**2. Processes in sessile drying drops of aqueous dispersions**

An evaporating droplet sitting on a solid wettable substrate is a convenient model for observing phase transformations in aqueous colloidal dispersions. The shape of a sitting drop in the form of a truncated ball ensures the appearance of temperature gradients on its surface and the development of flows of thermocapillary nature: centrifugal flow and Marangoni flow (**Figure 1**).

Since the thinnest layer of liquid is located at the three-phase boundary, solidstate microdeposits are formed there first of all, ensuring the attachment of the droplet to the substrate. Further evaporation is accompanied by flattening of the droplet dome while maintaining its area. In this case, capillary forces arise, which ensure the predominant evaporation of water through the edges of the drop [1–5]. It is shown that the direction of the flows depends on the ratio of the thermal conductivities of the liquid and the substrate material [6]: if this ratio does not exceed 1.57, then the Marangoni flow promotes the removal of the colloidal phase to the edge of the droplet. If it exceeds, then the direction of the flow changes sign, and the colloidal phase is "swept away" to the center [7]. The ratio of thermal conductivity of glass and water is 0.6. Therefore, when a drop of hydrocolloid dries up, the remaining solid sediment on the glass has the shape of a saucer with a volumetric rim along the edge. The same phenomenon is associated with the "effect of a coffee drop" - the formation of a colored rim along the periphery of the drop (**Figure 2**).

More complex and interesting processes take place in drying droplets if the water-colloidal system contains salt (for example, human biological fluids). **Figure 3** shows fragments of the drying process of a drop of a protein - salt solution, in which the ratio of total protein to salt corresponds to that in human serum (7% in BSA in 0.9% NaCl). At the beginning of drying (**Figure 3a**–**c**) the visible dynamics of the process is the same as in the salt-free solution. However, further (**Figure 3d**–**f**), salt crystallization begins in the center of the drop, and the final picture of the drop acquires a specific image [8, 9].

Let us take a closer look at the structure of the light circle that appears on the inner side of the protein roller (**Figure 3f**). In **Figure 4** it can be seen that this ring is composed of individual micron-sized protein aggregates. Closer to the center of the drop, the layer of protein structures transforms into a homogeneous layer of the protein gel, inside which salt crystallizes.

With the help of physical modeling, it was found out how the ratios of the components in a protein-salt solution, drying in the form of a drop on a glass slide,

*Dried drop of protein-salt water solution (left) 10. Light-diffusing circle is a place of protein structures formation. Right picture shows protein structures evolution from separated precipitates (right) to protein*

*Dried drops (5 μl volume) of an aqueous solution of coffee (a) and a 7% solution of bovine serum albumin (BSA) in distilled water (b). Formation of the roller of the colloidal phase along the droplet periphery.*

*Consecutive fragments of the drying process of drop of 7% BSA in a 0.9% NaCl physiological solution: (a-c) redistribution of the colloidal phase and the formation of a protein roller; (d-f) - the process of salt crystallization in the protein matrix and the formation of the final image of the drop (f).*

The protein roll formation time for a 3 μL drop is 4-6 minutes. During this time, the liquid part of the droplet loses 30% of water (evaporates) and 70% of albumin (is carried out to the periphery of the droplet and becomes solid). As a result, the initial ratio of the components in the remaining solution changes, causing coacervation of albumin. The mechanism of these events is associated with the competition for hydration between colloidal particles and salt ions. The concentration of salt

change (**Figure 5**).

*clusters that transform into gel. Magnification: 280 [10].*

**Figure 4.**

**95**

**Figure 2.**

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

**Figure 3.**

#### **Figure 1.**

*Scheme of flows in a drying drop of an aqueous colloidal solution sitting on a glass substrate (a half of the 2D image). Capillary flow (black arrows) and Marangoni flow (blue arrows) promote the removal of the colloidal phase (black balls) to the periphery of the drop. T1 ˃ T2.*

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

#### **Figure 2.**

**2. Processes in sessile drying drops of aqueous dispersions**

*Colloids - Types, Preparation and Applications*

temperature gradients on its surface and the development of flows of thermocapillary nature: centrifugal flow and Marangoni flow (**Figure 1**).

(**Figure 2**).

