Multiple-interface solutions of one dimensional generalized parabolic Cahn-Hilliard equation

Abstract

We consider one dimensional generalized parabolic Cahn-Hilliard equation $$ u_t=-\partial_{xx}\big[\partial_{xx}u-W'(u)\big]+W''(u)\big[\partial_{xx} u -W'(u)\big], \qquad \forall\, (t,x)\in [0,+\infty)\times {\mathbb R}, $$ where the function $W(\cdot)$ is the standard double-well potential. For any given positive integer $k\geq2$, we construct a solution $u(t,x)$ with $k$ interfaces, which has the form $$ u(t,x)\approx\sum_{j=1}^k(-1)^{j+1}\omega\big(x-\gamma_j(t)\big)-\frac{1+(-1)^k}{2}\qquad \text{as}\ t\rightarrow +\infty, $$ where $\omega$ is the solution to the Allen-Cahn equation $$ \omega''-W'(\omega)=0,\quad\omega'>0\quad\mbox{in }{\mathbb R}, \quad \omega(0)=0, \quad \omega(\pm\infty)=\pm 1. $$ The interfaces are described by the functions $\gamma_j(t)$ with $j=1,\cdots,k$, which are determined by a Toda system and have the forms $$ \gamma_j(t)=\frac{1}{2\sqrt{2}}\left(j-\frac{k+1}{2}\right)\ln t +O(1). $$ The Toda system is different from the one that determine the dynamics of the multiple interfaces of solutions to one dimensional parabolic Allen-Cahn equation established by M. del Pino and K. Gkikas in {\em Proc. R. Soc. Edinb. Sect. A}, 148 (2018), 6: 1165-1199.