Structure of Polymer Rings in Linear Matrices: SANS Investigation

We have presented a systematic small angle neutron scatteringinvestigationof ring-linear blends, where we vary either the ring volumefraction for a given ring in a long linear matrix or the matrix lengthat a low ring fraction. We found that the ring radius of gyration(R (g)) shrinks with increasing ring fractionand nearly reaches the R (g) of the ringmelt at a volume fraction of & phi;(R) = 0.5. At the sametime, the fractal dimension, which is close to a Gaussian conformationat low & phi;(R), decreases to the value of the ring melt.Aside from very short matrices, the ring size is independent of thehost length. Following a random phase approximation treatment, theeffective Flory-Huggins parameter (& chi;(F,RL))is negative and independent of & phi;(R), signifying ring-linearattraction that leads to ring-ring repulsion. & chi;(F,RL) decreases with decreasing ring size, which might be related to thedecreasing possibility of threading events, when the ring size becomessmaller. The & phi;(R)-dependent data in the cross-overregime between low Q Porod scattering & SIM; Q (-4) and polymer RPA contribution displaysan intermediate Q (-2) regime, theintensity of which increases proportional to & phi;(R).The origin of this Q (-2) contributionis not clear but may be related to critical fluctuations or microphaseseparation induced by a nonlocal positive contribution to & chi;(F,RL). The experimental results fit well into the general picturethat is mainly based on simulations, even though in detail, quantitativedifferences are obvious. Finally, our results are in qualitative agreementwith earlier studies on polystyrene ring-linear blends.