**Figure 1.**

**94**

An evaporating droplet sitting on a solid wettable substrate is a convenient model for observing phase transformations in aqueous colloidal dispersions. The shape of a sitting drop in the form of a truncated ball ensures the appearance of

Since the thinnest layer of liquid is located at the three-phase boundary, solidstate microdeposits are formed there first of all, ensuring the attachment of the droplet to the substrate. Further evaporation is accompanied by flattening of the droplet dome while maintaining its area. In this case, capillary forces arise, which ensure the predominant evaporation of water through the edges of the drop [1–5]. It is shown that the direction of the flows depends on the ratio of the thermal conductivities of the liquid and the substrate material [6]: if this ratio does not exceed 1.57, then the Marangoni flow promotes the removal of the colloidal phase to the edge of the droplet. If it exceeds, then the direction of the flow changes sign, and the colloidal phase is "swept away" to the center [7]. The ratio of thermal conductivity of glass and water is 0.6. Therefore, when a drop of hydrocolloid dries up, the remaining solid sediment on the glass has the shape of a saucer with a volumetric rim along the edge. The same phenomenon is associated with the "effect of a coffee drop" - the formation of a colored rim along the periphery of the drop

More complex and interesting processes take place in drying droplets if the water-colloidal system contains salt (for example, human biological fluids).

**Figure 3** shows fragments of the drying process of a drop of a protein - salt solution, in which the ratio of total protein to salt corresponds to that in human serum (7% in BSA in 0.9% NaCl). At the beginning of drying (**Figure 3a**–**c**) the visible dynamics

(**Figure 3d**–**f**), salt crystallization begins in the center of the drop, and the final

Let us take a closer look at the structure of the light circle that appears on the inner side of the protein roller (**Figure 3f**). In **Figure 4** it can be seen that this ring is composed of individual micron-sized protein aggregates. Closer to the center of the drop, the layer of protein structures transforms into a homogeneous layer of the

*Scheme of flows in a drying drop of an aqueous colloidal solution sitting on a glass substrate (a half of the 2D image). Capillary flow (black arrows) and Marangoni flow (blue arrows) promote the removal of the colloidal*

of the process is the same as in the salt-free solution. However, further

picture of the drop acquires a specific image [8, 9].

protein gel, inside which salt crystallizes.

*phase (black balls) to the periphery of the drop. T1 ˃ T2.*

*Dried drops (5 μl volume) of an aqueous solution of coffee (a) and a 7% solution of bovine serum albumin (BSA) in distilled water (b). Formation of the roller of the colloidal phase along the droplet periphery.*

#### **Figure 3.**

*Consecutive fragments of the drying process of drop of 7% BSA in a 0.9% NaCl physiological solution: (a-c) redistribution of the colloidal phase and the formation of a protein roller; (d-f) - the process of salt crystallization in the protein matrix and the formation of the final image of the drop (f).*

#### **Figure 4.**

*Dried drop of protein-salt water solution (left) 10. Light-diffusing circle is a place of protein structures formation. Right picture shows protein structures evolution from separated precipitates (right) to protein clusters that transform into gel. Magnification: 280 [10].*

With the help of physical modeling, it was found out how the ratios of the components in a protein-salt solution, drying in the form of a drop on a glass slide, change (**Figure 5**).

The protein roll formation time for a 3 μL drop is 4-6 minutes. During this time, the liquid part of the droplet loses 30% of water (evaporates) and 70% of albumin (is carried out to the periphery of the droplet and becomes solid). As a result, the initial ratio of the components in the remaining solution changes, causing coacervation of albumin. The mechanism of these events is associated with the competition for hydration between colloidal particles and salt ions. The concentration of salt

**Figure 5.**

*Change in the relative content of components in the protein-salt solution when it dries in the form of a drop on a glass substrate (according to materials in [10]).*

#### **Figure 6.**

*Zones in dried drop of BSA-salt solution: 1 – homogenous protein film (colloidal glass); 2– zone of protein precipitates, from single ones to their clusters; 3 – gel; 4 - zone of salt structures in shrinking protein gel. Magnification: 70.*

per unit volume of protein increased greatly, which led to the loss of its aggregate stability and the beginning of the coagulation process. **Figure 6** shows the zones of different phase states of the protein, formed in the gradient of increasing salt concentration.

The cascade of protein phase transitions, according to the authors, can be represented as follows (**Figure 7**).

To examine the bottom adsorption layer in a dried drop of 7% BSA solution in saline NaCl, the top of the dried protein roll was carefully removed with a scalpel, as shown in **Figure 8**.

