Peel-to-Roll Transition: Mechanics & Applications

• Peel-to-roll transition is a mechanical instability defined by a shift from localized fracture-driven detachment to a continuous rolling mode.
• Experimental and simulation studies reveal that parameters like the Deborah number, humidity, and film geometry govern the regime transition.
• The insights from this phenomenon underpin advanced manufacturing processes such as wafer-scale 2D material exfoliation and programmable adhesive interfaces.

The peel-to-roll transition defines a class of mechanical instabilities in adhesive systems where a conventional peeling process abruptly gives way to a rolling or continuous detachment mode. This transition is observed in a diverse range of contexts, including the unrolling of adhesive tapes, roll-to-roll exfoliation of two-dimensional materials, and the de-adhesion of blistered thin films. The governing principles are rooted in nonlinear mechanics, fracture kinetics, interface physics, and the dynamical control of force, geometry, and rate-dependent adhesion.

1. Mechanistic Principles of the Peel-to-Roll Transition

The peel-to-roll transition is fundamentally a shift from localized fracture-driven detachment (peeling) to a more global, often propagating, rolling process of the adhesive layer or film. In its archetypal manifestation, such as the unrolling of a Scotch tape under gravity, the transition bifurcates into two physical regimes based on environmental, rheological, and mechanical parameters.

• Viscoelastic Peeling Regime: At humidities above ~10%, pressure-sensitive adhesives (PSA) soften due to water-plasticization, reducing the glass-transition temperature and mobilizing the network strands. Peeling is governed predominantly by viscous dissipation in the adhesive bulk. The strain-energy release rate ($G$) obeys a power law with peel speed ($V$): $G \propto V^n$ with $0.3 \lesssim n \lesssim 0.5$ for RH $\gtrsim 50\%$.
• Fracture-like Peeling Regime: For low humidity (RH $\lesssim$ 10%), bulk dissipation is suppressed. The adhesive behaves elastically, and debonding is controlled by thermally activated bond rupture at the interface. Here, $G(V)$ increases weakly as $[\ln V]^2$ and becomes insensitive to further decreases in peel speed, with characteristic activation energies ($E_a \approx 105\, \text{kJ mol}^{-1}$) typical of collective hydrogen-bond rupture.
• Key Parameter—the Deborah Number: The dimensionless Deborah number, $De = \tau_d a_{RH} V / e$, demarcates the transition. $\tau_d$ is the terminal relaxation time, $a_{RH}$ an empirically determined time-humidity shift factor, $V$ the peel speed, and $e$ the film thickness. $De \ll 1$ signals bulk viscous dissipation (viscoelastic peeling); $De \gg 1$ signals elasticity-dominated, fracture-like peeling. The crossover occurs near $De \sim 1$ (Grzelka et al., 2021).

2. Model Systems and Experimental Observations

2.1 Scotch Tape Unrolling (PSA)

A suspended roll of tape, acting under its own weight, exhibits continuous slow rolling even at nanometer-per-second velocities, never reaching a strict static state. RH-modulated experiments show that increased humidity increases $V$ by multiple orders of magnitude for fixed loading. Fluctuations in $V$ mirror RH changes with a delay reflecting moisture diffusion (Grzelka et al., 2021).

2.2 Wafer-Scale Mechanical Exfoliation

In roll-to-roll exfoliation platforms, the peel-to-roll transition is crucial for achieving wafer-scale, uniform 2D materials such as WSe$_2$. The transition from stick-slip (static peeling) to steady rolling is achieved by exceeding the critical peel force governed by the classical Kendall model: $G = \frac{T}{w} (1 - \cos \theta)$ where $T$ is tape tension, $w$ the width, and $\theta$ the peel angle. Continuous rolling is realized when $G \geq G_c$, the interfacial fracture energy (Sozen et al., 10 Nov 2025).

2.3 Blistered Thin Films on Soft Substrates

When a blistered film is peeled, superposed curvature fields exist between the peel front and the blister edge. As the peeled length $\ell_c$ decreases to a critical value $\ell_c^r$, these fields overlap, and rolling at the contact edge initiates. This process is marked by a sudden drop in peel force, which then plateaus (Pandey et al., 21 Dec 2025).

