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ADSORBED POLYMER LAYERS: LOOPS, TAILS AND STIFFNESS. A.N. Semenov Physics Department, Moscow State University, Moscow 119992, Russia email: semenov@polly.phys.msu.su ABSTRACT Polymer adsorption is a remarkable phenomenon that is widely used to modify properties of surfaces and interfaces. I will review theoretical results on the structure of adsorbed polymer layers focusing on the role of loops and tails on the one hand, and the chain stiffness on the other hand. 1. Adsorbed layers formed by flexible polymers Self-similar structure of saturated polymer layers adsorbed from a good solvent onto an attracting surface was elucidated by De Gennes long ago [1]: in the central region (at the distances z from the surface longer than the molecular extrapolation length b but shorter than the coil size R) the monomer concentration decay as φ = z −a , where a = 4/3( a = 2 in the marginal solvent regime). The layer can be viewed as a system of loops of different lengths (chains sections starting and terminating at the adsorbing surface). More recently it was shown [2,3,4] that loops do not dominate everywhere in the central region: the contribution of tails (chain sections starting at the surface and terminating in the bulk) is important at distances z > z * , where z * is a length-scale that is much longer than the monomer size, but much shorter than the coil size R ( u z* N , where u = 1/ 2 in good solvent and u = 1/ 3 in marginal solvent). Hence two subregions: the inner sublayer z < z * formed by loops, and the outer sublayer z > z * dominated by tails (the tail subregion resembles a layer of broadly polydisperse end-grafted chains). Hence a significant portion of the adsorbed layer contains mostly tail monomers. It is remarkable that this conclusion was first obtained in the numerical studies by J. Scheutjens, G. Fleer and their co-workers [5,6] and then stayed unexplained for a long while. The tail sublayer is considerably thicker than the loop layer (at a given distance z from the surface). This results in a surprising behavior: monomer concentration at the given point z ( z >> b) in a saturated layer of shorter chains (N1) may be higher (by a large factor ~ 10) than concentration in a layer of longer chains (N2) provided that z * (N1) < z < z * (N2). The effect of polymer tails is responsible for a number of important effects. The `thicker' tail sublayer is relatively less permeable: it is rather difficult for an unadsorbed chain to penetrate through this layer, the main mechanism of penetration being often end-entry (rather than hairpin entry) [7]. Two saturated adsorbed layers repel each other when their tail sublayers are overlapping (at the distances z* < h< R). This is in contrast with the well-known normal behavior: attraction due to bridging by polymer fragments which is predicted at shorter distances (in the regime of loops) [8]. 2. Adsorption of a stiff worm-like macromolecule Polymers with stiff backbone (including many biological polymers) show a rather different adsorption behavior as compared to that characteristic of flexible chains [9]. I present a theoretical description of adsorption of a single semiflexible chain onto a flat surface. Both scaling and quantitative approaches are discussed. A self-similar monomer concentration profile cx ( )~ z −4/3 is predicted near the surface (when the distance to the surface z is much smaller than the chain persistence length / 2 ). The typical conformation of a weakly adsorbed chain can be viewed as a sequence of alternating 2-dimensional (flat) and 3-dimensional blobs forming a double-layer structure: a thin contact layer (of molecular thickness d, d
the transition temperature T * when τ = 1 −T */ T is smaller than ( d / ) −4/3; otherwise (at larger τ ) the lion's share of the chain is staying in the d-layer very close to the surface. The adsorption transition is continuous although it looks like a discontinuous (first-order) transition outside a narrow region around the adsorption temperature, τ > ( d / ) −4/3. References 1 De Gennes, P.G., 1981. Macromolecules 14, 1637. 2 Semenov, A.N., Joanny, J.F., 1995. Europhys.Lett. 29, 279. 3 Semenov, A.N., Joanny, J.F., Johner, A. Polymer Adsorption: mean-field theory and ground state dominance approximation. In: Theoretical and Mathematical Models in Polymer Science, Chapter 2, pp.37-81 (Ed. A. Grosberg, Academic Press, Boston, 1998). 4 Johner, A., Bonet-Avalos, J., Van der Linden, C.C., Semenov, A.N., Joanny, J.F., 1996. Macromolecules 29, 3629. 5 Scheutjens, J., Fleer, G., 1980. J. Phys.Chem. 84, 178. 6 Scheutjens, J., Fleer, G. In: The Effect of Polymers on Dispersion Properties, Th.F. Tadros Ed., Academic Press, New York, 1982. 7 Semenov, A.N., Joanny, J.-F., 1995. J. de Physique 5, 859. 8 Semenov, A.N., Joanny, J.F., Johner, A., Bonet-Avalos, J., 1997. Macromolecules 30, 1479. 9 Van der Linden, C.C., Leermakers, F.A.M., Fleer, G.J., 1996. Macromolecules 29, 1172.
Page 1 and 2: Frontis - Wageningen International
Page 3 and 4: Prof. dr. Hans Fraaije Leiden Unive
Page 5 and 6: Prof. Ullrich Steiner University of
Page 7 and 8: Preface Self-consistent field model
Page 9 and 10: covered by polymers), and R. Rajago
Page 11 and 12: FIRST-ORDER WETTING TRANSITION AT F
Page 13 and 14: MOLECULAR SCF MODELLING OF PORES IN
Page 15 and 16: COLLAPSE OF POLYMER BRUSHES GRAFTED
Page 17 and 18: SURFACE FORCES, SUPRAMOLECULAR POLY
Page 19 and 20: SWEET BRUSHES: SYNTHESIS AND INTERF
Page 21 and 22: EFFECT OF MIXING OF TWO CHARGED PHO
Page 23 and 24: Figure 2 show a semi-log comparison
Page 25 and 26: MODELING OF STATIONARY POLYMER DIFF
Page 27 and 28: THEORY AND SIMULATION OF BILAYER ME
Page 29 and 30: Figure 1. Time evolution of the she
Page 31 and 32: SALT EFFECT TO RAYLEIGH DROPLETS OF
Page 33 and 34: MACROMOLECULES AT INTERFACES, A FLE
Page 35 and 36: APPLICATION OF HETEROGENEOUS LATTIC
Page 37 and 38: 8. Linse, P., 1993b. Phase behavior
Page 39 and 40: MODELING INTERFACIAL EFFECTS ON THE
Page 41 and 42: Using this patterned electrode, we
Page 43 and 44: span the gap between the electrodes
Page 45 and 46: desirable to use a probe with a muc
Page 47 and 48: span the gap between the electrodes
Page 49: MEMBRANE FUSION: RESULTS FROM SIMUL
Page 53 and 54: PROTEIN ADSORPTION ON SURFACES WITH
Page 55 and 56: MODELLING STRUCTURE AND ADHESION AT
Page 57 and 58: References 1. Fischel, L.B. and The
Page 59 and 60: MULTIDOMAIN CONFORMATIONS OF RANDOM
Page 61 and 62: SUPRAMOLECULAR COORDINATION POLYMER
Page 63 and 64: INFLUENCE OF POLYMERS ON THE BENDIN
Page 65 and 66: SPINODAL DECOMPOSITION IN BINARY PO
Page 67 and 68: PERSISTENCE LENGTH OF WORM-LIKE MIC
Page 69 and 70: For small particles with radius R <
Page 71: MEAN-FIELD THEORY FOR THE ADSORPTIO

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