Designed Organic-Inorganic Nanohybrids from Layered Clays: Montmorillonite and Layered Double Hydroxides

• Main Authors: Tzong-Yuan Juang, 莊宗原
• Other Authors: 戴 憲 弘
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/88399990605764557740

博士 === 國立中興大學 === 化學工程學系所 === 95 === In this work, four parts (Chapter 2 - Chapter 5) of studies involving the intercalation of polymeric surfactants into layered clay (sodium montmorillonite (Na+-MMT) and layered double hydroxides (LDH)) prepared by an ionic exchange reactions were included. These materials were further investigated in terms of physical properties, chemistry, morphology and applications in biomaterials and nanocomposites. (1) Previously, a highly dispersible organic MMT of 58 and 92 Å spacing by using poly(oxyalkylene)-amines as the intercalants has been prepared in Professor Lin’s laboratories. LDH are a family of anionic clays which are significantly different from the commonly utilized aluminosilicate clays with respect to the presence of positive ion charges on the layer surface. Mg-Al LDHs were intercalated with various molecular-weight poly(oxypropylene)-bis-amidoacid salts (POP-acid), synthesized from polyoxyalkylene-diamines and maleic anhydride. The intercalation involves an ionic exchange reaction of LDHs at 120 oC and under N2 atmosphere in an autoclave to afford a series of organoclays with a maximal basal spacing of 92 Å, revealed by XRD and TEM analyses. The unusually wide interlayer spacing was ascribed to the self-alignment of the hydrophobic POP backbone in the layer confinement. In contrast, the intercalation of poly(oxyethylene)-bis-amidoacids (POE-acid) afforded a low basal spacing (7.8 Å) due to their oxyethylene-backbone interaction with the layered surface. The resultant POP- and POE-acid intercalated LDHs also exhibited different dispersing properties in toluene or water. Particularly, the organically-modified and space-enlarged hybrids with a proper amount of the embedded POPs possessed an amphiphilic property of lowering the toluene/water interfacial tension. (2) Epoxy nanocompoistes were prepared from a one-component epoxy system consisting of organophilic anionic clay and diglycidyl ether of bisphenol-A resin. The requisite organic clays were derived from the intercalation of Mg-Al LDH with the poly(oxypropylene)-bis-amindocarboxylic acid salts (POP-acid) (POP2000-2MA/LDH and POP400-3MA/LDH, 68 and 27 Å). At an elevated temperature, the organo-LDH enabled the initiation of the epoxy self-curing to form a crosslinked polymer network without additional curing agents. Among the screened organo-LDH, the spatially-expanded clay with the intercalation of hydrophobic POP-acid up to 68 Å XRD basal spacing was found to be suitable for finely dispersing in epoxy resins. Consequently, the organic diffusion and curing rendered the organoclays exfoliated into individual platelets which were observed by TEM and XRD analysis. (3) Dendrimers and hyperbranched polymers have aroused great interests because of their potential applications. Three generations of dendrons (G1, G2 and G3) with phenyl end-groups were intercalated into MMT layered silicates in dimethylformamide/water cosolvent. These dendrons synthesized via the convergent route were different in size and shape with molecular weights ranging from 930 to 5975 g/mol. XRD and high resolution transmission electron microscopy (HRTEM) indicate that the respective intercalations of MMT with G1, G2 and G3 dendrons exhibited self-assembly characteristics, and the interlayer spacings were 38, 77 and 115 Å for G1/MMT, G2/MMT and G3/MMT, respectively. Furthermore, the modified dendritic organo-clay could be well dispersed into organic solvents, such as DMF, due to the presence of hydrophobic dendritic molecules. Our results indicate that organic/inorganic hybrids resulting from the association of dendrons and inorganic layered silicate can be obtained not only by ionic exchange reaction, but possibly by a direct self-assembly route as well. Moreover, the preparation of dendron/MMT hybrids was investigated at different dendron/MMT molar ratios regarding the changes of interlayer distance. When the molar ratio is within the range of 0.25 ─ 1.0 cationic exchange capacity (CEC) equivalents, the d spacings increase from 19 Å to 38 Å for G1/MMT, 15 Å to 77 Å for G2/MMT and 14 Å to 115 Å for G3/MMT, revealing a conformation change of the intercalating dendrons. (4) Hybrids of the model BSA protein and layered silicate clay with d spacing of ~62 Å were prepared from either direct or stepwise intercalation. The pristine Na+-MMT was first modified by poly(oxypropylene)-amine (POP-amine) salts to a highly-expanded silicate (d spacing = 53 Å) which became accessible for BSA protein embedding. Subsequent substitution allowed the embedding of BSA into the layered MMT in an uncompressed conformation. The process of embedding large molecules into the silicate gallery provides a new method for synthesizing biomaterial/clay hybrids potentially useful in drug delivery or biomedical design.