Phase Transition Behaviors of Hydroxypropyl Methylcellulose Induced By Small Molecular Weak Acids

In this paper, phase change material hydroxypropyl methylcellulose (HPMC) was chosen to investigate the influence of small molecular weak acids on its phase transition temperature. The results showed that all of the chosen small molecular weak acids such as acrylic acid (AA), methacrylic acid (MAA), DL-lactic acid (LA), citric acid (CA) and acetic acid (AAc) can trigger the decrease of phase transition temperature of HPMC at different pH. With the increase of pH, AA, LA, CA and AAc can further lower the phase transition temperature, on the contrary, the phase transition temperature of HPMC increased with MAA. The change range of LCST was largest around pKa compared with other pH values because triggering effect changed gradually from hydrogen bonding effect to salt effect upon the increase of pH. Besides, phase transition temperature can also be reduced by the increase of acid concentration. This is attributed to smaller distance between molecules caused by higher concentration leading to stronger hydrogen bonding effect or salt effect. This paper provided a new perspective to modulate the LCST of phase change material by small molecular weak acids at different pH.

Fluctuation In the Phase Transition Temperature of Poly (NIPAAm-co-HEMA-co-DMAMVA)-Post-guanine Affected by Hydrophilic/hydrophobic Interaction: Fabrication and Characterizations

The phase separation and transition temperature of poly (N-isopropylacrylamide) have been developed by the terpolymerization with new pH-responsive monomer and highly hydrophilic 2-Hydroxyethyl methacrylate. The new monomer based on vanillin is called 2-((dimethylamino)methyl)-4-formyl-6-methoxyphenyl acrylate (DMAMVA), and is investigated by chemical methods (1H, 13C NMR, FTIR, and mass spectroscopy). Terpolymers of dual-responsive thermo-pH with functional groups were fabricated via free radical polymerization of N-isopropylacrylamide (NIPAAm), 10 mol% 2-Hydroxyethyl methacrylate (HEMA), and 5, 10, and 20 mol% DMAMVA. A selected terpolymer was used for post-polymerization with guanine via click reaction and the formation of an imine between the aldehyde group of DMAMVA and the amine group of guanine. All terpolymer and post-terpolymer are chemically evaluated. The physical properties have been implemented by GPC (molecular weight and dispersity), DSC (glass transition temperature Tg), TGA (steps of degradation), and SEM (morphological features). The fluctuations in phase transition temperature Tc or the lower critical solution temperature LCST of the polymer solution in different pH solutions have been performed by two methods, first, the turbidity test by UV-Vis-spectroscopy, second, by micro-DSC for aqueous polymer solution. This work will be extended for more applications in bio-separation technology.

Composition of the Frenkel–Kontorova and Ising models for investigation the magnetic properties of a ferromagnetic monolayer on a stretching substrate

In the article, computer simulation on the behavior of a ferromagnetic thin film on a non-magnetic substrate by computer simulation is performed. The substrate is described by the two-dimensional Frenkel–Kontorova potential. The Ising model is used to describe the magnetic properties of a two-dimensional ferromagnetic film. The Wolf cluster algorithm is used to model the magnetic behavior of the film. A square lattice is considered for an unperturbed ferromagnetic film. Computer simulations show that mismatch of film and substrate periods results in film splitting into regions with different atomic structures. Magnetic properties for the obtained structure have been investigated. The hysteresis loop is calculated using the Metropolis algorithm. Deformations of the substrate lead to a decrease in the phase transition temperature. The Curie temperature decreases both when the substrate is compressed and when stretched. The change in phase transition temperature depends on the decreasing rate of exchange interaction with distance and the amplitude of interaction with the substrate. When the substrate is compressed, an increase in the amplitude of the interaction between the film and the substrate results in an increase in the phase transition temperature. The opposite effect occurs when the substrate is stretched. The hysteresis loop changes its shape and parameters when the substrate is deformed. Compression and stretching of the substrate results in a decrease in coercive force. The reduction in coercive force when compressing the substrate is greater than when stretching. The magnetization of the film is reduced by deformations at a fixed temperature.

Effect of Temperature on Phase Transformation of NiTi-based Shape Memory Alloy

For NiTi-based alloys, the phase transition temperature directly affects and limits their application fields. In order to apply the NiTi-based shape memory alloy in the wider field, it is necessary to control the phase transformation temperature. Studies have shown that the content of Ni element in the NiTi-based alloy and the precipitates of the alloy, such as NiTi2, Ni3Ti2 and Ni4Ti3, will affect the phase transition temperature of the alloy. At the same time, adding a third or even a fourth element to the NiTi binary alloy can also effectively regulate the phase transition temperature of NiTi-based alloy. We then pay attention to the problems confronting the current state of the NiTi-based shape memory alloy. We have confidence that the NiTi-based shape memory alloy have a bright future in the development and innovation of excellent properties.

Metal-Formate Framework Stiffening and Its Relevance to Phase Transition Mechanism

In the last decade, one of the most widely examined compounds of motel-organic frameworks was undoubtedly ((CH3)2NH2)(Zn(HCOO)3), but the problem of the importance of framework dynamics in the order–disorder phase change of the mechanism has not been fully clarified. In this study, a combination of temperature-dependent dielectric, calorimetric, IR, and Raman measurements was used to study the impact of ((CH3)2NH2)(Zn(DCOO)3) formate deuteration on the phase transition mechanism in this compound. This deuteration led to the stiffening of the metal-formate framework, which in turn caused an increase in the phase transition temperature by about 5 K. Interestingly, the energetic ordering of DMA+ cations remained unchanged compared to the non-deuterated compound.