Self-diffusion and spin-spin relaxation in blends of linear and cyclic polydimethylsiloxane melts

Cosgrove, Terence; Turner, Michael J.; Griffiths, Peter Charles; Hollingshurst, J.; Shenton, M. J.; Semlyen, J.A.

doi:10.1016/0032-3861(96)83701-3

Cited by 46 publications

(64 citation statements)

References 35 publications

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“…Seemingly, the internal motions qualitatively change: there is no sign of the loop dynamics or of the loop migration prominent in the pure ring system. This contrasts with assertions that ring motion in linear matrices may occur through loop formation extending through the walls of the tube [34]. The initially stronger decaying structure factor in the long chain blend compared to the ring melt points to much more freedom of motion than in the ring melts.…”

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confidence: 50%

Caught in the Tube

Napolitano

2015

Physics

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Using neutron spin echo spectroscopy, we show that the segmental dynamics of polymer rings immersed in linear chains is completely controlled by the host. This transforms rings into ideal probes for studying the entanglement dynamics of the embedding matrix. As a consequence of the unique ring topology, in long chain matrices the entanglement spacing is directly revealed, unaffected by local reptation of the host molecules beyond this distance. In shorter entangled matrices, where in the time frame of the experiment secondary effects such as contour length fluctuations or constraint release could play a role, the ring motion reveals that the contour length fluctuation is weaker than assumed in state-of-the-art rheology and that the constraint release is negligible. We expect that rings, as topological probes, will also grant direct access to molecular aspects of polymer motion which have been inaccessible until now within chains adhering to more complex architectures. [7]. Furthermore, in the fields of material science and engineering, blends of different polymer architectures including rings are employed aiming to produce polymer materials with emerging properties [8,9]. Recently, simulation science in particular led to new insights into ring dynamics on a coarse grained level [10,11]. In chemistry, novel procedures have enabled the production of appreciable amounts of pure, well-defined rings [12][13][14][15][16] that in turn permit detailed physical investigations of their structure and dynamics.One of the important and fundamental goals of this broad approach is the understanding of entangled polymer dynamics far beyond the state-of-the-art standpoint. For cyclic polymers, reptation as well as the related relaxation through contour length fluctuations (CLFs) and constraint release (CR) are fully suppressed, requiring qualitatively different relaxation behavior in ring melts. The center of mass (c.m.) motion in such melts was found to be subdiffusive, characterized by a t 3=4 power law [17] which was understood in terms of the lattice animal theory [18] as well as in a recent approach of the diffusion of centrality [19]. Very recently the internal dynamics was also successfully addressed experimentally [17]: Rings relax via a combination of free internal loop-motion and loop migration. As a result, the mean-square displacement for internal segment motion follows a weak t 0.3 power law, a finding also supported by simulation [20].The unique ring topology also severely affects the ring structure and dynamics when blended with linear chains. Simulations showed that other than in the ring melts the ring conformation is close to Gaussian and no compaction is visible, at least in the range of ring concentrations below overlap [21]. On the other hand, rheological investigations display a very strong influence of small amounts of linear chains on the rheological response of a ring melt [22]. Threading linear chains through the rings crucially influences the long-range diffusion of rings [23,24], e.g., single-molecul...

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contrasting

confidence: 50%

Caught in the Tube

Napolitano

2015

Physics

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“…289 Various bulk properties of cyclic PDMS were investigated 261,[290][291][292][293][294][295][296][297] and compared to those of their linear analogues and to theoretical predictions. 298 T g measurements were conducted in the mass range of 0.37-24.5 kDa by DSC.…”

Section: Bulk Propertiesmentioning

confidence: 99%

“…Information about segmental mobility and diffusion was derived from Raman spectroscopy 295 from dielectric relaxation 296,297 and from spin-spin relaxation measurements. 298 Finally, a SANS study of conformations of cyclic and linear PDMS in bulk should be mentioned. 299 Blends of protonated and deuterated cyclic PDMSs and also blends of protonated and deuterated linear PDMS were studied.…”

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Cyclic polymers: Synthetic strategies and physical properties

Kricheldorf

2009

J. Polym. Sci. A Polym. Chem.

397

442

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Syntheses of cyclic polymers including cyclic homopolymers, cyclic block copolymers, sun-shaped polymers, and tadpole polymers are discussed on the basis of a differentiation between synthetic methods and synthetic strategies (e.g., polycondensation, ring-ring equilibration, or ring-expansion polymerization). Furthermore, all synthetic methods are classified as kinetically or thermodynamically controlled reactions. Characteristic properties of cyclic polymers such as smaller hydrodynamic volume, lower melt viscosities, and higher thermostabilities are compared to the properties of their linear counterparts. Furthermore, the nanophase separation of cyclic diblock copolymers is discussed.

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“…This behavior is similar to that found by NMR in the C-C and C-L cases (ν C-C = 1 and ν C-L =0.83). [19][20][21] Scaling exponents with the 25 and 45 kbp molecules, in contrast, ranged from <1 to ∼2 at high concentrations for all the topological cases. Similar behavior was reported previously for C-C and L-L melts in three simulation studies and one of the NMR studies.…”

Section: At Roughly the Same Concentration As D L-c And D C-c Leadimentioning

confidence: 99%

Self-Diffusion of Entangled Linear and Circular DNA Molecules: Dependence on Length and Concentration

2007

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Self-diffusion coefficients (D) of DNA molecules of varying length and concentration were measured by tracking the Brownian motion of individual fluorescently labeled tracer molecules. Four possible cases were examined: linear tracer molecules surrounded by linear molecules (L-L), circular tracers surrounded by linears (C-L), linear tracers surrounded by circles (L-C), and circles surrounded by circles (C-C). With 6 and 11 kilobasepair (kbp) DNA D was largely insensitive to topology and varied consistent with Rouse scaling (D ∼ L -1 C -0.5 ). In contrast, with 25 and 45 kbp DNA topology had a strong influence. At 1 mg/mL we foundIn the L-L, L-C, and C-C cases a crossover from scaling consistent with the Rouse model to scaling consistent with the reptation model (D ∼ L -2 C -1.75 ) was observed at ∼6 times the molecular overlap concentration. In contrast, D C-L decreased much more steeply with concentration, indicating that a process much slower than reptation governs that case.

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Self-diffusion and spin-spin relaxation in blends of linear and cyclic polydimethylsiloxane melts

Cited by 46 publications

References 35 publications

Caught in the Tube

Caught in the Tube

Cyclic polymers: Synthetic strategies and physical properties

Self-Diffusion of Entangled Linear and Circular DNA Molecules: Dependence on Length and Concentration

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