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arxiv: 2604.20299 · v1 · submitted 2026-04-22 · ❄️ cond-mat.soft · physics.class-ph

Polymeric Solvents Control Swelling-Induced Surface Creasing

Zechao Jiang , Zhaoyu Ding , Shaohua Yang , Ye Xu , Dongshi Guan , Abdelhamid Maali , Joshua D Mcgraw , Thomas Salez (LOMA)
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Zaicheng Zhang Xingkun Man
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Pith reviewed 2026-05-09 23:37 UTC · model grok-4.3

classification ❄️ cond-mat.soft physics.class-ph
keywords polymer gelssurface creasingswellingpolymeric solventsosmotic pressuremechanical stabilityPDMS
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0 comments X

The pith

The polymerization degree of the solvent independently sets whether a swelling polymer gel develops surface creases.

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

The authors demonstrate that raising the polymerization degree Ns of the solvent causes a clear shift from creased to stable surfaces in surface-bound PDMS gels swollen by silicone oils. This shift occurs even though swelling kinetics and the through-thickness solvent concentration profiles stay nearly identical. Their theory connects the reduced mixing entropy caused by longer solvent chains to a change in osmotic pressure, which raises the mechanical threshold for creasing while leaving the final swelling ratio adjustable. A reader would care because surface creasing has been hard to suppress without also changing how much the gel expands or how fast it swells. The result supplies a thermodynamic handle that acts separately from network elasticity.

Core claim

Polymeric solvents reduce the mixing entropy between gel and solvent, thereby modifying the osmotic pressure that drives swelling against the elastic network. This modification allows the solvent polymerization degree Ns to tune the equilibrium swelling and the critical condition for surface creasing as two distinct quantities. Experiments show the transition from creased to stable surfaces occurs with increasing Ns at fixed network properties, and the coupled thermodynamic-mechanical model reproduces the observed stability boundary across both Ns and crosslink density.

What carries the argument

The coupling of swelling thermodynamics to mechanical stability, in which Ns lowers the entropy of mixing and thereby shifts the osmotic pressure relative to the elastic restoring force.

If this is right

  • The stability boundary in the plane of solvent polymerization degree and network elasticity is quantitatively captured by the entropy-modified osmotic pressure model.
  • Crease suppression is achieved without altering swelling speed or the final through-thickness solvent profile.
  • Equilibrium swelling ratio and mechanical instability threshold can be set independently by choice of Ns.

Where Pith is reading between the lines

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

  • Designers could select solvent chain length to reach a target swollen thickness while keeping the surface flat, which would matter for thin-film coatings or microfluidic channels.
  • The same entropy-tuning route might stabilize other swelling-driven instabilities such as wrinkling or folding if the mechanical criterion is replaced by the appropriate one.
  • Varying temperature would provide a further test, since entropy terms in the mixing free energy are temperature-dependent and should shift the crease threshold predictably.

Load-bearing premise

The change in crease threshold with Ns arises from the reduction in mixing entropy rather than from differences in solvent viscosity, chain mobility, or other unaccounted interactions.

What would settle it

An experiment that measures the actual mixing free energy or osmotic pressure as a function of Ns and finds no shift large enough to explain the observed change in crease onset, or a test in which crease threshold remains fixed while Ns is varied but entropy contributions are held constant by another means.

Figures

Figures reproduced from arXiv: 2604.20299 by Abdelhamid Maali, Dongshi Guan, Joshua D Mcgraw, Shaohua Yang, Thomas Salez (LOMA), Xingkun Man, Ye Xu, Zaicheng Zhang, Zechao Jiang, Zhaoyu Ding.