Investigation of the lower adsorption layer of a dried drop of a protein-salt solution using an atomic force microscope in zone 2 in **Figure 6** showed the presence of protein precipitates corresponding to the structures of the second order in **Figure 7**. Investigation of the lower adsorption layer of a dried drop of a protein-salt solution using an atomic force microscope in zone 2 in **Figure 6** showed the presence of protein precipitates corresponding to the structures of the second order in **Figure 7** (**Figure 9**).

At a lower concentration of protein in physiological saline solution, the coacervation process begins earlier, which confirms the author's opinion about the nature of the observed phenomenon (**Figure 10**).

form materials with different properties. The authors [11] argue that colloidal particles can form different structures: from colloidal glasses with very high volume fractions and low strength of interparticle attraction to colloidal gels with very low volume fractions and strong attraction between the particles (**Figure 11**). Before gelation, colloidal particles form fractal clusters, which turn into space-filling

*bottom protein adsorption layer is used for AFM investigation.*

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

*Fragments of dried drops of 7% BSA in 0.9% NaCl water solution. Left – zone of protein ring (in a white rectangle) before removing; right – the same zone after removing the upper film. Black circle shows the area of*

*Protein phase transitions in fluid part of a sessile drying drop of protein-salt-water solution. R is a radius of the*

**Figure 7.**

**Figure 8.**

**97**

*structure [10].*

Thus, due to protein redistribution during drop drying, protein deposits on the drop edge and protein in the middle part of the drop are in different conditions, and *Structure and Dynamics of Aqueous Dispersions DOI: http://dx.doi.org/10.5772/intechopen.94083*

per unit volume of protein increased greatly, which led to the loss of its aggregate stability and the beginning of the coagulation process. **Figure 6** shows the zones of different phase states of the protein, formed in the gradient of increasing salt

*Zones in dried drop of BSA-salt solution: 1 – homogenous protein film (colloidal glass); 2– zone of protein precipitates, from single ones to their clusters; 3 – gel; 4 - zone of salt structures in shrinking protein gel.*

*Change in the relative content of components in the protein-salt solution when it dries in the form of a drop on a*

The cascade of protein phase transitions, according to the authors, can be

To examine the bottom adsorption layer in a dried drop of 7% BSA solution in saline NaCl, the top of the dried protein roll was carefully removed with a scalpel, as

Investigation of the lower adsorption layer of a dried drop of a protein-salt solution using an atomic force microscope in zone 2 in **Figure 6** showed the presence of protein precipitates corresponding to the structures of the second order in **Figure 7**. Investigation of the lower adsorption layer of a dried drop of a protein-salt solution using an atomic force microscope in zone 2 in **Figure 6** showed the presence of protein precipitates corresponding to the structures of the second order in **Figure 7** (**Figure 9**). At a lower concentration of protein in physiological saline solution, the coacervation process begins earlier, which confirms the author's opinion about the nature

Thus, due to protein redistribution during drop drying, protein deposits on the drop edge and protein in the middle part of the drop are in different conditions, and

concentration.

*Magnification: 70.*

**Figure 6.**

**Figure 5.**

*glass substrate (according to materials in [10]).*

*Colloids - Types, Preparation and Applications*

shown in **Figure 8**.

**96**

represented as follows (**Figure 7**).

of the observed phenomenon (**Figure 10**).

*Protein phase transitions in fluid part of a sessile drying drop of protein-salt-water solution. R is a radius of the structure [10].*

#### **Figure 8.**

*Fragments of dried drops of 7% BSA in 0.9% NaCl water solution. Left – zone of protein ring (in a white rectangle) before removing; right – the same zone after removing the upper film. Black circle shows the area of bottom protein adsorption layer is used for AFM investigation.*

form materials with different properties. The authors [11] argue that colloidal particles can form different structures: from colloidal glasses with very high volume fractions and low strength of interparticle attraction to colloidal gels with very low volume fractions and strong attraction between the particles (**Figure 11**). Before gelation, colloidal particles form fractal clusters, which turn into space-filling

