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.

Mutual Comparison Studies of Mono and Di Cations in Binary and Ternary Aqueous Electrolytes Solution at 298.15 K

Densities and viscosities of binary and ternary electrolytes solution have been determined experimentally at 298.15 K. The results obtained from density and viscosity measurement have been used to calculate apparent molar volume φv partial molar volume φov at infinite dilution, relative viscosities hrel, A and B coefficients, and free energies of activation of viscous flow of solvent Δ µ10# and solute Δ µ20. The results are discussed in terms of the dehydration effect of the weak ion-ion and strong ion-solvent interactions. The properties of these systems are discussed in terms of the charge, size, and hydrogen bonding effect.