  In the present article we study diffuse interface models for two-phase
biomembranes. We will do so by starting off with a diffuse interface model on
$\mathbb{R}^n$ defined by two coupled phase fields $u,v$. The first phase field
$u$ is the diffuse approximation of the interior of the membrane; the second
phase field $v$ is the diffuse approximation of the two phases of the membrane.
We prove a compactness result and a lower bound in the sense of
$\Gamma$-convergence for pairs of phase functions
$(u_\varepsilon,v_\varepsilon)$. As an application of this first result, we
consider a diffuse approximation of a two-phase Willmore functional plus line
tension energy.
