Some Aspects of the Phenomenon of Coacervation

Probing and Manipulating Noncovalent Interactions in Functional Polymeric Systems

Noncovalent interactions, which usually feature tunable strength, reversibility, and environmental adaptability, have been recognized as driving forces in a variety of biological and chemical processes, contributing to the recognition between molecules, the formation of molecule clusters, and the establishment of complex structures of macromolecules. The marriage of noncovalent interactions and conventional covalent polymers offers the systems novel mechanical, physicochemical, and biological properties, which are highly dependent on the binding mechanisms of the noncovalent interactions that can be illuminated via quantification. This review systematically discusses the nanomechanical characterization of typical noncovalent interactions in polymeric systems, mainly through direct force measurements at microscopic, nanoscopic, and molecular levels, which provide quantitative information (e.g., ranges, strengths, and dynamics) on the binding behaviors. The fundamental understandings of intermolecular and interfacial interactions are then correlated to the macroscopic performances of a series of noncovalently bonded polymers, whose functions (e.g., stimuli-responsiveness, self-healing capacity, universal adhesiveness) can be customized through the manipulation of the noncovalent interactions, providing insights into the rational design of advanced materials with applications in biomedical, energy, environmental, and other engineering fields.

Adhesive Coacervates Driven by Hydrogen-Bonding Interaction

Coacervation plays a critical role in numerous biological activities such as constructing biological tissues and achieving robust wet adhesion of marine sessile organisms, which conventionally occurs when oppositely charged polyelectrolytes are mixed in aqueous solutions driven by electrostatic attraction. Here, a novel type of adhesive coacervate is reported, driven by hydrogen-bonding interactions, readily formed by mixing silicotungstic acid and nonionic polyethylene glycol in water, providing a new approach for developing coacervates from nonionic systems. The as-prepared coacervate is easily paintable underwater, show strong wet adhesion to diverse substrates, and has been successfully applied as a hemostatic agent to treat organ injuries without displaying hemolytic activity, while with inherent antimicrobial properties thus avoiding inflammations and infections due to microorganism accumulation. This work demonstrates that coacervation can occur in salt-free environments via non-electrostatic interactions, providing a new platform for engineering multifunctional coacervate materials as tissue glues, wound dressings and membrane-free cell systems.

Role of pH in the coacervation of the systems: gelatin-water-ethanol and gelatin-water-sodium sulphate

Phase boundary determination, coacervate volume measurements and analysis of the phases have been made to assess the influence of pH on the coacervation of gelatin solutions by ethanol and sodium sulphate. Coacervation was found to be pH dependent. In the ethanol system coacervation was noticeable only within a pH range in the vicinity of the isoionic point; at other pH values either a viscous gel phase or floccules occurred. In the sodium sulphate system, coacervation occurred at all pH values examined. The effect of pH in changing the overall charge on the gelatin molecule is explained in relation to the formation of gelatin coacervates. Finally, the role of the coacervate phase in the microencapsulation of oil and solid particulates is discussed.

Phase relationships in the simple coacervating system isoelectric gelatin: ethanol: water

The influence of molecular weight on coacervation in the system iso-electric gelatin: ethanol: water has been studied. The minimum concentration of ethanol required to produce coacervation decreased as the molecular weight of the gelatin increased. Analysis of the coacervate phase showed that the ethanol content was approximately constant and independent of both the molecular weight of the gelatin and the total concentration of ethanol in the system.