Interfacial Friction Dynamics of Erucamide Derivatives under Hot Bar Sealing
Primary erucamide melts under hot bar sealing platens, increasing viscous drag and tooling varnish; secondary amides preserve boundary slip and seal integrity.
Capillary Pinning
Meaning
Liquid flow control in micro-moulded channels relies on geometric features that arrest the movement of a fluid meniscus. This phenomenon is capillary pinning, where a sharp step or edge in a polymer part halts the liquid front. The surface energy of the moulded polymer determines the strength of the barrier.
Geometric Boundary
Designing micro-moulded devices requires sharp internal angles to create a localized rise in capillary pressure. When a liquid front encounters a ninety-degree step, the contact line is pinned until the liquid can build enough pressure to overflow the boundary. Moulders must achieve high replication accuracy at these sharp edges to ensure reliable fluidic behavior.
Rounded corners from poor mould filling weaken the pinning effect and cause premature fluid leakage.
Moulding Precision
Achieving the necessary sharpness requires elevated tool temperatures and high injection pressures to force the polymer into micro-features before solidifying. Incomplete filling rounded edges that fail to pin the liquid front. Rapid tooling wear from abrasive resins can also degrade the sharp features over time.
This creates a trade-off between the durability of the tool steel and the design of the polymer part.
Material Properties
The surface energy of the chosen polymer resin governs the contact angle and determines the energy barrier at the pinned line. Virgin polymers provide consistent surface chemistry that ensures predictable capillary pinning behavior in diagnostic parts. Regrind material or additives can migrate to the surface of the moulded part, changing the wetting behavior and causing fluidic failure.
Post-moulding surface treatments are sometimes used to alter the surface energy to make the pinning effect more reliable.