Self-Assembly Calculator

The packing parameter p = v/(a·l) is a dimensionless shape factor comparing how much volume the tail occupies against the cylinder implied by the head area and tail length — a cone-shaped molecule (small p) naturally curves into a sphere, while a cylinder-shaped molecule (p near 1) packs flat into a bilayer. This calculator buckets the computed p into five ranges (below 1/3, 1/3–1/2, 1/2–1, ~1, above 1) and reports the corresponding structure directly from that geometric argument, without modeling any other physics.

The critical micelle concentration output is deliberately a placeholder: it starts from an SDS-like 8 mM baseline and only adjusts for the temperature you enter, using a simple rule that doubles CMC per 20°C rise. It does not use your tail volume, head area, or tail length inputs at all, so for a surfactant with substantially different head chemistry than SDS, this number will be inaccurate — treat it as illustrative rather than a real CMC prediction.

Both are only computed when the packing parameter is below 0.5, i.e. when the structure is predicted to be a spherical or cylindrical micelle. Once p reaches 0.5 or higher (vesicles, bilayers, or inverted structures), those fields are set to 0 and bilayer thickness — twice the tail length — is populated instead, since aggregation number and micelle radius aren't meaningful concepts for a bilayer-forming system.

Solution pH, ionic strength, and counterion binding all change the effective head-group area in real surfactant systems — for example, adding salt can screen electrostatic repulsion between charged head groups and shrink the effective area, pushing p higher and favoring less-curved structures. This calculator takes head area as a fixed input rather than deriving it from solution chemistry, so it's best used as a first-pass structural prediction to guide formulation, not a substitute for actual CMC measurement or scattering data.