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DOI: http://dx.doi.org/10.20534/AJT-16-11.12-85-88
Yarkulov Akhror Yuldashevich, teacher department of «Physical chemistry» of the National University of Uzbekistan named of Mirzo Ulugbek
E-mail: yaaxror@ rambler.ru.
Umarov Bakhrom Smanovich, senior teacher of "Department of physical chemistry" of the National University of Uzbekistan named of Mirzo Ulugbek.,
E-mail: [email protected].
Akbarov Khamdam Ikramovich, doctor of sciences, professor, department of "Physical chemistry" of the National University of Uzbekistan named of Mirzo Ulugbek
E-mail: [email protected]
Thermodinamical properties of mechanical mixtures and nanocompositions diacetatcellulose-silica
Abstract: With using of microbalance Mak-Ben sorbtion of water steams by nanocompositions and mechanical mixtures of diacetatcellulose (DAC)-silica has been investigated. On the base of isotherms of sorbtion of water steams values of the middle free energy of mixing and Gibbs energy have been calculated. By theory of polymolecular adsorption (theory of Braynayr-Emmet-Teller) BET "water" surface and parameters of capillary-porous structure of investigated samples were determined. On the base of results of comparison of thermodinamical parameters conclusions were made about particulates of interactions of mechanical mixtures and nanocompositions DAC-silica.
Keywords: nanocomposition, sorbtion, isotherma, Gibbs energy, theory BET, capillary-porous structure, theory of De Bur-Zviker.
Nanocomposites are materials including in their stable chemical bonds. Such materials are used as en-composition particles both organical (molecules or mac- ergetical nanomaterials, at production of sensor, spe-romolecules) and inorganical compounds dispergated to cial types of ceramics, thin-films structures and optical nanodemension level and forming between themselves surfaces and are characterized by properties charply
different from properties of materials obtained with using of individual components including in their compo-sition.The larges adventages in obtain of nanocompozits were reached at using sol-gel technology.
Sol-gel technology of obtain of compositional nanomaterials is based on carring out of hydrolysis of molecular chemical substances-precurces forming at this nano-dimention particles dispergaited in solvent "sol". Then policondensation of sol particles is carried out at which nano-particles have formed clasters forming matrix named "gel" and containing in porous molecules of solvent. Following evaporation of solvent has allowed to obtain ligh solid body with development inner surface named "aerogel" or "kserogel". Sol-gel synthesis is carried out at relatively low temperatures
and has allowed to obtain materials homogeneous by their structure properties and also has gave an possibility to introduce in their composition of particles of
Figurel. Isotherms of sorption of water steams
by initial components and their mechanical mixtures at 298K: 1. DAC; 2. Silica; 3. DAC-silica
50:50; 4. DAC-silica 40:60; 5. DAC-silica 60:40
The aim of this work was sorptional and thermodin-amical investigations of nanocompositions and mechanical mixtures of diacetylcellulose (DAC)-silica [4].
On fig.1,,2 isotherms of sorption of water steams by initial DAC, silica, their mechanical mixtures and nanocompositions DAC-silica at ratio of components 40:60; 50:50 and 60:40 are presented.
It is shown that introduction in composition of amorphous silica of hydrophilic polymers has carried out to following effects: in first character of isotherms of sorption has changed: at transition from polymer to polymer-inorganical systems they have S-shape character. In second on isotherms of sorption for samples with increasing of silica content the sorption ability
different nature. The grate part of inner volume of gels (aerogels) is atribited to meso-porouses (diametr from 1 to 100nm) which are especially attractive for disper-gation in them nanodimension particles and obtain of composit nanomaterial.
Sience about nanocomposits — class of nanocom-positional materials distinguishing beature of which is nanodimension degree of their structural components (particles of metal and metalloids, their oxides, halhoge-nids and so on) has been arised in last years on the inaction of different filds of nowladges. In litrature for designation materials containing from organical phase (polymer) and nanodispesrional mineral phase termin "hybrid nanocomposits" is used and sometime-'metalomatrixal composits", "monophasal hybrids".
If compositional part or such polymer-inorganical materials are polymers of biological origin then the termin "nanobiocomposits " is used [1-3].
Figure 2. Isotherms of sorption of water steams at 298K by nanocompositions:1. DAC-silica
(40:60); 2. DAC-silica (40:60)+limonic acid (LA);
3. DAC-silica (50:50) 4. DAC-silica (50:50)+LA;
5. DAC-silica (60:40) 6. DAC-silica (60:40)+LA
sharply increased what can be connected with capillary condensation of water in porous structure of silica. Increasing of polymer concentration has carried out to it's degenerations and in last at equaled consentration of components in mixtures and nanocompositions it is possible to note a full coincidence of sorption isotherms.
