Abstract. Maghemite (γ-Fe 2 O 3 ) nanoparticles have been synthesized using a chemical co-precipitation method. The morphology and particle size is characterized using Transmission Electron Microscopy (TEM), and magnetic characterization using Alternating Gradient Magnetometry (AGM). The stability of the maghemite nanoparticles suspension were studied at different pH and time of storage. Dynamic Light Scattering (DLS) and Zeta Potential were conducted to determine the stability of the suspensions. TEM observation showed that the particles size is 9.6 nm and have spherical morphology. The particles showed superparamagnetic behavior with saturation magnetization 25.5 emu/g. The suspensions are stable in the acidic condition at pH 4 and alkaline condition at pH 10. The suspensions remain stable after 4 weeks of storage.

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The stability study of alumina nanoparticle suspensions has been investigated by using gum arabic as a surfactant. The effect of particle volume fraction of alumina nanoparticle and gum arabic concentration were observed. The stability of the suspension was characterized using zeta potential and particle size distribution analysis. Several volume fractions of alumina and gum arabic concentration were dispersed in water as a solvent for suspension stability. The result showed that the stability of water-based alumina nanoparticle suspensions was increase with the decreasing of particle volume fraction and increasing of gum arabic concentration. The particle size distribution was narrow with decreasing particle volume fraction and increasing gum arabic concentration. The hydrodynamic diameter of the particles was smaller with the increasing of gum arabic concentration. The smallest particle size recorded was 164.6 nm at 0.5% gum arabic concentration. Zeta potential values were increased with the increasing of gum arabic concentration. The highest zeta potential was recorded at -36.0 mV. It can be concluded that gum arabic can be used for stabilization of water-based alumina nanoparticle suspensions.

Maghemite (γ-Fe 2 O 3 ) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM) and thermogravimetryanalysis (TGA). The stability of the maghemite nanoparticles suspension was studied at different pH and time of storage by dynamic light scattering (DLS) and zeta potential measurements. The XRD patterns confirmed that the particles were maghemite. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with good thermal stability. The increasing of temperature in the synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability and more stable maghemite nanoparticle suspension.

The coating material used for the manufacture of polyurethane paint with the addition of bentonite into the matrix can improve thermal capability. The purpose of this study is to produce new material namely hybrid bentonite-chitosan which can be used as a filler for the manufacture of polyurethane paint, chitosan intercalation process into bentonite interlayer and increase the concentration of surfactant against the opening of bentonite interlayer. By varying the CEC of cationic surfactants (0.7 CEC, 1 CEC, and 1.3 CEC) and CEC anionic surfactants (0.1 CEC, 0.2 CEC and 0.3 CEC) to obtain the highest basal spacing, structure, and morphology, several characterization procedures have been carried out. From the results of interlayer bentonite analysis with modification of cationic and anionic surfactants using XRD (X-Ray Diffraction) an increase in basal spacing from 14.18393 Å to 23,00023 Å. While the FTIR (Fourier Transform Infrared) chemical structure of hybrid bentonite-chitosan at a wavelength of2800 cm-1 shows the C-H group, 1025 cm-1 shows the C-O group and polyurethane in the -OH absorption (3445 cm-1 ). This study can produce hybrid bentonite-chitosan material as a filler in the manufacture of polyurethane paint.

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