#### **Figure 9.**

*AFM data: single protein precipitate (structure of the second generation) lying on the protein film in dried drop of BSA-salt – water solution. It consists of some subunits (structures of the first generation), which admittedly represents consolidated micells. (a) three-dimensional image; (b) precipitate profile.*

networks. Current investigations show that a drying drop of protein–salt aqueous solution is an excellent illustration of this dynamics. Taking into account hydrodynamic motion of the colloidal phase to the drop periphery and its rapid consolidation there, we suppose that this solid phase really represents the protein glass transition: it is transparent and extremely fragile. In contrast to the drop periphery, low protein volume fraction and high ionic strength in liquid residuals in the middle part of a drying drop stimulate liquid–liquid separation and further cascade of protein phase transitions leading to gel formation. Thus, protein gel probably forms

*Schematic state diagram of colloidal particles with short-range potentials, after V. Trappe, R. Sandkuhler [11].*

More detailed information on the processes in drying drops of protein-salt

disrupted, which is revealed in experiments with drying drops [23, 24]. **Figure 12** shows dried drops of blood serum of women after delivery at term and premature birth. Noteworthy is the significant expansion of the zone of protein structures and

that in the case of severe diseases, the processes of protein structuring are

When working with biological fluids of healthy and sick people, it was noticed

It is surprising that in some cases, in seriously ill people, regardless of the nature of the disease, micron-sized protein precipitates can be observed already in liquid

The magnitude of the osmotic pressure created by the solution depends on the amount, and not on the chemical nature of the substances dissolved in it (or ions, if the molecules of the substance dissociate), that is, the osmotic pressure is a colligative property of the solution. The higher the concentration of a substance in a solution, the greater the osmotic pressure it creates. The volume and mass of a colloidal particle is much larger than the volume and mass of a molecule of lowmolecular substances. At the same mass concentration of a substance, a unit volume of a sol contains significantly fewer particles than a unit volume of a true solution. Therefore, it is generally accepted that the osmotic pressure of colloidal solutions is negligible compared to that in true solutions. However, there is an opinion that a relatively small number of particles, much less than required by the "usual" colligation law, can create a high osmotic pressure if they have extensive hydrophilic surfaces [25]. Since, in addition to salts, blood serum contains other osmotically

only inside the protein glass ring of a drying drop.

*Φ – volume fraction of colloid phase; U – strength of the interparticle attraction.*

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

solutions can be obtained in publications [12–22].

the formation of larger precipitates.

blood serum (**Figure 13**).

**99**

**Figure 11.**

#### **Figure 10.**

*Dried drops of protein-salt solutions: 7% BSA in 0.9% NaCl (above), and 2.5% BSA in 1.8% NaCl (bottom). Light-diffusing ring of protein structures has different positions (see the text). Magnification: left – 10; right - 70.*

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

#### **Figure 11.**

**Figure 9.**

**Figure 10.**

*right - 70.*

**98**

*AFM data: single protein precipitate (structure of the second generation) lying on the protein film in dried drop of BSA-salt – water solution. It consists of some subunits (structures of the first generation), which admittedly*

*Dried drops of protein-salt solutions: 7% BSA in 0.9% NaCl (above), and 2.5% BSA in 1.8% NaCl (bottom). Light-diffusing ring of protein structures has different positions (see the text). Magnification: left – 10;*

*represents consolidated micells. (a) three-dimensional image; (b) precipitate profile.*

*Colloids - Types, Preparation and Applications*

*Schematic state diagram of colloidal particles with short-range potentials, after V. Trappe, R. Sandkuhler [11]. Φ – volume fraction of colloid phase; U – strength of the interparticle attraction.*

networks. Current investigations show that a drying drop of protein–salt aqueous solution is an excellent illustration of this dynamics. Taking into account hydrodynamic motion of the colloidal phase to the drop periphery and its rapid consolidation there, we suppose that this solid phase really represents the protein glass transition: it is transparent and extremely fragile. In contrast to the drop periphery, low protein volume fraction and high ionic strength in liquid residuals in the middle part of a drying drop stimulate liquid–liquid separation and further cascade of protein phase transitions leading to gel formation. Thus, protein gel probably forms only inside the protein glass ring of a drying drop.

More detailed information on the processes in drying drops of protein-salt solutions can be obtained in publications [12–22].

When working with biological fluids of healthy and sick people, it was noticed that in the case of severe diseases, the processes of protein structuring are disrupted, which is revealed in experiments with drying drops [23, 24]. **Figure 12** shows dried drops of blood serum of women after delivery at term and premature birth. Noteworthy is the significant expansion of the zone of protein structures and the formation of larger precipitates.

It is surprising that in some cases, in seriously ill people, regardless of the nature of the disease, micron-sized protein precipitates can be observed already in liquid blood serum (**Figure 13**).

