Semi-dilute solutions intramolecular

Since the transition from dilute to semi-dilute solutions exhibits the features of a second-order phase transition, the characteristic properties of the single- chain statics and dynamics observed in dilute solutions on all intramolecular length scales, are expected to be valid in semi-dilute solutions on length scales r < (c), whereas for r > E,(c) the collective properties should prevail [90]. 

In the previous chapter, we considered the structures of single chains in the dilute regime. Now we may inquire, how these become altered in semi-dilute solutions. Discussions can be based on the pair distribution function of the individual chains, thereby focusing on the structure of single chains in states where chains overlap and interpenetrate. We choose for this intramolecular pair correlation function a symbol with a hat, g(r), to distinguish it from the general pair distribution function g(r) which includes monomers from all chains. 

Physico-chemical behaviour in aqueous solution was studied by viscosity measurements. Expected associative behaviour has been evidenced in pure water, while in salt media, the associative behaviour strongly depends on PCL chains length. For shorter PCL chains, intramolecular hydrophobic interactions are predominant, even in the semi-dilute regime. This non-classical behaviour for an associative polyelectrolyte opens the way to the conception of amphiphilic matrices with hydrophobic clusters for controlled release applications. 

Fedors has proposed a relationship between ( /l and c, which is valid over a wide concentration range and can be used to measure > 1 from the determination of the relative viscosity at a single polymer concentration. Nishio and Wada have observed the transition from intramolecular motion within a polystyrene molecule to a co-operative diffusion process on passing from dilute to concentrated solutions, where D also increased despite a corresponding increase in viscosity. The radius of gyration of polymers in semi-concentrated solutions has been investigated by Aharoni and Walsh. ... 

However, the rheological behaviors of associative polymers can be divided into a dilute region and a semi-dilute region by a critical concentration c. At concentrations below c, it is in a dilute region where intramolecular hydrophobic associations within the polymer dominate the behavior of the polymer, and the viscosity decreases with the solution concentration increase. At a concentration above c, it is in a semi-dilute region where intermolecular associations between polymers control the polymer rheology and the viscosity increases with the solution concentration increases (Taylor and Nasr-El-Din 2007). 

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