| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 103 === The aim of this research is to prepare the modified Halloysite nanotubes (HNTs) by surface-grafting polystyrene (PS) to bear both the hydrophilic and hydrophobic characteristics. The modified HNTs is suitable for Pickering emulsion agents to emulsify the oil in water. Then, the factors of emulsification by modified HNTs such as the emulsification diameter and morphology of modified HNTs were studied. Finally, with 1,6-hexanediol diacrylate (HDDA) as oil phase, the solid Pickering films were produced by UV polymerization in W/H emulsions from modified HNTs.
The preparation of grafted polystyrene on HNTs was divided into two systems. In system (A), the cation exchange capacity (CEC) of HNTs was assumed to be one fifteenth that of montmorillonite (MMT). Cationic surfactants such as vinylbenzyl dimethyl dodecyl ammonium chloride (VBDDAC) and cetyl trimethyl ammonium bromide (CTAB) were mixed to form bilayer micelles on outer surface of HNTs and the grafted polystyrene by styrene monomers were prepared. The formulations of bilayer micelles can be separated into two parts. One is VBDDAC containing half times CEC (5V) on HNTs surface and the other is VBDDAC containing 0.75 times CEC (7.5V) on HNTs surface. In system (B), the HNTs was grafted with 3-(trimethoxy silyl)-1-propanol, adsorbed with CTAB to form bilayer micelles, and polymerized with different weights of styrene. Also, the difference between with and without purification for HNTs was studied.
Pickering emulsions were prepared by modified HNTs with toluene and water as liquid phases. In system (A), the averaged emulsion particle diameter for 5V sample was found to be 88 μm, 198 μm and 248 μm for increasing volume ratio of water/toluene at 0.5, 1.0, and 2.0. And for 7.5V, the diameter was 81 μm, 87 μm,176 μm which increased with the rising volume ratio 0.5, 1.0, and 2.0. All of these emulsions was water in oil (W/O), the emulsion size of 7.5V was smaller than that of 5V which could be explained that 7.5V grafted more PS to make its HNTs surface more hydrophobic.
For system (B), we found that W/O emulsions were formed by the weights ratio of HNTs to styrene from 1/1 to 1/4 due to their hydrophobic charater. With the increasing volume ratio of the water to toluene from 0.5 to 1.0, the emulsion particle diameter of sample H-M3C-1S-e (after extraction) the particle diameter is 1850 μm and 2852 μm; With the increasing volume ratio of the water to toluene from 0.5, 1.0 to 2.0, the emulsion diameter of H-M3C-2S-e is 73 μm, 178 μm, and 217 μm; For H-M3C-3S-e is 60 μm, 154 μm, and 209 μm; For H-M3C-4S-e is 38 μm, 80 μm, and 101 μm, respectively. Under the same condition, after purifying, the emulsion particle diameter of PH-M3C-1S-e is 1056 μm ,1811 μm, and 2278μm; For PH-M3C-2S-e is 89 μm, 104 μm, and 130 μm; For PH-M3C-3S-e is 80 μm, 88 μm, and 116 μm; and for PH-M3C-4S-e is 40 μm, 80 μm, and 115 μm, respectively. After grinding, the average particle diameter of sample H-M3C-1S-e-g is 308 μm, 331 μm, and 452 μm for the same ratio of water to toluene. For H-M3C-2S-e-g the diameter is 71 μm, 157 μm, and 203 μm; For H-M3C-3S-e-g is 42 μm, 110 μm, and 151 μm; For H-M3C-4S-e-g is 33 μm, 67 μm, and 77 μm, respectively. All emulsification types were W/O. In system (B), the particle diameter of sample with purification was smaller than that without purification. This might due to more grafted PS chains on sample after purification. After grinding, HNTs might lose aggregation ability and have smaller size and disperse well in continuous phase (oil phase).
By FT-IR monitoring, modified HNTs with PS had C-H aromatic stretching vibration at 3030 cm-1, aliphatic stretching vibration at 2924 and 2852 cm-1 and overtones of mono-substituted benzene at 1945, 1872, 1800, 1745, and 1673 cm-1. These results indicate that polystyrene was polymerized on the surface of HNTs successfully. By XRD analysis, the peak at around 12 o was the characteristic diffraction peaks of HNTs. For system (B), after PS grafting there was no difference in XRD diffraction angle of HNTs because the silanol may react with surface hydroxyl groups from internal and external surfaces.
For static water contact angle analysis for system (A), the contact angle of 5V and 7.5V were measured at 67.7o, and 71.4o. For system (B), the contact angles of H-M3C-1S-e, H-M3C-2S-e, H-M3C-3S-e, and H-M3C-4S-e were measured at 71.3o, 78.3o, 85.5o, and 89.8o. For purified samples, the angles of PH-M3C-1S-e, PH-M3C-2S-e, PH-M3C-3S-e and PH-M3C-4S-e were increased to 85.8o, 88.2o, 90.9o and 91.2o. This indicated that the contact angle would increase as the grafting weight of PS on HNTs increased. For purified sample, the HNTs surface have been found to have the higher hydrophobic.
Finally, 5V and H-M3C-4S-e were used to make oil phase from HDDA with W/O to produce solid Pickering films by UV polymerization. Through SEM analysis, many sphere particles inside the cavity could be observed due to HDDA. When initiator was added and UV light was on, HDDA would polymerize to spheres like the emulsifier free polymerization pathway. The interface was found to be coated by tubular HNTs. This might prove that HNTs exist at the interface of water and HDDA.
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