Blob-chain model

The Weill-des Cloizeaux theory assumes that no expansion takes place within subchains shorter than aN. On this assumption we may consider a chain model which consists of Gaussian subcoils, each being made of Nc beads and interacting with one another. With such a subcoil viewed as a blob, this model is often referred to as the blob model. However, it is important to recognize that the Weill-des Cloizeaux theory concerns interactions between beads but not those between blobs. Therefore, contrary to many other authors, the author does not consider it relevant to call it the blob theory. 

Assuming that the blobs have a Gaussian distribution and the Kuhn model of the blob chain applies then... 

The above-mentioned conformational fluctuations can be easily understood on the basis of the blob model [104-109]. For example, this is illustrated for the transition from I to I. Within the chain swollen by excluded-volume... 

If the polymer concentration increases so that the number of high order bead-bead interactions is significant, c>>c =p, (when c is expressed as the polymer volume fraction. Op), the fluctuations in the polymer density becomes small, the system can be treated by mean-field theory, and the ideal model is applicable at all distance ranges, independent of the solvent quaUty and concentration. These systems are denoted as concentrated solutions. A similar description appHes to a theta solvent, but in this case, the chains within the blobs remain pseudoideal so that =N (c/c ) and Rg=N, i.e., the global chain size is always in-... 

The effect of excluded volume on g for linear chains has been calculated, first more qualitatively by Weill and des Cloiseaux193 on the basis of scaling arguments, then by Akcasu and Benmouna202 quantitatively on the basis of the blob-model. The result is as follows... 

Fig. 3.16 Star polymer model for chains tethered to a curved surface. Chains are represented as a string of blobs extending radially from the core of the star.

Furthermore we should stress that the length scales identified by the blob model concern characteristic features of the segment-segment correlations. Thus the appealing picture of a chain build up from well defined individual blobs should not be taken literally. Rather each segment can be taken as the center of its correlated blob, and translational invariance along the chain is not destroyed. 

Temperature blobs have been introduced in [DJ78]. They have been exploited to model the internal structure of a chain for instance in [WC79]. 

In cases of intermediate degrees of chain swelling, the temperature blob approach [21] has been useful in modeling excluded volume effects. It consists in defining a blob comprising a number nt of monomers that obey ideal chain statistics while the blobs themselves show excluded volume effects ... 

Most of the discussion above has been for brushes in a good solvent. Williams [75] has applied the blob model for polymer brushes to grafted chains in a poor solvent. In this case, the blobs no longer repel but attract, leading to a reduction... 

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