Part 2. Determination of dispersion with a microscope.

Dispersion is determined by its visual observation under a microscope. For a quantitative assessment it is needed to make straight measurements of dispersed particles (globules) size. From the big amount of measurements integral curves of globules distribution by size and by value of a total surface area are to be statistically obtained.

The main equations for calculation of integral distribution curves are:

(1),

(2),

where Q and S_y are relative sizes of the globules and their relative specific surface area within the given fraction with the upper and lower limits

N and S_f are the numbers of globules of the fraction and their total surface area with an average diameter

N_∑ and S_∑ are the total number of the measured globules and their averaged total surface area.

Equipment

1. microscope (resolution x250)

2. slide

3. microglasses

The drop of the emulsion is to be put onto the slide and covered on by a microglass. The size of emulsion’s globules is to be determined with the help of microscope. Then determine the total number of globules per unit surface and the number of the globules by fractions. According to formulas 1 and 2 determine the relative size of the globules and the total surface area of fraction with the average diameter. The measurement results are to be recorded in table 1.

The data in table 1 is to be presented graphically as distribution curves (the vertical axis is relative size Q and relative specific surface area of fraction Sy (%), and the horizontal axis is average globules diameter).

Table 1

Size of globules  , µ (microns)	Number of globules at the fraction, N	Total surface area Sf, µ2	Relative size of globules, Q, %	Relative specific surface area of fraction, Sу, %
1-5
6-10
11-15
16-20
Etc.
	N	S

Questions for self-testing:

1. Describe the main principles of emulsion classification by the type of disperse phase and dispersion medium, by the content of disperse phase, by the level of dispersion and by the level of interphase interaction.

2. Explain how you can regulate the processes of coalescence and dispersion of globules while preparing an emulsion.

3. Name the factors which can effect the value of interfacial tension and the viscosity of emulsions.

4. Explain the reasons for dispersing oil in water duringat alkaline and acid treatments.

5. Describe the areas of practical application of direct, inverse, multiple emulsions and semiemulsions in the oil industry.