Influence of Janus Particle Shape on their. Interfacial Behavior at Liquid-Liquid Interfaces

Transcription

1 1 SUPPORTING INFORMATION 2 to 3 4 Influence of Janus Particle Shape on their Interfacial Behavior at Liquid-Liquid Interfaces 5 6 By Thomas M. Ruhland, André H. Gröschel, Nicholas Ballard, Thomas S. Skelhon, Andreas Walther, Axel H. E. Müller and Stefan A. F. Bon 7 1. TEM characterization of Janus particles The synthetic pathway to obtain Janus structures is based on a template-assisted synthesis, involving crosslinking of the microphase-segregated morphologies of a bulk film of the respective triblock block terpolymer, followed by a sonication treatment as outlined in 11 previous work. 1 This process results in the formation of tightly core-crosslinked Janus particles, possessing a PB core and two hemicylinders of PS and PMMA. Figure S1 displays a typical transmission electron microscopy (TEM) micrographs of Janus sphere (S1 A), Janus cylinders (S1 B) and Janus discs (S1 C). The Janus particles are characterized by an extremely well-defined cross section, originating from the well-ordered block terpolymer bulk structure. Figure S1 D-E points out the size and diameter distribution of the Janus particles used in the experiments. The Janus spheres are monodisperse in form and shape with a diameter of ca. 50 nm. A polydisperse length distribution can be found for the Janus cylinders with the main peak at ~ 2300 nm. From earlier investigations we know that the PB cylinder has an average diameter of ca. 23 nm with a surrounding corona, leading to a total diameter of the cross 1

2 section of 80 nm. 2 The Janus discs show a bimodal size distribution with a fraction of relatively large Janus discs (ca. 350 nm in diameter) and a fraction of smaller ones with a diameter of around 250 nm. The height of the discs, investigated in prior studies of our group, approaches values between 30 nm and 40 nm, respectively Figure S1 TEM micrographs of (A) Janus spheres, (B) Janus discs and (C) Janus cylinders. Length and diameter distribution of (D) Janus spheres, (E) Janus discs and (F) Janus cylinders Reference system for pendant drop measurement Figure S2 Interfacial tension isotherm of the pristine toluene/water interface. 2

3 Interpretation of the different adsorption stages in the adsorption process of the Janus particles at the toluene/water interface Figure S3 Interpretation of the different adsorption stages in the adsorption process of the Janus particles at the toluene/water interface. (A) Adsorption curves of Figure 1 in logarithmic presentation for all Janus particles. Logarithmic presentation of the interfacial values for (B) Janus discs, (C) Janus spheres and (D) Janus cylinder The logarithmic plots in Figure S3 show the different stages of adsorption of the Janus particle assembly at the toluene/water interface as they manifest in regions of different slopes. All shapes of Janus particles reached a plateau value in the final stage. For all types of Janus particles almost the same adsorption process can be observed except of slightly different adsorption mechanism due to the different shapes. The interfacial tension decreases with time and approaches different quasi-equilibrium values due to different particle shapes. The adsorption process is characterized by different adsorption stages. At early stages of adsorption, the interfacial tension decreases rapidly. Subsequently, the decrease in interfacial 3

4 tension slows down, and finally, it approaches a plateau, where the maximum coverage of the interface with particles is obtained. After reaching the plateau value, the Janus particles are located and arranged at the interface. Different particle geometries lead to minimal different adsorption mechanism and kinetics, and the plateau value is reached earlier. In the beginning, free diffusion to the interface occurs (I), followed by continuous adsorption of Janus particles including ordering and domain formation at the interface and the decrease in interfacial tension slows down (II). Finally, similar to stage II additional packing leads to a rearrangement of the domains in order to get more particles to the interface. The adsorption of new Janus particles comes along with a rearrangement and better ordering of already adsorbed particles at the interface and to the formation of a multilayer system (III). In case of the Janus discs the adsorption process is based on a slightly different adsorption mechanism so that an additional adsorption step takes places (IV) Free energy simulation of Janus particles at a toluene/water interface The simulation method is the same Bon et al. used for their calculations of orientation of hematite particles at a liquid-liquid interface. 4 First, it is important to define the form of the particles in a mathematic way. X, y, z are cartesian coordinates. r x, r y, r z are the radii of the particles. n 1 and n 2 act as parameter in the z -axis and the x-y plane respectively. The values in Table S1 are in agreement with the shape of the Janus particles used in the measurements, already characterized in former studies and in figure S1. Table S2 describes the interfacial tension values we used as assumptions for our calculations. 71 Table S1 Geometrical data for the different shapes of the Janus particles. x [nm] y [nm] z [nm] n 1 n 2 Janus spheres Janus discs Janus cylinders

5 Table S2 Interfacial tension values used in the calculations. 5 γ [mn/m] Toluene Water PS PMMA Toluene Water Keep in mind that this model neglects some factors which may contribute to the complete adsorption energy. The influence of gravity, interfacial deforming and line tension is also ignored as the influence of capillary bridging described by Stebe et al. 6,7 due to the fact that we are calculating with isolated particles. We believe that these assumptions are acceptable for this kind of simulations Shape simplifications of the Janus particles for scheme Scheme S1 Overview of possible Janus particle architectures and their simplifications for the description of their adsorption process in scheme 2. (A) Spheres, (B) cylinders and (C) discs References 1. Walther, A.; Müller, A. H. E. Janus particles. Soft Matter 2008, 4, Ruhland, T. M.; Gröschel, A. H.; Walther, A.; Müller, A. H. E. Janus Cylinders at Liquid Liquid Interfaces. Langmuir 2011, 27, Walther, A.; André, X.; Drechsler, M.; Abetz, V.; Müller, A. H. E. Janus Discs. J. Am. Chem. Soc. 2007, 129, Morgan, A. R.; Ballard, N.; Rochford, L. A.; Nurumbetov, G.; Skelhon, T. S.; Bon, S. A. F. Understanding the multiple orientations of isolated superellipsoidal hematite particles at the oil-water interface. Soft Matter 2013, 9, Binks, B. P.; Clint, J. H. Solid Wettability from Surface Energy Components: Relevance to Pickering Emulsions. Langmuir 2002, 18,

6 Lewandowski, E. P.; Bernate, J. A.; Tseng, A.; Searson, P. C.; Stebe, K. J. Oriented assembly of anisotropic particles by capillary interactions. Soft Matter 2009, 5, Lewandowski, E. P.; Cavallaro, M.; Botto, L.; Bernate, J. C.; Garbin, V.; Stebe, K. J. Orientation and Self-Assembly of Cylindrical Particles by Anisotropic Capillary Interactions. Langmuir 2010, 26,