The magnitude of the osmotic pressure created by the solution depends on the amount, and not on the chemical nature of the substances dissolved in it (or ions, if the molecules of the substance dissociate), that is, the osmotic pressure is a colligative property of the solution. The higher the concentration of a substance in a solution, the greater the osmotic pressure it creates. The volume and mass of a colloidal particle is much larger than the volume and mass of a molecule of lowmolecular substances. At the same mass concentration of a substance, a unit volume of a sol contains significantly fewer particles than a unit volume of a true solution. Therefore, it is generally accepted that the osmotic pressure of colloidal solutions is negligible compared to that in true solutions. However, there is an opinion that a relatively small number of particles, much less than required by the "usual" colligation law, can create a high osmotic pressure if they have extensive hydrophilic surfaces [25]. Since, in addition to salts, blood serum contains other osmotically

#### **Figure 12.**

*Dried drops of serum of women in early afterbirth period: (a) is in-time birth (40 weeks); (b) is premature birth (34 weeks). Narrows show ring of micelles; (c) and (d) are selected by tetragon regions in more enlargement. Magnification: 15* � *40.*

active components, it is customary in clinical practice to operate with the concept of "osmolarity," meaning the sum of the concentrations of cations, anions and nonelectrolytes, that is, all kinetically active particles in 1 liter of plasma or serum. The osmolarity of biological fluids is a fairly strict indicator of homeostasis. So, the osmolarity of blood plasma in normal conditions can vary in the range of 280-300 mosm/l [26] (1).

relationships of these transformations. Also similar processes occurred in real human biological fluids was found. In this regard, it would like to note the amazing results of the successful treatment of hundreds of cases of serious diseases of a different nature, obtained by the Soviet doctor A.S. Samokhotskiy, which were carried out according to the method developed by him [28, 29]. Here is the

*The initial drying process of blood serum drops is the formation of a solid rim along the periphery of the drops: (a) - norm, (b) - chronic hepatitis B + C; (c) - burn disease; (d) - coxarthrosis. In the liquid phase of the patient's serum, micron-sized protein precipitates are visible. The initial volume of each drop is 3 μl.*

1.The concentration of electrolytes (sodium, potassium, calcium, magnesium) in the blood serum changes in a wide variety of diseases, but the ratios of these electrolytes can be similar in different diseases and different in the same disease in different people, as well as in one person for different stages of the

2.The use of medicinal compositions containing electrolytes, the concentration of which in the blood serum is relatively low, naturally increased their content

3.The use of medicinal compositions containing electrolytes, the concentration of which in the blood serum is relatively high, naturally increased their content (increased the gap in the ratios) and worsened the patient's condition. The

conclusion of one of his articles [30]:

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

and improved the patient's condition.

deterioration usually was significant.

painful process.

**101**

**Figure 13.**

Osmolarity ¼ 195*:*1 þ 0*:*74 � sodium þ 0*:*25 � urea nitrogen þ 0*:*03 � glucose (1)

where 195.1 is a free member; 0.74; 0.25; 0.03 - empirically found coefficients in the equation; sodium - in mmol/l, urea nitrogen and glucose - in mg%.

Calculations showed that in the examined patients with burn disease, the plasma osmolarity averaged 301.6 � 6.56 mosm/l, fluctuating within the range of 286.16-320.01 mosm/l. However, in patients, the content of both total protein and albumin was decreased. That is, against the background of normal ionic strength of the solution, there was an average decrease in the mass fraction of albumin [27]. Violation of the protein-electrolyte balance led to coacervation of albumin in the liquid phase of the serum. In the course of successful treatment of the underlying disease, the disturbance of this balance began to decline, and coacervation in the liquid serum was not observed.

In this brief review, the phase transformations of protein in droplets of proteinsalt solutions drying on glass were examined, and analyzed the cause-and-effect

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

**Figure 13.**

active components, it is customary in clinical practice to operate with the concept of "osmolarity," meaning the sum of the concentrations of cations, anions and nonelectrolytes, that is, all kinetically active particles in 1 liter of plasma or serum. The osmolarity of biological fluids is a fairly strict indicator of homeostasis. So, the osmolarity of blood plasma in normal conditions can vary in the range of 280-300

*Dried drops of serum of women in early afterbirth period: (a) is in-time birth (40 weeks); (b) is premature birth (34 weeks). Narrows show ring of micelles; (c) and (d) are selected by tetragon regions in more*

