Experimental Measurement of Coil–Rod–Coil Block Copolymer Tracer Diffusion through Entangled Coil Homopolymers

Abstract

The diffusion of coil-rod-coil triblock copolymers in entangled coil homopolymers is experimentally measured and demonstrated to be significantly slower than rod or coil homopolymers of the same molecular weight. A model coil-rod-coil triblock was prepared by expressing rodlike alanine-rich α-helical polypeptides in E. coli and conjugating coillike poly(ethylene oxide) (PEO) to both ends to form coil-rod-coil triblock copolymers. Tracer diffusion through entangled PEO homopolymer melts was measured using forced Rayleigh scattering at various rod lengths, coil molecular weights, and coil homopolymer concentrations. For rod lengths, L, that are close to the entanglementh length, a, the ratio between triblock diffusivity and coil homopolymer diffusivity decreases monotonically and is only a function of L/a, in quantitative agreement with previous simulation results. For large rod lengths, diffusion follows an arm retraction scaling, which is also consistent with previous theoretical predictions. These experimental results support the key predictions of theory and simulation, suggesting that the mismatch in curvature between rod and coil entanglement tubes leads to the observed diffusional slowing.

Anomalous Diffusion in Associative Networks of High-Sticker-Density Polymers

“…Samples that were not equilibrated gave decay curves that exhibited additional relaxation processes that were not reproducible when different positions on the sample were tested (Figure S2), and this was used to determine the minimum time required for equilibration. The self-diffusion measurements were performed using forced Rayleigh scattering (FRS), as previously described. ,, Briefly, a 100 mW continuous wave laser with λ = 488 nm was split into two beams, which were individually refocused and crossed on the sample at an angle θ. This generated a holographic grating of characteristic spacing d that is defined by the following equation On exposure of the sample for 100–500 ms, the photochromic fluorescein dye conjugated to the tracer molecules was irreversibly isomerized in the areas of constructive interference, producing an amplitude grating of dye concentration.…”

“…The self-diffusion measurements were performed using forced Rayleigh scattering (FRS), as previously described. 21,26,27 Briefly, a 100 mW continuous wave laser with λ = 488 nm was split into two beams, which were individually refocused and crossed on the sample at an angle θ. This generated a holographic grating of characteristic spacing d that is defined by the following equation…”

Relaxation Processes in Supramolecular Metallogels Based on Histidine–Nickel Coordination Bonds

“…Carbonyl­diimidazole was purchased from Alfa Aesar. 2-(Dodecylthio­carbonothioyl­thio)-2-methyl­propionic acid (DMP) and maleimide-functionalized 4′-( N , N ′-dimethyl­amino)-2-nitrostilbene (ONS-M) were synthesized following published procedures. N , N -Dimethyl­acrylamide (DMA) was purified through a basic alumina column to remove inhibitor before polymerization.…”

Effect of sticker clustering on the dynamics of associative networks

“…The self-diffusion measurements were performed using forced Rayleigh scattering (FRS), as previously described. 5,29,30 Briefly, a 100 mW continuous wave laser with l = 488 nm was split into two beams which were individually refocused and crossed at an angle of y onto the sample. This generated a holographic grating of characteristic spacing d that is defined by the following equation…”