Polymers external fields

A natural extension of the studies in Sec. VIIA would be the investigation of the drift of a polymer chain in random environment when a constant external field B is applied in one direction [21,22]. 

Phase behavior in complex fluids such as polymer blends and block copolymers has been a rich area of the chemical sciences. Near-critical and other transitional phenomena are frequently prominent. Since molecular movement in viscous systems such as these is comparatively slow, phase transitions can be studied more easily in time, and manipulated by quenching and other external influences. Processes for controlled growth of ordered materials are often readily influenced by diffusion, a variety of external fields, and the influence of interacting boundaries, or flow. 

These postulated mechanisms3 are consistent with the observed temperature dependence of the insulator dielectric properties. Arrhenius relations characterizing activated processes often govern the temperature dependence of resistivity. This behavior is clearly distinct from that of conductors, whose resistivity increases with temperature. In short, polymer response to an external field comprises both dipolar and ionic contributions. Table 18.2 gives values of dielectric strength for selected materials. Polymers are considered to possess... 

By definition, polymer brushes are made up of polymer chains grafted (tethered) by one end to a surface or an interface (Fig. 1) [ 1 - 3]. The density can be small or high in the latter case, the polymer chains are crowded and forced to stretch in order to avoid other chains. This results eventually in an equilibrium condition where no external field is necessary to force the chains into this geometry. 

In general, the motion of a polymer chain in solution is governed by intermolecular interaction, hydrodynamic interaction, Brownian random force, and external field. The hydrodynamic interaction consists of the intra- and intermolecular ones. The intramolecular hydrodynamic interaction and Brownian force play dominant roles in dilute solution, while the intermolecular interaction and the intermolecular hydrodynamic interaction become important as the concentration increases. 

In addition to the above effects, the intermolecular interaction may affect polymer dynamics through the thermodynamic force. This force makes chains align parallel with each other, and retards the chain rotational diffusion. This slowing down in the isotropic solution is referred to as the pretransition effect. The thermodynamic force also governs the unique rheological behavior of liquid-crystalline solutions as will be explained in Sect. 9. For rodlike polymer solutions, Doi [100] treated the thermodynamic force effects by adding a self-consistent mean field or a molecular field Vscf (a) to the external field potential h in Eq. (40b). Using the second virial approximation (cf. Sect. 2), he formulated Vscf(a), as follows [4] ... 

Most data about the Ludwig-Soret effect of polymers in solution have been obtained from thermal field-flow fractionation (TFFF), developed by Giddings and coworkers [17,18]. TFFF is one member of the family of field-flow fractionation techniques, which are all characterized by a laminar flow of the polymer solution or colloidal suspension within a relatively narrow channel. An external field, which may be gravitation, cross-flow, or temperature as in TFFF, is applied... 

In the previous sections, theories were reviewed where the optical properties of polymer liquids were cast in terms of the microscopic properties of the constituent chains. The dynamics of polymer chains subject to external fields that orient and distort these complex liquids are considered in this section for a variety of systems ranging from dilute solutions to melts. Detailed descriptions of theories for the dynamics and structure of polymer fluids subject to flow are found in a number of books, including those by Bird et al. [62], Doi and Edwards [63], and Larson [64],... 

---