ABSTRACT
Natural and synthetic polymers are used in numerous applications, and the interfacial phenomena at polymer surfaces play an important role in the efciency of their use, especially in the case of medical, food, and adsorption applications (Zhang et al. 2009, Jayakumar et al. 2010a,b, Long et al. 2011). Here we will analyze the interfacial phenomena with participation of different natural and synthetic polymers both hydrophilic and hydrophobic. In contrast to solid materials, polymers as soft materials can strongly change their texture during interaction with water or other solvents (a striking example with starch swelling and gelatinization). With changing temperature and hydration, polymer chains exhibit a complex hierarchy of dynamic processes, e.g., starting with very fast and local conformational rearrangements on the ps scale (γ relaxation at low temperatures), and extending into the range of seconds for slow, diffusive, and cooperative motions at T > Tg (Doi and Edwards 1986, Kimmich and Fatkullin 2004, Saalwächter 2007). These processes are strongly affected by water or other solvents because of swelling, plasticizing, bonding, and other effects. As a whole, the behavior of polymers and bound water at the interfaces of solid and soft materials depends on several factors such as topology, topography, porosity, and chemistry of a surface, content and type of solvents and/or co-adsorbates, polymer length, cross-linking degree, temperature, etc. NMR techniques can give information on all the mentioned factors for polymers in native state, as well as differently treated (dried, heated, frozen, thawed, MCA, HTT, etc.). This is especially important for hydrogels, hydrated natural polymers, and materials, which can strongly change their characteristics during drying, wetting, or suspending. Therefore, the nature of the interactions between small guest molecules or ions (such as water, organics, salt ions) and large soft host structures (such as carbohydrate polymers, lipid membranes, proteins, swollen gels, cryogels) is of importance in many aspects. The properties of these structures can be intermediate between those of hard solids (crystalline, semicrystalline, amorphous) and liquids. Water bound to polymers can be divided into several types (strongly bound water [SBW] and weakly bound water [WBW], strongly associated water [SAW], and weakly associated water [WAW], nearly bulk water) as well as in the case of solid adsorbents discussed earlier.
