Diffusion of Tracer Molecules within Symmetric Diblock Copolymers

Abstract

Forced Rayleigh scattering has been used to investigate tracer diffusion of a tetrahydrothiophene-indigo derivative (TTI), a photochromic dye molecule, in a macroscopically isotropic lamellar poly(styrene-b-isoprene) diblock copolymer of relative high molecular weight. As anticipated from the large difference of segmental mobility between the constituent blocks, three relaxation processes termed fast, intermediate, and slow, respectively, have been observed as a function of temperature and grid spacing for the decay curve of scattered light from the photoinduced grating in the experiments. The fast process exhibits a q2 dependence, which is characteristic of Fickian diffusion, whereas the slow process is independent of q. Model calculations have identified the nature of these two processes. In addition, the role of the size of the grid spacing chosen in these experiments, relative to the lamellar period of the microstructure, has been elucidated. A means of extracting diffusion coefficients for TTI in PI and PS lamellae from the experimental results has been demonstrated. A comparison of the diffusion coefficients obtained from the PI and PS lamellae in the block copolymer with those of TTI diffusion in PI and PS homopolymers revealed differences in the temperature dependence between the homogeneous and microstructured materials.

Homopolymer and small‐molecule tracer diffusion in a gyroid matrix

“…Zielinski et al15 also observed fast and slow modes in FRS measurements of TTI tracer diffusion within a lamellar PS–PI diblock copolymer ( M = 176,400 g/mol) at temperatures ranging from −40 to 100 °C. The fast mode was diffusive and was attributed to diffusion within the PI domains, but in contrast to our results, the diffusion coefficients were retarded by less than an order of magnitude compared with TTI diffusion in PI.…”

“…However, the effects of different rates of diffusion within each domain and the connectivity of the fast domain have been shown to influence the tracer diffusion particularly strongly. For instance, Zielinski et al15 studied the tracer diffusion of a small dye molecule within a lamellar SI diblock copolymer and found two distinct modes of relaxation. The fast mode was attributed to diffusion within the PI domains, and the slow mode was attributed to the equilibrium exchange of the dye between PS and PI.…”

Probe diffusion in homogeneous diblock copolymers

“…A memweight characteristics of the block copolymers discussed in this work are summarized in Table I, brane of this sort, in other words, isotropic on both small and large size scales, is expected to have along with corresponding homopolymer data. 30,54 Absence of microstructural ordering was confirmed physical properties intermediate to those of the parent homopolymers (much like a random coby transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and DSC. polymer).…”

“…Polymeric membranes that are not macbile phase if microdomain co-continuity exists. [29][30][31][32][33][34][35][36] roscopically phase separated can be tailored Microstructural ordering in block copolymers through the use of block copolymers.…”

Spatially heterogeneous dynamics in thermoset resins below the glass-transition temperature

“…The complicated transport phenomena observed in these diblock copolymer systems in the microphase regime have been attributed to these structural heterogeneities. 26,27 Here we report the use of a photobleaching technique 28 to measure probe rotation in thermoset resins to study heterogeneity in microscopic environments. This technique has provided considerable insight into the nature of spatial heterogeneities in dynamics near T g for homopolymers.…”