The structure of a rotational isomeric state alkane melt near a hard wall

Sen, Sudeepto; Cohen, Jennifer; McCoy, John D.; Curro, John G.

doi:10.1063/1.468028

Cited by 65 publications

(74 citation statements)

References 40 publications

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“…In one approach the free energy is expanded in a functional series in the density (about some uniform fluid density); the kernels of successive terms in the expansion are direct correlation functions of increasing order. This is the approach followed by Chandler and coworkers (5) and Sen et al (11) and is described later. The other approach is more phenomenological.…”

Section: Density Functional Theorymentioning

confidence: 95%

Weighted Density Approximation for Polymer Melts

Yethiraj

1996

ACS Symposium Series

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This chapter describes a density functional theory for polymer melts which combines a weighted density approximation for the ex cess free energy functional with an exact treatment of the ideal gas free energy functional. The theory employs a Monte Carlo simulation to calculate the properties of a single chain in an arbitrary external field. The bulk fluid properties required in the theory are obtained from a generalized Flory equation of state. The theory is found to be accurate for the density profiles of semiflexible polymer melts con fined between flat plates for several densities and molecular stiffnesses. The theory is also compared to other theories for nonuniform polymer melts.In many applications, such as the processing of polymer melts, the behaviour of polymer molecules within a few Angstroms of a surface is of critical importance. Consequently there have been a number of recent studies devoted to obtaining an understanding of polymers near surfaces using liquid state methods such as computer simulation (1-3) integral equations (4), and density functional theories (5-11). In this chapter I describe the density functional theory recently proposed by Yethiraj and Woodward (10) and compare the predictions of this theory to Monte Carlo simulations (12, 13) and to other theories.The quantity of primary interest in nonuniform fluids is the density profile of the fluid. For simple liquids, the two theoretical approaches that have been em ployed to calculate the density profile are integral equations and density functional theories. Integral equations are based on the growing adsorbent model (14,15) where the equations are solved for a mixture of the fluid and an adsorbent in the limit as the adsorbent species becomes infinitely dilute and infinitely large. The fluid density profile is simply related to the adsorbent-fluid pair correlation

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Section: Density Functional Theorymentioning

confidence: 95%

Weighted Density Approximation for Polymer Melts

Yethiraj

1996

ACS Symposium Series

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“…On the other hand, as in the case of atomic hard sphere liquids, high packing fractions result in an enhancement of the density near the wall since effective occupation of space is the primary consideration. In figure 1, this interplay of conformational and packing entropies can be seen [3,4]. At low packing fractions (d=0), there is a large density depletion near the wall.…”

Section: The Density Functional Of This Form Was First Introduced By mentioning

confidence: 92%

“…In the series of studies reviewed here [1][2][3][4], the intrachain interactions were described by the Rotational Isomeric State (RIS) model. In the freezing studies [1,2], polyethylene in the long chain limit was modeled, and, in the wall / polymer studies [3,4], tridecane was modeled between smooth, hard walls which were adequately separated so that bulk behavior occurred in the center of the slit.…”

Section: System Modelmentioning

confidence: 99%

“…In the freezing studies [1,2], polyethylene in the long chain limit was modeled, and, in the wall / polymer studies [3,4], tridecane was modeled between smooth, hard walls which were adequately separated so that bulk behavior occurred in the center of the slit. In both cases, the RIS parameters were as in Flory [24].…”

Section: System Modelmentioning

confidence: 99%

“…Interestingly, a short ranged depletion region remains even at high packing fraction. Because the chains were explicitly simulated [3,4], more detailed information concerning the chain structure, the distribution of site type, etc. can be obtained.…”

Section: The Density Functional Of This Form Was First Introduced By mentioning

confidence: 99%

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Inhomogeneous Rotational Isomeric State Polyethylene and Alkane Systems

McCoy

Nath

1996

ACS Symposium Series

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The density functional modeling of Rotational Isomeric State (RIS) chains is reviewed. Two cases are considered. First, the freezing of polyethylene is investigated, and the melt and solid densities at the transition are predicted. New results are reported which incorporate the attractive as well as the repulsive contribution of the site-site potential. Good agreement is found with experimental measurements. Second, the structure of a tridecane melt near a hard wall is considered. Both the site density profile and the distortion of the backbone structure are predicted. Good agreement is found with the results of simulation and equation-of-state predictions. Recently there has been considerable interest in applying density functional (DF) methodology to inhomogeneous polymeric systems [1-18]. Here we focus on the Chandler-McCoy-Singer (CMS) formulation of molecular DF theory [19-21] where bonding constraints are explicitly retained in the "ideal" system. In addition, we restrict ourselves to the case where the homogeneous liquid state input is included through sitesite correlation functions as opposed to being introduced through the equation-of-state. Related work on inhomogeneous polymeric systems is reviewed by McMullen [10], Rosenberg [14], and Yethiraj [18].Ubiquitous to all density functional theories is the expression of a free energy, usually the grand potential, Ω = -PV, as a functional of the inhomogeneous density distribution, p(r), as well as of more traditional variables such as the temperature, T; the volume, V; the chemical potential, μ; and the external field, U(r). Since the chemical potential and the external field conveniently couple as \|/(r) = μ-UCr), the grand potential functional can be denoted as Ω[Τ, V, \|/(r); p(r)j. Of course, because p(r) itself is a functional of Τ, V, and \|/(r), only three of the variables in the brackets are independent and including p(r) in the expression for Ω

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