Osmolarity ¼ 195*:*1 þ 0*:*74 � sodium þ 0*:*25 � urea nitrogen þ 0*:*03 � glucose (1)

the equation; sodium - in mmol/l, urea nitrogen and glucose - in mg%.

osmolarity averaged 301.6 � 6.56 mosm/l, fluctuating within the range of

where 195.1 is a free member; 0.74; 0.25; 0.03 - empirically found coefficients in

Calculations showed that in the examined patients with burn disease, the plasma

In this brief review, the phase transformations of protein in droplets of proteinsalt solutions drying on glass were examined, and analyzed the cause-and-effect

286.16-320.01 mosm/l. However, in patients, the content of both total protein and albumin was decreased. That is, against the background of normal ionic strength of the solution, there was an average decrease in the mass fraction of albumin [27]. Violation of the protein-electrolyte balance led to coacervation of albumin in the liquid phase of the serum. In the course of successful treatment of the underlying disease, the disturbance of this balance began to decline, and coacervation in the

mosm/l [26] (1).

*enlargement. Magnification: 15* � *40.*

*Colloids - Types, Preparation and Applications*

**Figure 12.**

liquid serum was not observed.

**100**

*The initial drying process of blood serum drops is the formation of a solid rim along the periphery of the drops: (a) - norm, (b) - chronic hepatitis B + C; (c) - burn disease; (d) - coxarthrosis. In the liquid phase of the patient's serum, micron-sized protein precipitates are visible. The initial volume of each drop is 3 μl.*

relationships of these transformations. Also similar processes occurred in real human biological fluids was found. In this regard, it would like to note the amazing results of the successful treatment of hundreds of cases of serious diseases of a different nature, obtained by the Soviet doctor A.S. Samokhotskiy, which were carried out according to the method developed by him [28, 29]. Here is the conclusion of one of his articles [30]:


4.Very small doses of these elements are useful to normalize the ratios of sodium, potassium, calcium and magnesium in the blood serum and improve the patient's condition.

fluid. Their size can reach hundreds of nanometers [33]. Investigation of suspensions of fluorescent polystyrene microparticles (d = 1 μm, C = 0.2% in highly purified water) using a confocal laser scanning microscope for several hours allowed the authors to observe the appearance and growth of "voids" inside the colloidal phase [34]. According to the authors, the reason for this is the attraction initiated by counterions between like-charged particles [35]. The ability to move a particle forcibly placed in the resulting voids was severely limited in comparison with particles located in adjacent areas with a high packing density [36]. The addition of salt to the solution reduced the distance between the colloidal particles,

The results of experiments on determining the size distribution of optical inhomogeneities (clusters) in bidistilled water by the method of small-angle light scattering are presented [37]. The measurements showed the presence of a spectrum of cluster sizes in the water in the range (1.5-6.0) μm. With the help of laser interferometry, the formation of supramolecular water complexes with linear dimensions of 30–100 μm, distributed in continuous water, was shown [38, 39]. A critical review of modern water purification methods [40] states that water is easily contaminated with chemicals, gases, vapors and ions that are washed out of pipelines and containers. These can include sodium and silica from glass, plasticizers and ions from pipes, microbial particles and their endotoxins, and contaminants. Soluble organic contaminants can even be introduced from deionizing resins used during processing, especially if inadequate resins are selected or the resins have previously

In our previous works it was also shown that water and aqueous solutions are microdispersed systems [41, 42]. Upon evaporation of free water, structures ranging in size from ten to hundreds of micrometers remain on the substrate, which are aggregates of a microdispersed phase (**Figure 14**). The aggregates do not evaporate at room temperature, have a viscous consistency and "melt" when the osmotic pressure rises. The unit of the microdispersed phase is NaCl microcrystals

surrounded by a thick hydration shell. The water of hydration shells evaporates at a temperature of ˃ 200° C and accounts for 20% of the dry sediment mass [43]. The hydration shells of hydrophilic microparticles are denser liquid crystalline water, which forms a zone around the particle, displacing all impurities, including ions, from its volume — Exclusion Zone (EZ) [45]. The microheterogeneous struc-

*Fragments of microstructure aggregates: (a) - dry white wine, in a thin layer of liquid (8 μm), frame width - 2.4 mm; (b) in the precipitate of a NaCl solution on a substrate after evaporation of free water, the frame*

ture of water was investigated using a conventional light microscope in the

but after reaching a certain limit, the "colloidal crystal" melted.

