Critical Role of Layer Thickness in Frontal Polymerization

Area of Science:

• Polymer Chemistry
• Chemical Engineering
• Materials Science

Background:

• Thermal frontal polymerization (FP) involves converting monomers to polymers via a propagating reaction front.
• Current theoretical models often simplify FP to one-dimensional (1D) reaction-diffusion (RD) systems, incorporating heat loss effects as effective parameters.
• These 1D models have limitations in accurately describing FP under non-adiabatic conditions.

Purpose of the Study:

• To investigate the limitations of 1D models for describing frontal polymerization (FP) under non-adiabatic conditions.
• To analyze the influence of system dimensionality and layer thickness on FP dynamics and front propagation.
• To explore the conditions under which a polymerization front can survive independently of heat loss rates.

Main Methods:

• Analytical and numerical analysis of polymerization front propagation in a two-dimensional (2D) rectangular layer.
• Investigation of the interplay between heat diffusion, reaction exothermicity, and heat loss effects.
• Scaling analysis to interpret the physical mechanisms behind front survival in 2D systems.

Main Results:

• Layer thickness critically controls polymerization front dynamics and its existence, demonstrating the inadequacy of 1D models.
• A minimum layer thickness is necessary for front propagation under specific heat loss conditions, aligning with recent experimental findings.
• Front survival independent of heat loss rates is observed above a critical thickness, a phenomenon not predicted by 1D models.

Conclusions:

• Two-dimensional (2D) analysis is crucial for accurately modeling thermal frontal polymerization (FP) under non-adiabatic conditions.
• System geometry, specifically layer thickness, plays a fundamental role in determining the feasibility and stability of FP.
• The study highlights the limitations of 1D models and provides insights into front survival mechanisms in multi-dimensional systems.