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Confinement and compression of an oligomer brush
Biointerphases volume 5, pages 69–73 (2010)
Self-assembled monolayers and oligomer brushes confined between two parallel plates show compressional forces that are nonmonotonic as a function of plate separation. In a realistic model of short alkanethiols, based on the rotationally isomeric state model with parameters from ab initio calculations, the authors show that nonmonotonic forces arise from the elimination of longer conformers as the distance between the plates is reduced. This nonmonotonicity is a size effect that disappears when the length of the polymer molecule is sufficiently increased. An analytical model is developed that allows experimentalists to extract energy-averaged brush height distributions from compressional force curves.
R. R. Netz and D. Andelman, Phys. Rep. 380, 1 (2003).
K. L. Prime and G. M. Whitesides, J. Am. Chem. Soc. 115, 10714 (1993).
J. Satulovsky, M. A. Carignano, and I. Szleifer, Proc. Natl. Acad. Sci. U.S.A. 97, 9037 (2000).
Y.-Y. Luk, M. Kato, and M. Mrksich, Langmuir 16, 9604 (2000).
R. E. Holmlin, X. Chen, R. G. Chapman, S. Takayama, and G. M. Whitesides, Langmuir 17, 2841 (2001).
S. Herrwerth, W. Eck, S. Reinhardt, and M. Grunze, J. Am. Chem. Soc. 125, 9359 (2003).
J. Groll, Z. Ademovic, T. Ameringer, D. Klee, and M. Moeller, Biomacromolecules 6, 956 (2005).
S. Alexander, J. Phys. 38, 983 (1977).
P. G. de Gennes, Macromolecules 13, 1069 (1980).
S. T. Milner, T. A. Witten, and M. E. Cates, Macromolecules 21, 2610 (1988).
R. R. Netz and M. Schick, Macromolecules 31, 5105 (1998).
R. R. Netz and M. Schick, Europhys. Lett. 38, 37 (1997).
M. Murat and G. S. Grest, Macromolecules 22, 4054 (1989).
M. P. Pépin and M. D. Whitmore, J. Chem. Phys. 111, 10381 (1999).
E. P. K. Currie, G. J. Fleer, M. A. Cohen Stuart, and O. V. Borisov, Eur. Phys. J. E 1, 27 (2000).
C. Seidel and R. R. Netz, Macromolecules 33, 634 (2000).
M. A. Carignano and I. Szleifer, Mol. Phys. 100, 2993 (2002).
L. Livadaru and H. J. Kreuzer, Z. Phys. Chem. 218, 929 (2004).
G. Oncins, C. Vericat, and F. Sanz, J. Chem. Phys. 128, 044701 (2008).
M. Heuberger, T. Drobek, and N. D. Spencer, Biophys. J. 88, 495 (2005).
L. L. Cai and S. Granick, Adv. Colloid Interface Sci. 94, 135 (2001).
T. W. Kelley, P. A. Schorr, K. D. Johnson, M. Tirrell, and C. D. Frisbie, Macromolecules 31, 4297 (1998).
C. S. Hodges, Adv. Colloid Interface Sci. 99, 13 (2002).
P. T. Mikulski and J. A. Harrison, J. Am. Chem. Soc. 123, 6873 (2001).
M. Salmeron, Tribol. Lett. 10, 69 (2001).
K. Ohno, T. Sakamoto, T. Minagawa, and Y. Okabe, Macromolecules 40, 723 (2007).
F. S. Csajka, R. R. Netz, C. Seidel, and J. F. Joanny, Eur. Phys. J. E 4, 505 (2001).
M. A. Carignano and I. Szleifer, Macromolecules 28, 3197 (1995).
A. E. van Giessen and I. Szleifer, J. Chem. Phys. 102, 9069 (1995).
O. J. Hehmeyer, G. Arya, A. Z. Panagiotopoulos, and I. Szleifer, J. Chem. Phys. 126, 244902 (2007).
L. Livadaru, R. R. Netz, and H. J. Kreuzer, J. Chem. Phys. 118, 1404 (2003).
J. B. Klauda, B. R. Brooks, A. D. J. MacKerell, R. M. Venable, and R. W. Pastor, J. Phys. Chem. B 109, 5300 (2005).
J. I. Siepmann and D. Frenkel, Mol. Phys. 75, 59 (1992).
J. I. Siepmann and I. R. McDonald, Phys. Rev. Lett. 70, 453 (1993).
D. B. Staple, F. Hanke, and H. J. Kreuzer, New J. Phys. 9, 68 (2007).
For example, peaks in the density of states are still visible in situations where many states are accessible, such that distributions appear otherwise smooth, see Ref. 35. D. B. Staple, F. Hanke, and H. J. Kreuzer, New J. Phys. 9, 68 (2007).
In the energy versus height plot of the conformers, there are lines or bands of equal energy. Their origin is simple: introducing a gauche state in an all-trans conformer costs 23 meV according to Table I, independent of where along the chain it is introduced, but resulting in different heights. The next band has two gauche states and the next after that has a gauche defect (ttg−g+tt), etc.
If the density is a series of delta-functions D(h) = Σa i δ(h−h i, as it would be if only a small number of distinct conformers contribute to the brush, we get steps in the free energy and spikes on the force/pressure curve.
G. Oncins (private communication).
R. L. C. Wang, H. J. Kreuzer, and M. Grunze, Phys. Chem. Chem. Phys. 2, 3613 (2000).
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Foster, S., Wainwright, C., Staple, D.B. et al. Confinement and compression of an oligomer brush. Biointerphases 5, 69–73 (2010). https://doi.org/10.1116/1.3455152