Abstract and Applied Analysis

Volume 2014 (2014), Article ID 407265, 7 pages

http://dx.doi.org/10.1155/2014/407265

Research Article

Weak Solutions for a Sixth Order Cahn-Hilliard Type Equation with Degenerate Mobility

Aibo Liu and Changchun Liu

Department of Mathematics, Jilin University, Changchun 130012, China

Received 29 January 2014; Accepted 4 March 2014; Published 1 April 2014

Academic Editor: Ming Mei

Copyright © 2014 Aibo Liu and Changchun Liu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

We study an initial-boundary problem for a sixth order Cahn-Hilliard type equation, which arises in oil-water-surfactant mixtures. An existence result for the problem with a concentration dependent diffusional mobility in three space dimensions is presented.

1. Introduction

We consider

in , where is a bounded domain, , is mobility, , , and , are constants [1]. From the physical consideration, we prefer to consider a typical case of the volumetric free energy ; that is, , in the following form [1, 2]:

Equation (1) is supplemented by the boundary value conditions

and the initial value condition

Equation (1) is the sixth order parabolic equation which describes dynamics of phase transitions in ternary oil-water-surfactant systems [2]. Here is the scalar order parameter which is proportional to the local difference between oil and water concentrations. Pawow and Zajączkowski [2] proved that the initial-boundary value problem (1)–(4) with admits a unique global smooth solution which depends continuously on the initial datum. Wang and Liu [3] proved that the solutions of problem (1)–(4) with might not be classical globally. In other words, in some cases, the classical solutions exist globally, while in some other cases, such solutions blow up at a finite time. They also discussed the existence of global attractor. Liu and Wang [4] considered the optimal control problem for the problem (1)–(4) with . They proved the existence of optimal solution. The optimality system is also established. Since the mobility depends on the concentration in general, the equation with nonlinear main part reflects even more exactly the physical reality comparing to the one with linear main part. Schimperna and Pawow [5] studied (1) with viscous term , and logarithmic potential

They investigated the behavior of the solutions to the sixth order system as the parameter tends to . The uniqueness and regularization properties of the solutions have been discussed. Liu [6] studied the problem (1)–(4) and he proved the existence of classical solutions for two dimensions and , , .

In this paper, we study the problem (1)–(4) with degenerate concentration dependent mobility. The main difficulties for treating the problem are caused by the degeneracy of the principal part, nonlinearity of the fourth order term, and the lack of maximum principle. Our method is based on Galerkin approximation and Simon's compactness results.

This paper is organized as follows. In Section 2, using Galerkin approximation, we prove the existence of the weak solution for positive mobility. In Section 3, we prove the existence of the weak solution for degenerate case.

2. Existence for Positive Mobilities

In this section, we study the Cahn-Hilliard equation with a mobility which is bounded away from zero. We prove existence of weak solutions.

Consider the following sixth order Cahn-Hilliard equation:

with the boundary conditions

and the initial value

In this section, we assume is a bounded domain with Lipschitz boundary and such that

(i) and there is such that .

Under these assumptions we can state the following theorem.

Theorem 1. Suppose . Then there exists a pair of functions such that

(1),(2),(3),(4),

which satisfies equation (1) in the following weak sense:

for all , and

for all , and almost all .

Proof. To prove the theorem we apply a Galerkin approximation. Let be the eigenfunctions of the Laplace operator with Neumann boundary conditions; that is,

The eigenfunction is orthogonal in the , , and scalar product. We normalize the such that . Furthermore we assume without loss of generality that . Now we consider the following Galerkin ansatz for (6):

This gives an initial value problem for a system of ordinary differential equations for :

By use of the Peano existence theorem, the initial value problem has a local solution. Now, we set

In order to derive a priori estimates we differentiate the and get

This implies

The last inequality follows the fact that .

On the other hand, we have

By the Young inequality

Combining the above inequalities and using , yield

This estimate implies that the are bounded and therefore a global solution to the initial value problem (6) exists. By Gagliardo-Nirenberg inequality (noticing that we consider only the three-dimensional case)

If we denote by the projection of onto span , we get

for all . This implies

Using compactness results, (Simon [7] and Lions [8]) we obtain for a subsequence (which we still denote by )

It remains to show the convergence of ; choosing in (14) gives

By (19) and Poincaré inequality, we obtain

and this implies weakly in .