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

been contaminated. No cleaning method is perfect.

**Figure 14.**

**103**

*width is 1 mm [44].*

Unfortunately, after the death of the author in 1986, his work was not continued. Current investigation shows that continued research in this direction is very promising.

#### **2.1 Materials and methods used when working with drying drops**

7% w bovine serum albumin solution (BSA, 68 kDa, Sigma, USA) in distilled water or in physiological salt solution (0.15 M NaCl, chemically pure, "Reactiv, Inc.," Russia) were used. All solutions were prepared without buffering, a day prior to experimentation, refrigerated overnight and allowed to come to room temperature before testing. The samples under study were placed, using micropipette, onto clean glasses in the form of drops of volume of 3 μl (6-8 drops for each sample), and let for drying at room conditions. Morphological observations were carried out during drying, and 2-3 days after placing on the glasses, using LUMAM-I-3 microscope and video camera – computer setup. Dried drops also were investigated by means of atom force microscope (AFM) "Smena" NT-MDT (Russia), Russia, using a sensor CSG11. Samples of blood plasma and serum were obtained from 30 clinically healthy donors (the material supplied by Hemotransfusion Station, Nizhny Novgorod); 18 patients with viral hepatitis B and C in acute stage (the material supplied by the Hepatological Center, Nizhny Novgorod); 30 patients with burn disease, and 8 patients with diseases of articulations of inflammatory and degenerative character (supplied by the Federal Burn Treatment Center, Nizhny Novgorod Research Institute of Traumatology and Orthopedics); 40 women after normal or premature (second- and third-trimester) childbirth (supplied by the maternity and child-welfare services of Nizhny Novgorod).

### **3. Structure and dynamics of water microdispersed systems**

Due to the thermodynamic instability of colloidal solutions, aggregation and disaggregation processes continuously occur in them, leading to a change in the number of osmotically active particles per unit volume, and, consequently, in the osmotic pressure. With an increase in the average radius of the particles of the system, as a result of their coagulation and the formation of aggregates, the osmotic pressure should drop very strongly. On the contrary, with the disintegration of aggregates into primary particles, the osmotic pressure should increase strongly. Since the phenomena of aggregation and disaggregation in colloidal systems very easily occur under the influence of sometimes even very weak external influences, the variability of the osmotic pressure of lyosols and their dependence on the prehistory of the solution becomes clear [31]. In recent years, evidence has appeared in the literature about the inhomogeneity of water and aqueous solutions at the micro level. For the first time, as far as we know, giant (millimeter-sized) clusters in a thin layer of water were detected using IR spectroscopy [32]. An assumption was made about their liquid crystal nature. As a result of the study of solutions of NaCl, citric acid, glucose, urea, vinegar and ethanol using static and dynamic light scattering, it was concluded that the dissolved substances in liquid media are distributed unevenly: areas with low and high concentration provide a contrast in light scattering during experimental observation. There are separate domains, close to spherical in shape, with a high density relative to the surrounding

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

4.Very small doses of these elements are useful to normalize the ratios of

**2.1 Materials and methods used when working with drying drops**

**3. Structure and dynamics of water microdispersed systems**

Due to the thermodynamic instability of colloidal solutions, aggregation and disaggregation processes continuously occur in them, leading to a change in the number of osmotically active particles per unit volume, and, consequently, in the osmotic pressure. With an increase in the average radius of the particles of the system, as a result of their coagulation and the formation of aggregates, the osmotic pressure should drop very strongly. On the contrary, with the disintegration of aggregates into primary particles, the osmotic pressure should increase strongly. Since the phenomena of aggregation and disaggregation in colloidal systems very easily occur under the influence of sometimes even very weak external influences, the variability of the osmotic pressure of lyosols and their dependence on the prehistory of the solution becomes clear [31]. In recent years, evidence has

appeared in the literature about the inhomogeneity of water and aqueous solutions at the micro level. For the first time, as far as we know, giant (millimeter-sized) clusters in a thin layer of water were detected using IR spectroscopy [32]. An assumption was made about their liquid crystal nature. As a result of the study of solutions of NaCl, citric acid, glucose, urea, vinegar and ethanol using static and dynamic light scattering, it was concluded that the dissolved substances in liquid media are distributed unevenly: areas with low and high concentration provide a contrast in light scattering during experimental observation. There are separate domains, close to spherical in shape, with a high density relative to the surrounding

the patient's condition.

