Formation of crystalline colloidal arrays by anionic and cationic polystyrene particles

Abstract

Cross-linked polystyrene microspheres bearing positive and negative charges have been prepared by surfactant-free emulsion polymerization by the use of various amounts of vinylbenzyltrimethylammonium chloride and sodium styrenesulfonate as comonomers, respectively. Increasing the amount of the ionic comonomers tends to decrease the particle size due to better surface stabilization, but a high concentration of an ionic comonomer leads to a competitive mechanism that increases the polydispersity of the particle size. The amount of cationic and anionic comonomers leads to differences in size, shape and uniformity of the particles. The cationic particles can self-assemble into crystalline colloidal arrays with intense visible light diffraction just like the anionic ones. It is particularly interesting to observe that good packing can be obtained even for particles not quite uniform in size. To better understand the packing behavior, the properties and stability of the colloidal crystals have been studied as a function of the particle concentration and ionic strength of the media. The presence of charges helps in the formation of periodic structure over a wide range of particle concentrations at low ionic strength.

Optically Evolved Assembly Formation in Laser Trapping of Polystyrene Nanoparticles at Solution Surface

“…The color was generated from the whole area of the assembly, while it changed from the center to the outside. It is reported that structural color of a colloidal crystal depends on particle distance; therefore observation of structural color change of the present nanoparticle assembly enables us to consider the nanoparticle association structure under the optical trapping conditions from the viewpoint of interparticle distance. Namely, the constituent nanoparticles are arrayed in a periodic manner over all areas of the assembly.…”

“…Below a certain concentration, the electrostatic repulsive force due to surface charge on nanoparticles possibly becomes weak with the increase in the salt concentration. 26 As the result, nanoparticles come closer to each other and can be packed more tightly. Above 100 μg/mL, the electrical double layer of nanoparticles is screened, and nanoparticles are gathered as close as possible, independent of the salt concentration.…”

“…These assemblies were at their steady states, where the apparent assembly sizes are kept constant and the spectral changes are saturated. The peak wavelength gives us the information on the interparticle distance according to the following Bragg’s equation; where m is diffraction order, λ is wavelength of diffracted light, n is a refractive index of the colloidal crystal, d is distance between the nanoparticle centers, and θ is an incident angle of light. The n can be approximately described with the volume fraction of nanoparticles (φ p ) and refractive indices of a constituent nanoparticle ( n p ) and medium ( n m ), as follows: …”

Effects of Crystallinity on the Photocatalytic Polymerization of 3,4-Ethylenedioxythiophene over CsPbBr3 Inverse Opals

“…where m is the order of diffraction, λ is the wavelength of the diffracted light, n is the refractive index of the crystalline colloidal arrays, d is the layer spacing, and θ is the angle between the incident light and the diffracting lattice plane. The stop band wavelength of the template with the microsphere diameter of 214 nm was 550 nm, which could be ascribed to the different order of diffraction compared with the other three opal structured templates [31]. As shown in Figure S1, low-resolution scanning electronic microscopy (SEM) images revealed that the template displayed a 3D ordered structure.…”

Understanding the thermo-sensitivity of crystalline colloidal arrays formed by poly(styrene-co-N-isopropylacrylamide) core–shell microspheres

“…11,15,16 Uniform polymeric microspheres with a soft and/or charged surface easily selfassemble by a simple concentration. Thus, charged polystyrene particles 17,18 and microgels 19,20 have demonstrated their ability to form CCAs in water when their concentrations are sufficiently high.…”