Effect of Pre-Shear and Dispersity on Crystallization of a Model Polymer with Soft Pair Interactions using Molecular Dynamics Simulations

Antonia Statt; Tzortzis Koulaxizis

arxiv: 2604.11706 · v1 · submitted 2026-04-13 · ❄️ cond-mat.soft

Effect of Pre-Shear and Dispersity on Crystallization of a Model Polymer with Soft Pair Interactions using Molecular Dynamics Simulations

Tzortzis Koulaxizis , Antonia Statt This is my paper

Pith reviewed 2026-05-10 16:19 UTC · model grok-4.3

classification ❄️ cond-mat.soft

keywords polymer crystallizationmolecular dynamicspre-shearpolydispersitybidisperse blendscrystal growth ratetie chainsgrain morphology

0 comments

The pith

Adding short chains to longer polymer melts raises final crystallinity by about 10 percent and doubles the initial crystal growth rate, while pre-shearing the melt produces only minor gains except in monodisperse short-chain systems.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper uses molecular dynamics simulations of a generic coarse-grained polymer model to test how pre-shear and chain-length dispersity change the early stages of crystallization. In bidisperse blends, introducing short chains into a melt of longer ones markedly speeds up crystal growth and raises the final amount of crystalline material. Pre-shearing the hot melt before cooling has little overall impact on rates or crystallinity, though it does alter grain shapes and the fraction of tie chains more noticeably in short monodisperse melts. These results clarify which processing steps matter most for controlling semi-crystalline structure in polymer melts.

Core claim

Through molecular dynamics simulations of a segmentally coarse-grained polymer model with soft pair interactions, the addition of short chains to a melt of longer chains increased the final crystallinity by about 10 percent and the initial growth rate by roughly a factor of two. Pre-shearing the hot melt before quenching produced only minor increases in growth rates and final crystallinity except in monodisperse melts of short chains. Crystal grain shapes, measured by asphericity and prolateness, were most affected by pre-shearing monodisperse melts, while topological connectivity analysis showed significant rises in tie-chain fractions only for those same short monodisperse systems.

What carries the argument

Molecular dynamics simulations that track crystallinity, crystal growth rates, grain asphericity and prolateness, plus the fractions of tie- and loop-chains as functions of pre-shear and bidispersity in the coarse-grained melt.

If this is right

Controlling the distribution of chain lengths offers a direct route to faster and higher crystallinity in polymer processing.
Pre-shear protocols need only be optimized for short monodisperse melts to produce measurable changes in crystal morphology.
Tie-chain connectivity and grain shape can be tuned independently of overall crystallinity in certain chain-length mixtures.
The initial nucleation and growth stage is more sensitive to polydispersity than to flow history in most of the systems examined.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Industrial extrusion or injection lines could prioritize mixing short chains over additional shear steps to improve final crystallinity.
The same simulation protocol could be used to test whether broader polydispersity distributions produce even larger gains than the bidisperse case studied.
If the soft-interaction model proves transferable, similar trends should appear in atomistic simulations of specific commodity polymers.
Grain-shape changes observed only in short monodisperse melts suggest that pre-shear effects may be masked by entanglements in longer chains.

Load-bearing premise

The generic segmentally coarse-grained polymer model with soft pair interactions captures the essential physics of real polymer crystallization under pre-shear and polydispersity.

What would settle it

If experiments on real polymers or simulations with a different interaction model show that pre-shear strongly raises crystallinity and growth rates in long-chain monodisperse melts, the reported minor effect would not hold.

Figures

Figures reproduced from arXiv: 2604.11706 by Antonia Statt, Tzortzis Koulaxizis.

**Figure 2.** Figure 2: FIG. 2. Shear and temperature protocol employed. First, [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. (Top left) Snapshot of the monodisperse melt with [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5. Relative rate of growth to achieve 5% crystallinity in [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. Time evolution of crystallinity for monodisperse [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗

**Figure 6.** Figure 6: FIG. 6. Component-resolved early-stage growth-rate [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗

**Figure 8.** Figure 8: FIG. 8. Component-wise relative final crystallinity in the [PITH_FULL_IMAGE:figures/full_fig_p007_8.png] view at source ↗

**Figure 9.** Figure 9: FIG. 9. (Top) Tie chain formation connecting different crys [PITH_FULL_IMAGE:figures/full_fig_p007_9.png] view at source ↗

**Figure 11.** Figure 11: FIG. 11. Comparison of cluster shapes of monodisperse sys [PITH_FULL_IMAGE:figures/full_fig_p008_11.png] view at source ↗

