The gel point of end-linked model networks is determined from computer simulation data. It is shown that the difference between the true gel point conversion, p c , and the ideal mean field prediction for the gel point, p c,id , is a function of the average number of cross-links per pervaded volume of a network strand, P , and thus, contains an explicit dependence on junction functionality f . On the contrary, the amount of intra-molecular reactions at the gel point is independent of f in a first approximation and exhibits a different power law dependence on the overlap number of elastic strands as compared to the gel point delay p c − p c,id . Therefore, p c − p c,id cannot be predicted from intramolecular reactions and vice versa in contrast to a long standing proposal in literature.Instead, the main contribution to p c − p c,id for P > 1 arises from the extra bonds (XB) needed to bridge the gaps between giant molecules separated in space and scales roughly ∝ (P − 1) −1/2 . Further corrections to scaling are due to non-ideal reaction kinetics, composition fluctuations, and incompletely screened excluded volume, which are discussed briefly.

Tendomers (pairs of rotaxanes connected at the first slide ring) display a jump-like strain softening under an applied external force with a switching point that is set by the slide ring density.

Laboratory flooding experiments with polymer solutions in sandstone cores are usually performed for studying the mechanisms of polymer flooding processes, and for measuring the properties which de processes, and for measuring the properties which describe the process. A determination of the slug profile of the polymer solution allows the measurement profile of the polymer solution allows the measurement of retention characteristics while taking into account the portion of the pore volume not in contact with the polymer solution. By means of a simple tracer test with the use of inorganic salts, the inaccessible pore volume for a xanthan-type and a scleroglucan-type polymer in highly saline brine was measured. The amount of inaccessible pore volume had to be considered in the determination of retention isotherms for these polymers in core flooding experiments. An analytical polymers in core flooding experiments. An analytical simulation model according to immiscible displacement theory was applied for simulating linear displacement experiments effectively by considering inaccessible pore volume and retention characteristics. Introduction In the present paper, laboratory flooding experiments conducted with the use of two representative products from the class of biopolymers stable toward salt (scleroglucan and xanthan) are described. The purpose is to measure those parameters which exert an essential influence on the oil recovery process, and which are required for simulating process, and which are required for simulating polymer flooding processes. The quantitative polymer flooding processes. The quantitative determination of the pore volume inaccessible to polymer molecules, and the consideration of this quantity for the calculation of retention values are thereby of special importance. An improvement of the displacement efficiency during polymer flooding is achieved by matching of the mobility of the displacing phase (water) to that of the displaced phase (oil). (1) In the ideal case, a decrease in the mobility ratio to values M less than unity gives rise to piston-like displacement. The mobility ratio can be piston-like displacement. The mobility ratio can be favorably influenced by the addition of polymers to the flood water. This is achieved by means of an increase in viscosity as well as a decrease in permeability for the displacing phase (aqueous polymer permeability for the displacing phase (aqueous polymer solution). The reduction in mobility of polymer solution due to the increase in viscosity and decrease in permeability as compared to water, is described with permeability as compared to water, is described with the use of the resistance factor RF: (2) In contrast, the residual resistance factor RRF describes only that effect of the permeability reduction which is caused by the polymer material which is retained in the porous medium, under steady-state conditions. (3) For economic reasons, only a limited volume of polymer solution (polymer slug) is injected into a reservoir. The polymer slug is driven through the reservoir by means of postflooding with water. During its travel through the reservoir from the injection well to the producing well, the polymer slug is subject to various influences which adversely affect its stability. They can be described by means of a comparison of the concentration profile for a polymer solution emerging from a model of the porous medium with that for the injected slug /5/. P. 467

We show by computer simulations that a melt of pairwise connected star polymers provides an approximation for the reference conformations of real polymer chains in a network. Reference conformations are needed to normalize the experimental data related to the chain size (multiple quantum NMR, scattering, polarization, etc.) or data from advanced tools for measuring the phantom modulus in simulations. The latter allows then to separate the contributions of the correlation hole and finite extensibility (FE) from other contributions to the phantom modulus. Shear simulation data of the networks with entanglements switched off serve as a test of these approaches and as a critical test for the reference conformations. A comparison of the different measurements shows that for analyzing the simulation data by the advanced tools, the correlation hole corrections outnumber the corrections of FE or the combined effect of loops, network defects, and excess strain for tightly cross-linked entanglement free-model networks.