Supporting Information

  • Yan Y
  • Yang S
  • Blake A
  • et al.
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Abstract

Ellipsometric characterization of the P2VP brush in the dry and swollen states We carried out in situ ellipsometric measurements of the 7.8-nm-thick P2VP brush in water at pH 5.5 and pH 2.5 to determine changes in the brush thickness upon the transition between the collapsed and swollen states. The refractive index and thickness of the collapsed brush (pH 5.5) was the very close to those in the dry state, specifically 1.59 and 8.9 nm, respectively. At pH 2.5, however, the strong swelling was observed with the corresponding values of the refractive index and thickness of 1.394 and 36.5 nm, respectively. The obtained value of the thickness of the swollen brush implies that the brush comprises 79% of water. A degree of swelling, defined as a ratio of the brush thickness in the swollen state to that in the collapsed state, is 4.7. We used the rule of mixtures, i.e. n = n P2VP ·ν P2VP + n water ·ν water , where n P2VP =1.59 is the refractive index of P2VP, ν P2VP =0.21 is the volume fraction of the P2VP component in the swollen brush, n water = 1.333 is the refractive index of water, and ν water =0.79 is the volume fraction of water in the swollen brush, to assess the effective refractive index of the swollen brush; the calculated value of 1.391 is very close to the experimental one (1.394). Some discrepancy in the values of the swelling degree between the AFM and ellipsometric measurements can be rationalized by the well-established fact that the highly swollen polymer brush exhibits a parabolic profile of the chain density in the direction normal to the substrate surface. It is reasonable to assume that at the SP value of 98% the AFM tip probed the brush region related to the tail of the density profile and hence the measured thickness is expected to be close to the maximum brush height. In the case of ellipsometry, we simulated the experimental data using a model, in which the brush was assumed to have the step-like profile of a refractive index; consequently, the calculated layer thickness represents the effective height of the brush. The swelling behavior and compressibility of the swollen hybrid layer as studied by AFM Figure S1. The plot displaying the dependence of the thickness of the swollen hybrid layer at pH 2.5 on the SP value. The experimental data are shown with the squares, while the solid and dotted lines denote the best fit to these data using the Boltzmann function (the coefficient of determination > 0.999) and the asymptote to the upper part of the fitting curve, respectively. This conclusion that the hybrid layer experience minor compression at SP 98 % is in accord with the results of our previous study of the conformation of single P2VP chains adsorbed on the surface of a solid substrate.[1] In particular, we demonstrated that at this SP value the conformation of the chains Electronic Supplementary Material (ESI) for Nanoscale This journal is

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Yan, Y., Yang, S., Blake, A. J., Lewis, W., Poirier, E., Barnett, S. A., & Champness, R. (2011). Supporting Information, 1–21.

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