Contact Angle Measurement Method Research Articles

A comparison of two contact angle measurement methods and inverse gas chromatography to assess the surface energies of theophylline and caffeine

The wettability of two powders has been assessed by three methods and values for surface energies have been determined. Two contact angle methods have been used, both of which are variations of the Wilhelmy plate approach. One method was to use compressed plates of powder, the other to stick uncompacted powder to a glass plate (as a support). It was found that the method using adhesion to the glass plate gave more realistic values for the surface energy of the powders than did the compacted plate approach. It can be concluded that the use of plates with powder adhered to the surface offers a significant advantage for contact angle assessment. The third method used was inverse gas chromatography, which has seen little application to date in the pharmaceutical sciences. It was found that the dispersion component of surface energy obtained by inverse gas chromatography (IGC) was almost identical to the equivalent (Lifshitz-van der Waals) term obtained by use of the contact angle data from the glass side method. The acid-base (polar) contributions to surface energy were not directly comparable, due to the different data manipulation methods associated with contact angle and IGC data. It can be concluded that the little used methods of adhering powder to an inert support for contact angle measurement and IGC have great promise as means of assessing the surface properties of powders. Both these techniques have the advantage of not requiring powder compaction (or any other surface damaging treatment) prior to use.

Influence of the surface properties of low contact angle surfactants on the body distribution of 14C-poly(methyl methacrylate) nanoparticles.

The body distribution of surfactant-coated and non-coated poly(methyl methacrylate) nanoparticles with a size of 131 +/- 30 nm after intravenous injection into rats was investigated. The coating materials were poloxamine 904, poloxamine 908, poloxamine 1508, poloxamer 338, and Brij 35. These materials were preselected by the method of contact angle measurement. No overall valid relation between contact angles and the modification of body distribution could be found. However, the classification of surfactants by determination of the contact angles of the surfactant solution on the polymer material seems to be a very helpful method for preselection of poloxamers and poloxamines. Another parameter for preselection could be molecular weights of the poloxamines. Poloxamine 1508 was the most efficient coating material in reducing the liver uptake and increasing the blood levels of poly(methyl methacrylate) nanoparticles.

Wetting characteristics and blood clotting on surfaces of copoly(γ‐Benzyl‐L‐glutamate, γ‐hydroxyethyl‐L‐glutamine)

The film surface of poly(gamma-benzyl-L-glutamate) (PBLG) was modified with 2-aminoethanol to enhance its hydrophilicity. Controlling the reaction conditions of PBLG and 2-aminoethanol, various types of copoly(gamma-benzyl-L-glutamate, gamma-hydroxyethyl-L-glutamine) film surfaces were obtained. Surface free energy (gamma sv), the dispersive component of gamma sv (gamma dsv), the nondispersive component of gamma sv (gamma psv), and the interfacial free energy of polymer surface with water (gamma sw), which were obtained by using the contact angle measurement and calculation method proposed by Andrade et al., were changed remarkably by the aminolysis. The gamma sv value increased after 2 h of aminolysis from 48.2 (PBLG) to 65.3 dyn/cm and gradually increased to around 70 dyn/cm after 12 h reaction. (gamma dsv) and (gamma psv) changed from 31.0 and 17.2 dyn/cm (PBLG) to 26.5 and 44.3 dyn/cm, respectively. These parameters of the material surfaces, modified over 12 h reaction, were found to be similar to those of the surfaces of canine aorta, vein, and human fibrin membrane. Blood clotting times on these polymer surfaces were comparatively longer than on siliconized glass surfaces.

Surface properties of solvent-cast thin films of synthetic polypeptides

The surface energy of solid polypeptide films — benzyloxycarbonyl derivatives of basic poly(α-amino acid), benzyl esters of acidic poly(α-amino acid) and poly(α-amino acid)'s consisting of nonpolar side chains — was determined from contact angle measurements. The London-dispersive component of surface free energy, γ D S may reflect the hydrophobicity of the side chain of α-helical polypeptide. The nondispersive component of the solid/water interfacial free energy, I P SW, which corresponds to the interaction energy of polypeptide solid with water, was compared with the transition pressure * tr, of the monolayer at the air/water interface. Irrespective of the difference in film nature, the comparison between contact angle measurement and monolayer method indicates a correlation in the interaction of polypeptide with water. For the polypeptides consisting of nonpolar side chains, the I P SW value of β-form PLVal is larger than that of α-helical PLLeu.