Collapse of polymer brushes grafted onto planar ... - Wageningen UR

More documents

Recommendations

Info

10-50 Å, which increases with the block length. Both experiments and theory reveal evidence for the existence of three regimes regarding the configuration of the dangling blocks: a “wet brush” regime, a “mushroom” regime, and a broad transition regime in between. SCF calculations can serve as a starting point for predicting mechanical failure at interfaces subjected to large-scale deformations. A hierarchical simulation approach has been designed for this purpose. Using as input the chemical constitutions and relative amounts of chain species present at the interface, the composition profiles and conformational characteristics for all these species are first calculated by SCF theory (Terzis 2000a). The statistical weights derived from the model are then used within a Monte Carlo procedure to generate large ( ≈ 0.1 µm-sized) three-dimensional computer “specimens” of the interfacial region. In these specimens the material is represented, in a coarse-grained sense, as a network of entanglement points. Each entanglement point is shared by two chains. Each chain is defined by the positions of its ends and of all entanglement points it traverses, as well as by its contour lengths between these points (Terzis 2000b). A coarse-grained free energy function incorporating excluded volume, dispersion attraction, and conformational entropy contributions is written for the network. An efficient numerical procedure is invoked for finding local minima of this free energy function with respect to the positions of all chain ends and entanglement points, and thereby imposing the condition of mechanical equilibrium. Deformation of the network to fracture (Figure 1) at prescribed temperature and strain rate is simulated through a kinetic Monte Carlo procedure, which tracks elementary events of chain slippage across entanglements, chain disentanglement, chain reentanglement, and chain rupture (Terzis 2002). This hierarchical procedure has been applied to study interfaces between polypropylene (PP) and polyamide 6 (PA6) compatibilised with the reaction product between maleic anhydride-functionalised PP (PP-g-MA) and PA6. Such interfaces can be viewed as consisting of a homopolymer (free PP) next to an impenetrable solid surface (PA6), onto which are grafted chains of the same chemical constitution as the homopolymer (endgrafted PP). The effects of the surface density of grafted PP and of the molecular weight distribution of free PP and grafted PP have been explored. It is clearly seen that increasing the surface grafting density does not necessarily enhance adhesion. For high surface grafting densities, a “brush” of grafted PP builds up next to the PA6 surface; as a consequence, the region over which grafted and free PP chains interentangle is of limited width. For monodisperse grafted PP of molar mass 40 kg/mol in a free PP matrix of molar mass 60 kg/mol, optimal adhesion (a maximum in the work required to destroy the interface) is seen at 0.1 grafted chains/nm 2 . TRUE STRESS (MPa) 250 200 150 100 50 1% per sec 10% per sec 0 1 2 3 4 DRAW RATIO Figure 1: Shapshots and stress-draw ratio curves from tensile deformation computer experiments carried out on network specimens modelling the PP/PP-g-MA/PA6 interface. Grafted and free PP chains are shown in red and green, respectively. The stress-strain curves have been obtained at two strain rates for a surface grafting density of 0.10 chains/nm 2 . The specimen, of initial dimensions 45 nm × 45 nm × 70 nm, contained 1300 chains.
References 1. Fischel, L.B. and Theodorou, D.N., 1995. Self-consistent field model of the polymer/diblock copolymer/ polymer interface. J. Chem. Soc. Faraday Trans., 91 (16), 2381-2402. 2. Retsos, H., Terzis, A.F., Anastasiadis, S.H., Anastassopoulos, D.L., Toprakcioglu, C., Theodorou, D.N., Smith, G.S., Menelle, A., Gill, G.E., Hadziioannou, G., Gallot, Y., 2002. Mushrooms and brushes in thin films of diblock copolymer/homopolymer mixtures. Macromolecules, 35(3), 1116-1132. 3. Russell, T.P., Anastasiadis, S.H., Menelle, A., Felcher, F.P., Satija, S.K., 1991. Segment density distribution of symmetric diblock copolymers at the interface between two homopolymers as revealed by neutron reflectivity. Macromolecules, 24(7), 1575-1582. 4. Scheutjens, J.M.H.M. and Fleer, G.J., 1979. Statistical theory of the adsorption of interacting chain molecules 1. Partition function, segment density distribution, and adsorption isotherms. J. Phys. Chem., 83(12), 1619-1635. 5. Terzis, A.F., Theodorou, D.N., Stroeks, A., 2000. Entanglement network of the polypropylene/polyamide interface. 1. Self-consistent field model. Macromolecules, 33(4), 1385-1396. 6. Terzis, A.F., Theodorou, D.N., Stroeks, A., 2000. Entanglement network of the polypropylene/polyamide interface. 2. Network generation. Macromolecules, 33(4), 1397-1410. 7. Terzis, A.F., Theodorou, D.N., Stroeks, A., 2002. Entanglement network of the polypropylene/polyamide interface. 3. Deformation to fracture. Macromolecules, 35(2), 508-521.
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 and 50: MEMBRANE FUSION: RESULTS FROM SIMUL
Page 51 and 52: the transition temperature T * when
Page 53 and 54: PROTEIN ADSORPTION ON SURFACES WITH
Page 55: MODELLING STRUCTURE AND ADHESION AT
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
show all

Collapse of polymer brushes grafted onto planar ... - Wageningen UR

Create successful ePaper yourself

Delete template?

Save as template?