^{1,a)}, László Pusztai

^{2,b)}, Zofia Sokołowska

^{3}and Stefan Sokołowski

^{4}

### Abstract

The behavior of Lennard-Jones fluid in slitlike pores with walls modified by tethered chain molecules is studied using density functional theory. The effects of confinement and chemical modification of pore walls on the solvation force are investigated. Two models of the pore walls are considered. According to the first model, the chain molecules are chemically bonded by their end segments to opposite walls of the pore, forming flexible pillars. In the second model the chains build up a brush at each wall due to bonding of the first segment at one wall. The nonbonded terminating segment of a molecule is strongly attracted via a short-range potential to any wall of the pore. Then a pillarlike or looplike structure of chains can be formed. In the first model the solvation force at the wall-to-wall is repulsive for narrow pores and strongly attractive for wider pores of the order of the nominal chain length. Oscillations of the solvation force are induced by adsorbed fluid structure and by ordered structure of segments on the fragment of entirely attractive force curve. In the second model, however, the solvation force decays to zero as the pore width increases. Attractive force can be induced at intermediate separation between walls due to modification of the pore walls.

This paper was partially supported by EU under TOK Contract No. 50924. O.P. acknowledges partial support from Grant No. IN223808-2 of the National University of Mexico. L.P. and O.P. are grateful for partial support from a bilateral agreement between the CONACyT of Mexico and the Hungarian Academy of Sciences.

I. INTRODUCTION

II. THE MODEL AND THE THEORY

III. RESULTS AND DISCUSSION

### Key Topics

- Density functional theory
- 12.0
- Adsorption
- 11.0
- Mean field theory
- 7.0
- Solid surfaces
- 6.0
- Chemical potential
- 5.0

## Figures

The solvation force (part a) and excess adsorption isotherms (part b) for model I. The results are for , , , , and for given in the figure.

The solvation force (part a) and excess adsorption isotherms (part b) for model I. The results are for , , , , and for given in the figure.

Density profiles of fluid particles (part a), total segment density profiles (part b), and profiles of particular segments (part c) in the pore . The calculations are for , , , , and for the values of given in parts a and b. In part c the values of give the segment number. In this panel lines are for and symbols are for . In part a the profile for the case was multiplied by 3, in part b the profile for was multiplied by 6 for better visualization.

Density profiles of fluid particles (part a), total segment density profiles (part b), and profiles of particular segments (part c) in the pore . The calculations are for , , , , and for the values of given in parts a and b. In part c the values of give the segment number. In this panel lines are for and symbols are for . In part a the profile for the case was multiplied by 3, in part b the profile for was multiplied by 6 for better visualization.

The solvation force for model I (part a) for , , , , and for different given in the figure. Part b: the density profiles in the pore of at conditions given in part a.

The solvation force for model I (part a) for , , , , and for different given in the figure. Part b: the density profiles in the pore of at conditions given in part a.

The solvation force (part a) and the excess adsorption isotherms (part b) vs the pore width. The results are for model I at , , , , and for different , , given in Fig. 4(a).

The solvation force (part a) and the excess adsorption isotherms (part b) vs the pore width. The results are for model I at , , , , and for different , , given in Fig. 4(a).

The solvation force for pillars of different length (model I). Part a: , dashed line is for and , whereas solid line is for and . Part b: and for , . All the curves are at and for .

The solvation force for pillars of different length (model I). Part a: , dashed line is for and , whereas solid line is for and . Part b: and for , . All the curves are at and for .

Part a. The solvation force for model II. The values of the bulk fluid density are given in the figure. Parts b and c show the fluid density profiles (part b) and the total segment density profiles (part c) in the pores of different width (the nomenclature of the lines is given in part b). The bulk fluid density in parts b and c is . All the calculations in parts a–c are at , , , , and .

Part a. The solvation force for model II. The values of the bulk fluid density are given in the figure. Parts b and c show the fluid density profiles (part b) and the total segment density profiles (part c) in the pores of different width (the nomenclature of the lines is given in part b). The bulk fluid density in parts b and c is . All the calculations in parts a–c are at , , , , and .

Part a: the solvation force for model II for different values of given in the figure. Part b: the total segment density profiles (solid lines) and fluid density profiles (dashed lines, the latter were multiplied by 10). In the upper panel , in the lower panel . All the calculations were carried out for the bulk density , , , , and .

Part a: the solvation force for model II for different values of given in the figure. Part b: the total segment density profiles (solid lines) and fluid density profiles (dashed lines, the latter were multiplied by 10). In the upper panel , in the lower panel . All the calculations were carried out for the bulk density , , , , and .

Part a: the solvation force for model II for different values of (solid line) and (dashed line). The bulk fluid density is , , , , and . Part b: the solvation force for model II and for the systems with chains . Solid line is for , , and and dashed line is for , , and . The temperature is and .

Part a: the solvation force for model II for different values of (solid line) and (dashed line). The bulk fluid density is , , , , and . Part b: the solvation force for model II and for the systems with chains . Solid line is for , , and and dashed line is for , , and . The temperature is and .

Article metrics loading...

Full text loading...

Commenting has been disabled for this content