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    Home > Preparation of colloid with adjustable rheological properties by ternary inclusion complex of Cucurbit [8] urea

    Preparation of colloid with adjustable rheological properties by ternary inclusion complex of Cucurbit [8] urea

    • Last Update: 2018-05-11
    • Source: Internet
    • Author: User
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    The rheological properties of liquids have always been the focus of scholars' research, including the research on the properties of elasticity, plasticity, viscosity and strength of fluids In recent years, with the development of supramolecular chemistry, more and more attention has been paid to stimulation responsive fluids Among them, photoresponsive fluids, such as colloids that can regulate viscosity (shear thinning and shear thickening) by external light stimulation, have been applied in many fields For example, some colloids dispersed in pigments, coatings and lubricants usually have the phenomenon of continuous viscosity increase in the process of rapid shear, which will damage the processing equipment and reduce the quality of products to a certain extent Therefore, it is of great practical significance to study the fluid with controllable rheological properties Figure 1 The main compounds that make up the supramolecular chemical colloid (photo source: small, 2018, 14, 1703352) Recently, Professor Oren a Scherman from the Department of chemistry, Cambridge University, UK, developed a simple and efficient controllable colloid preparation method based on the research on the recognition properties of Cucurbit [8] urea (CB [8]) The raspberry like colloid was prepared by assembling Fe3O4 nanoparticles onto silicon nucleus by the interaction of methyl viologen (MV), azobenzene and cucurbit [8] urea Due to the positive charge on the surface, colloidal particles will repel each other, so at high shear rate, colloidal particles will form hydrodynamic clusters When the colloidal particles are disassembled by light, the positively charged nano particles and negatively charged silicon core will attract each other and shear thinning will occur This achievement was published in small (DOI: 10.1002 / small 201703352) under the title of "curibit [8] uril regulatedcolloidal disorders exhibiting photocontrolled physiological behavior" Fig 2 A) SEM of raspberry colloid; b) SEM of colloid after UV irradiation; c) SEM of colloid after visible light irradiation (picture source: small, 2018, 14, 1703352) The preparation method of colloid is relatively simple Firstly, the author prepared the colloidal particles with methyl viologen rich surface Fe 3O 4 and azobenzene rich surface respectively Then, an excessive amount of Cucurbit [8] urea is added to the solution of Fe3O4 nanoparticles At this time, cucurbit [8] urea will be loaded on the surface of nanoparticles through intermolecular interaction and methyl viologen binding Next, add the prepared colloidal particles to the solution containing mv-cb [8] - Fe3O4 nanoparticles, and then ultrasonic for 5 minutes to obtain the mixed colloid with raspberry structure (Fig 2a) Because the mixed colloid is formed by the interaction between azobenzene, methyl viologen and cucurbit [8] urea, and light can change the CIS trans structure of azobenzene to regulate the formation of ternary inclusion complex Therefore, after the colloidal particles are irradiated by UV, the Fe3O4 nanoparticles on the surface will dissociate (Fig 2b); after the visible light irradiation, the nanoparticles will be loaded on the colloid again to form a mixed colloid (Fig 2C) Fig 3 A) ζ potential of colloid before and after illumination; b) viscosity of fluid changes with shear rate; c) repeatability of fluid changes (picture source: small, 2018, 14, 1703352); after illumination, colloid changes not only its surface morphology, but also its rheological characteristics The zeta potential of the non illuminated colloid surface is about + 17 MV (Fig 3a), and they will repel each other in the solution Therefore, if the solution contains high concentration of such colloidal particles, it will show some characteristics of non-Newtonian fluid, and the flow will appear shear thickening when the shear rate reaches a certain degree (Fig 3b) However, after UV irradiation, only shear thinning occurs when the shear rate of the fluid increases However, after exposure to visible light, the fluid can return to its previous state, and the change can last several times (Fig 3C) All authors: C Hu, J Liu, Y Wu, K R West, O a Scherman corresponding author: O.A Scherman
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