An Effective Method for the Preparation of Stable LC Composites with High Concentration of Quantum Dots

Abstract

COMMUNICATION modifi cation of QDs with complex mesogen containing ligands, which resulted in the preparation of thermodynamically stable QDs solution in LC matrix, yet with still low concentration of the additive (0.25%). In the most of other papers devoted to QDs solutions in LC media the concentration of QDs does not exceed 0.1%.There are several recent works concerning the LC-QDs mixtures with higher concentration of the QDs. [ 21,22 ] Yet, these experimental results are in strong contradiction with other publications devoted to the similar mixtures and lack strong experimental proofs of the thermodynamic stability of these composites.In most cases, the methods of preparation of QD-LC composites are based on simple mixing of components in common solvent followed by spin coating or drying. [ 23,24 ] In some cases, bi-or multilayer fi lms containing QDs-rich layers were prepared by sequential spin-coating method. [ 25,26 ] As a resume, from the literature data, we may conclude that the development of new methods for embedding of high amount of QDs in LC media without the loss in the optical properties of any of the component is still challenging and highly relevant. In the present paper, we propose a new method of preparation of stable QD-LC composites containing very high (up to 10 wt%) amount of QDs.The idea of the elaborated procedure is schematically depicted in Figure 1 . On the fi rst stage, the polymer-stabilized LC fi lm (with any type of LC phase) is prepared (Figure 1 a). For this purpose, LC mixture consisting of ≈ 10% of mesogenic diacrylate, ≈ 15% of LC monoacrylate, ≈ 75% of lowmolar-mass LCs and 1%-2% of photoinitiator (see Table 1 ) is placed into asymmetrical cell with two glass substrates coated by different polymer layers -polyvinyl alcohol (PVA) and polyvinyl-cinnamate (PVCin). Rubbing of the substrates with polymer layers allows one to achieve uniaxial orientation of LCs molecules. UV irradiation of these cells leads to photopolymerization of acrylates. The presence of reactive C C double bonds in the cinnamate fragment of PVCin warrants a good adhesion of polymer network to PVCin-coated glass substrate, which makes mechanical removal of the PVA-coated glass plate (Figure 1 b) on the next stage more easy. The LC fi lm obtained after photo polymerization has microheterogeneous structure consisting of LC polymer network and low-molarmass LC microphase. Nevertheless, under appropriate irradiation conditions (light intensity, monomers, and photoinitiator structure and their concentration), characteristic dimensions of these microphases are comparable or even smaller than the wavelength of visible light, which minimizes light scattering of LC-composite fi lms. [ 20,21 ] LC-polymer network stabilizes the alignment of the LCs molecules, and has the possibility Organic-inorganic hybrid materials, in particular, liquid crystals doped with nanoparticles, quantum dots (QDs) and other nanometer-scale colloid particles attract a great attention of large number of research groups due to their unique opti...

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Technology for Creation and Detailed Analysis of Polymer Composites with Uniform Distribution of Quantum Dots and Liquid Crystals

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