Preparation of uniform microcapsules with silicone oil as continuous phase in a micro-dispersion process

Abstract

This paper presents an improved solvent evaporation method with silicone oil (PDMS) as the continuous phase for preparation of microcapsules to make more polymer solvents available. A microchannel device was used to produce emulsions instead of mechanical stirring to prepare the mono-dispersed microcapsules. Under the conditions of lower evaporation temperature and shorter evaporation time, uniform polyacrylonitrile (PAN) microcapsules containing Aliquat 336 (ALQ) have been successfully prepared. N,N-dimethylformamide (DMF) with lower evaporation ability was applied as the polymer solvent. The prepared microcapsules have rough surfaces and homogeneously internal structures. By changing the two-phase flow rate, the mean size of microcapsules can be easily controlled. When more ALQ was added in polymer solution, the loading ratio of microcapsules increased. The mass transfer performance and stability were determined by extraction of Cr (VI) ions from its aqueous solution. The mass transfer rate was fast enough. After three times of repeated extraction and stripping, the microcapsules kept almost the same extraction ability, which indicated that the microcapsules have very good stability.

Key Words: :

• Microcapsule
• poly(dimethylsilicane)
• solvent evaporation
• silicone oil
• microchannel

Abbreviations:
	=	De, effective diffusivity in the microcapsules (m2 s−1); Df, diffusivity in the stagnant liquid film (m2 s−1); kc, apparent chemical reaction rate constant (dm4 (mol s) −1); qmax, ALQ encapsulated in the microcapsules (mol kg−1); qt, concentration of Cr (VI) in the microcapsules (mol kg−1); qe, equilibrium concentration of Cr (VI) in the microcapsules (mol kg−1); R, radius of the resin particle (m); t, time (min); x, concentration of Cr (VI) in the bulk liquid phase (mol L−1); X, fractional conversion of the microcapsules (equation ); Xe, fractional conversion of microcapsules at equilibrium (); δ, thickness of the stagnant liquid film (m).

Abbreviations:
	=	De, effective diffusivity in the microcapsules (m2 s−1); Df, diffusivity in the stagnant liquid film (m2 s−1); kc, apparent chemical reaction rate constant (dm4 (mol s) −1); qmax, ALQ encapsulated in the microcapsules (mol kg−1); qt, concentration of Cr (VI) in the microcapsules (mol kg−1); qe, equilibrium concentration of Cr (VI) in the microcapsules (mol kg−1); R, radius of the resin particle (m); t, time (min); x, concentration of Cr (VI) in the bulk liquid phase (mol L−1); X, fractional conversion of the microcapsules (equation ); Xe, fractional conversion of microcapsules at equilibrium (); δ, thickness of the stagnant liquid film (m).