Multi-component phase separation and small deformations of a spherical biomembrane

Abstract We focus on the derivation and analysis of a model for multi-component phase separation occurring on biological membranes, inspired by observations of lipid raft formation. The model integrates local membrane composition with local membrane curvature, describing the membrane’s geometry through a perturbation method represented as a graph over an undeformed Helfrich minimising surface, such as a sphere. The resulting energy consists of a small deformation functional coupled to a Cahn–Hilliard functional. By applying Onsager’s variational principle, we obtain a multi-component Cahn–Hilliard equation for the vector $$\varvec{\varphi }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>φ</mml:mi> </mml:mrow> </mml:math> of protein concentrations coupled to an evolution equation for the small deformation u along the normal direction to the reference membrane. Then, in the case of a constant mobility matrix, we consider the Cauchy problem and we prove that it is (globally) well posed in a weak setting. We also demonstrate that any weak solution regularises in finite time and satisfies the so-called “strict separation property”. This property allows us to show that any weak solution converges to a single stationary state by a suitable version of the Łojasiewicz–Simon inequality.