Photonic colloidal crystals: How do salt types, combined with electric field, change colloidal structure formation?

Photonic colloidal crystals: How do salt types, combined with electric fields, change colloidal crystal structure formation? Colloidal particles and their self-assembly into an ordered structure play an important role in the formation of photonic crystals that can have a diverse range of uses such as optical transistors, smart shock absorbers or as a part of electronic paper [1,2]. However one of the main difficulties is related to the fact that formation of well-ordered, defect free large domain 3D crystal structures is extremely difficult task [3,4]. Up to date different techniques were used for 3D crystal formation such as vertical self-assembly, spin-coating, dielectrophoretic field and gravitational field application - that have each been successful only in producing face centred cubic (FCC) structures. Lack of the possibility to manipulate and control crystal packing and therefore the photonic band gap is essential limitation for the wide range of applications [5-7]. In this proposal we would like to suggest the idea of exploring the influence of different anions (SO42-, Cl- and NO3-) on colloidal particles packing on various hydrophobic surfaces (PDMS, Teflon and octadecyltrichlorosilane monolayers on Sillicon surfaces) both in the presence and absence of an applied electric field in order to control the packing. It was observed that 3D well-ordered colloidal structures prefer hydrophobic surfaces while a hydrophilic surface gives rise to an amorphous structure with a relatively well-ordered 2D colloidalmonolayer at the periphery of the ring [8,9]. One possible reason for that is the presence of a close-packed population of relatively new phenomena of nanobubbles on the hydrophobic surface that affects the arrangement of the colloidal particles [10-12]. The nanobubbles are stabilized by small quantities of salt anions that are present in the water [13]. However different anions possess different propensity to water/air interface that is indicated by the Hofmeister series [14]. It is anticipated that this characteristic will affect the order of the nanobubbles on the surface and therefore the order of the colloidal particles allowing a crystal growth with various unit cells. The size of the nanobubbles is controlled by the concentration of anions adsorbed on the water/air interface [13]. Therefore one can expect that by varying salt concentration and consequently the size of the nanobubbles, their separation and even their arrangement will be altered. In this manner structures other than FCC can be produced, for example opal-like structure with low fill factor. The size and the packing of the nanobubbles will be monitored by AFM,Total Internal Reflection Fluorescence and Dynamic Light Scattering Technique. X-ray Diffraction will be used to determine the crystal structure formed by the colloidal particles. The charge present on the nanobubbles allows their manipulation with the electric field. Itcan be achieved by using small droplets of a solutioncontaining particles and different types of salts on hydrophobic surfaces to which an electric field is applied. In electrowetting experiments, droplets with different types of salts have shown distinct responses on electric field application [15], a behaviour that can be attributed to the different size and properties of nanobubbles on the hydrophobic surface. This behaviour of droplets can be used to order colloidal particles. These particles will have an induced dipole moment in an electric field so their alignment along the electric field can be correlated with nanobubbles due to a layer of anions and dipole moment interaction. It is therefore expected to affect the crystal structure that will be formed by colloidal particles acting as a template for crystal growth. Application of the electrowetting phenomena is proved to be efficient for the colloidal crystal growth from a solution of deionized water with polystyrene particles on Mica surfaces [16]. For experiments we will use standard