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Curvature-Dependent Polarity of Interfacial Energy Flow in Functionalized CNT Polymer Nanocomposites: A Reactive Molecular Dynamics Perspective

Mehedi Hasan, Khayrul Islam, Michael T. Kio, AKM Masud

Abstract

Carbon nanotube (CNT)-polymer composites are widely engineered using surface coatings and chemical treatments to improve interfacial bonding and load transfer. It has been suggested in the nanocomposite literature that nanotube curvature, in conjunction with surface functionalization such as polydopamine (PDA) coating, could serve as an additional control knob for tuning interfacial bonding and energy dissipation in polymer-CNT systems. While experimental and simulation studies have demonstrated the benefits of PDA functionalization, the fundamental mechanism by which nanotube curvature modulates interfacial energy flow and mechanical polarity remains unresolved. This gap is sharpened by a persistent paradox: identical PDA functionalization strengthens some CNT-polymer systems while weakening others, a curvature-dependent inconsistency that has remained unexplained. Here, we employ reactive molecular dynamics (ReaxFF) simulations to resolve how curvature and PDA functionalization jointly govern interfacial energy evolution in CNT-polyvinyl alcohol (PVA) nanocomposites. Our investigation reveals that curvature and PDA functionalization jointly produce opposite regimes of interfacial energy flow: high-curvature CNTs generate dissipative, frictional interphases, whereas low-curvature CNTs confine energy in rigid, cohesive shells. This polarity inversion originates from a curvature-induced transition in PDA adsorption geometry that transforms the interphase from an energy-releasing to an energy-storing configuration. These results establish curvature as a fundamental design parameter for engineering polymer-nanotube interfaces, offering a predictive route to tune interfacial energy flow, mechanical resilience, and transport properties beyond the limits of conventional chemical functionalization.

Curvature-Dependent Polarity of Interfacial Energy Flow in Functionalized CNT Polymer Nanocomposites: A Reactive Molecular Dynamics Perspective

Abstract

Carbon nanotube (CNT)-polymer composites are widely engineered using surface coatings and chemical treatments to improve interfacial bonding and load transfer. It has been suggested in the nanocomposite literature that nanotube curvature, in conjunction with surface functionalization such as polydopamine (PDA) coating, could serve as an additional control knob for tuning interfacial bonding and energy dissipation in polymer-CNT systems. While experimental and simulation studies have demonstrated the benefits of PDA functionalization, the fundamental mechanism by which nanotube curvature modulates interfacial energy flow and mechanical polarity remains unresolved. This gap is sharpened by a persistent paradox: identical PDA functionalization strengthens some CNT-polymer systems while weakening others, a curvature-dependent inconsistency that has remained unexplained. Here, we employ reactive molecular dynamics (ReaxFF) simulations to resolve how curvature and PDA functionalization jointly govern interfacial energy evolution in CNT-polyvinyl alcohol (PVA) nanocomposites. Our investigation reveals that curvature and PDA functionalization jointly produce opposite regimes of interfacial energy flow: high-curvature CNTs generate dissipative, frictional interphases, whereas low-curvature CNTs confine energy in rigid, cohesive shells. This polarity inversion originates from a curvature-induced transition in PDA adsorption geometry that transforms the interphase from an energy-releasing to an energy-storing configuration. These results establish curvature as a fundamental design parameter for engineering polymer-nanotube interfaces, offering a predictive route to tune interfacial energy flow, mechanical resilience, and transport properties beyond the limits of conventional chemical functionalization.

Paper Structure

This paper contains 27 sections, 9 equations, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Computational Method
  3. Interatomic Potential
  4. Molecular Model Construction
  5. Simulation Protocol
  6. Interphase Identification and RDF-Based Thickness Determination
  7. Validation of simulation model
  8. Results and Discussion
  9. mechanical, trnasportation, and structal properites analysis
  10. Structural Integrity Analysis
  11. Energy Dissipation and Mechanical Integrity Under Tensile Strain
  12. Diffusion behavior and mean-squared displacement analysis
  13. Porosity evolution and interphase stability
  14. Structure–Property Trends and Curvature-Dependent Deviations
  15. Canonical Scaling Laws Linking Porosity, Mechanics, and Transport
  16. ...and 12 more sections

Figures (5)

  • Figure 1: Schematic illustration of CNT–PVA nanocomposite assembly. Functionalized CNTs (HNO$_3$ and PDA) are embedded within a PVA network, showing polymer chain architecture and the interphase region identified through radial distribution function (RDF) analysis.
  • Figure 2: Mechanical and transport properties of PVA–CNT nanocomposites. (a, b) Stress–strain curves for (10,10) and (12,12) CNT-based composites with pristine, HNO$_3$-treated, and polydopamine (PD)-functionalized CNTs. (c, d) Energy–strain responses for (10,10) and (12,12) systems. (e) Diffusivity values of different composites. (f, g) Porosity evolution with strain for (10,10) and (12,12) composites, respectively.
  • Figure 3: Correlation plots among key structural, transport, and mechanical descriptors for all simulated CNT–polymer composites. Panels (a–c) show modulus, strength, and toughness as functions of porosity, respectively; panel (d) presents diffusivity versus porosity; panel (e) correlates toughness with diffusivity; and panel (f) combines diffusivity, toughness, and strength into a unified mechano–transport map. Each data point corresponds to a distinct CNT chirality $(10,10)$ or $(12,12)$ under different surface conditions (non-treated, HNO$_3$-treated, and PDA-treated).
  • Figure 4: Energetic resolution of the curvature–functionalization puzzle. (a–d) Total, CNT, PVA, and PDA potential energies versus strain. (e–h) van der Waals (vdW) energy evolution for each subsystem. (i–l) Electrostatic-energy trends showing curvature-dependent polarization. (m–n) Time-resolved vdW-energy fluctuations distinguishing sliding vs rupture. (o) PDA adsorption energy-distribution profile. (p) Interphase-energy evolution showing polarity inversion between (10,10) and (12,12). All energies are expressed in kcal mol$^{-1}$.
  • Figure 5: Overall workflow of the CNT–polymer nanocomposite study. (a) CNT-centered polymer packing. (b) Reactive molecular dynamics simulation using LAMMPS. (c) Data analytics revealing curvature–functionalization interactions. (d) Resolution of the puzzle through interphase energy decomposition combining potential, vdW, electrostatic, and interphase energies.