3. Critical Criteria and Scaling Laws

Several universal scaling results and process windows are established across multiple studies:

Critical Quantity	Governing Expression (LaTeX)	Remarks
Energy release rate $G$	$G = \frac{T}{w}(1-\cos \theta)$	Kendall model for peeling
Critical peel force $F_c$	$F_c(\theta) = \frac{G_c w}{1 - \cos \theta}$	Steady rolling when $F_{\text{peel}} > F_c$
Bending length (blistered films)	$$\ell \sim \left(\frac{B}{E_a}\right)^{1/6} h_a^{1/2}$$	Transition insensitive to work of adhesion
Force drop at rolling onset	$$\frac{\Delta F}{\Delta F_m} \sim \left(\frac{t_r}{t_w}\right)^{n},\ n\approx0.55$$	$t_r = \ell_c^r/V$, $t_w=$ contact dwell time
Thickness per transfer (exfoliation)	$t_n \approx n \cdot \Delta t$	$\Delta t \approx 28\ \text{nm}$ per transfer
Uniformity improvement	$\sigma_t \propto 1/\sqrt{A_s \cdot \omega \cdot n}$	$A_s$: slider amplitude, $\omega$: roller speed

A key insight from (Pandey et al., 21 Dec 2025): in blister-driven peel-to-roll, the critical contact length $\ell_c^r$ and thus the transition are determined exclusively by mechanical parameters (bending rigidity $B$, elastic modulus $E_a$, and substrate thickness $h_a$), not by the interfacial adhesion.

4. Process Engineering and Optimization

• Wafer-Scale Exfoliation: Uniformity and throughput in 2D material transfer are optimized by engineering roller diameters in a prime ratio (e.g., $53:23$ mm), optimizing peel angles ($90^\circ$–$120^\circ$), and controlling tape tension (0.4–0.8 N). Lateral sliding (amplitude $\sim \pm10$ mm, speed $1$–$5$ mm/s) suppresses defects and enforces coverage uniformity ($>95\%$ for four passes versus $\sim80\%$ for static peeling), decreasing defect density by an order of magnitude (Sozen et al., 10 Nov 2025).
• PSA Applications: Humidity tuning provides rapid, reversible control of peel velocity across several orders of magnitude, enabling slow-release, clean-removal, or brittle sticking depending on application. Modifying monomer composition or cross-linking enables specific targeting of $\tau_d$ and, thus, shifting the regime boundary for tailored performance (Grzelka et al., 2021).
• Blistered Films: The capacity to control dwell times spatially through the distribution of blisters enables programmed, heterogeneous adhesive landscapes from homogeneous materials. The force–displacement response becomes stepwise, tunable by the geometric placement of blisters, not chemical patterning (Pandey et al., 21 Dec 2025).

5. Micromechanical and Molecular Dynamics Insights

Coarse-grained molecular dynamics (MD) simulations, as deployed in the analysis of blistered films, recapitulate the critical features of the peel-to-roll transition. MD confirms that:

• Once the critical length is reached, the system shows no additional energetic barrier for initiation—the transition is kinematically governed.
• Adjusting the work of adhesion modifies neither the value of $\ell_c^r$ nor the nature of the rolling onset.
• At the atomic scale, bond formation and rupture are local and governed by geometry and mechanics rather than interfacial chemistry (Pandey et al., 21 Dec 2025).

6. Implications and Applications

The peel-to-roll transition provides a unified mechanical perspective for a spectrum of systems: pressure-sensitive adhesives, large-area 2D material fabrication, and the design of reconfigurable or patterned adhesive interfaces. The phenomenon enables:

• Large-area, high-throughput production of mechanically exfoliated 2D materials with controlled thickness and defect suppression (Sozen et al., 10 Nov 2025).
• Precision control of slow-release adhesives and shape-reconfigurable devices through environmental or geometric modulation (Grzelka et al., 2021).
• Creation of programmable adhesion landscapes in multilayer systems by spatial placement of geometric defects (blisters), without recourse to chemical heterogeneity (Pandey et al., 21 Dec 2025).

A plausible implication is that future platforms exploiting the peel-to-roll mechanism can leverage geometry and mechanical rates, rather than surface chemistry alone, as dominant levers for both adhesion tuning and device-scale manufacturing.