electrowetting setup: droplet with the solution resting on coated hydrophobic surface with the ITO conductive layer; another electrode will be immersed in that droplet and then electric field will be applied. Application of the electric field will enhance evaporation of the liquid as well. We would like to use colloidal crystals, obtained by the above mentioned method, to investigate the influence of the photonic band gap, pseudo or complete, on the intensity of the Second Harmonic Generation (SHG). The formation mechanism of SHG signal is somewhat similar to that of fluorescence signal differing in the presence of a virtual energy state for the first and real energy state for the last. Recent experiments have demonstrated that the fluorescence signal of dye molecules embedded into a FCC colloidal crystal was suppressed due to photon confinement and the presence of photonic band gap [17]. Given the mechanism formation similarity, this gives rise to the question: what will happen to the intensity of SHG signal in the colloidal crystal? Unlike the real energy state, virtual energy state has no lifetime and therefore it cannot be delayed or suppressed. Will it therefore be enhanced? To answer these questions we will embed a solution of octupolar molecules (for example 1,3,5-tris[(4-nitrophenyl)ethynyl]-2,4,6-tris(octyloxy)benzene) that possess hyperpolarizability [18] and thus respond with a SHG signal when illuminated by light with a certain wavelength into colloidal crystal. Prepared in such a way, we will illuminate the sample with light of a specific wavelength and then analyze the SHG signal comparing it with a reference signal. The outcome of this study can be applied towards more efficient SHG microscopy and laser applications. In conclusion, the major goals of the project are: 1) to understand the physics the colloidal particle and water/polymer interface interaction that can be used as a unique method for controlling colloidal crystal packing and growth, combining the effects of confinement and the application of an electric field 2) to use these colloidal crystals to study the effect of photon confinement on the SHG signal intensity. [1] B. Comiskey, J. D. Albert, H. Yoshizawa and J. Jacobson, NATURE 1998, 394 (16), 253 [2] R. Biswas, M. M. Sigalas, G. Subramania, and K.-M. Ho, Phys. Rev. B, 1998, 57, 3701 [3] T. Solomon and M. J. Solomon, J. Chem. Phys., 2006,124, 134905. [4] J. Hilhorst, M. M. van Schooneveld, J. Wang, E. de Smit, T. Tyliszczak , J. Raabe , A. P. Hitchcock, M. Obst, F. M. F. de Groot, and A. V. Petukhov, Langmuir, 2012, 28, 3614. [5] E. C. M. Vermolen, A. Kuijk, L. C. Filion, M. Hermes, J. H. J. Thijssen, M. Dijkstra, and A. van Blaaderen PNAS , 2009, 106 (38), 16063 [6] V. N. Manoharan and D. J. Pine, MRS BULLETIN, 2004, 91 [7] L. González-Urbina, K. Baert, B. Kolaric, J. Pérez-Moreno and K. Clays, Chem. Rev., 2012, 112 (4), 2268. [8] H.-Y. Ko, J. Park, H. Shin, and J Moon, Chem. Mater., 2004, 16 (22), 4212 [9] D. M. Kuncicky, K. Bose, K. D. Costa, and O.D. Velev, Chem. Mater. 2007, 19, 141 [10] O.I. Vinogradova, N.F.Bunkin, N.V.Churaev, O.A. Kiseleva, A.V.Lobeyev and B.W.Ninham, Journal of Colloid and Interface Science, 1995, 173, 447 [11] A. C. Simonsen, P. L. Hansen, and B. Klösgen, Journal of Colloid and Interface Science 2004, 273, 291. [12] A. Poynor, L. Hong, I. K. Robinson, S. Granick, Z. Zhang and P. A. Fenter Phys Rev Lett., 2006,97, 266101. [13] E. Duval , S. Adichtchev, S. Sirotkin and A. Mermet, Phys Chem Chem Phys., 2012,14(12), 4125 . [14] D. J. Tobias and J. C. Hemminger, SCIENCE, 2008, 319, 1197. [15] O.Kruglova Unpublished results. [16] J. Kleinert, S. Kim, and O. D. Velev, Langmuir, 2010, 26(12), 10380 [17] B. Kolaric, K. Baert, Renaud A. L. Vallée, M. Van der Auweraer and K. Clays, Chemistry of Materials, 2007, 19(23), 5547. [18] S. V. Cleuvenbergen, G. Hennrich, P. Willot, G. Koeckelberghs, K. Clays, T. Verbiest, and M. van der Veen, Journal of Physical Chemistry C, 2012, 116(22), 12219.

Keywords:Photonic colloidal crystals

Disciplines:Analytical chemistry, Physical chemistry, Condensed matter physics and nanophysics