Preparation and characterization of novel nanoencapsulated phase change materials Yutang Fang * , Shengyan Kuang, Xuenong Gao, Zhengguo Zhang The Key Laboratory of Enhanced Heat Transfer and Energy Conversation, Ministry of Education, College of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510640, China article info Article history: Received 10 April 2007 Received in revised form 2 December 2007 Accepted 29 June 2008 Available online 30 August 2008 Keywords: Thermal energy storage Phase change materials (PCMs) Miniemulsion polymerization n-Octadecane abstract A kind of novel nanoencapsulated PCM with polystyrene as the shell and n-octadecane as the core was synthesized by the ultrasonic-assistant miniemulsion in-situ polymerization, and its morphology, structure and thermal properties were characterized by TEM, FT-IR, XRD, DSC and TG. The nanocap- sules were regular spherical and ranged from 100 nm to 123 nm in size. All the characteristic peaks of n-octadecane and styrene were observed in the FT-IR spectrum of the nanoencapsulated PCM. The XRD result suggested that n-octadecane was encapsulated by the shell of polystyrene. The phase change temperature of the nanoencapsulated PCM was very closer to that of n-octadecane, and its latent heat was equivalent to that of the calculated value based on the mass ratio of n-octadecane mea- sured by TG. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Thermal energy storage (TES) is considered as one of the most important advanced energy technologies, and an increasing attention has been paid to utilization of the technique for ther- mal applications [1,2]. A phase change material (PCM) can ab- sorb or release a large quantity of latent heat when it changes phase from solid state to liquid state or vice versa. Latent ther- mal energy storage based on the PCMs is the most important TES technology, which has very wide applications ranging from heating to cooling [3–5]. PCMs are usually classified into two categories: inorganic PCMs and organic PCMs. Although inorganic PCMs possess large latent heat, there are some problems inher- ent in organic PCMs, such as the need for special container due to their corrosiveness, tendency of super cooling, segregation, etc. Organic PCMs suffer from low conductivity, instability and li- quid leakage. Therefore, encapsulation of PCMs is an effective solution for the above problems inherent in inorganic and organ- ic PCMs. In recent years, several kinds of microencapsulated PCMs pre- pared by in-situ polymerization, interface polymerization and coacervation, had been utilized in many fields including latent functionally thermal fluids, thermoregulating textiles, thermal storage building materials, etc. [6–14]. However, in some fields especially in latent functionally thermal fluids, microencapsulat- ed PCMs had not well done under repeated cycling, because the large particles of the microencapsulated PCM not only in- creased the fluid’s viscosity, but also were often crushed during pumping. Therefore, it is necessary to develop nanoencapsulated PCMs with smaller particle size as compared with microencapsu- lated PCMs. Although the concept of nanocapsule was presented out by Narty in the 1970s and the nanocapsulation technology has been widely utilized in medicine dye and perfume [15–16], there is limited precedence for producing nanoencapsulated PCMs. Zhang et al [17] synthesized a kind of nanoencapsulated PCM by the in- situ polymerization, which melaming-formaldehyde resin was used as the shell, n-octadecane and cyclohexane as the core. How- ever, the particle size of the nanoencapsulated PCM was as large as 770 nm. Miniemulsion polymerization was a convenient one- step encapsulation technique for preparing nanocapsules. Luo and Zhou [18] studied the nanoencapsulation of hydrophobic compounds by miniemulsion polymerization in terms of the ther- modynamics and kinetics, and it was found that thermodynamic factors (the level and type of surfactant, the level of the hydro- philic comonomer, and the monomer/paraffin ratio), kinetic fac- tors (the level of the crosslinking agent or chain-transfer agent), and nucleation modes all have a great influence on the latex mor- phology. Park et al. [19] prepared polystyrene (PS) nanoparticles containing paraffin wax as the PCM by miniemulsion polymeriza- tion. In the current work, a kind of nanoencapsulated PCM with polystyrene as the shell and n-octadecane as the core was synthe- sized by the ultrasonic-assistant miniemulsion in-situ polymeriza- tion. The morphology, structure and thermal properties of the nanoencapsulated PCM were characterized by TEM, FT-IR, XRD, DSC and TG. 0196-8904/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2008.06.027 * Corresponding author. Tel.: +86 20 87113870; fax: +86 20 87113870. E-mail address: ppytfang@scut.edu.cn (Y. Fang). Energy Conversion and Management 49 (2008) 3704–3707 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman