**3.1 Methods used for studying dynamical processes in water microdispersed systems**

#### *3.1.1 Drying drop technology (DDT)*

To monitor fluctuations of physicochemical properties of colloidal systems the DDT method was used based on acoustical impedancemetry developed in our laboratory earlier [55, 56]. Here only its main features would be explained. A coffee drop (volume of 3 μl) without any pretreatment dries on a polished end of a quartz plate. The quartz oscillates with a constant frequency of 60 kHz, which is equal to the resonance frequency of unloaded resonator. Acoustical – Mechanical Impedance (AMI) of the drop during drying is displayed as a curve on a screen (**Figure 16**). The parameter BS\_2 reflects the dynamics of complex mechanical properties of the drying drop deposit (mechanical stress) and is calculated automatically by the software. In the same environment this parameter depends strongly on liquid composition and structure. The diagrams were built for temporal fluctuations of BS\_2 parameter using Excel.

at T = 22-23°C and H = 64-65%. A dry coffee sample was placed in a chemical glass, filled in with hot tap boiled water, and mixed by a glass stick until the coffee dissolved. Sampling was begun after cooling of solution to room temperature, at 9 o'clock Moscow time. Sampling was made each 30 minutes from the same glass of coffee solution standing on a table, using the zone equidistant from the center and edges of the glass, from the depth of about 2 cm by a microdispenser with removable tips. Such 30 minute intervals were stipulated by the duration of one test (20 min) and quartz treatment procedure. In some experiments we added to the colloidal system surfactant sodium dodecyl sulfate (SDS) with a concentration of 0.2% w. Ten repeated experiments were made for every type of investigation. The tests were carried out simultaneously with BS\_2 parameter measurements. For every 30-minutecounting we took four drops having a volume of 3 μl: one drop for BS\_2 parameter measurement, and 3 drops for coffee ring width measurements. Those 3 drops were placed on a new (without any treatment) microscope slides

*DDT scheme: (a) – a drop as an object having a set of unique physical properties is drying on the surface of oscillating quartz resonator; (b) – typical AMI curve for drying drop of coffee: 1 – portion of the curve measured*

The preparations were drying in horizontal position under room conditions, and

ApexLab, 7 countings of each slide (**Figure 17**), up to 22 countings.

*Arrangement of drops on a glass for drying and microscopy.*

**Figure 16.**

**Figure 17.**

**105**

*by total derivative (parameter BS\_2).*

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

were investigated the next day. Coffee ring width was measured using the

### *3.1.2 Optical investigation of coffee ring width fluctuations*

The experiments were carried out using water solutions of the Nescafe Gold sublimated instant coffee bought in a store, with a concentration of 2.50 g/100 ml,

#### **Figure 15.**

*Microstructure of liquids in the "hanging drop" preparation. Liquid placed in a hole in a plastic plate with a diameter of 0.5 mm: (a) - distilled water; (b) - tap water; (c) - water from the Black Sea. The drops were looked via microscope right through.*

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

**Figure 16.**

preparation between the slide and cover glass (layer thickness 8 μm), as well as in a drop of water placed in a hole in a plastic plate 0.5 mm in diameter (**Figure 15**). The dry residue mass after evaporation of free water from these liquids was

Now, when it became known that water and aqueous solutions are not homoge-

neous media, but are microheterogeneous dispersions with their characteristic dynamic processes, facts that previously did not have an adequate explanation become clear. For example, oscillatory processes in liquids revealed by different physical methods of analysis: determination of enzyme activity [46–48]; dynamic light scattering [49, 50], IR spectroscopy, Raman spectroscopy, UHF radiometry and NMR [51]. Continuous multi-hour studies of autonomous oscillatory processes in a number of beverages (tea, dry red wine [52], instant freeze-dried coffee [53, 54]), were conducted registering several parameters simultaneously: the dynamics of the complex mechanical properties of drying drops of these liquids, the dynamics of the surface tension of the solution, and the width of the edge roller for drops dried on glass. For periodic registration of complex mechanical characteristics

**3.1 Methods used for studying dynamical processes in water microdispersed**

To monitor fluctuations of physicochemical properties of colloidal systems the DDT method was used based on acoustical impedancemetry developed in our laboratory earlier [55, 56]. Here only its main features would be explained. A coffee drop (volume of 3 μl) without any pretreatment dries on a polished end of a quartz plate. The quartz oscillates with a constant frequency of 60 kHz, which is equal to the resonance frequency of unloaded resonator. Acoustical – Mechanical Impedance (AMI) of the drop during drying is displayed as a curve on a screen (**Figure 16**). The parameter BS\_2 reflects the dynamics of complex mechanical properties of the drying drop deposit (mechanical stress) and is calculated automatically by the software. In the same environment this parameter depends strongly on liquid composition and structure. The diagrams were built for temporal fluctuations of BS\_2 parameter using Excel.

The experiments were carried out using water solutions of the Nescafe Gold sublimated instant coffee bought in a store, with a concentration of 2.50 g/100 ml,

*Microstructure of liquids in the "hanging drop" preparation. Liquid placed in a hole in a plastic plate with a diameter of 0.5 mm: (a) - distilled water; (b) - tap water; (c) - water from the Black Sea. The drops were*

0.25%, 0.48% and 2.5% of the initial mass, respectively.

*Colloids - Types, Preparation and Applications*

of drying drops, a method developed by us earlier was used.

*3.1.2 Optical investigation of coffee ring width fluctuations*

**systems**

**Figure 15.**

**104**

*looked via microscope right through.*

*3.1.1 Drying drop technology (DDT)*

*DDT scheme: (a) – a drop as an object having a set of unique physical properties is drying on the surface of oscillating quartz resonator; (b) – typical AMI curve for drying drop of coffee: 1 – portion of the curve measured by total derivative (parameter BS\_2).*

at T = 22-23°C and H = 64-65%. A dry coffee sample was placed in a chemical glass, filled in with hot tap boiled water, and mixed by a glass stick until the coffee dissolved. Sampling was begun after cooling of solution to room temperature, at 9 o'clock Moscow time. Sampling was made each 30 minutes from the same glass of coffee solution standing on a table, using the zone equidistant from the center and edges of the glass, from the depth of about 2 cm by a microdispenser with removable tips. Such 30 minute intervals were stipulated by the duration of one test (20 min) and quartz treatment procedure. In some experiments we added to the colloidal system surfactant sodium dodecyl sulfate (SDS) with a concentration of 0.2% w. Ten repeated experiments were made for every type of investigation. The tests were carried out simultaneously with BS\_2 parameter measurements. For every 30-minutecounting we took four drops having a volume of 3 μl: one drop for BS\_2 parameter measurement, and 3 drops for coffee ring width measurements. Those 3 drops were placed on a new (without any treatment) microscope slides ApexLab, 7 countings of each slide (**Figure 17**), up to 22 countings.

The preparations were drying in horizontal position under room conditions, and were investigated the next day. Coffee ring width was measured using the


**Figure 17.** *Arrangement of drops on a glass for drying and microscopy.*

**Figure 18.** *Measurement of coffee ring width under microscope.*

Levenhuk ToupView program in 3 positions into every drop (**Figure 18**), so for each 30-minute account 9 measurements were made. Arithmetic mean and standard deviation were calculated for further analysis.

#### *3.1.3 Optical investigations of liquid samples*

The microscopy investigation of coffee solution was carried out in freshly prepared samples by the method of "flattened drop." For this purpose a drop with a volume of 5 μl was placed on a new (without any treatment) microscope slide ApexLab (25.4 � 76.2 mm) then the drop was covered with a cover glass 24 � 24 mm in size (ApexLab), avoiding formation of air bubbles, and was studied under microscope Levenhuk with a digital camera connected to a computer. We made 10 pictures for every 30-minute step with the same magnitude and analyzed them later using the Levenhuk ToupView program. Morphometric measurements (diameters of avoids in the pictures) were made for every 30-minute step. Statistical analysis (calculation of mean and standard deviation) were made by Excel program. In some experiments, in parallel with the flattened drop, freshly prepared smears (without cover glass) were also examined under a microscope in polarized light.

