Preparation and characterization of SiO2@n-octadecane capsules with controllable size and structure

• Published in: Thermochimica acta 2021-11, Vol.705, p.179037, Article 179037
• Main Authors: Liu, Lei, Cheng, Xiang, Miao, Xiwang, Zhang, Ying, Guo, Min, Cheng, Fangqin, Zhang, Mei
• Format: Article
• Language: English
• Subjects: Emulsion polymerization; Microcapsule encapsulation; Phase change capsule; Size and structure controlled preparation
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2021.179037

•Conducted comprehensive analysis of the parameters of emulsion polymerization.•Clarified the relationship between performance and structure.•Proposed formation mechanism of structure such as differentiation phenomenon.•Realized the controllable preparation of capsules within a certain range. In this work, a series of SiO2@n-octadecane capsules were prepared by one step emulsion polymerization, the influence of emulsifying speed, ammonia and TEOS contents, reaction temperature, concentration of emulsifier and the amount of PVP on the size, structure and performance was detailed investigated. It can be seen from SEM characterization that among these factors emulsification speed had the greatest influence on capsule size, while followed by the ammonia and TEOS content. According to TEM results, the ammonia and TEOS contents were the most important factors on the structure (shell thickness and surface smoothness) of the capsules, attributing to ammonia and TEOS were the catalyst and reactant of hydrolysis polymerization, respectively. Generally, the crystallinity of the samples became worse as the size decreased. DSC results showed that excessive ammonia or TEOS caused a significant drop in the enthalpy of the samples, furthermore, the enthalpy basically decreased with the attenuation of the inner radius of the sample. The target SiO2@n-octadecane capsule was sample C2 with high enthalpy (127.7 J/g), size of 1.62 μm, shell thickness of 68 nm, and smooth surface. More importantly, within the parameters studied, a series of SiO2@n-octadecane capsules were successfully synthesized with different enthalpy values (min 85.9 J/g, max 144.3 J/g), sizes ranging from 0.63–2.75 μm, shell thickness 32–79 nm and different smooth surfaces. Therefore, the controllable synthesis of SiO2@n-octadecane capsules within the above range can be achieved by simulating different parameters and their development.