, styrene, n-butyl methacrylate, and butyl acrylate with sodium p-styrenesulfonate. Surface morphology, particle size (D n ), and wavelength () of photonic crystals were determined from scanning electron microscopy (SEM), effective refractive index equation, and modified Bragg's law, respectively. The reflection wavelength ( max ) was measured from ultraviolet-visible spectroscopy. SEM results showed that hard nanospheres were distributed around PS spheres in their photonic crystals. On the other hand, soft nanospheres were coated onto PS spheres in their photonic crystals. With increasing weight fraction of hard or soft nanospheres in the photonic crystals, D n and were increased. The value of max corresponded to that of . The mechanical property of the photonic crystals was measured by the pencil hardness (PH) test. The result showed that by decreasing the T g and increasing the weight fraction of nanospheres, PH was increased. The opal film prepared from PS spheres with 20% N-54 nanospheres had the highest PH (H).

In this study, the photonic bandgap (PBG) film with tunable mechanical properties and photonic stop band was prepared by a simple and feasible approach. Colloid polymer spheres with a relatively large diameter (approximate D n of 200 nm) and different glass transition temperatures (T g ) were blended with small polystyrene (PS) latex (D n 5 20 nm) and were subsequently casted on a substrate for 3 h at 50 C for self-assembly of the PBG film. The monodispersed polymer spheres were synthesized by soap-free emulsion polymerization in the boiling state. The T g values of the spheres were predetermined based on the Fox equation, and designed to fall in the region of 234 C to 112 C. Small PS could also be synthesized by this approach using the comonomer, sodium p-styrenesulfonate (NaSS), to ensure the small diameter. The long-range ordered structure constructed by embedding the small PS in the PBG film was indirectly confirmed on the basis of SEM analysis, from which the monochromatic film color was determined based on Bragg's diffraction law. Tunable film color was achieved by adjusting the diameter of the spheres, as evaluated using UV-Vis. Tunable mechanical properties of the PBG film were also achieved by varying the T g of the spheres or the filling ratio of small PS. Based on these approaches, the ultimate tensile strength could be tuned in the region between 0.39 to 4.7 Mpa, and the relative strain could be varied from 1236% to 16%, illustrative of the excellent deformability of the film. Furthermore, by variation of these two parameters, the film properties could be changed from typical elastomer behavior to brittle plastic polymer type behavior, greatly extending the prospective application fields.