Virtual Samples

Example: Polyethylene (PE) Architectures

Even with identical repeating chemical units (CH₂-CH₂), macroscopic material properties vary drastically depending on chain topology:

• HDPE (Linear Chains): High packing density and crystallinity lead to high modulus, stiffness, and chemical resistance.
• LDPE (Branched Chains): Long and short branches inhibit tight crystal packing, yielding flexibility, clarity, and melt elasticity.
• LLDPE (Copolymer Short Branches): Regular short-chain branches provide superior puncture resistance, tear strength, and elongation.

Atomistic vs. Coarse-Grained Models

Simpal operates across multiple scales to balance computational efficiency with physical accuracy:

• Atomistic Models (All-Atom / United-Atom):Explicitly track chemical groups and local dihedral rotations. Used for thermodynamic mixing energy (χ parameters), small-molecule gas permeability, and interfacial adhesion.
• Coarse-Grained (Mesoscopic) Models: Lumps groups of 3–6 repeat units into bead-spring particles. This allows Simpal to simulate entangled melt dynamics over hundreds of nanoseconds, essential for calculating non-Newtonian viscosity and relaxation spectra.

What Defines a Digital Sample?

A virtual sample is a dynamic, 3D simulation ensemble. To ensure it accurately mirrors physical materials, we capture:

• Chain Architecture & MWD: Tacticity, molecular weight distribution, branching frequency, and polydispersity index (Mw/Mn).
• Blend Ratios: Mass and volume fractions of primary polymers, compatibilizers, and additives.
• Morphology & Phase Separation: Spatial distribution of co-continuous or droplet-matrix domains.
• Thermal Ensemble & Density: Temperature (e.g., melt state vs. solid state), pressure, and initial Boltzmann-distributed velocities.

Once this digital sample is packed and thermodynamically equilibrated, it is ready to undergo our virtual tests.