If the polymer chain is long, its size can be described by simple proportion ratios called scaling laws: When the number of monomers N is doubled, the size is increased by the scaling factor 2^v. The exponent v is universal in the sense that it is the same for all polymer chains although it depends on the polymer concentration.
    In the blob model de Gennes represents the concentration by a sphere (blob). The diameter of the sphere is given by the average distance x between two chains and increases as concentration decreases. Inside the sphere the chain segment is swollen like in a good solvent (v= 3/5). For segments longer than x the blobs can be taken as the basic units and then the law for concentrated solutions holds (v= 1/2).
    The blob model is used to describe polymer solutions, crosslinked polymers (gels), polymer welds, interfaces, polymers at surfaces etc.

The basis for the modern physics of polymers was laid by pioneers such as P. Debye, W. Kuhn, H.A. Kramers, and P. Flory. A milestone was set in 1949 when Flory (Nobel Prize 1974) described the size of a polymer chain. He took into account that a certain volume occupied by the chain segments (self-excluded volume) is not available to the other segments of the chain.
    The next phase depended on new experimental methods. With neutron scattering one could determine the chain dimensions. Using light scattering techniques, which advanced after the invention of the laser in 1960, one could measure the movements of polymers. At the same time sophisticated theoretical methods developed (functional integrals, correlation functions, renormalisation groups, and the techniques of manybody theory), which were first applied to polymers by S.F. Edwards. With high speed computers and numerical methods models of polymers could be tested using computer simulations.
    With classical physics as a basis, by using the latest experimental results and theoretical tools, Pierre-Gilles de Gennes reshaped and developed the physics of polymers.