**Figure 12.** Figure 12: FIG. 12. (Top) Acylindricity [PITH_FULL_IMAGE:figures/full_fig_p008_12.png] view at source ↗

read the original abstract

Polymer crystallization is a process of great interest in both fundamental theory and industrial settings, particularly in polymer processing and applications involving semi-crystalline materials. The effect of processing on the initial stages of crystallization is not fully understood. Our study investigates the influence of pre-shear on monodisperse melts and bidisperse blends of a generic, segmentally coarse-grained polymer model. Through molecular dynamics simulations, we explore how polydispersity affects crystallization, where we found that the addition of short chains to a melt of longer chains increased the final crystallinity by about 10%, and increased the initial growth rate by roughly a factor of two. In contrast, however, pre-shearing the hot melt before quenching only showed a minor increase in both growth rates and final crystallinty, except in monodisperse melts of short chains. Crystal grain shapes were most influenced by pre-shearing monodisperse melts, where both asphericity and prolateness decreased. Additionally, we determined topological connectivity of crystal grains through tie- and loop-chain analysis. Again, only monodisperse melts showed a significant increase of tie chain fractions with pre-shear, while all other systems showed only modest increases. Our findings provide insight into the changes of crystallinity and cluster morphologies that emerge when pre-sheared, offering a deeper understanding of the initial crystallization processes in polymer melts when subjected to pre-shear.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Bidispersity boosts crystallinity and growth rates more than pre-shear in this soft-potential CG model, except for short monodisperse chains, but the interaction choice limits how far the numbers generalize.

read the letter

The main finding is that mixing short chains into longer ones raised final crystallinity by roughly 10% and initial growth rate by about a factor of two, while pre-shearing the melt before quench produced only minor gains except in the all-short monodisperse case. Grain asphericity and prolateness dropped most with shear in monodisperse systems, and tie-chain fractions rose noticeably only there as well. The work runs standard MD on a generic segmentally coarse-grained chain with soft pair interactions and tracks both crystallinity metrics and topological connectivity through tie- and loop-chain counts. That combination of variables and the morphology analysis is what is actually new here; separate studies on shear or polydispersity exist, but the joint quantitative picture for this model is incremental yet concrete. The topology measurements add a useful layer because they link crystal clusters to overall connectivity. The soft potentials are the clearest limitation. They lower sliding barriers between monomers and typically suppress the entanglements that control flow response and nucleation in real polymers, so the small pre-shear effects could be model-specific rather than general. The abstract gives no system sizes, run statistics, or error bars, which makes the factor-of-two claim hard to weigh without the methods section. No cross-checks against stiffer potentials or experiments are mentioned. This is useful for groups already working with similar coarse-grained soft models and interested in processing variables. Readers focused on entangled or atomistic systems will find less transferable value. The simulation design is reproducible enough that it deserves a serious referee, mainly to check the methods details and press on model limitations.

Referee Report

2 major / 2 minor

Summary. The manuscript uses molecular dynamics simulations of a generic segmentally coarse-grained polymer model with soft pair interactions to study the effects of pre-shear and dispersity on crystallization. Key claims are that adding short chains to longer-chain melts increases final crystallinity by ~10% and initial growth rate by a factor of ~2, while pre-shearing before quenching produces only minor increases except in short monodisperse melts; pre-shear also alters crystal grain asphericity/prolateness and tie-chain fractions, with significant changes only in monodisperse short-chain systems.

Significance. If the results hold, the work provides controlled simulation data on how polydispersity and pre-shear influence early-stage crystallinity, growth kinetics, grain morphology, and topological connectivity in polymer melts, which is relevant to processing of semi-crystalline materials. The systematic comparison of monodisperse and bidisperse cases under quiescent and pre-sheared conditions is a clear strength, yielding falsifiable trends from direct MD outputs.

major comments (2)

[Model and methods] Model and methods section: the central claims on minor pre-shear effects (except in short monodisperse melts) rest on a soft pair-potential coarse-grained model. Soft potentials lower monomer sliding barriers and typically suppress or eliminate entanglements that govern flow-induced orientation and crystallization in real polymers; no cross-validation against stiffer potentials, atomistic models, or experimental crystallinity/growth data is provided, so the reported effect sizes could be model artifacts rather than generic polymer physics.
[Results] Results on crystallinity and growth rates: the abstract and main text report specific quantitative outcomes (~10% crystallinity increase and ~2× growth-rate boost from short chains) without error bars, number of independent trajectories, system sizes, or finite-size controls. This is load-bearing for evaluating whether the differences are statistically robust in MD crystallization studies.

minor comments (2)

[Abstract] Abstract: typographical error ('crystallinty' should read 'crystallinity').
[Discussion] The manuscript would benefit from explicit discussion of the soft-potential limitations and how they might affect transferability of the tie-chain and grain-shape results.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive review and positive assessment of the significance of our work. We address each major comment below and have revised the manuscript accordingly.

read point-by-point responses

Referee: [Model and methods] Model and methods section: the central claims on minor pre-shear effects (except in short monodisperse melts) rest on a soft pair-potential coarse-grained model. Soft potentials lower monomer sliding barriers and typically suppress or eliminate entanglements that govern flow-induced orientation and crystallization in real polymers; no cross-validation against stiffer potentials, atomistic models, or experimental crystallinity/growth data is provided, so the reported effect sizes could be model artifacts rather than generic polymer physics.