Fluctuations of surface tension in the same coffee solution could be measured more frequently. It was shown that one period took 30-40 minutes (**Figure 20**). Correlation coefficient between BS\_2 and surface tension fluctuations in one and the same experiment was 0.8 0.2 (p = 0.01) (**Figure 21**). It is interesting to note that fluctuations of these parameters did not disappear either on the third day of stay of this liquid in the same glass without cover on the table in laboratory. Despite a long

*Joint dynamics of parameter BS\_2 (solid line) and level of rising of liquid in a capillary (dashed line) in coffee*

*Fluctuations of surface tension in coffee water solution (2.5 g/100 ml).*

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

*Joint dynamics of parameter BS\_2 (solid line) and coffee ring width (dashed line) in coffee water solution*

**Figure 19.**

**Figure 20.**

**Figure 21.**

**107**

*water solution (2.5 g/100 ml).*

*(2.5 g/100 ml).*

## *3.1.4 Surface tension fluctuations detection*

For detecting surface tension temporal changers we used a set of certified glass capillaries (10 μl Drummond Microdispenser, 100 Replacement Tubes, made in the USA by Drummond Scientific Company. Cat.# 3-000-210G). Each capillary was used once. A new dry capillary was submerged into liquid at regular intervals to a certain mark on a capillary and liquid raising level was measured. Simultaneously, the fluctuations of BS\_2 were usually measured. Diagrams and calculations of the correlation coefficient were done by means of Excel program.

#### **3.2 Results and discussion**

#### *3.2.1 Dynamic processes in liquid media*

**Figure 19** shows joint temporal fluctuations of parameter BS\_2 and coffee ring width. Direct linear correlation between them at significant value p = 0.005 was 0.7 � 0.16. This testified to a causal relationship between these parameters.

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

**Figure 19.**

Levenhuk ToupView program in 3 positions into every drop (**Figure 18**), so for each 30-minute account 9 measurements were made. Arithmetic mean and stan-

The microscopy investigation of coffee solution was carried out in freshly prepared samples by the method of "flattened drop." For this purpose a drop with a volume of 5 μl was placed on a new (without any treatment) microscope slide ApexLab (25.4 � 76.2 mm) then the drop was covered with a cover glass 24 � 24 mm in size (ApexLab), avoiding formation of air bubbles, and was studied under microscope Levenhuk with a digital camera connected to a computer. We made 10 pictures for every 30-minute step with the same magnitude and analyzed them later using the Levenhuk ToupView program. Morphometric measurements (diameters of avoids in the pictures) were made for every 30-minute step. Statistical analysis (calculation of mean and standard deviation) were made by Excel program. In some experiments, in parallel with the flattened drop, freshly prepared smears (without

For detecting surface tension temporal changers we used a set of certified glass capillaries (10 μl Drummond Microdispenser, 100 Replacement Tubes, made in the USA by Drummond Scientific Company. Cat.# 3-000-210G). Each capillary was used once. A new dry capillary was submerged into liquid at regular intervals to a certain mark on a capillary and liquid raising level was measured. Simultaneously, the fluctuations of BS\_2 were usually measured. Diagrams and calculations of the

**Figure 19** shows joint temporal fluctuations of parameter BS\_2 and coffee ring width. Direct linear correlation between them at significant value p = 0.005 was 0.7 � 0.16. This testified to a causal relationship between these parameters.

cover glass) were also examined under a microscope in polarized light.

correlation coefficient were done by means of Excel program.

dard deviation were calculated for further analysis.

*3.1.3 Optical investigations of liquid samples*

*Measurement of coffee ring width under microscope.*

*Colloids - Types, Preparation and Applications*

**Figure 18.**

*3.1.4 Surface tension fluctuations detection*

**3.2 Results and discussion**

**106**

*3.2.1 Dynamic processes in liquid media*

*Joint dynamics of parameter BS\_2 (solid line) and coffee ring width (dashed line) in coffee water solution (2.5 g/100 ml).*

**Figure 20.** *Fluctuations of surface tension in coffee water solution (2.5 g/100 ml).*

Fluctuations of surface tension in the same coffee solution could be measured more frequently. It was shown that one period took 30-40 minutes (**Figure 20**). Correlation coefficient between BS\_2 and surface tension fluctuations in one and the same experiment was 0.8 0.2 (p = 0.01) (**Figure 21**). It is interesting to note that fluctuations of these parameters did not disappear either on the third day of stay of this liquid in the same glass without cover on the table in laboratory. Despite a long

#### **Figure 21.**

*Joint dynamics of parameter BS\_2 (solid line) and level of rising of liquid in a capillary (dashed line) in coffee water solution (2.5 g/100 ml).*

period of storage, fluctuations of parameters persist, and direct correlation link between them remains high (r = 0.7 0.2, p = 0.01).

had more flat coffee ring and did not contain the reticular structures. Instead of them separate clamps on a surface of the drops were observed. Our data agree with results of the work [58], showed that the interactions of colloids with (and at) liquid-solid and liquid-gas interfaces as well as bulk particle-particle interactions affect the morphology of the deposit. Now we can add that such interactions influence also the mechanical properties of dried materials from these colloids, which may be represented quantitatively. After surfactant addition the area of drops considerably increased, formation of the coffee ring has been complicated and structurization was suppressed, which corresponds to results of the research [59]. Thus, it can be stated that autonomous temporal fluctuations of mechanical properties of drying drops of colloidal suspensions revealed by us earlier [43, 52, 53], are also followed by coordinated fluctuations of surface tension. The authors will try to disclose the internal mechanism of these fluctuations looking directly into

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

Observation of colloidal systems under optical microscope followed the same scheme: samples from one and the same volume of coffee solution were taken in certain periods of time and investigated them by the method of flattened drop. Perfectly shaped circles contoured by colloidal particles, sitting close to each other were observed everywhere (**Figure 23**). The circles were sitting on a glass substrate. Commonly it could be possible to find one central particle in each circle. Those

It seems that growing "circles" pushed back colloidal particles, creating conditions for their convergence and coagulation. The size of the particles observed by us was not less than 1 μm so they did not participate actively in Brownian motion. Therefore during creation of spatial reticular structures their passive crowding due to the growing external structures seems to us more convincing than their active movement at the expense of the long-range attraction forces. **Figure 24** shows stages of temporal evolution of round structures in bulk, from small to big, and the remains of arches from colloidal particles after collapse of "round structures." Similar arches after collapse of round structures could be observed for some time in

The dynamics of growth and destruction of such round structures and their associates is shown in **Figure 26**. On the ascending and descending parts of the curve, size distribution of structures became bimodal due to the presence in the field of view, along with round structures, their large associates (see **Figure 23**, left). Nevertheless, our observations have revealed the rhythmic nature of formation and

*Microphoto of water solution of coffee. Round figures and associates of round figures.*

round figures could associate, forming large – scale agglomerates [54].

a liquid phase.

free floating (**Figure 25**).

**Figure 23.**

**109**

It is important to note that when the concentration of coffee in the sample was halved, the amplitude was halved, and the period of oscillations doubled [53]. This makes it probable that oscillatory processes in liquids are associated with aggregation - disaggregation of the microdispersed phase.

A very important problem for the theory and practice is the development of methods for increasing the stability of colloidal systems. Such tasks can be decided in particular by means of adding surface modifying polymers [57] and a literature there]. In our research it was important to find out how addition of surfactant influences parameters of fluctuations and structurization of the drops drying on a glass support. According to **Figure 22**, SDS adding drastically reduced BS\_2 value (mechanical stress during drop drying). It occurred due to decrease in interaction between colloidal particles as well as between the particles and quartz surface.

Diameter of the dried drops considerably increased, and the relief of their surfaces became smooth (**Figure 22**, drops 12, 13). Drops 5 and 6, corresponding to one of maxima of fluctuations of the BS\_2 parameter before SDS adding were characterized by the relief coffee ring and presence of fragments of reticular structures on the surface. Drops 4 and 7, corresponding to the minimum BS\_2 values,

#### **Figure 22.**

*Fluctuations of the BS\_2 parameter in the drying drops of coffee solution (2.5 g/100 ml) before and after SDS addition (the moment of addition is specified by an arrow). From below - photos of the dried drops of coffee solution on glass support taken from total volume in different phases of the process (numbers of photos correspond to numbers of counting in above diagram).*

#### *Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

period of storage, fluctuations of parameters persist, and direct correlation link

It is important to note that when the concentration of coffee in the sample was halved, the amplitude was halved, and the period of oscillations doubled [53]. This makes it probable that oscillatory processes in liquids are associated with aggrega-

A very important problem for the theory and practice is the development of methods for increasing the stability of colloidal systems. Such tasks can be decided in particular by means of adding surface modifying polymers [57] and a literature there]. In our research it was important to find out how addition of surfactant influences parameters of fluctuations and structurization of the drops drying on a glass support. According to **Figure 22**, SDS adding drastically reduced BS\_2 value (mechanical stress during drop drying). It occurred due to decrease in interaction between colloidal particles as well as between the particles and quartz surface. Diameter of the dried drops considerably increased, and the relief of their surfaces became smooth (**Figure 22**, drops 12, 13). Drops 5 and 6, corresponding to one of maxima of fluctuations of the BS\_2 parameter before SDS adding were characterized by the relief coffee ring and presence of fragments of reticular structures on the surface. Drops 4 and 7, corresponding to the minimum BS\_2 values,

*Fluctuations of the BS\_2 parameter in the drying drops of coffee solution (2.5 g/100 ml) before and after SDS addition (the moment of addition is specified by an arrow). From below - photos of the dried drops of coffee solution on glass support taken from total volume in different phases of the process (numbers of photos*

between them remains high (r = 0.7 0.2, p = 0.01).

*Colloids - Types, Preparation and Applications*

tion - disaggregation of the microdispersed phase.

**Figure 22.**

**108**

*correspond to numbers of counting in above diagram).*

had more flat coffee ring and did not contain the reticular structures. Instead of them separate clamps on a surface of the drops were observed. Our data agree with results of the work [58], showed that the interactions of colloids with (and at) liquid-solid and liquid-gas interfaces as well as bulk particle-particle interactions affect the morphology of the deposit. Now we can add that such interactions influence also the mechanical properties of dried materials from these colloids, which may be represented quantitatively. After surfactant addition the area of drops considerably increased, formation of the coffee ring has been complicated and structurization was suppressed, which corresponds to results of the research [59]. Thus, it can be stated that autonomous temporal fluctuations of mechanical properties of drying drops of colloidal suspensions revealed by us earlier [43, 52, 53], are also followed by coordinated fluctuations of surface tension. The authors will try to disclose the internal mechanism of these fluctuations looking directly into a liquid phase.

Observation of colloidal systems under optical microscope followed the same scheme: samples from one and the same volume of coffee solution were taken in certain periods of time and investigated them by the method of flattened drop. Perfectly shaped circles contoured by colloidal particles, sitting close to each other were observed everywhere (**Figure 23**). The circles were sitting on a glass substrate. Commonly it could be possible to find one central particle in each circle. Those round figures could associate, forming large – scale agglomerates [54].

It seems that growing "circles" pushed back colloidal particles, creating conditions for their convergence and coagulation. The size of the particles observed by us was not less than 1 μm so they did not participate actively in Brownian motion. Therefore during creation of spatial reticular structures their passive crowding due to the growing external structures seems to us more convincing than their active movement at the expense of the long-range attraction forces. **Figure 24** shows stages of temporal evolution of round structures in bulk, from small to big, and the remains of arches from colloidal particles after collapse of "round structures." Similar arches after collapse of round structures could be observed for some time in free floating (**Figure 25**).

The dynamics of growth and destruction of such round structures and their associates is shown in **Figure 26**. On the ascending and descending parts of the curve, size distribution of structures became bimodal due to the presence in the field of view, along with round structures, their large associates (see **Figure 23**, left). Nevertheless, our observations have revealed the rhythmic nature of formation and

**Figure 23.** *Microphoto of water solution of coffee. Round figures and associates of round figures.*

[34]). Unfortunately, the authors did not pay attention to their shape. Those cavities looked empty, but now we believe that they were filled by transparent liquid crystal water. If so, then it is easy to explain the restricted movement of the particle placed in such media [16]. This assumption is confirmed by our observations of freshly prepared smears of coffee solution (**Figure 27c** and **d**). We could see real agglomerates of liquid crystal water. In a flat variant (between substrate and cover glasses), these agglomerates consist of round structures, which have visible borders due to

The mechanism of particle interaction in solution is currently actively discussed. Attraction of like charged gel beads with a diameter of 400-650 μm spaced several hundred micrometers apart in water was described in [60]. The authors measured the charge distribution around the beads with a pH sensitive dye and conjectured that the cause of the long-range attraction was a shell of multilayer structured water, formed around beads' hydrophilic surface. Here we can see the analogy with our experiment, where colloidal particles rather than gel beads interact. Moreover, their interaction is caused by spatial convergence which is due to the growing spheres of the liquid crystal water. In soft matter and nano-science, critical Casimir forces attract an increasing interest thanks to their capability of reversible particle assembly [61–67]. These forces are the thermodynamic analogue of the quantum mechanical Casimir force arising from the confinement of vacuum fluctuations of electromagnetic field. In its thermodynamic analogue, solvent fluctuations confined between suspended particles give rise to an attractive or repulsive force between them. Due to its unique temperature dependence, this effect allows in situ control of

*Microphoto of water solution of coffee (a, b) prepared by the method of flattened drop; (c, d) – agglomerates of microdispersed particles with hydration shells of liquid crystal water (smears of the same coffee solution in*

adsorbing colloid particles (**Figure 27a** and **b**).

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

**Figure 27.**

**111**

*polarized light). Each frame width is 1700 μm.*

#### **Figure 24.**

*Microphoto of water solution of coffee. Temporal evolution of round structures in bulk. Some structures in every picture are encircled (as a guide for eyes). Sampling time from the solution: (a) – 12:50, (b) – 13:30, (c) – 14:00.*

#### **Figure 25.**

*Water immersion. Microphoto of water solution of coffee. Remainders of arches floating in solution after destruction of round structures.*

**Figure 26.** *Dynamics of growth and destruction of "round structures" in coffee solution (2.5 g/100 ml).*

destruction of round structures, similar to a rhythm of fluctuations of physicochemical parameters of this colloidal system. Our equipment allowed observing events only in two-dimensional option. Therefore, circular structures can be a projection of the balls on the plane. Data obtained by means of a laser scanning microscope manifestly showed spherical cavities in latex suspension (**Figure 2** in *Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

[34]). Unfortunately, the authors did not pay attention to their shape. Those cavities looked empty, but now we believe that they were filled by transparent liquid crystal water. If so, then it is easy to explain the restricted movement of the particle placed in such media [16]. This assumption is confirmed by our observations of freshly prepared smears of coffee solution (**Figure 27c** and **d**). We could see real agglomerates of liquid crystal water. In a flat variant (between substrate and cover glasses), these agglomerates consist of round structures, which have visible borders due to adsorbing colloid particles (**Figure 27a** and **b**).

The mechanism of particle interaction in solution is currently actively discussed. Attraction of like charged gel beads with a diameter of 400-650 μm spaced several hundred micrometers apart in water was described in [60]. The authors measured the charge distribution around the beads with a pH sensitive dye and conjectured that the cause of the long-range attraction was a shell of multilayer structured water, formed around beads' hydrophilic surface. Here we can see the analogy with our experiment, where colloidal particles rather than gel beads interact. Moreover, their interaction is caused by spatial convergence which is due to the growing spheres of the liquid crystal water. In soft matter and nano-science, critical Casimir forces attract an increasing interest thanks to their capability of reversible particle assembly [61–67]. These forces are the thermodynamic analogue of the quantum mechanical Casimir force arising from the confinement of vacuum fluctuations of electromagnetic field. In its thermodynamic analogue, solvent fluctuations confined between suspended particles give rise to an attractive or repulsive force between them. Due to its unique temperature dependence, this effect allows in situ control of

#### **Figure 27.**

destruction of round structures, similar to a rhythm of fluctuations of physicochemical parameters of this colloidal system. Our equipment allowed observing events only in two-dimensional option. Therefore, circular structures can be a projection of the balls on the plane. Data obtained by means of a laser scanning microscope manifestly showed spherical cavities in latex suspension (**Figure 2** in

*Dynamics of growth and destruction of "round structures" in coffee solution (2.5 g/100 ml).*

*Water immersion. Microphoto of water solution of coffee. Remainders of arches floating in solution after*

*Microphoto of water solution of coffee. Temporal evolution of round structures in bulk. Some structures in every picture are encircled (as a guide for eyes). Sampling time from the solution: (a) – 12:50, (b) – 13:30,*

**Figure 24.**

*Colloids - Types, Preparation and Applications*

*(c) – 14:00.*

**Figure 25.**

**Figure 26.**

**110**

*destruction of round structures.*

*Microphoto of water solution of coffee (a, b) prepared by the method of flattened drop; (c, d) – agglomerates of microdispersed particles with hydration shells of liquid crystal water (smears of the same coffee solution in polarized light). Each frame width is 1700 μm.*

reversible assembly [63, 64]. The authors of [62] showed that in the system with negligible van der Waals forces a simple competition between repulsive screened Coulomb and attractive critical Casimir forces can account quantitatively for the reversible aggregation. Above the temperature Ta, the critical Casimir force drives aggregation of the particles into fractal clusters, while below Ta, the electrostatic repulsion between the particles breaks up the clusters, and the particles resuspend by thermal diffusion [62]. If the gap between the interacting surfaces is filled with a specially designed substance, the attraction between the surfaces can change their repulsion. If such interaction of surfaces with a dielectric constant Ɛ1 or Ɛ2, respectively, occurs in a medium with a dielectric constant Ɛ3, they will be attractive at (Ɛ1 - Ɛ3) (Ɛ2 - Ɛ3) ˂ 0, and repulsive at (Ɛ1 - Ɛ3) (Ɛ2 - Ɛ3) ˃ 0. These interactions are extremely sensitive to temperature, chemical composition of the medium and its physical characteristics [65, 66]. According to our data, the observed process is characterized by cyclic changes both in liquid solute concentration due to displacement of the ions and particles from Exclusion Zones (EZs) to the bulk, and in particle surface properties due to EZ shell growth around them. As these zones routinely generate protons in the water regions beyond, unequal proton concentrations in the respective areas may be responsible for creating both the pH and potential gradients, which may be ultimately responsible for the osmotic drive [30]. On the other hand, the surface water has different water activity and chemical potential to the bulk, leading to differences in osmotic pressure and other colligative properties [25]. When this increase in osmotic pressure next to the surface reaches a threshold, the mechanical instability of the system sharply growths, velocity of microstreams enhances, and aggregates of EZ spheres start to collapse. They break into small pieces and melt. Solute concentration and osmotic pressure decline. Free colloidal particles are distributed uniformly. Chains of particles coagulated on the surface of the water balls remain in solution. Growth of EZ balls begins again and the process recurs (**Figure 28**). As similar events (EZ growth) are registered for other polar liquids, we believe that the autonomous fluctuations based on rhythmic formation and destruction of liquid crystal spheres are the universal law of the nature. The considered processes have been used for creation of a phenomenological model showing a possibility of the existence of self-oscillatory modes in similar systems.