Figure 2
Figure 2. Figure 2: FIG. 2. Characteristics of swelling-induced surface instability. [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Mechanism governing swelling-induced surface creas [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Experimental phase diagram and theoretical stabil [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

Surface creasing in swelling polymer gels is commonly attributed to compressive strain or interlayer mismatch, yet its general control remains unclear. Here we show that solvent polymerization degree $N_{\rm s}$ provides an independent control parameter for crease onset in surface-bound polydimethylsiloxane gels swollen by silicone oils. Despite nearly identical swelling kinetics and through-thickness solvent concentration profiles, we observe a transition from creased to stable surfaces with increasing $N_{\rm s}$. A theory coupling swelling thermodynamics and mechanical stability reveals that polymeric solvents reduce the mixing entropy and thereby modify the osmotic pressure, allowing $N_{\rm s}$ to tune separately the equilibrium swelling and the crease threshold. This framework captures the stability boundary across solvent polymerization degree and network elasticity. These results identify polymeric solvents as active thermodynamic-mechanical regulators of swelling-induced surface.

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.

Referee Report

0 major / 3 minor

Summary. The manuscript claims that the polymerization degree Ns of polymeric solvents acts as an independent control parameter for the onset of swelling-induced surface creasing in surface-bound PDMS gels swollen by silicone oils. Experiments reveal a transition from creased to stable surfaces with increasing Ns, despite nearly identical swelling kinetics and through-thickness solvent concentration profiles. A theory that couples swelling thermodynamics (via reduced mixing entropy in the free energy) with mechanical stability analysis shows that Ns modifies the osmotic pressure contribution to stress, allowing separate tuning of equilibrium swelling and the crease threshold; the framework accounts for the observed stability boundary across Ns and network elasticity.

Significance. If the central claim holds, the work identifies a thermodynamic mechanism for controlling surface instabilities that is decoupled from the local deformation gradient, offering a new design handle for soft materials. The experimental demonstration of identical φ(z) profiles yet differing stability, combined with the entropy-based explanation, strengthens understanding of swelling-induced creasing beyond strain-mismatch models and could inform applications in coatings and responsive gels.

minor comments (3)
  1. [Abstract] The abstract states that the theory 'captures the stability boundary across solvent polymerization degree and network elasticity,' but the manuscript would benefit from an explicit statement of the quantitative metric used for agreement (e.g., predicted vs. observed critical Ns) and the range of network moduli tested.
  2. [Theory] In the theory development, the incremental stability operator is said to shift with Ns at fixed φ(z); include a brief derivation sketch or reference to the precise form of the osmotic-pressure term (arising from the φ/Ns ln φ contribution) to make the decoupling transparent.
  3. [Experiments] Figure captions or the experimental section should report the number of independent samples and any error bars on the observed transition Ns to allow assessment of reproducibility.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our work and the recommendation for minor revision. The summary accurately captures the central claim that polymerization degree Ns serves as an independent control parameter decoupling swelling from mechanical instability via reduced mixing entropy. As the report lists no specific major comments, we have no individual points to rebut or revise at this stage, though we will incorporate any minor editorial improvements in the revised version.

Circularity Check

0 steps flagged

No significant circularity; derivation is self-contained

full rationale

The paper derives the effect of Ns on crease threshold from the standard Flory-Huggins mixing free energy term (φ/Ns ln φ) that reduces solvent entropy and thereby shifts osmotic pressure in the total stress, even at fixed local volume fraction φ(z) and deformation gradient. This thermodynamic contribution is then inserted into the incremental stability operator for surface creasing. The resulting boundary is independent of the observed swelling profiles, which the experiments hold fixed while varying Ns. No parameter is fitted to the target crease data and then renamed a prediction, no self-citation supplies a uniqueness theorem or ansatz, and the central claim does not reduce to its inputs by construction. The framework therefore remains externally falsifiable against the reported stability boundary across Ns and network elasticity.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Abstract-only view limits visibility into exact parameters; theory relies on standard swelling thermodynamics assumptions and mechanical stability analysis without evident new entities or many free parameters.

axioms (1)
  • domain assumption Swelling thermodynamics can be directly coupled to mechanical stability criteria for surface creasing
    Central to the theory that allows Ns to tune swelling and threshold separately.

pith-pipeline@v0.9.0 · 5467 in / 1230 out tokens · 54935 ms · 2026-05-09T23:37:53.459679+00:00 · methodology

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Reference graph

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