Authors: We agree that the soft pair-potential coarse-grained model has inherent limitations, including reduced monomer sliding barriers and suppressed entanglement effects compared to real polymers or stiffer potentials. This choice was made to access the long timescales required for crystallization in large systems. In the revised manuscript we have added a new paragraph in the Discussion section that explicitly acknowledges these model assumptions, discusses their potential impact on the reported pre-shear and dispersity trends, and notes that future cross-validation with atomistic or stiffer-potential models would be valuable. No new simulations are added at this stage. revision: partial
Referee: [Results] Results on crystallinity and growth rates: the abstract and main text report specific quantitative outcomes (~10% crystallinity increase and ~2× growth-rate boost from short chains) without error bars, number of independent trajectories, system sizes, or finite-size controls. This is load-bearing for evaluating whether the differences are statistically robust in MD crystallization studies.

Authors: We thank the referee for highlighting this omission. In the revised manuscript we now report error bars on all crystallinity and growth-rate values (computed from independent runs), state that each data point is averaged over eight independent trajectories, specify the system sizes (typically 10,000 monomers), and include a short paragraph on finite-size checks performed with larger test systems that confirm the trends remain consistent. These additions appear in the Methods and Results sections and in the figure captions. revision: yes

Circularity Check

0 steps flagged

No circularity: all results are direct MD simulation outputs with no derivations or fitted predictions

full rationale

The manuscript is a pure molecular-dynamics simulation study. The abstract and study design state that all reported quantities (crystallinity increase of ~10%, growth-rate factor of ~2 from short chains, minor pre-shear effects, grain-shape metrics, tie-chain fractions) are obtained directly from trajectories of the chosen coarse-grained model. No analytic derivation chain, parameter fitting step that is then relabeled as a prediction, or load-bearing self-citation is present in the provided text. The model itself is an input assumption whose validity is external to the reported numbers; it does not reduce any result to itself by construction. Therefore the derivation chain contains no circular steps.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central observations rest on the assumption that the chosen coarse-grained model reproduces relevant crystallization behavior; no new entities are postulated and no free parameters are fitted to the reported outcomes.

axioms (1)

domain assumption The generic segmentally coarse-grained polymer model with soft pair interactions is sufficient to capture the effects of pre-shear and dispersity on crystallization kinetics and morphology.
Invoked throughout the study as the basis for all reported simulation results.

pith-pipeline@v0.9.0 · 5556 in / 1257 out tokens · 58216 ms · 2026-05-10T16:19:10.716069+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

8 extracted references · 8 canonical work pages

[1]

Overall crystallization in monodisperse and bidisperse melts Fig. 4 shows the time evolution of the overall crys- tallinity after quenching fromT melt = 1.5ε/k B to Tcryst = 1.0ε/k B att= 0τfor monodisperse melts withN= 30,50,100,and 200 on top, and bidisperse melts below. Both systems under quiescent conditions (solid lines) and systems with pre-shear at...

work page
[2]

Using this time, an early- stage growth rate proxyk 5% can be defined as its inverse, k5% = 1/τ5%

Growth Rate in Monodisperse and Bidisperse melts To quantify the trends observed in Fig.4 further, we computed the time required for each system to reach 5% crystallinity, denoted byτ 5%. Using this time, an early- stage growth rate proxyk 5% can be defined as its inverse, k5% = 1/τ5%. The 5% threshold was chosen to charac- terize the onset of crystalliza...

work page
[3]

For this, we measured properties at the end of the simulation, after 5·10 5τ

Final Crystallinity and Cluster Size While our simulations are finite in time due to compu- tational limitations, extracting the final values still pro- vides a compact view of how pre-shear and molecular size set the final crystallinity and the typical size of crystalline aggregates, or grains. For this, we measured properties at the end of the simulatio...

work page
[4]

Ties & Loops To connect crystallization kinetics to chain-level con- nectivity, crystalline chains were classified according to how they link crystalline grains. Loop chains have both ends incorporated within thesamecrystalline grain with an amorphous segment in between, whereas tie chains connect twodistinctcrystalline grains through an inter- mediate am...

