The Slowly Formed Guiselin Brush

We study polymer layers formed by irreversible adsorption from a polymer melt. Our theory describes an experiment which is a ``slow'' version of that proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered instantaneously irreversibly adsorbing chains and predicted a universal density profile of the layer after swelling with solvent to produce the ``Guiselin brush.'' Here we ask what happens when adsorption is not instantaneous. The classic example is chemisorption. In this case the brush is formed slowly and the final structure depends on the experiment's duration, $t_{final}$. We find the swollen layer consists of an inner region of thickness $z^* \sim t_{final}^{-5/3}$ with approximately constant density and an outer region extending up to height $h \sim N^{5/6}$ which has the same density decay $\sim z^{-2/5}$ as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter

Irreversibility and Polymer Adsorption

Physisorption or chemisorption from dilute polymer solutions often entails irreversible polymer-surface bonding. We present a theory of the non-equilibrium layers which result. While the density profile and loop distribution are the same as for equilibrium layers, the final layer comprises a tightly bound inner part plus an outer part whose chains make only fN surface contacts where N is chain length. The contact fractions f follow a broad distribution, P(f) ~ f^{-4/5}, in rather close agreement with strong physisorption experiments [H. M. Schneider et al, Langmuir v.12, p.994 (1996)].Comment: 4 pages, submitted to Phys. Rev. Let

Validity of the scaling functional approach for polymer interfaces as a variational theory

We discuss the soundness of the scaling functional (SF) approach proposed by Aubouy Guiselin and Raphael (Macromolecules 29, 7261 (1996)) to describe polymeric interfaces. In particular, we demonstrate that this approach is a variational theory. We emphasis the role of SF theory as an important link between ground-state theories suitable to describe adsorbed layers, and "classical" theories for polymer brushes.Comment: 8 pages, 1 figure, to be published in Phys. Rev.

Non-Equilibrium in Adsorbed Polymer Layers

High molecular weight polymer solutions have a powerful tendency to deposit adsorbed layers when exposed to even mildly attractive surfaces. The equilibrium properties of these dense interfacial layers have been extensively studied theoretically. A large body of experimental evidence, however, indicates that non-equilibrium effects are dominant whenever monomer-surface sticking energies are somewhat larger than kT, a common case. Polymer relaxation kinetics within the layer are then severely retarded, leading to non-equilibrium layers whose structure and dynamics depend on adsorption kinetics and layer ageing. Here we review experimental and theoretical work exploring these non-equilibrium effects, with emphasis on recent developments. The discussion addresses the structure and dynamics in non-equilibrium polymer layers adsorbed from dilute polymer solutions and from polymer melts and more concentrated solutions. Two distinct classes of behaviour arise, depending on whether physisorption or chemisorption is involved. A given adsorbed chain belonging to the layer has a certain fraction of its monomers bound to the surface, f, and the remainder belonging to loops making bulk excursions. A natural classification scheme for layers adsorbed from solution is the distribution of single chain f values, P(f), which may hold the key to quantifying the degree of irreversibility in adsorbed polymer layers. Here we calculate P(f) for equilibrium layers; we find its form is very different to the theoretical P(f) for non-equilibrium layers which are predicted to have infinitely many statistical classes of chain. Experimental measurements of P(f) are compared to these theoretical predictions.Comment: 29 pages, Submitted to J. Phys.: Condens. Matte

Characteristic discontinuity of the reflectivity curve in vicinity of total reflection in the case of an attractive slowly varying potential

The reflection of a plane wave on a potential which is zero at infinity may be calculated by a one dimensional Schrödinger equation (ħ 2/2m)ψ" + Eψ = Vψ, where E is the energy of the incidental wave and V the potential. When the energy is negative, the reflection is total (R(E) = 1) ; consequently we expect lim E →0+ R(E) to be equal to 1, the reflectivity curve being then continuous. But this is not always the case. When the potential is attractive and proportional to -1/(Z+Z0)α where 0 < α < 2, lim E→0+R (E ) does exist, but is strictly lower than 1. So we remark a discontinuity. The purpose of this study is to demonstrate the existence of this limit and to explicitly calculate the value.La réflexion d'une onde plane sur un potentiel nul à l'infini est susceptible d'être calculée à partir de l'equation de Schrödinger à une dimension : (ħ 2/2 m) ψ" + Eψ = Vψ où E est l'énergie de l'onde incidente et V le potentiel. Lorsque l'énergie est négative, la réflexion est totale (R (E) = 1) ; on s'attend donc à ce que lim R (E) = 1, la courbe de réflectivité étant E→0+ alors continue. Mais ce n'est pas toujours le cas. Lorsque le potentiel est attractif et est proportionnel à -1/(Z+Z0)α où 0 < α < 2, lim E→0+ R( E) existe bien, mais est inférieure à 1. On observe donc une discontinuité. L'objet de l'étude que voici est de démontrer l'existence de cette limite et d'en calculer explicitement la valeur

Polymer-surfactant films at the air-water interface, Part II: a neutron reflection study

Mixed polymer-surfactant films at the air-water interface have been studied using neutron reflectivity. When poly(dimethylsiloxane) is spread on the surface of a surfactant layer, the resultant mixed film is a superposition of two layers: one surfactant-rich and one polymer-rich. The composition and the degree of mixing of the layers depend on the nature of the surfactant. We find significant penetration of the polymer into a monolayer of single-chain nonionic surfactant, C 10E 5. For a double-chain anionic surfactant, AOT, no interpenetration of the two layers is detected. This difference is most probably due to the greater flexibility of the C 10E 5 monolayer compared to that of AOT. The higher degree of hydration of the nonionic surfactant layer could also play a role in the mixing behavior of the polymer and surfactant layers. The molecular thickness of the polymer layer indicates a flat two-dimensional conformation of the spread polymer. The results from this study together with those in part 1 our paper suggest that the wetting behavior of the polymer is related to the degree of interpenetration of the polymer and surfactant layers. © 1993 American Chemical Society