Preparation of hydrophobic microspheres from low-temperature melting polymeric materials

A novel procedure for the preparation of hydrophobic spherical particles from thermoplastic materials, such as polyethylene (PE) or fossil resin (FR), is presented. These particles are particularly useful in the determination of surface forces with the atomic force microscope using the colloidal probe technique. The preparation steps include (i) suspending powdered polymer (PE and FR) in glycerol, (ii) heating the suspension above the melting point of the polymer, (iii) solidification of dispersed PE/FR droplets at a reduced temperature, (iv) filtration of the particles, and (v) washing/drying of the product. Such produced particles of PE and FR had a broad size distribution (2-50 μm) and a spherical shape. The surfaces of these particles were relatively smooth, with a small number of asperities, and/or attached satellite particles or non-spherical debris. Analytical examination of the polymer surface, before and after treatment with hot glycerol, by SEM, AFM, contact angle, XPS, and FTIR measurements revealed only slight chemical changes on the surface caused by this treatment, which included a decrease in the hydrophobicity of the polymer surface caused by an increased amount of oxygen-containing polar groups. These changes were greatly diminished after drying, and the hydrophobicity of the PE and FR surfaces was, at least partially, restored.