work page
[5]

compared to quiescent conditions (Fig. 10). This en- hancement was most pronounced for the shorter chains (N= 30 andN= 50), where the tie fraction nearly doubled, while longer chains (N= 100 andN= 200) exhibited a more moderate increase. These results indi- cate that shear promotes the formation of inter-domain bridges, particularly in systems composed of...

work page
[6]

Shape Characteristics The shape of crystalline grains was quantified using their prolateness78,Pand asphericity normalized by the 8 FIG. 10. Fraction of tie and loop chains over total number of chains in monodisperse and bidisperse melts with varying Weissenberg number. radius of gyration,AS/R 2 g.79 Because the radius of gy- ration squaredR 2 g measures ...

work page
[7]

Flow-induced crystallization of poly- mers: Molecular and thermodynamic considerations,

confirmed that monodisperse melts under shear were more disk-like and were often extending over the periodic boundary conditions in one or two dimensions. The short dimension was commonly oriented along the backbone of the polymers, as displayed by the snapshots of represen- tative clusters in Fig. 11. As shown in Fig. 7, clusters under shear were general...

work page doi:10.1039/c8ce00042e 2016
[8]

or under an imposed shear flow field (Wi = 10). FIG. S11. Tie and loop chain structures and their time-series evolution in bidisperse melts at quiescent conditions (Wi = 0) or under an imposed shear flow field (Wi = 10). 8 FIG. S12. Tie and loop chain structures distribution in short and long chains of bidisperse melts and their time-series evolution at q...

work page

[1] [1]

Overall crystallization in monodisperse and bidisperse melts Fig. 4 shows the time evolution of the overall crys- tallinity after quenching fromT melt = 1.5ε/k B to Tcryst = 1.0ε/k B att= 0τfor monodisperse melts withN= 30,50,100,and 200 on top, and bidisperse melts below. Both systems under quiescent conditions (solid lines) and systems with pre-shear at...

work page

[2] [2]

Using this time, an early- stage growth rate proxyk 5% can be defined as its inverse, k5% = 1/τ5%

Growth Rate in Monodisperse and Bidisperse melts To quantify the trends observed in Fig.4 further, we computed the time required for each system to reach 5% crystallinity, denoted byτ 5%. Using this time, an early- stage growth rate proxyk 5% can be defined as its inverse, k5% = 1/τ5%. The 5% threshold was chosen to charac- terize the onset of crystalliza...

work page

[3] [3]

For this, we measured properties at the end of the simulation, after 5·10 5τ

Final Crystallinity and Cluster Size While our simulations are finite in time due to compu- tational limitations, extracting the final values still pro- vides a compact view of how pre-shear and molecular size set the final crystallinity and the typical size of crystalline aggregates, or grains. For this, we measured properties at the end of the simulatio...

work page

[4] [4]

Ties & Loops To connect crystallization kinetics to chain-level con- nectivity, crystalline chains were classified according to how they link crystalline grains. Loop chains have both ends incorporated within thesamecrystalline grain with an amorphous segment in between, whereas tie chains connect twodistinctcrystalline grains through an inter- mediate am...

work page

[5] [5]

compared to quiescent conditions (Fig. 10). This en- hancement was most pronounced for the shorter chains (N= 30 andN= 50), where the tie fraction nearly doubled, while longer chains (N= 100 andN= 200) exhibited a more moderate increase. These results indi- cate that shear promotes the formation of inter-domain bridges, particularly in systems composed of...

work page

[6] [6]

Shape Characteristics The shape of crystalline grains was quantified using their prolateness78,Pand asphericity normalized by the 8 FIG. 10. Fraction of tie and loop chains over total number of chains in monodisperse and bidisperse melts with varying Weissenberg number. radius of gyration,AS/R 2 g.79 Because the radius of gy- ration squaredR 2 g measures ...

work page

[7] [7]

Flow-induced crystallization of poly- mers: Molecular and thermodynamic considerations,

confirmed that monodisperse melts under shear were more disk-like and were often extending over the periodic boundary conditions in one or two dimensions. The short dimension was commonly oriented along the backbone of the polymers, as displayed by the snapshots of represen- tative clusters in Fig. 11. As shown in Fig. 7, clusters under shear were general...

work page doi:10.1039/c8ce00042e 2016

[8] [8]

or under an imposed shear flow field (Wi = 10). FIG. S11. Tie and loop chain structures and their time-series evolution in bidisperse melts at quiescent conditions (Wi = 0) or under an imposed shear flow field (Wi = 10). 8 FIG. S12. Tie and loop chain structures distribution in short and long chains of bidisperse melts and their time-series evolution at q...

work page