*Colloids - Types, Preparation and Applications*

child-welfare services of Nizhny Novgorod).

promising.

**102**

sodium, potassium, calcium and magnesium in the blood serum and improve

Unfortunately, after the death of the author in 1986, his work was not continued. Current investigation shows that continued research in this direction is very

7% w bovine serum albumin solution (BSA, 68 kDa, Sigma, USA) in distilled water or in physiological salt solution (0.15 M NaCl, chemically pure, "Reactiv, Inc.," Russia) were used. All solutions were prepared without buffering, a day prior to experimentation, refrigerated overnight and allowed to come to room temperature before testing. The samples under study were placed, using micropipette, onto clean glasses in the form of drops of volume of 3 μl (6-8 drops for each sample), and let for drying at room conditions. Morphological observations were carried out during drying, and 2-3 days after placing on the glasses, using LUMAM-I-3 microscope and video camera – computer setup. Dried drops also were investigated by means of atom force microscope (AFM) "Smena" NT-MDT (Russia), Russia, using a sensor CSG11. Samples of blood plasma and serum were obtained from 30 clinically healthy donors (the material supplied by Hemotransfusion Station, Nizhny Novgorod); 18 patients with viral hepatitis B and C in acute stage (the material supplied by the Hepatological Center, Nizhny Novgorod); 30 patients with burn disease, and 8 patients with diseases of articulations of inflammatory and degenerative character (supplied by the Federal Burn Treatment Center, Nizhny Novgorod Research Institute of Traumatology and Orthopedics); 40 women after normal or premature (second- and third-trimester) childbirth (supplied by the maternity and

fluid. Their size can reach hundreds of nanometers [33]. Investigation of suspensions of fluorescent polystyrene microparticles (d = 1 μm, C = 0.2% in highly purified water) using a confocal laser scanning microscope for several hours allowed the authors to observe the appearance and growth of "voids" inside the colloidal phase [34]. According to the authors, the reason for this is the attraction initiated by counterions between like-charged particles [35]. The ability to move a particle forcibly placed in the resulting voids was severely limited in comparison with particles located in adjacent areas with a high packing density [36]. The addition of salt to the solution reduced the distance between the colloidal particles, but after reaching a certain limit, the "colloidal crystal" melted.

The results of experiments on determining the size distribution of optical inhomogeneities (clusters) in bidistilled water by the method of small-angle light scattering are presented [37]. The measurements showed the presence of a spectrum of cluster sizes in the water in the range (1.5-6.0) μm. With the help of laser interferometry, the formation of supramolecular water complexes with linear dimensions of 30–100 μm, distributed in continuous water, was shown [38, 39]. A critical review of modern water purification methods [40] states that water is easily contaminated with chemicals, gases, vapors and ions that are washed out of pipelines and containers. These can include sodium and silica from glass, plasticizers and ions from pipes, microbial particles and their endotoxins, and contaminants. Soluble organic contaminants can even be introduced from deionizing resins used during processing, especially if inadequate resins are selected or the resins have previously been contaminated. No cleaning method is perfect.

In our previous works it was also shown that water and aqueous solutions are microdispersed systems [41, 42]. Upon evaporation of free water, structures ranging in size from ten to hundreds of micrometers remain on the substrate, which are aggregates of a microdispersed phase (**Figure 14**). The aggregates do not evaporate at room temperature, have a viscous consistency and "melt" when the osmotic pressure rises. The unit of the microdispersed phase is NaCl microcrystals surrounded by a thick hydration shell. The water of hydration shells evaporates at a temperature of ˃ 200° C and accounts for 20% of the dry sediment mass [43].

The hydration shells of hydrophilic microparticles are denser liquid crystalline water, which forms a zone around the particle, displacing all impurities, including ions, from its volume — Exclusion Zone (EZ) [45]. The microheterogeneous structure of water was investigated using a conventional light microscope in the

#### **Figure 14.**

*Fragments of microstructure aggregates: (a) - dry white wine, in a thin layer of liquid (8 μm), frame width - 2.4 mm; (b) in the precipitate of a NaCl solution on a substrate after evaporation of free water, the frame width is 1 mm [44].*

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

Now, when it became known that water and aqueous solutions are not homogeneous 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 of drying drops, a method developed by us earlier was used.
