No abstract

As a continuation of a previous paper, the rheological properties of a concentrated solution of rod-like macromolecules are discussed. A procedure for calculating the stress tensor for a given flow history is presented and, as a special case, simple steady shear flow is studied in detail. Some interesting features of the results are : (i) the steady state viscosity ~( 0 ) at zero shear rate and the first and second normal stress coefficients Yl(0) and Y2(0) all depend very strongly on molecular weight M and mass concentration p, with ~(0)cc p3M6 and Yl(0), Y2(0)a p5M13; (ii) Y 2 ( g ) is negative and about -2/7 of Y1(g) where g is the velocity gradient; (iii) the shear stress shows an extremum as a function of shear rate, indicating an instability of flow at certain shear rate. As a byproduct of the theory, a stress-optical law is predicted.

When an electric field is applied to an ionic gel in a buffer solution, the anode side of the gel shrinks if the gel is contacting with the electrode, while it swells if the gel is placed with sufficient separation from the electrode. We calculate the changes of ion concentration profiles under an electric field, taking account of ion transports and electrochemical reactions. Combining these results with Flory's theory for the swelling of ionic gels, we explain the above phenomena. We predict that the swelling behavior is governed by the concentration of the dominant ions and that the swelling speed is proportional to the square of the electric current.

The microdomain structure in block-copolymer melts with short A blocks which strongly attract each other separated by long B blocks is studied for the case of narrow interphases between the microdomains.It is shown that as the temperature is lowered (or attraction of A blocks becomes more intensive), the behavior of the system changes qualitatively: instead of the usual strong segregation regime a new regime emerges which we define as the "superstrong segregation regime". In this regime A chains within the micelles become practically completely extended and steric restrictions on the chain conformations in the micelles become important. Although the superstrong segregation regime is not characteristic for ordinary block copolymers, it is easily realized for the case when one of the blocks is ionomeric. By considering the limiting case of one monomer link in the A block we obtain the results for microdomain (multiplet) structure in random ionomers. In most cases multiplets in ionomers correspond to microdomains in block copolymers in the superstrong segregation regime. We calculate the limiting size of the multiplet, the average distance between the multiplets, and the expansion of the chains in ionomer melts. The comparison of multiplets for random and telechelic ionomers is also performed.

In the drying process of polymer solution droplets, we propose an experimental procedure for visualizing the solute concentration profile by combining the fluorescent microscopy with the lateral profile observation. We have conducted a dynamical observation of the transport process of the solute polymer toward the edge that causes the "coffee stain phenomenon". We have found that the polymer concentration increases sharply near the edge, while it remains almost constant in the central region until the last stage of drying. The method is useful to understand the dynamical process that occurs near the contact line.