Changzhong Chen,Rong Chen,Tangyuan Zhao,Linge Wang
To reveal the influence of organic polymer supports on the properties of shape stabilized phase change materials (ssPCMs), a linear polyurea (LP) and crosslinked polyurea (CP) were synthesized for stabilizing polyethylene glycol (PEG) for thermal energy storage . Though the surface area of LP are about 25 times of that of CP, the shape stability of CP for melt PEG is better than that of LP. Due to the crosslinked network, CP has much stronger interactions with PEG, which could promote the adsorption capacity of PEG. The highest PEG loading capability of LP and CP without liquid leakage above melting point is 70 wt% and 80 wt% respectively, and the corresponding melting enthalpy is 95.42 J/g and 107.60 J/g respectively. However, the heat storage efficiency of PEG/LP ssPCMs is higher than that of PEG/CP ssPCMs with the same PEG content, which caused by the weak restrictions of free movement of PEG chains from LP. Both types of ssPCMs exhibit good reusability from thermal cycle test and good thermal stability from thermal analysis, and the thermal conductivity of ssPCMs can effectively enhance after adding some carbon materials. The study supplied an inspiration to select proper polymer matrix for ssPCMs.
Hongyan Cao,Bin Li,Xubao Jiang,Xiaoli Zhu,Xiang Zheng Kong
In contrast to conventional fluorescent polymers featured by large conjugation structures, a new class of fluorescent polymers without above conjugations are gaining constant interest owing to their significant academic importance and promising applications in diverse fields. These unconventional fluorescent polymers are in general composed of heteroatoms (e.g. N, O, P, and S) under different forms. Here we report our recent study on polyurea, prepared by a very simple one step precipitation polymerization of toluene diisocyanate in a binary solvent of water-acetone. This polyurea, basically consisting of phenyl ring and urea group, shows fluorescent emission in a broad concentration range, from very low (10 −5 mg/mL) to its solubility limit (50 mg/mL), and in a wide range of emission wavelength from UV to visible regions of up to 500 nm under varied excitation wavelength. The emission behaviors were fully studied under different concentrations and excitations. It was concluded that the emission in UV region was intrinsic due to the conjugation between the phenyl and the adjacent urea unit; while the emission in visible region, strongly excitation dependent, was caused by the cluster formation of the molecular chains, in accordance with the cluster-triggered-emission (CTE) mechanism. The formation of the cluster was tested through dynamic light scattering, FTIR and UV absorbance. Tested in presence of different metal ions, Fe 3+ demonstrated a quenching effect with high selectivity. Based on this study, different paper-based sensors were designed to detect Fe 3+ , H 2 O 2 in bioanalysis and for data encryption. This work provides a simple way to prepare a polyurea, a novel type of unconventional fluorescent polymer, with high emission performance distinct from its known analogues.
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