Polymer interface theories

When attempting to use these polymer interface theories (1-22) in planning and interpreting experiments, we encounter two problems associated with the interaction parameter in polymer-polymer systems. First we have to find a way of determining the values of the interaction parameters for the polymer pairs of interest. There is as yet no general experimental procedure which allows us evaluation of the x parameter. Without reliable values of the x parameter, comparative tests of the competing theories can only be made qualitatively. Secondly, to be able to use these theories with more confidence we have to have some idea about the dependence of the x parameter on concentration, temperature, etc. 

Because of these uncertainties, equations 1, 2, 3, 4, and 5 may not be relied upon as a means of quantitative evaluation of A until more data for other polymer-solvent systems become available. The equation-of-state thermodynamics is, however, useful in its ability to give us insight into the physical factors and their relative magnitudes which contribute to the polymer-polymer interaction parameter. The results in this work clearly show that the dependence of A on concentration and temperature is moderate. This gives a justification as a good approximation to the use of a constant polymer-polymer interaction parameter in the polymer interface theories where the polymer concentration encompasses the whole range Wi = 0 to 1 across the phase boundary. 

In numerous applications of polymeric materials multilayers of films are used. This practice is found in microelectronic, aeronautical, and biomedical applications to name a few. Developing good adhesion between these layers requires interdiffusion of the molecules at the interfaces between the layers over size scales comparable to the molecular diameter (tens of nm). In addition, these interfaces are buried within the specimen. Aside from this practical aspect, interdififlision over short distances holds the key for critically evaluating current theories of polymer difllision. Theories of polymer interdiffusion predict specific shapes for the concentration profile of segments across the interface as a function of time. Interdiffiision studies on bilayered specimen comprised of a layer of polystyrene (PS) on a layer of perdeuterated (PS) d-PS, can be used as a model system that will capture the fundamental physics of the problem. Initially, the bilayer will have a sharp interface, which upon annealing will broaden with time. 

Once intimate contact is achieved, bonding of the ply interfaces can occur. The mathematical relationships between interply bond formation and processing temperature and time were discussed in Section 7.3. The analyses are based on the theories explaining strength development of a polymer-polymer interface and crack healing in polymers. 

Polymer brush theory was applied to the compatibilization of homopolymers A and B by an AB diblock by Leibler (1988). The reduction in interfacial tension due to the segregation of copolymers to the interface was calculated. Considering a film of block copolymers at the homopolymer-homopolymer interface, the free energy was found to be... 

To use an expression such as Eq. (9-19) for predicting droplet sizes, one also needs a value for the interfacial tension F, which for polymer-polymer interfaces are hard to measure. However, the theory of Helfand and Sapse (1975) allows F to be estimated from the interfacial width A ... 

Theories of the polymer Interface have been presented by, among others, Helfand using lattice calculations or diffusion calculations. They yield the following scaling relations. 

Recently, much attention is being placed on fibres-reinforced/polymer systems as subjects of study. It was caused by increasing emphasis on high performance reinforced polymer composites. The concept of acid/base interactions across the fibre/polymer interface was noted particularly and the relevance of acid/base theories to the behaviour of po-... 

Theories of the interfacial tension were reviewed by Wu [1], who also provided an extensive tabulation of experimental values for amorphous polymer-polymer interfaces [2], including both homopolymers and copolymers, at several temperatures. For example, the interfacial tensions between a number of pairs of homopolymers [2] are listed in Table 7.3. 

Shull KR, Kramer EJ. Mean field theory of polymer interfaces in the presence of block copolymers. Macromolecules 1990 23 4769-4779. 

Another theoretical aspect of adhesion can be optimized with surface treatment. The interdiffusion theory described by Voyutski [6] involves the diffusion of macromolecular chains across a polymer interface. In this case the interface is transformed progressively to a wide interphase. Welding of composites is then the main technique that can enhance this particular aspect. This welding can be performed with ultrasonic, electric induction, or resistance techniques [7]. 

We are interested in the following questions How does a polymer move or flow on its own monolayer, or more generally, how do macromolecules slide past each other What are the consequences of the autophobic behavior between grafted and free polymers for dewetting What is the value of the friction coefficient at such polymer-polymer interfaces After a brief description of our experimental conditions, we present the experimental results, which are discussed in light of the theory described above. Finally, we show what we can learn about molecular parameters controlling interfacial properties. 

Helfand, E., 1975. Block copolymers, polymer-polymer interfaces, and theory of inhomogeneous polymers. Acc. Chem. Res. 8 (9), 295-299. 

D.J. Meier, and T. Inoue, Polymer blends theory of interface, Poiym. Prepr. Japan 24 293 (1975). 

The interpenetration between the polymer chains and the mucin chains in the mucosa is believed to be the main physical mechanism for mucoadhesion, and together with the adsorption theory is the most accepted in the literature. This mechanism was first proposed in the polymer-polymer interface" " but was later applied to mucoadhesion due to the polymeric nature of mucin. Basically, during interpenetration the molecules of the mucoadhesive and the mucin molecules in the mucosa are brought into contact, and due to the concentration gradient the polymer chains penetrate into the mucin network with specific diffusion coefficients (Figure 52.4). 

There is no unified theory to explain the process of mucoadhesion. The total phenomenon of mucoadhesion is a combined result of all these theories. First, the polymer gets wet and swells (wetting theory) followed by the noncovalent (physical) bonds created within the mucus-polymer interface (electronic and adsorption theory). Then, the polymer and protein chains interpenetrate (diffusion theory) and entangle together to form further noncovalent (physical) and covalent... 

Another theory claims that a protective complex between the metal and the CP is formed in the metal-polymer interface. Kinlen et al. [73] found by electron spectroscopy chemical analysis (ESCA) that an iron-PANl complex in the intermediate layer between the steel surface and the polymer coating is formed. By isolating the complex, it was found that the complex has an oxidation potential 250 mV more positive than PANI. According to Kinlen et al. [73], this complex more readily reduces oxygen and produces a more efficient electrocatalyst. 

Metal/polymer interfaces which do follow the Schottky model theory, and PLEDs, for which Equation 19.12a is valid, have been often observed in experiments where deposition and test conditions were carefully controlled [4,6,8,73,74,77,78]. 

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