A new kind of phase change material n-octadecane microcapsules containing peppermint fragrance scent has been synthesized through the interfacial polymerization of isophorone diisocyanate (IPDI) and hexamethylenediamine (HMDA). The average size, morphology, and chemical components of the microcapsules were characterized by laser particle size analyzer, scanning electron microscope (SEM), and Fourier transform infrared (FTIR), respectively. The thermal characterizations of the microcapsules were studied by differential scanning calorimetry (DSC) and thermal gravity analysis (TGA). The results show that the average size of the microcapsules was in the range of 4.0 to 7.0 μm and decreased with increasing emulsifier. The microcapsulated phase change materials (MicroPCMs) are spherical, and their surface is dented. The MicroPCMs without nucleating agents demonstrated high heat storage capacity but had supercooling phenomena. It was found that the addition of approximately 8.3 wt % nucleating agents 1-tetradecanol or paraffin in core materials can suppress MicroPCMs from supercooling. The MicroPCMs maintained a good thermal stability below 150 °C.

Methacrylic acid (MAA)-triggered phase transition of thermosensitive hydroxypropyl cellulose (HPC) was studied. The phase transition temperature of 0.1 wt.% HPC aqueous solutions was dramatically reduced from 41 °C to 8 °C as the MAA concentration increased from 0 wt.% to 4 wt.%. The sharp decrease of HPC phase transition temperature triggered by MAA may be attributed to strong hydrogen bonding between MAA and HPC. It may be proposed that the hydrogen bonding of MAA with HPC restricts the interaction of water with HPC and so reduces the solubility of HPC in water and improves the hydrophobic association of HPC. Furthermore, MAA attaching on HPC polymer chains was polymerized to form surfactant-free PMAA nanogels around ambient temperature when HPC collapsed forming PMAA nanogels. Effect of MAA concentration and polymerization temperature on the size and size distribution of PMAA nanogels was investigated.Highlights► MAA triggered the sharp phase transition of HPC aqueous solution. ► PMAA nanogels have been synthesized directly in HPC aqueous solution. ► An increasing MAA concentration led to a larger size of the resulting PMAA nanogels. ► The size distributions of PMAA nanogels were narrow.

We report the synthesis and study of surfactant-free poly(acrylic acid) (PAA) nanogels using hydroxypropylcellulose (HPC) as a template in aqueous HPC solutions at room temperature or above. Through the hydrogen bonding interaction of acrylic acid (AA) with hydroxypropylcellulose (HPC), AA absorbed on the HPC polymer chains and triggered the phase transition of HPC at a lower temperature, with increasing AA concentration, than the HPC intrinsic phase transition temperature 41 °C. As AA polymerized to form PAA, the much stronger interpolymer hydrogen bonding triggered the phase transition of HPC at a temperature around room temperature, causing HPC coil-global phase transition to collapse and form nanospheres at room temperature, PAA hydrogen-bonded HPC chains collapsed and formed nanogels chemically crosslinked by poly(ethylene glycol) diacrylate (PEGDA) or methylenebisacrylamide (BIS). The results showed that all the PAA nanogels demonstrated a narrow size distribution with diameters ranging from 60 nm to 600 nm.Highlights► Hydroxypropylcellulose (HPC) can form hydrogen bonding with acrylic acid (AA). ► HPC aqueous solution undergoes AA-triggered phase transition at lower temperature. ► HPC are employed as template to prepare surfactant-free poly(acrylic acid) (PAA) nanogels. ► The size and size distribution of PAA nanogels can be adjusted by varying HPC concentration.