Influence of tannin on aqueous layers at a surface of hydrophilic and hydrophobic nanosilicas

Pharmaceutical tannin was stirred with hydrophilic nanosilica A-300, hydrophobic nanosilica AM1 or their mixture (1:1). Tannin microparticles were strongly grinded during mechanical treatment with nanosilica to form much smaller tannin micro- and nanoparticles. The composites were studied with addition of water or acidic solution of HCl or F3CCOOD using low-temperature H-1 NMR spectroscopy, NMR cryoporometry, microscopy, infrared spectroscopy, and quantum chemistry. Treated composites are characterized by reduced affinity toward water in comparison to hydrophilic A-300, but greater than that for initial tannin or hydrophobic AM1. The composites are characterized by increased mobility of organic molecules interacting with adsorbed water, acidic solution or chloroform. Consequently, grinded tannin can be more active in composites with nanosilicas than in the initial powder with microparticles. Chloroform affects location of bound water or acidic solution in voids between silica nanoparticles or weakly porous tannin particles because water and chloroform are practically immiscible and tend to reduce the contact area of one to another. Therefore, smaller water molecule can locate in narrow nanopores inaccessible for CDCl3 or in broad pores to form large domains. Upon location of a mixture of tannin with A-300/AM1 with bound water or acidic solution in the chloroform medium, hydrophobic AM1 nanoparticles can form a shell around hydrophilic A-300/tannin particles with bound water. In this case, contacts between bound water and chloroform can be minimal. Therefore, the system can be stable. This stability is higher for the composites with tannin than that for A-300/AM1 alone.