Revealing the Aggregation Mechanism, Structure, and Internal Dynamics of Poly(vinyl alcohol) Microgel Prepared through Liquid–Liquid Phase Separation

Abstract

The use of technologies based on soft polymer particles represents an effective way to deliver target molecules with a specific function. To design a well-performing delivery system, it is fundamental to rationalize both the aggregation and the structural properties of such particles. In this study, we present the kinetic and structural characterization over time of poly­(vinyl alcohol) (PVA) microgels obtained through a salting-out process in the presence of NaCl. We have analyzed how both the polymer and salt concentrations affect the aggregation process. The aggregation rate as well as the morphology and physico-chemical parameters, such as mass and chain density of the microgels, have been determined through static and dynamic light scattering and discussed in the framework of the diffusion-limited and reaction-limited colloid aggregation. Insights into the polymer chain arrangements and their dynamics have been gained by means of small-angle neutron scattering and neutron spin-echo measurements. As a result, it was found that NaCl induces a liquid phase separation in solution with the formation of spherical PVA microaggregates, which grow under a reaction-limited aggregation mechanism. The particles increase their size and compactness over time. Within the aggregate, the polymer chains are locally organized to form randomly oriented lamellae with a thickness of about 60 Å. The internal dynamics is a complex mixture of diffusion, Zimm dynamics, and possibly effects from crowding with the transition to a Rouse-like behavior. The microparticle preparation based on the salting-out process constitutes a novelty, if compared to the methods already existing and based on the use of chemical cross-linkers, and is a cheap and easy protocol that allows tuning both particle size and density by varying the salt concentration.

Physicochemical Approach to Understanding the Structure, Conformation, and Activity of Mannan Polysaccharides

“…In general, if the second virial coefficient displays positive values, a good solvent condition is suggested, i.e., macromolecular–solvent interactions are favored, whereas negative values indicate a bad solvent condition. 40 , 42 In dilute solutions, the polymer conformation, and consequently the dimension of the coil it forms, depends on the interaction between the polymer and the solvent. 43 In the present case, all of the three polysaccharides exhibit positive values of the second virial coefficient, which in general indicate an efficient water hydration, as already observed for several glycan macromolecules.…”

In situ synthesis of polyynes in a polymer matrix via pulsed laser ablation in a liquid

“…53,54 In order to observe whether we can improve polyyne signal in highly viscous solvents (PVA 4 1%) by increasing the ablation time, we ablated graphite for a longer time (30 minutes instead of 15 minutes) in a solution of PVA10% (B25.91 mPa s at 25 1C), 55 which is the maximum concentration of PVA that can dissolve in water. 56 Increasing the ablation time, only a slight increment of the intensity of polyyne SERS signal is recorded (see inset of Fig. 2) but always in the presence of one broad band without the features observed in the other cases.…”

Towards the Development of Antioxidant Cerium Oxide Nanoparticles for Biomedical Applications: Controlling the Properties by Tuning Synthesis Conditions

“…Dynamic Light Scattering (DLS) analysis was employed to determine the size of CeO 2 nanoparticles as well as to evaluate the possible aggregates formation. DLS measurements were performed using a home-made instrument, composed of a Photocor compact goniometer, an SMD 6000 Laser Quantum 50 mW light source (Quantum Laser, Heaton Mersey, UK) operating at 532.5 nm, a photomultiplier (PMT-120-OP/B), and a correlator (Flex02-01D) from Correlator.com [ 41 , 42 , 43 ]. All measurements were performed at 25 °C, with the temperature controlled through a thermostatic bath.…”