The biggest challenge in dispersion of nanoparticles in phase change materials (PCMs) is the physical stability of these particles in PCM. Numerous studies have evaluated the effect of different parameters on the stability of nanoparticles in PCM, but the effect of PCM polarity has rarely been investigated. In this study, the stability of functionalized and pristine multi-walled carbon nanotubes (MWCNTs) in three different PCMs with various polarity levels was investigated. The utilized PCMs were paraffin wax (nonpolar), stearic acid (partially polar), and polyethylene glycol (polar). Two different methods of functionalization of MWCNTs, with stearic acid and hexadecyl amine, were used to compare their stability in PCMs. The FTIR analysis and FESEM images reveal that the surface modification reactions were done thoroughly and MWCNTs are well dispersed in PCM. The results showed that pristine MWCNT is more stable in nonpolar PCMs (paraffin and stearic acid), while the samples containing functionalized MWCNT or surfactant had higher stability in polyethylene glycol. The three most stable samples were used to measure their thermal conductivity and heat release/storage capability. The addition of nanoparticles to all kinds of PCMs led to higher rate of heat storage and release. Moreover, the thermal conductivity of all PCMs improved by the introduction of nanoparticles. In both liquid and solid phases, nanoenhanced PCM had higher thermal conductivity compared to pure PCM with stearic acid containing 1 mass% of pristine MWCNT having the highest rate of enhancement at 16.82% for solid phase.

中文翻译：

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含原始和功能化多壁碳纳米管的相变材料的稳定性和导热性的实验研究

将纳米颗粒分散在相变材料（PCM）中的最大挑战是这些颗粒在PCM中的物理稳定性。大量研究评估了不同参数对PCM中纳米颗粒稳定性的影响，但很少研究PCM极性的影响。在这项研究中，研究了功能化和原始的多壁碳纳米管（MWCNT）在三种不同极性级别的PCM中的稳定性。所使用的PCM是石蜡（非极性），硬脂酸（部分极性）和聚乙二醇（极性）。用硬脂酸和十六烷基胺两种不同的功能化MWCNTs的方法来比较它们在PCM中的稳定性。FTIR分析和FESEM图像表明，表面改性反应进行得很彻底，并且MWCNTs很好地分散在PCM中。结果表明，原始的MWCNT在非极性PCM（石蜡和硬脂酸）中更稳定，而包含功能化的MWCNT或表面活性剂的样品在聚乙二醇中具有更高的稳定性。使用三个最稳定的样品来测量其热导率和热量释放/存储能力。向各种PCM中添加纳米颗粒导致了更高的热量存储和释放速率。此外，通过引入纳米颗粒，所有PCM的导热率都得到了提高。在液相和固相中