Chains grafted/tethered

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. 

Fig. 2. Schematic of a flat, tethered layer. L is the average layer thickness while d is the average spacing between chain graft points on the surface...

To investigate these interactions, we determined the effect of compressing two surfaces that are sparsely covered with end-grafted AB diblocks [19]. We consider symmetric diblocks where the length of the A and B blocks are equal. There are two cases (1) the chains are tethered by the B end, and (2) they are grafted by the A end. In both cases, the interactions between the surfaces display an attractive region, even when the blocks are incompatible. 

The structure formed when one end of a chain is tethered to d = 2 surface, is referred to as a grafted layer or more commonly as a brush . Brushes can be made by attaching a functional group to one end of a chain that can then bind to the surface. The binding energy can either be quite high (several hundred kaJ), in which case the end is chemically attached,or of order ten kaT, in which case it is physi-adsorbed. Diblock copolymers, in which one of the blocks (usually the shorter one) adsorbs strongly to the surface, while the other does not, also form brushes, as well as a... 

Even more interesting electrochemical properties were discovered for the polymer brash tethered to an electrode surface and functionalized with bound redox species [30]. Os(dmo-bpy)2 (dmo-bpy = 4,4 -dimethoxy-2,2 -bipyridine) redox groups were covalently bound to the P4VP brash chains grafted on an ITO electrode. The polymer-bound redox species were found to be electrochemically active at pH <5 when the polymer is... 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

The Alexander model and its descendants impose strong restrictions on the allowed chain configurations within the tethered assembly. The equilibrium state thus found is subject to constraints and may not attain the true minimum free energy of the constraint-free system. In particular, the Alexander model constrains the segment density to be uniform and all the chain ends to be at the same distance from the grafting surface. Related treatments of curved systems retain only the second... 

Tethering may be a reversible or an irreversible process. Irreversible grafting is typically accomplished by chemical bonding. The number of grafted chains is controlled by the number of grafting sites and their functionality, and then ultimately by the extent of the chemical reaction. The reaction kinetics may reflect the potential barrier confronting reactive chains which try to penetrate the tethered layer. Reversible grafting is accomplished via the self-assembly of polymeric surfactants and end-functionalized polymers [59]. In this case, the surface density and all other characteristic dimensions of the structure are controlled by thermodynamic equilibrium, albeit with possible kinetic effects. In this instance, the equilibrium condition involves the penalties due to the deformation of tethered chains. 

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