Evidence of a Transition Layer Between the Free Surface and the Bulk

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Supporting Information for the Manuscript:

Evidence of a Transition Layer Between the Free Surface and the Bulk

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Wojciech Ogieglo*,

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Kristianne Tempelman,

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Simone Napolitano and

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Nieck E. Benes

$Films in Fluids, University of Twente, Enschede, The Netherlands

#Laboratory of Polymer and Soft Matter Dynamics, Faculté des Sciences, Université libre de Bruxelles (ULB), Boulevard du Triomphe, Bâtiment NO, Bruxelles 1050, Belgium

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corresponding author: [email protected]; Author’s current affiliation: Advanced Membranes & Porous Materials Center, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia

Fig S1 The influence of optical modeling parameters on the obtained swelling factor, SF a) SF versus fixed window delta offset parameter #1 with simultaneous fit for the film thickness and index b) SF versus fixed values of the film refractive index during fitting for the film thickness with window offset determined from calibration against a calibration wafer

Fig S1 shows the influence of selected measurement parameters on the obtained film swelling. It is obvious that the cell windows birefringence (window delta offset) has a major influence on the film swelling factor (SF = hswollen / hdry), especially for the thinnest films, as seen from Fig S1a. It is absolutely critical that this parameter is accurately corrected for by using a calibration wafer measured inside of the measurement chamber. In this study the determined window delta offset was #1 = 4.976 for the 280 kg∙mol^-1 and 0.250 for the 500 and 1000 kg∙mol^-1 samples. On the other hand, the obtained swelling is virtually insensitive to the film refractive index, Fig S1b. The sensitivity increases slightly for thicker films, however in those cases the index can be determined simultaneously with the thickness at sufficiently high accuracy and does not need to be fixed in the optical model.

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Fig S2 Original (uppermost) Figure 1 from the main manuscript compared with different presentations of data with square root of time (middle) and squared extent of thickness change (lowermost). In particular, the middle graph shows the non-Fickian (non-linear on the square root of time) behavior within the transition layer.

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