Effect of Polyvinyl Alcohol on Ice Formation in the Presence of a Liquid/Solid Interface

Tuning ice formation is of great importance in biological systems and some technological applications. Many synthetic polymers have been shown to affect ice formation, in particular, polyvinyl alcohol (PVA). However, the experimental observations of the effect of PVA on ice formation are still conflicting. Here, we introduced colloidal silica (CS) as the model liquid/solid interface and studied the effect of PVA on ice formation in detail. The results showed that either PVA or CS promoted ice formation, whereas the mixture of these two (CS–PVA) prevented ice formation (antifreezing). Using quantitative analysis based on classical nucleation theory, we revealed that the main contribution came from the kinetic factor <i>J</i>₀ rather than the energy barrier factor Γ. Combined with the PVA adsorption behavior on CS particles, it is strongly suggested that the adsorption of PVA at the interface has significantly reduced ice nucleation, which thus may provide new ideas for developing antifreezing agents

Kinetics of Polymer Desorption from Colloids Probed by Aggregation-Induced Emission Fluorophore

Polymer adsorption and desorption are fundamental in many industrial and biomedical applications. Here, we introduce a new method to monitor the polymer desorption kinetics in situ based on the behavior of aggregation-induced emission. Poly­(ethylene oxide) and colloidal silica (SiO₂) were used as a model system. It was found that the aggregation-induced emission method could be successfully used to determine the polymer desorption kinetics, and the polymer desorption followed the first-order kinetics. It was also found that the polymer desorption rate constant decreased with the increasing molecular weight, which could be described by a power law function <i>k</i>_d ≈ <i>M</i>^–0.28, close to that of the adsorption rate constant

Effect of Peptide Charge Distribution on the Structure and Kinetics of DNA Complex

The complexes formed by DNA or siRNA interacting with polycations showed great potential as nonviral vectors for gene delivery. The physicochemical properties of the DNA/siRNA complexes, which could be tuned by adjusting the characteristics of polycations, were directly related to their performance in gene delivery. Using 21 bp double-stranded oligonucleotide (ds-oligo) and two icosapeptides (with the repeating units being KKGG and KGKG, respectively) of the same charge density as model molecules, we investigated the effect of charge distribution on the kinetics of complexation and the structure of the final complexes. Even though the distribution of the charged groups in peptides was only adjusted by one position, the complexes formed by (KKGG)₅ and ds-oligo were larger in size and easier to precipitate than those formed by (KGKG)₅. Counterintuitively, it was not the charged groups but the hydrophilic neutral spacers that determined the kinetics and the structure of the complex. We attributed such an effect to the water-mediated disproportionation process. The hydrophilic spacers next to each other were better than that in the separated pattern in holding water molecules after forming the complex. The water-rich domains in the complex functioned as a lubricant and facilitated the relaxation of the polyelectrolyte, resulting in a fast complexation process. The resulting complex was thus larger in size and lower in surface energy