Microencapsulated phase-change materials (MPCMs) with excellent thermal properties for low-temperature cold storage were developed in this study. Using 1-decanol as the core and methyl methacrylate as the shell precursor, the effects of emulsifier type and ultrasonic emulsification conditions were investigated. Styrene-maleic anhydride copolymer served effectively as a protective colloid emulsifier, producing MPCMs with high enthalpy and a well-defined, uniform microstructure. Under optimal conditions of 5 wt% emulsifier content relative to the oil phase, an ultrasonic power of 375 W, and an emulsification time of 12 min, the MPCMs exhibited a phase-change enthalpy of 126.7 kJ/kg. To further improve the thermal properties, a binary eutectic mixture was prepared by combining 1-decanol and 1-tetradecane at an optimal molar ratio (51.1:48.9). This binary-core MPCM showed a higher storage enthalpy (144.3 kJ/kg), with an increase of 13.9% compared to the single-core material (1-decanol). It also exhibited improved microstructural uniformity due to the stabilizing role of 1-tetradecane. These optimized MPCMs demonstrate phase-transition temperatures particularly suitable for low-temperature thermal storage, providing a practical and innovative technical solution for cold-chain logistics and vaccine refrigeration applications.

Nontoxic, low-cost microcapsule phase change materials (MicroPCMs) were successfully manufactured via suspension polymerization, in which n-dodecanol was employed as the core material and crosslinked polymethyl methacrylate as the wall material. Alkylphenol polyoxyethylene ether (OP-10), polysorbate-20 (Tween-20), sodium salt of styrene-maleic anhydride polymer (SMA), sodium dodecyl sulfonate (SDS), and hexadecyltrimethylammonium chloride (1631) were employed as emulsifiers to investigate the effects of the type and amount of emulsifier on MicroPCMs. In addition, the effects of different types of crosslinking agents on the fabrication of MicroPCMs were investigated. Scanning electron microscopy was used to observe the micro-morphology of MicroPCMs. The chemical structure of the MicroPCMs was detected via Fourier transform infrared spectroscopy. The thermal properties and thermal stability of the MicroPCMs were analyzed using a differential scanning calorimeter and a thermal gravimetric analyzer, respectively. Particle size distributions of the MicroPCMs were measured using a particle size analyzer. The results demonstrate that MicroPCMs with regular morphology were prepared when the mass ratio of the SMA to the oil phase was 3%, and the latent heat and yield of the MicroPCMs were 80.29 J g⁻¹ and 84%, respectively. Furthermore, the MicroPCMs were successfully synthesized using pentaerythritol triacrylate containing the hydroxyl group as the crosslinking agent with an average particle size of 14.18 μm and excellent thermal stability.

In mass concrete, shrinkage resulting from temperature drop and drying leads to cracking, which can seriously affect the strength and durability of cement-based materials. Fortunately, expansion agents can deter or prevent these effects, especially MgO expansion agents (MEAs). In this study, the effects of four MEAs of different activity on the expansion properties, strength, and hydration of cement paste were explored. The different expansion phenomena between the high activity and low activity MgO was especially explained by the hydration model and dynamic theory. The results indicate that when the other conditions were the same, higher curing temperature and dosage could improve the expansion to some extent. Moreover, the hydration of high activity MgO and the expansion behavior occurred mainly in the early hydration stage, while the hydration of low activity MgO and the expansion behavior had a high contribution rate in the later stage, and the final expansion of cement mixed with low activity MgO was larger.

Methyl methacrylate (MMA)-based repair material for concrete has the characteristics of low viscosity, excellent mechanical properties, and good durability. However, its application is limited due to its large shrinkage. Existing studies have shown that adding perchloroethylene can reduce the shrinkage. On this basis, other properties of modified MMA-based repair materials were tested and analyzed in the present study. The results revealed that the addition of perchloroethylene (PCE) can hinder the polymerization reaction of the system. When CaCO₃ with a mass fraction of 30% was added, the viscosity of the material was within the range of 450–500 mPa·s, and the shrinkage decreased to approximately 10%. The bending strength of MMA, and MMA modified by PCE, repair materials at 28 days could reach up to 28.38 MPa and 29.15 MPa, respectively. After the addition of HS-770 light stabilizer with a mass fraction of 0.4%, the retention ratios of the bending strength of materials with ratios of P0 and P3 could reach 91.11% and 89.94%, respectively, after 1440 h of ultraviolet radiation. The retention ratio of the bending strength of the material could reach more than 95% after immersion in different ionic solutions for 90 days.