(EZ) are formed. Let n be the number of ions and colloidal particles determining osmotic pressure *P* at the interface between water spheres of radius *r* and dispersive medium. *V* is the amplitude of mean speed of microflows with a characteristic lateral dimension smaller than *πr*. This corresponds to the excited mode of mechanical instability for the sphere surface: 2*πr=m*, where *m* = 2, 3, 4, 5 … The estimated equations for integral processes in such a system can be written down in

the following form: EZ growth near a seed particle can be described as (2).

pressure *Pcrit* can be described as (3)

*Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

from equation (5)

*dV=dt* ¼ �*V=τvisc* þ 4*πr*

*x=P-Pcrit 0,* and equal to 1 if *x=P-Pcrit > 0.*

can use Vant Hoff's law for stationary conditions (4)

where *R* is universal gas constant, T is absolute temperature.

be described by Eqs. (2)–(5). We introduce the following notation:

and rewrite the above equations correspondingly:

8 >>><

>>>:

**113**

*<sup>V</sup>* <sup>¼</sup> *<sup>L</sup>*<sup>3</sup> � <sup>1</sup> � <sup>4</sup>*=*3*π<sup>r</sup>*

where *V* is the average velocity of microstreams in bulk near the water balls; *Vcrit* is the critical velocity of microstreams in bulk with sufficient energy for destruction of external borders of the water balls; *l*<sup>0</sup> is the increment of EZ shell thickness around a hydrophilic particle during time *τgr*. From the works [68, 69] and our own experiments we know that *l*<sup>0</sup> /*τgr*≈ 1 – 10 μm/sec. Formation of microstreams near the interface between the EZ shell and free water on achieving critical osmotic

where *τvisc* is the characteristic time of reduction of microstreams velocity due to solution viscosity; *τvisc*≈const; *γ<sup>m</sup>* is the coefficient characterizing average change of destruction force depending on the created mode of spatial nonuniformity on the destroyed external border of EZ; *F[x]* is the step-type function equal to zero if

We assume that the speed of diffusion of ions and colloidal particles is much more than the growth rate of EZ shell and speeds of delay of microstreams. Then we

The volume of colloidal liquid except for the volume of water spheres is found

Thus, the status of water spheres in the bulk of the remaining colloidal liquid can

*dr=dt* ¼ *l*0*=τgr*ð Þ 1 � *V=Vcrit* (2)

<sup>2</sup> � *<sup>γ</sup><sup>m</sup>* � *<sup>P</sup>* � *<sup>F</sup>*½ � *<sup>x</sup>* � *<sup>P</sup>* � *Pcrit* ½ � (3)

*P* ¼ *n* � *R* � *T=V* (4)

<sup>3</sup> � *<sup>N</sup>*1*=L*<sup>3</sup> � � (5)

*<sup>β</sup>* <sup>¼</sup> <sup>4</sup>*πN*1*=*3*L*<sup>3</sup> (6)

*χ* ¼ *V=Vcrit* (8)

*<sup>α</sup>* <sup>¼</sup> <sup>4</sup>*πγ<sup>m</sup>* � *nRT=L*<sup>3</sup> � *Vcrit* (7)

*dr=dt* ¼ *l*0*=τgr*ð Þ 1 � *χ* ð9Þ

*<sup>d</sup>χ=dt* ¼ �*χ=τvisc* <sup>þ</sup> *<sup>α</sup>r*<sup>2</sup>*=*<sup>1</sup> � *<sup>β</sup>r*<sup>3</sup> � *<sup>F</sup>*½ � *<sup>x</sup>* � *<sup>P</sup>* � *Pcrit* ½� ð10<sup>Þ</sup>

*<sup>P</sup>* <sup>¼</sup> *<sup>n</sup>* � *<sup>R</sup>* � *<sup>T</sup>=L*<sup>3</sup> � <sup>1</sup> � *<sup>β</sup>r*<sup>3</sup> ð Þ¼ ð Þ� *Vcrit=*4*πγ<sup>m</sup> <sup>α</sup><sup>=</sup>* <sup>1</sup> � *<sup>β</sup>r*<sup>3</sup> ð Þð11<sup>Þ</sup>
