Generating in-plane Orientational Order in Multilayer Films Prepared by Spray-Assisted Layer-by-Layer Assembly

Transcription

1 Supporting information Generating in-plane Orientational Order in Multilayer Films Prepared by Spray-Assisted Layer-by-Layer Assembly Rebecca Blell,, Xiaofeng Lin, Tom Lindström, Mikael Ankerfors,,# Matthias Pauly,, Olivier Felix and Gero Decher *,,, CNRS Institut Charles Sadron, 23 Rue du Loess, F Strasbourg, France Innventia AB, Drottning Kristinas väg 61, Box 5604, SE Stockholm, Sweden Faculté de Chimie, Université de Strasbourg, 1 Rue Blaise Pascal, F-67008, Strasbourg, France International Center for Frontier Research in Chemistry, 8 Allée Gaspard Monge, F Strasbourg, France # present address: BillerudKorsnäs AB, Uggelviksgatan 2B, SE Stockholm, Sweden present address: Borregaard Norway (S/P), Hjalmar Wessels vei 6, 1701 Sarpsborg, Norway Corresponding author decher@unistra.fr S-1

2 S-I/ CNF Size Distribution Figure S1. AFM image of a sub-monolayer of cellulose nanofibers (CNFs) deposited on a PEI coated Si-wafer. The size distribution of CNFs has been estimated by analyzing a sub-monolayer of CNFs by AFM (Figure S1). This distribution has been determined on more than 100 CNFs in order to get a representative statistic. CNFs have an estimated diameter of 2 nm and an average length between 250 and 500 nm. S-II/ Relative Brightness as a Function of the Incidence Angle The angular variation of the in-plane relative brightness of oriented (PEI/CNF) 1 (CHI/CNF) 120 samples prepared by GIS at an incidence angle below 5 and at 15 has been determined by cross polarized optical microscopy to evidence their birefringence properties and compared to non oriented samples built by orthogonal spraying. As expected, the film obtained by orthogonal spraying shows only negligible birefringence (red data points), i.e. that the relative brightness between the crossed polarizers is independent of the in-plane orientation of the sample. For anisotropic films a clear dependence of the reflected intensity between the crossed polarizers is observed both when the sample is rotated and when S-2

3 the deposition is carried out at different incident spraying angles. Thicker films were obtained for films sprayed at 15 (d = 135 nm, blue data points) than films sprayed below 5 (d = 115 nm, green data points). It seems reasonable to assume that the induced liquid shear decreases progressively with increasing incidence angle. The thicker the film is the more intense the the relative brightness gets (Figure S-5). Figure S2. Angular dispersion of the in-plane relative brightness under crossed polarizers for a non aligned sample prepared by orthogonal spraying ( ) and aligned (PEI/CNF)1(CHI/CNF)120 samples sprayed below 5 ( ) and at 15 ( ) by GIS. S-III/ Relative Brightness as a Function of the Nozzle/Receiving Surface Distance The variation of the relative brightness of the oriented (PEI/CNF)1(CHI/CNF)40 sample has been measured with an optical microscope in the crossed polarizer configuration as a function of the S-3

4 distance between the nozzle and the receiving surface. As longer trajectory lengths correspond to longer flying times of the spray droplets and therefore smaller droplet speeds, it seems reasonable to assume that the induced liquid shear decreases with longer trajectory lengths and therefore causes a reduced orientation with increasing distance from the nozzle and thus a reduced birefringence. The experimental conditions were chosen such the difference in relative brightness as depending on the distance is easily observable across few centimeters. Figure S3. Dispersion of the in-plane relative brightness under crossed polarizers for an aligned (PEI/CNF) 1 (CHI/CNF) 40 sample as a function of the distance between the nozzle and the receiving surface. S-IV/ Analysis of the CNF Orientation In order to extract the distribution of orientation of the CNFs with respect to the spraying direction, the plugin OrientationJ for ImageJ has been used. 1 Although it has been originally S-4

5 developed for the analysis of optical micrographs of biological tissues or cells, this tool can be readily used for the analysis of AFM images. S-5

6 Figure S4. (a) Top view of the spray cone arriving on the receiving surface. The red spots (1-4) indicate the location where the AFM images were taken. (b) Color-code for the orientation. (c) For each red dot (1-4) in (a), an original AFM image (left), a color-coded image obtained after applying the OrientationJ plugin (middle), and a normalized angle distribution extracted from the image analysis (right) are depicted. Specific areas (indicated by doted blue squares) of AFM images were used for image treatment to limit the influence of large aggregates on the orientation distribution of the CNFs. S-6

7 The analysis, which is based on the computation of the local structure tensor in the local neighborhood of each pixel, is applied to the original AFM image (Figure S4c left). As a result, an orientation angle is given for each pixel, and a color-code which represents each angle by a color (Figure S4b) is used to build Figure S4c middle. Finally, the angle distribution can be extracted (Figure S4c right). The distribution is non-weighted (i.e. 1 pixel = 1 count), but the pixels for which the values of the coherency or the energy are lower than 20% have been ignored. Indeed, these pixels are often artifacts, for instance noisy pixels or located at edges and corners. S-V/ Relative Brightness as a Function of the Layer Number Figure S5. Angular dispersion of the in-plane relative brightness under crossed polarizers for aligned (PEI/CNF) 1 (CHI/CNF) m samples with m equal 21 ( ), 41 ( ) and 71 ( ). The relative brightness of the oriented (PEI/CNF) 1 (CHI/CNF) m samples, where m = 21, 41 or 71, has been measured with an optical microscope in the crossed polarizer configuration. The angle S-7

8 between the CNF orientation direction and the incident light polarization plane has been varied. While a negligible birefringence was observed for isotropic film prepared by dipping or orthogonal spraying (see Figure 4b in the main manuscript). On contrary, for anisotropic films the relative brightness increases with the film thickness. The optical relative brightness depends clearly on the amount of oriented materials and can therefore be used to demonstrate that the whole film possesses an anisotropic structure and not just the first layers. S-VI/ Relative Brightness on Crossed Polarized Micrographs Figure S6. Optical gray-scale micrographs used to determine the relative brightness of oriented PEI(aCNF/chitosan) 80 LbL-film for the angles between the orientation direction and crossed polarizers showing minimum (0, 90, 180 ) and maximum (45, 135 ) intensities on the half polar plot. A defect has been circled to evidence the sample rotation. The reflected intensity under polarized white light has been measured with an optical microscope in the crossed polarizer configuration. The sample is placed between the two polarizer oriented at 90 from each other, and the angle between the CNF orientation direction and the incident light S-8

9 polarization plane has been varied. For each angle, a micrograph has been taken and transformed to a 8-bit gray-scale picture. The average gray-value is measured for each picture and plotted as function of the angle. The intensity is minimum when the CNFs are oriented along the same direction as either the polarizer or the analyzer (0, 90, 180, 270 ), and the reflected intensity is maximum when the CNFs are oriented exactly between the polarizer and analyzer axes (more intense lobe at 45 and 255 ; less intense lobe at 135 and 315 ). References 1. Rezakhaniha, R.; Agianniotis, A.; Schrauwen, J. T. C.; Griffa, A.; Sage, D.; Bouten, C. V. C.; Vosse, F. N.; Unser, M.; Stergiopulos, N. Experimental Investigation of Collagen Waviness and Orientation in the Arterial Adventitia using Confocal Laser Scanning Microscopy. Biomech. Model. Mechanobiol. 2012, 11, S-9