Temperature-triggered fast-disintegrating polyNIPAM particles via semicontinuous heterophase polymerisation

Crosslinker-free poly(n-isopropylacrylamide) (polyNIPAM) particles produced by conventional emulsifier-free heterophase polymerisations contain gels and do not easily and completely disintegrate in water, if at all. These particles, when cooled below lower critical solution temperature (LCST) swell first and then gradually shrink, due to their slow rate of disintegration. We first show that only particles formed using very low monomer concentration, which have a low molecular weight, are fully soluble in water. Then, we describe a seeded semicontinuous route which was designed in order to be able to maintain a low monomer concentration in water in the course of reaction and control the length and location of growing chains. Nanoparticles produced via semicontinuous approach not only disintegrated in water very quickly but also dissolved in water completely as soon as LCST was reached. This finding may also find applications in technologically important processes for dissolution of macromolecules in solvents.

Hydrogen production via CO2-reforming of methane over Cu and Co doped Ni/Al2O3 nanocatalyst: impregnation versus sol–gel method and effect of process conditions and promoter

In this study, Cu and Co doped Ni/Al₂O₃ nanocatalyst was synthesized via impregnation and sol–gel methods. The physiochemical properties of nanocatalyst were characterized by XRD, field emission scanning electron microscopy (FESEM), particle size distribution, BET, fourier transform infrared spectroscopy (FTIR), TG–DTA and energy dispersive X-ray (EDX) analysis. The samples were employed for CO₂-reforming of methane in atmospheric pressure, temperature range from 550 to 850 °C, under various mixture of CH₄/CO₂ and different gas hourly space velocity. XRD patterns besides indicating the decline of the peaks intensity in sol–gel method, proved the potential of this procedure in diminishing the crystal size and preventing the NiAl₂O₄ spinel formation. Moreover, high surface area might derive of smaller particle size and uniform morphology of sol–gel prepared ones, confirmed by FESEM and BET analysis. TG–DTG analysis as well supported the higher surface area for sol–gel made ones, represented the proper calcination temperature (approximately 600 °C). Also, presence of the active phases and elemental composition of nanocatalysts determine via EDX analysis. Promoting the basicity and the adsorption rate of CO₂, is attributed to the higher amount of OH groups for sol–gel prepared samples, proved by FTIR. Ni–Co/Al₂O₃ due to the synergetic effect of sol–gel method and cobalt addition depicted excellent characterization such as higher surface area, smaller particle size, supplying more stable support and enhanced morphology. Therefore, this nanocatalyst represented the best products yield (H₂ = 98.21 and CO = 95.64), H₂/CO close to unit (0.92–1.05) and stable conversion during 1,440 min stability test. So, Ni–Co/Al₂O₃ among all of the prepared nanocatalysts demonstrated the best catalytic performance and presented it as a highly efficient catalyst for dry reforming of methane. Despite of the stable yield of Ni–Cu/Al₂O₃, it depicted the lower catalytic activity and H₂/CO ratio than the unprompted nanocatalysts.     

Nanoemulsion formation by phase inversion emulsification: on the nature of inversion

Emulsification processes are usually characterized by the way they allow the surfactants, as well as the dispersed phase, to be incorporated into emulsions. A model cyclohexane-in-water emulsion using a pair of polyoxyethylene nonylphenyl ether surfactants, one oil-soluble and one water-soluble, was considered. Two surfactant mixing approaches consisting of mixed surfactants (agent-in-oil and agent-in-water) and segregated surfactants (agent in corresponding oil and water phases) were used to produce the model emulsion. Formation of oil-in-water nanodroplets could be only achieved if emulsification was associated with the formation of a three-phase microemulsion structure (transitional phase inversion) across the path. This occurred only if segregated surfactants were used in a process in which water was added to oil. With decreasing surfactant concentration, a point was reached below which the inversion mechanism transformed from transitional to catastrophic, leading to the formation of large droplets. The transformation was also accompanied by a shift in the evolution of the drop size. Drop size variations showed a minimum at the inversion point for the transitional phase inversion, whereas they showed a maximum for the catastrophic phase inversion. The agent-in-oil technique followed a catastrophic phase inversion mechanism and ranked second in terms of drop size.     

Nanoparticle formation by monomer-starved semibatch emulsion polymerization

Latexes with very small particle size are usually manufactured by microemulsion polymerization. This article explains the preparation of nanolatexes by monomer-starved nucleation in a conventional semibatch emulsion polymerization with a low surfactant/monomer ratio and with no need for a cosurfactant. The semibatch emulsion polymerization reactions started with an aqueous solution of a surfactant and a water soluble initiator. Monomer was added at a fixed rate. The size of particles decreased with decreasing rate of monomer addition. High solids content nanolatexes with particles as small as 25 nm in diameter were produced. Several monomers with different water solubilities were compared. The order of the number of particles in terms of the rate of monomer addition was found to depend on the type of monomer. Water soluble monomers produced more particles due to associated chain transfer to monomer and radical exit. The monodispersity of particles at the end of nucleation increased as the rate of monomer addition decreased. The technique seems to be preferable to microemulsion polymerization, which uses a high concentration of surfactant/cosurfactant and is limited to low monomer holdup.     

Unseeded semibatch emulsion polymerization of butyl acrylate: Bimodal particle size distribution

Unseeded semibatch emulsion polymerization of butyl acrylate (BA) using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator was carried out at the conditions where secondary nucleation was probable. This was achieved by using no emulsifier in the initial reactor charge. The effects of changes in monomer emulsion feed rate, initiator concentration and distribution, emulsifier concentration in the feed, and temperature on the evolution of particle size averages and distribution were investigated. Bimodal particle size distributions (PSD) were obtained for most of the latexes. Inhibition effects were found to be important in the development of PSD. Primary particle formation occurred through micellar nucleation, whereas secondary nucleation probably occurred through homogenous nucleation. The polydispersity index (PDI) of the latexes increased with the decreasing monomer emulsion feed rate. The application of a larger amount of initiator to the reactor charge or using a higher temperature, reduced the formation of secondary particles and resulted in a formation of an unimodal PSD. The overall steady‐state rate of polymerization was found to approach the rate of monomer addition (R_p ≈ R_a ), if the emulsifier concentration in the aqueous phase was appreciable. This is different from the correlation 1/R_p = 1/K + 1/R_a obtained for the BA semibatch process with neat monomer feed. This suggests that different rate expressions can be used for BA semibatch emulsion polymerization at different conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 528–545, 2000     

Convergence analysis of the product integration method for solving the fourth kind integral equations with weakly singular kernels

Numerical Algorithms - In this paper, we consider product integration method based on orthogonal polynomials to solve mixed system of Volterra integral equations of the first and second kind with...