Jiaqing He,Qiang Zhou,Zhiqing Ge,Shunfeng Jiang,Jiahe Li,Wei Feng,Haiyang Yang
Temperature-responsive hydrogels including lower critical solution temperature (LCST)- and upper critical solution temperature (UCST)-type hydrogels are attractive in various fields. However, the swift switch between LCST and UCST stimuli-responsive behaviors remains intriguing and challenging. Here is reported a kind of hydrogel with pH-gated LCST and UCST response behaviors. This is achieved using the hydrogen bonding between carboxylic acid groups of poly(acrylic acid- co -acrylamide) and hydroxyl groups of hydroxypropyl cellulose (HPC). The poly(acrylic acid- co -acrylamide)-HPC (PACA-HPC) hydrogels exhibit pH-gated reversible LCST-UCST phase transition behavior. When the transparent PACA-HPC hydrogel is placed in an acid bath, the COO − groups get protonated, rapidly forming hydrogen bonds with HPC to render a light-scattering state making the hydrogel opaque. Furthermore, the opaque hydrogel exhibits UCST phase transition behavior at 20–45 °C. When the opaque PCAC-HPC hydrogel is placed in an alkaline environment, hydrogen-bonded complexes gradually dissociate as the COOH groups are deprotonated to form a homogeneous transparent state. The transparent hydrogel exhibits LCST phase transition behavior at 20–45° C. Therefore, is shown the hydrogen bonding strategy to fabricate hydrogels with tunable LCST and UCST responses. With this pH-gated hydrogel with switchable LCST/UCST responsive behaviors, are demonstrated its applications in smart windows and information encryption.
In this study, novel thermo-responsive nanogels were facilely fabricated via ternary cross-linking copolymerization of ionic liquid (IL)-based monomers and cross-linker in methanol. To achieve the thermo-responsive performance of nanogels, monomers with hydroxyl or carboxyl group which can contribute to hydrogen (H)-bonding interaction is the key point of this strategy. The thermo-responsive behavior of poly(ionic liquid)s (PIL)-based nanogels were testified using dynamic light scattering (DLS), turbidimetric method, and differential scanning calorimetry (DSC) measurements. The results demonstrated that these novel nanogels presented reversible upper critical solution temperature (UCST) phase transition with the temperature changing. And their UCSTs could be tuned via the feed ratio of IL-based monomers and cross-linker. The nanogels were also measured using scanning electronic microscopy (SEM), thermo-gravimetric analyses (TGA) and Fourier transform infrared spectroscopy (FT-IR) techniques. In addition, a possible mechanism of thermo-responsive performance was suggested based on the above results. As a result, our findings provide an efficient and applicable platform for the fabrication of thermo-responsive polymeric nanomaterials .
Zihao Dong,Yajuan Qu,Yuyang Jiao,Ke Xue,Wenguang Zhu,Hai Liu,Jianguang Qi,Yinglong Wang
A series of poly(1-vinyl-3-methylimidazole dimethyl phosphate- co -N-isopropylacrylamide) oligomers was synthesized by reversible addition-fragmentation chain transfer polymerization. The co-oligomers exhibited a pH-tunable lower critical solution temperature (LCST) phase transition in aqueous solutions. By changing the pH of the aqueous solution (HCI), the hydrogen bonding between the internal molecules of the co-oligomers and water molecules was weakened, which effectively reduced the cloud-point temperature. Poly(1-vinyl-3-methylimidazole dimethyl phosphate- co - N -isopropylacrylamide) oligomers exhibit an upper critical solution temperature (UCST) type of phase transition in an ester solution, which is associated with the formation and breaking of hydrogen bonds within the co-oligomers molecules. FT-IR analysis revealed the effect of temperature on hydrogen bonding between the functional groups. Energy decomposition, Electrostatic Potential (ESP), Atoms-in-Molecules (AIM), and Interaction region indicator (IRI) analyses demonstrated the presence of hydrogen bond donors N–H and imidazole ring C–H, and hydrogen bond acceptors C = O and P = O in the co-oligomers. The sites of hydrogen bonding between the co-oligomers and the solvent molecules as well as intermolecular forces were found to be the main factors contributing to the LCST/UCST-type phase transition.
危险品化学品经营许可证（带存储）