Facile fabrication of Sudan red particle microcapsules by a polymerizable gemini surfactant and molecular assembly mechanisms

Abstract

An efficient method was developed to encapsulate water insoluble organic particles of Sudan red III (SR) in aqueous suspensions by using a polymerizable cationic gemini surfactant, 1,3-bis(N,N-dimethyl-N-cetylammonium)-2-(propylacrylate dibromide) (AGC₁₆). The AGC₁₆ coated SR microcapsules (AGC₁₆@SR) were prepared by absorption of AGC₁₆ on the surface of SR, followed by in situ homopolymerization (PAGC₁₆). Several measurements, including transmission and scanning electron microscopy, isothermal titration calorimetry, zeta potential, electron paramagnetic resonance and small angle X-ray scattering, were performed to determine the adsorption amount of AGC₁₆, and the layer structures and the molecular assembly mechanism in the AGC₁₆@SR and PAGC₁₆@SR systems, respectively. For comparison purposes, the polymerizable cationic surfactant with one head group and a single alkyl chain, acryloyloxyethyl-N,N-dimethyl-N-cetylammonium bromide (referred to as ASC₁₆), as well as the systems of ASC₁₆@SR and PASC₁₆@SR were also investigated in parallel. It was found that AGC₁₆ molecules and their aggregates were simultaneously assembled into a shell layer, in which the saturated adsorption amount of AGC₁₆ on SR is less than 1/2 that of ASC₁₆, but the assembly layer of AGC₁₆ is more hydrophobic with greater packing tightness compared with that of ASC₁₆. It was also revealed that after in situ homopolymerization, the microcapsule shell becomes more compact. In the case of PAGC₁₆@SR, the layers show higher surface roughness and irregularity compared with that of PASC₁₆@SR. Moreover, the sustained release behavior of SR was also evaluated. The results revealed that PAGC₁₆@SR performed well for SR controlled release, which was sorted by release performance as the following sequence: PAGC₁₆@SR > AGC₁₆@SR > PASC₁₆@SR > ASC₁₆@SR. Thus, the polymerizable cationic gemini surfactant holds substantial potential to be developed as an ideal candidate of soft matter to construct efficient controllable release systems.