One-Dimensional Model of Polymer Adsorption

DiMarzio, Edmund A.; McCrackin, Frank L.

doi:10.1063/1.1696778

Cited by 195 publications

(56 citation statements)

References 8 publications

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“…The theoretical description of polymer adsorption at surfaces is in terms of structures having "trains" of sequential segments adsorbed to the surface, "loops" of desorbed segments between the trains, and desorbed "tails" at either end. Early descriptions based on random walks and Monte Carlo simulations modeled the case of the isolated chain at a surface [13,14]. These showed that the fraction of adsorbed segments for a polymer of length n is proportional to n 1͞2 for critical values of the segmentsurface interaction energy that are of order k B T .…”

Section: Figmentioning

confidence: 99%

Kinetics and Energetics of Oligomer Desorption from Surfaces

2001

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The dynamics of oligomer desorption from surfaces has been studied by measuring the desorption kinetics of a set of straight chain alkanes [H͑CH 2 ͒ n H, with n 5 to 60] from the surface of single crystalline graphite. Desorption is observed to be a first-order process and the preexponent of the desorption rate constant has a value n 10 19.660.5 sec 21 and is independent of the oligomer chain length. More interestingly, we find that the barrier to desorption has a nonlinear dependence on chain length and takes the form DE This Letter reports the barriers to desorption ͑DE z des ͒ of straight chain alkanes [H͑CH 2 ͒ n H, with n 5 to 60] from the surface of graphite into vacuum and the finding of a nonlinear dependence of DE z des on chain length, n. This nonlinear behavior reveals something of the dynamics of the complex process or mechanism by which oligomeric species desorb from surfaces. Independent of its fundamental interest, this result has implications for a number of technologically important surface phenomena such as the evaporation of thin lubricant films from the surfaces of magnetic data storage disks and the desorption of alkanes from the surfaces of Fischer-Tropsch catalysts.The vast majority of measurements of molecular desorption kinetics from surfaces have used relatively small species for which the desorption process is considered simply as a displacement along the surface normal. This desorption mechanism can be adequately modeled using a single well-defined reaction coordinate through a fairly simple potential energy surface describing the interaction of the molecule with the surface. The desorption rate constant is usually considered to have the form given by the transition state theory [1]where h is Planck's constant and k B is Boltzmann's constant. The DE z des is the difference between the zero-point energies of the adsorbed state and the transition state for desorption. At best the multidimensional nature of the adsorbate-substrate potential energy surface influences the desorption kinetics through the partition functions for the adsorbed state ͑q͒ and the transition state for desorption ͑q z ͒.Consider the desorption of an oligomeric species such as H͑CH 2 ͒ 60 H from a surface. Many scanning tunneling micrographs (STM) of alkanes adsorbed on graphite at room temperature reveal an all-trans conformation stretched out and interacting with the surface along its length [2][3][4][5]. Since the desorbed state has no segments interacting with the surface one might predict that the DE z des should be linear in the chain length. There have been several prior sets of measurements which observe the effects of alkyl chain length on the desorption kinetics of species such as alkyl alcohols and simple alkanes adsorbed on metal surfaces [6][7][8][9]. In these cases the range of alkyl chain lengths has been limited to n # 12. Needless to say, over this limited range the measured values of DE

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Section: Figmentioning

confidence: 99%

Kinetics and Energetics of Oligomer Desorption from Surfaces

2001

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“…[6] It is well known that the introduction of a boundary can alter the physical character of a statistical system. [7] As an example of the subtle effects that our method reveals for statistical systems near curved boundaries, we discuss the adsorption-desorption transition of polymers growing near an attractive boundary. [8] In the limit of an infinitely extended polymer, a finite fraction P (κ) of monomers gets adsorbed on the boundary as soon as the attractive potential κ on the boundary increases above a critical value.…”

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confidence: 99%

Statistical Models on Spherical Geometries

Boettcher

Moshe

1995

Phys. Rev. Lett.

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We use a one-dimensional random walk on D-dimensional hyper-spheres to determine the critical behavior of statistical systems in hyper-spherical geometries. First, we demonstrate the properties of such a walk by studying the phase diagram of a percolation problem. We find a line of second and first order phase transitions separated by a tricritical point. Then, we analyze the adsorption-desorption transition for a polymer growing near the attractive boundary of a cylindrical cell membrane. We find that the fraction of adsorbed monomers on the boundary vanishes exponentially when the adsorption energy decreases towards its critical value.

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“…For example, an additional increase of the adsorbed macromolecule dimension was observed for PEO [2]. DiMarzio and McCrackin have shown [25] that for high-molecular polymers the mean squared dimension of a statistical chain, perpendicular to an interface, approaches an asymptotic value Adopted from our previous paper [2].…”

Section: Discussionmentioning

confidence: 92%