Solvated polymer layer

Fitting the data shown in Figure 3 reveals a dry polymer thickness of 2.6 nm, which corresponds to an adsorbed mass of 290 100 ng/cm. This implies an average distance of grafting points of about = 3.5 nm and an average PEG monomer volume fraction of 4> = 0.17 of the uncompressed, solvated polymer layer. 

The presence of a solvated polymer layer, especially the outer layer composed of water-soluble, flexible PEG side chains, proves to be favorable to the reduction in friction. The observed lubricity with the duration of polymer deposition is, therefore, a function of the development of this solvated polymer layer on the surface. Not only is the coverage increased over time, but as discussed below, the increase in the packing density drives the PEG chains to form more extended conformations as well. 

There is already a large number of different conductive polymers. A typical monomer is 3-methylthiophene, which can be electrically polymerized to a polymer coupled by the 2-and 5-positions of the monomer. In the oxidized form, usually called doped , the chains contain positive charges at about every fourth monomer unit. In order to keep the polymer layer electrically neutral, also counter anions should be present in the polymer matrix. It is analytically interesting that the diffusion rate of these counter anions controls the rate of oxidation and reduction of the polymer, and the diffusion rate depends on the size, degree of solvation etc. of the anion. Hence, by a suitable choice of the polymer, it should be possible, at least in principle, to tailor-make sensors for different anions. In addition, it has been shownthat electrically neutral polymers can be incorporated from the solution into the polymer matrix during the polymerization process. This of course extends enormously the possibilities for developing selective sensors without undue efforts to synthesize new electrically polymerizable monomers. 

An adsorbed layer of a well-solvated polymer (good solvent conditions) creates a steric barrier protecting the particles from flocculating. This type of interaction is very common in food and feed systems as a result of protein adsorption. Under some conditions, steric repulsion could also be caused by the adsorption of surface-active polysaccharides, such as gum arabic. 

For effective stabilization the droplet surfaces should be fully covered by the adsorbed surfactant or polymer, otherwise uncovered regions of adjacent particles or droplets may come into contact with each other, or bridging flocculation between them may occur. Further, the stabilizing surfactant or polymer should be strongly adsorbed (firmly anchored) to the surfaces. Molecular structure and solvation, adsorption layer thickness and hydrodynamic volume, and temperature also determines the effectiveness of steric stabilization [75-79]. One way to predict whether steric stabilization is likely for a given dispersion is to estimate the protrusion distance of the surfactant or polymer chains [80]. 

When the polymer adsorbs in a loose train-loop-tail-like structure, as shown in Figure 15.11, the polymer segment density in the adsorbed layer is usually low, so that A3 == A2. Furthermore, as the adsorbed layer is highly solvated and (nearly) freely penetrable for counterions, the electrostatic potential at x = is relatively low. Such flexible, loopy polymer layers may protrude into the surrounding medium over a... 

This is produced by the presence of adsorbed surfactant and/or polymer layers. These layers wUl extend from the particle or droplet surface to some distance in the bulk solution. Provided these layers are strongly solvated by the molecules of the medium, they produce repulsion as a result of the unfavourable mixing of these chains. When two particles or droplets approach to a distance of separation h that is smaller than twice the adsorbed layer thickness IS, overlap and/or compression of these layers may take place, resulting in strong repulsion. In addition, when these adsorbed layers begin to overlap, the chains lose configurational entropy, resulting in an additional repulsion. 

When two particles or droplets containing adsorbed polymer layers (with an adsorbed layer thickness 6) approach to a distance of separation h whereby these layers begin to overlap, i.e., when h < 26, repulsion occurs as a result of two main effects [6]. The first repulsive force arises from the unfavorable mixing of the polymer layers when these are present in a good solvent (i.e., the chains are strongly solvated by the medium). The unfavorable mixing of... 

Studies of the thickness of adsorbed layers of copolymers at liquid interfaces using neutron reflectivity showed strong dependence of the structure of adsorbed polymer layer on the distribution of monomeric units within polymer chains (71). In the case of a diblock copolymer with both blocks selectively solvated by water and oil phases, the chains stretch at the interface forming thick adsorbed layers. With a random copolymer having the same composition as the diblock copolymer, the interfacial thickness is significantly smaller as a result of the localization of... 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

---