water; iv) drying in a nitrogen flow; and v) plasma treatment (Harrick Plasma cleaner/sterilizer PDC-32G) for 2 min. This cleaning procedure results in hydrophilic substrates with a waterΒ±air contact angle of less than 10 .
The surface modification proceeds as follows: i) adsorption of QNHEC with an average molar mass of 360 kg mol Β±1 (AKZO-Nobel Arnhem) from solution (100 mg l Β±1 , 0.1 M NaCl, pH 10) onto the silicon wafer for 30 min; ii) rinsing with demineralized water; iii) adsorption of negatively charged uniform spheres of silica of different sizes (LUDOX grades HS-40, SM-30, and TM-50, Aldrich Chemical Company, Inc.; the numbers indicate the silica weight percent in the original purchased colloidal dispersions) from a dilute suspension (100 mg l Β±1 , 0.05 M NaCl, pH 7); and iv) rinsing successively with demineralized water and acetone. Finally, the samples are sintered at 1000 C for 5Β±10 min. In this way the polymer is burnt away, and we end up with a pure silica surface with the same chemical structure as the smooth silicon substrate, which has a native oxide layer. After the cleaning procedure the new surface is again found to be hydrophilic (y H 2 O < 10).
The adsorption of QNHEC on silica has recently been studied by Hoogendam et al. [16], from whose results we have chosen our experimental parameters such that we can expect a sufficient adsorption of the polymer on the substrate. Similarly, the conditions for the silica adsorption were taken from publications by BΓΆhmer [13] and BΓΆhmer et al. [14]. By rinsing with water and acetone, respectively, we tried to prevent surface salt deposition and silica particle aggregation as much as possible.
Surface and Film Characterization: Ellipsometry (Sentech ellipsometer model SE400, with a rotating analyzer) was used to determine the thickness of the QNHEC film. The topography of this film was imaged using a Nanoscope III AFM (Digital Instruments, Santa Barbara, California). Both contact mode (CM; silicon nitride cantilevers with a spring constant of about 0.58 N/m) and tapping mode atomic force microscropy (TM-AFM; silicon cantilevers with a resonance frequency of about 350Β±380 kHz) were used. AFM was also used to study the topography and surface roughness of the (sintered) silica particle layer.
LCP films were prepared by spin-coating from 1,2-dichloroethane. The repeating unit of the LCP used, as well as its phase behavior, is given in Figure . The synthesis and characterization of the phase behavior has been described by Nieuwhof et al. [17].
The topography was also measured by AFM. However, for rough surfaces it is impossible to measure the LCP film thickness accurately by ellipsometry. Therefore, test films of the LCP were spin-coated also onto smooth silicon wafers to determine the film thickness. The phase behavior and stability of the LCP films were investigated by optical microscopy (Olympus BX60 equipped with a hot stage and crossed polarizers).