We have presented a systematic small angle neutron scattering
investigation
of ring–linear blends, where we vary either the ring volume
fraction for a given ring in a long linear matrix or the matrix length
at a low ring fraction. We found that the ring radius of gyration
(R
g) shrinks with increasing ring fraction
and nearly reaches the R
g of the ring
melt at a volume fraction of ϕR = 0.5. At the same
time, the fractal dimension, which is close to a Gaussian conformation
at low ϕR, decreases to the value of the ring melt.
Aside from very short matrices, the ring size is independent of the
host length. Following a random phase approximation treatment, the
effective Flory–Huggins parameter (χF,RL)
is negative and independent of ϕR, signifying ring–linear
attraction that leads to ring–ring repulsion. χF,RL decreases with decreasing ring size, which might be related to the
decreasing possibility of threading events, when the ring size becomes
smaller. The ϕR-dependent data in the cross-over
regime between low Q Porod scattering ∼ Q
–4 and polymer RPA contribution displays
an intermediate Q
–2 regime, the
intensity of which increases proportional to ϕR.
The origin of this Q
–2 contribution
is not clear but may be related to critical fluctuations or microphase
separation induced by a nonlocal positive contribution to χF,RL. The experimental results fit well into the general picture
that is mainly based on simulations, even though in detail, quantitative
differences are obvious. Finally, our results are in qualitative agreement
with earlier studies on polystyrene ring–linear blends.