The strong convergence of in and the fact that in give . By weakly in and weakly in we can pass limit in (9). Using (22), we know . Then we can pass the limit in (10).

3. Existence for the Degenerate Case

Our approach is to approximate the degenerate problem by nondegenerate equations. By Theorem 1, we know the existence of weak solution to the problem

where .

We denote the solution by ; from now on we assume either or is convex.

Lemma 2. The solution belongs to the space and .

Proof. Since

for all , and almost all , from elliptic regularity theory, we get . By , (22) and (23), we have

Then we get

which implies . Therefore, we get

for all .

In the next step we prove the energy estimates.

Lemma 3. There exists an such that for all , and the following estimates hold with a constant C independent of

Proof. The is a valid test function in (33). Therefore, we obtain

Define functions

where we set when . It is easily proved that

for at least a subsequence . Furthermore we can show strongly in . For any we have

Since

it follows that

Using we have for almost all

Pass to the limit in the equation, where we apply the convergence properties of . Hence, we get

and (2) follows easily from (1), and this finishes the proof of Lemma 3.

Theorem 4. Let either or convex and suppose that . Then there exists a pair such that

(1),(2),(3),(4),

which satisfies in ; that is,

for all and

in the following weak sense:

for all which fulfill on .

Proof. From Lemma 2, we get

Now we apply the compactness result [7] with , , and to conclude the existence of a subsequence of such that

Furthermore using standard compactness properties we obtain the convergence

It remains to show that fulfills the limit equation. The weak convergence of and gives in the limit

for all . Now we have identified . Therefore, we want to pass to the limit in

where with on and the left hand side converges to . Since may not have a limit in , we integrate the first term on the right hand side of (50) by parts to get

It is easily proved that uniformly. Hence, we have

Since weakly in and is uniformly bounded, we conclude

Now we pass to the limit in . We consider the case . As for , we have uniformly, which gives

By using

and the fact that is uniformly bounded, a generalized version of the Lebesgue convergence theorem yields

Hence

where we use the fact that .

To complete the proof of Theorem 4 we have to show

In fact, we have

On the other hand, we know

Hence, when , the right hand side of the inequality tends to zero. Similarly, we can pass to the limit, and this finishes the proof of Theorem 4.

Conflict of Interests

The authors declare that they have no conflict of interests in this paper.

References

G. Gompper and J. Goos, “Fluctuating interfaces in microemulsion and sponge phases,” Physical Review E, vol. 50, no. 2, pp. 1325–1335, 1994.

I. Pawłow and W. M. Zajączkowski, “A sixth order Cahn-Hilliard type equation arising in oil-water-surfactant mixtures,” Communications on Pure and Applied Analysis, vol. 10, no. 6, pp. 1823–1847, 2011.

Z. Wang and C. Liu, “Some properties of solutions for the sixth-order Cahn-Hilliard-type equation,” Abstract and Applied Analysis, vol. 2012, Article ID 414590, 24 pages, 2012.

C. Liu and Z. Wang, “Optimal control for a sixth order nonlinear parabolic equation,” Mathematical Methods in the Applied Sciences, 2013.

G. Schimperna and I. Pawłow, “On a class of Cahn-Hilliard models with nonlinear diffusion,” SIAM Journal on Mathematical Analysis, vol. 45, no. 1, pp. 31–63, 2013.

C. Liu, “Regularity of solutions for a sixth order nonlinear parabolic equation in two space dimensions,” Annales Polonici Mathematici, vol. 107, no. 3, pp. 271–291, 2013.

J. Simon, “Compact sets in the space ,” Annali di Matematica Pura ed Applicata. Serie Quarta, vol. 146, pp. 65–96, 1987.

J. L. Lions, Quelques méthodes de résolution des problèmes aux limites nonlinéaires, Dunod, Paris, France, 1969.