ИСТИНА

In our research we study dissolution of polymers in water saturated with carbon dioxide under high pressure (carbonic acid). It is rather challenging to reveal the conformation of the macromolecules in solutions, which exist only at high pressure, by means of the commonly used methods for conformational characterization, such as light scattering, small-angle neutron and X-Ray scattering. Indeed the polymer solutions under high pressure exist only in the pressurized tightened metal autoclave. Therefore, using of ex situ atomic force microscopy (AFM) as a tool to observe macromolecules as adsorbed on mica from pressurized solutions seems to be easy-to-perform experiment (Figure 1). The solvent that we used, carbonic acid, combines two important properties thanks to which it appears to be very beneficial solvent for biomedical applications. Those are strong antimicrobial activity at the very moment of coating formation on some medical device and remaining absolute biocompatibility later on, when using this device with the adsorbed coating in the human body. Moreover, this solvent is appropriate from the viewpoint of developing area of green chemistry. Indeed after the dissolution of polymers or formation of some nanoobjects in the carbonic acid no neutralisation, washing out or dialysis is required for removal of the solvent. Thus carbonic acid is a solvent that is safe for the environment. Indeed after decrease of the applied pressure carbonic acid turns spontaneously into H2O and CO2, which are to be removed easily. We succeeded in dissolution of chitosan in carbonic acid [1]. With the aim of AFM we demonstrated that chitosan macromolecules in carbonic acid self-organise into stable elongated cigar-like aggregates (Figure 2). It was experimentally found out and theoretically confirmed that the size of the aggregates increases with increase of the number of charged units. We also demonstrated that it is possible to form micelles of the diblock copolymers with one hydrophobic block and one polar block in the solutions of carbonic acid. We visualized with AFM spherical micelles with polystyrene core and poly(4-vinylpiridine) corona (Figure 3).