## 4 Features of the Transport and Dissolution of Substances in Polymer Nanocomposites  
The separation of polymer nanocomposite membranes is contingent on dissolution mechanism. Dissolution entails the conversion of polymer nanocomposites from their natural and particulate physical form into its ionic components [184]. Polymer dissolution into a solvent entails two transport routes, which are solvent diffusion and chain disentanglement [185]. Diffusivity is computed by measuring the mobility of discrete molecules that transient across the voids amid the polymeric chains in a membrane material [184]. The mechanism of dissolution comprises of the interactions of the infiltrating molecule at the molecular-scale in conjunction with the membrane polymer. The mechanism is contingent on the assumption that each molecule is sorbed at one interface of the membrane transported via diffusion through the membrane by means of voids amid the polymeric chains (or free volume), and desorbed at the other end of the interface [186]. This is attained by the affinity of the composite together with the polymer membrane, which is dependent on its capability to dissolve [187]. In addition, the mechanism is contingent on desorption, in which nano materials adsorbed at the polymer-liquid interface impulsively partition into the liquid [188]. During the course of diffusion and desorption, the nano materials released continue in nano particulate nature; however, their composition, morphology, or surface properties could change in the course of the release process or at the end of the release process. In dissolution, the nano materials do not remain in the particulate form at the end of the release process; nonetheless, subsequent reformation of nanoscale particles from the dissolved residuals is possible, should there be favorable conditions [188]. The transport operation of a given infiltrate is not the same for all polymers. The characteristics of nanocomposite transport is contingent on the free volume within the polymer and polymer chains' segmental mobility [189]. Polymer molecules could be considered as chains that arise from flexible segments (known as Kuhn segments), entangled with one other. Their shape position can be changed through two means; which are rotation of the Kuhn segments and reptation of the whole molecule. The Kuhn segments in a polymer molecule can rotate in any direction owing to the thermal vibrations of the atoms (see Figure 6). As a result, the molecule can locally alter its shape within a blob or alter its whole shape under load; should there be any need for it. The rotations of the Kuhn segments results in polymer flexibility. Polymer chains segmental mobility is influenced by the degree of unsaturation, the degree of cross-linking the degree of crystallinity, and the type of substituent. Introducing bulky or polar substituents on a polymer chain affects the transport process. The transport properties is greatly influence by the glass transition temperature of polymers. Polymers that display low glass transition temperatures are accorded with a superior segmental mobility and higher diffusivity [190]. When nanoparticles are added into polymer matrices, the composite significantly alters the optical [191], mechanical [192], structural, and electrical [193] properties in relation to the host polymer. This is illustrated in Figure 7. Polymer-surface interactions is recognized to be instrumental in the determination of dynamics of interfacial polymers [194]; this governs the macroscopic characteristics of polymer nanocomposites [195]. Usually,  
Figure 6: Rotation of the Kuhn segments resulting in alteration of polymer shape as a result of thermal vibration of atoms. attractive or repulsive polymer-surface interactions leads to an enhanced mobility or slower aging. This is documented in the study of thin films [196] or nanopores [197], for mobility in confined polymers.