Rheological properties of thin gelatin films
Tóm tắt
The stability of oil-in-water emulsions depends ultimately on the physical nature of the oil-water interface. If a hydrocolloid or protein is used as an emulsifying agent an interfacial film is formed at the oil-water interface and this may be liquid or viscoelastic solid in properties. The film is formed by the two processes of diffusion from the bulk to the interface and the formation of secondary intermolecular cross-links. Gelatine solutions of up to 2% w/v were used to form an interface with light liquid paraffin over a restricted range of p h . For the 2% w/v gelatin solutions, the p h range was confined to the acid region p h 2.5–3.2 owing to the onset of gelation of the whole aqueous phase, at room temperature, if the p h was increased numerically above this range. At lower concentrations of gelatin, e. g., 0.5% w/v, the useful p h range could be extended to p h 4. The interfacial rheological properties were examined using the surface rheometer described in a previous paper. Preliminary results showed that, in the case of the 1% w/v gelatin solution at p h 3, the interfacial film was liquid up to the end of the first half-hour after formation. Solid properties then developed. After 4 hs it was possible to carry out a creep experiment on the film which exhibited a longest retardation time of several minutes. Further creep and recovery experiments conducted up to 200 h after the formation of the film clearly showed that the growth of solid properties of the film was continuing. The gelatin interfacial films were considerably more compliant than similar films of acacia Senegal, over a comparative period of time, and at the same bulk concentration. This difference in behaviour can be attributed to differences in the basic molecular structure of the two polymers.
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