Mass dependence of the activation enthalpy and entropy of unentangled linear alkane chains

Jeong, Cheol; Douglas, Jack F.

doi:10.1063/1.4932601

Cited by 51 publications

(69 citation statements)

References 125 publications

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“…Moreover, for chains we observe conformational transition at about M ≈ 30. A similar conformational transition between rod-like conformations and flexible coil was recently discussed for the charged bipolymer DNA [25] and even unentangled linear alkane chains [26]. Ring polyelectrolytes exhibit similar trends for n int and n cont , but stars and trefoil knots attract more counter-ions and at the same time coil more efficiently.…”

Section: Discussionsupporting

confidence: 61%

Magnetic Iron Sulfide Nanoparticles for Potential Applications in Gas Sensing

Chremos

Douglas

2016

MRS Advances

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We explore the impact of monovalent counter-ions on the molecular conformation of highly charged flexible polyelectrolytes for a range of molecular topologies (linear chains, stars, and unknotted and trefoil rings) by molecular dynamics simulations that include an explicit solvent having short range interaction with the polyelectrolyte. In particular, we investigate how the counter-ions near the polyelectrolytes with variable mass influence the average molecular shape. We also characterize the interfatially “bound” counter-ions by calculating the time-averaged number of interfacial counter-ions, as well as the degree to which the polyelectrolytes wrap around the counter-ions by calculating the number of contacts between the counter-ions and the polyelectrolyte.

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Section: Discussionsupporting

confidence: 61%

Magnetic Iron Sulfide Nanoparticles for Potential Applications in Gas Sensing

Chremos

Douglas

2016

MRS Advances

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“…This means that even at high temperature T / T g ≈ 2, there is significant deviation from Rouse predictions, see Refs. 11 for further discussion. Ring polymers diffuse at a higher rate compared to the linear chain analogues, consistent with previous studies.…”

Section: Resultsmentioning

confidence: 99%

“…5,6 Despite the wide use of such models in the last three decades, a universal description of the dynamics of polymers with different molecular architectures in melt conditions is lacking. 7 Recent work has established that the Rouse model is not generally applicable even in the relatively simple case of unentangled polymers 8–11 so we take a fresh look at the problem of the dynamics of unentangled polymer melts based on established hydrodynamic models and the assumption that continuum hydrodynamic theory is applicable to molecular fluids.…”

Section: Introductionmentioning

confidence: 99%

Influence of polymer architectures on diffusion in unentangled polymer melts

2017

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Recent simulations have indicated that the thermodynamic properties and the glassy dynamics of polymer melts are strongly influenced by average molecular shape, as quantified by the radius of gyration tensor of the polymer molecules, and that average molecular shape can be tuned by varying molecular topology (e.g., ring, star, linear chain, etc.). In the present work, we investigate if molecular shape is similarly a predominant factor in understanding the polymer center of mass diffusion D in the melt, as already established for polymer solutions. We find that all our D data for unentangled polymer melts having a range of topologies can be reasonably described as a power law of the polymer hydrodynamic radius Rh. In particular, this scaling is similar to the scaling of D for a tracer sphere having a radius on the order of the chain radius of gyration, Rg. We conclude that chain topology influences molecular dynamics in as much as the polymer topology influences average molecular shape. Experimental evidence seems to suggest that this situation is also true for entangled polymer melts.

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“…Atomistic molecular dynamics (MD) simulation of ring‐linear polyethylene (PE) blends in the melt was performed by using GROMACS package and united atom (UA) model at 509 K (high enough to avoid crystallization on reasonable timescale) and 1 atm. The longest chain length N = 500 corresponds to 7.2 N e where N e was the entanglement chain length for linear PE in the UA model . Our simulation then covered the ring‐linear PE blends from unentangled to partially entangled regimes.…”

Section: Simulation Methodsmentioning

confidence: 99%

Relation between Polymer Conformational Structure and Dynamics in Linear and Ring Polyethylene Blends

Jeong

Douglas

2017

Macro Theory & Simulations

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Flory theorem," stating that polymers in the melt are nearly "ideal," [28] in the specific sense that they should have similar excluded volume (EV) interactions as polymers at their theta point, i.e., ν = 1/2, simply does not hold for ring melts. Instead, ν for ring melts has often been reported to be near 2/5 [11,12,21,24] which is consistent with the theoretical estimate of Cates and Deutsch. [29] Recent computational studies [16][17][18]30,31] have suggested that very long rings in the melt should be in a collapsed globular state for which ν equals 1/3. On the other hand, Lang et al. [32] have argued for a value of ν = 3/8 for high mass rings, an exponent close, but not equal to the value for collapsed chains. Despite the uncertainty in the exact exponent value, it seems safe to conclude that ν is significantly less than 1/2 so that the conformation of melt rings does not conform to random walk (RW) chains with screened excluded volume interactions.The absence of screening of excluded volume in rings implies that the addition of solvents and linear polymers to ring melts should lead to different effects than adding these molecular species to linear polymer chain melts. This phenomenon has been considered in previous work, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] but the nature of this swelling process is not yet entirely clear, and the present work is devoted to further elucidating this problem from a new perspective not relying on the reptation model. There have admittedly been numerous arguments, [29,33,34] experiments, [33][34][35][36][37][38][39][40][41] and simulations [42][43][44][45][46][47][48] pertaining to the configurational properties and dynamics of rings diluted by linear chains. Originally, Cates and Deutsch [29] suggested that the topologically induced EV interactions in the ring melt are relieved upon diluting the rings by linear chains so that the rings in the melt should become "ideal" upon dilution by linear chains. Recent simulations [44][45][46][47][48] and experiments [40,41] on ring-linear polymer blends have reported that rings increase their size upon the dilution and their conformational structure resembles ideal rings in a theta solvent, clearly supporting a change in the EV interactions in ring melts upon adding linear chains. Moreover, the rate of diffusion of tracer ring polymers in the melt was found to be greatly slowed by adding linear chains, an effect interpreted as arising from the ring-linear polymer threadings. [33,[35][36][37][38][39]43,48] Although there have been many attempts at quantifying this physically appealing "threading effect," [7,[35][36][37][38][43][44][45][46]48] the validity of the threading model has not yet been established. In this communication, we consider an alternative explanation of the slowing down of Ring-Linear Chain BlendsAtomistic molecular dynamics simulations of ring-linear polyethylene blends are employed to understand the relationship between chain conformational structure and the melt dynamics of these blends. As o...

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Mass dependence of the activation enthalpy and entropy of unentangled linear alkane chains

Cited by 51 publications

References 125 publications

Magnetic Iron Sulfide Nanoparticles for Potential Applications in Gas Sensing

Magnetic Iron Sulfide Nanoparticles for Potential Applications in Gas Sensing

Influence of polymer architectures on diffusion in unentangled polymer melts

Relation between Polymer Conformational Structure and Dynamics in Linear and Ring Polyethylene Blends

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