For quantitave value of thermodinamical stability of system DAC-silica also were calculated the free energies of mixing polymer-solvent Agm on the base of calculations of chemical potentials of solvent A^1 and polymer A^2 and by concentration dependence (table 1) values of Gibbs energy AGi were determined for initial polymers and ther mixtures of different compositions.
Table 1. - Values of the middle free energy of mixing polymer-solvent and the Gibbs energy for initial samples DAC, silica, their mixtures and nanocompositions calculated by isotherms of sorptions of water steams
-AG, Dj/g
№ Samples Mechanical Nanocom- Mechanical Nanocom-
mixture positions mixtures positions
1 DAC (powder) 2,89 - 3,10 —
2 SiO2 (powder) 4,73 — 4,95 —
3 DAC--silica 40:60 6,67 6,45 7,40 6,60
4 DAC-silica 40:60+LA — 4,87 — 5,10
5 DAC-silica 50:50 5,02 2,44 5,30 2,50
6 DAC-silica 50:50+LA — 2,87 — 3,00
7 DAC-silica 60:40 3,57 1,40 3,75 1,50
8 DAC-silica 60:40+LA - 3,78 — 3,90
Obtained values of the Gibbs energy are in range of negative values what has whitnessed about spontaneity of earring out of process of solution of mixture components and nanocompositions in water and good affinity of investigated mixtures to solvent. Thermodinamical affinity to water was the most for mechanical mixtures and nanocompositions: composition DAC-silica 40:60 and their nanocompositions in presence of limonic acid have occupied the midlle state and for
them affinity to water is decreased with increasing of DAC content in system.
In table 2 and 3 results of calculations by method Braunauer-Emmet-Teller (BET) of values of nanoma-lecular layer, general volume of porouses, middle radius of porouses and specifical surface of initial polymers, their mechanical mixtures and nanohybrid compositions DAC-silica (40:60, 50:50, 60:40) have been determined.
Table 2. - Parameters of capillyar-porous structure of initial samples of DAC, silica and their mechanical mixtures calculated by sorption of water steams
№ Sample Xm g/g Ssp' m 2/g W0, sm 3/g rmid'
1 DAC (pouder) 0,0078 27,68 0,051 36,85
2 SiO2 (pouder) 0,0102 36,03 0,033 18,31
3 DAC-silica (40:60) 0,0119 42,08 0,082 38,97
4 DAC-silica (50:50) 0,0104 36,75 0,055 29,93
5 DAC-silica (60:40) 0,0060 21,19 0,046 43,42
Table 3. - Parameters of capillyar-porous structure of nanocompositions DAC-silica calculated by sorption of water steams
№ Sample *m> g/g Ssp' m 2/g Wo, sm 3/g rmid'
1 DAC-silica (40:60) 0,014 48,16 0,044 18,3
2 DAC-silica (40:60)+LA 0,0086 30,23 0,035 23,15
3 DAC-silica (50:50) 0,004 13,84 0,0225 32,514
4 DAC-silica (50:50)+LA 0,0034 12,05 0,04 66,4
5 DAC-silica (60:40) 0,0026 9,14 0,0185 40,5
6 DAC-silica (60:40)+LA 0,0085 29,88 0,034 22,27
Calculations have shown that at comparison of mechanical mixtures with nanohybrid compositions the values of monolayer capacity and specifical surface for all mechanical mixtures are higher than for nanohy-brid compositions. With increasing of DAC content values of these parameters decreased.
Value rmidle has a highest value for nanogybrid composition DAC-silica at their ratio 50:50 in the presence of acid (LA) what obviously is connected with fact that LA carrying-out role of structural agent. Absence of correla-
tion between W0 and Ssp can be explaine by differences in distribution of porouses by radiuses.
Adsorption theory De Bur and Zwiker elaborated for describtion of processes of interaction of polar sor-bates with polar sorbents can be used in case of compositional systems DCA-silica-water. It also can be used to processes bonding of water both by adsorption and absorption mechanisms. Results of experimental control of equation De Bur and Zwuker are carried out in work [5]. Linearization isotherm of sorption ofwater has
allowed to determine value "real" sorption didn't com- are linear. For nanocompositions DAC-silica (40:60);
plicating by capillary condensation and clasterization of DAC-silica (40:60)+LA in all range of the relative pres-
water. From fig.3. it is shown that in range of relative pres- sure isotherms are linear. sure 0,65 for mechanical mixtures DAC-silica isotherms
Figure 3. Isotherms of sorption of water steams by mechanical mixtures DAC-silica in coordinates of equation De Bur Zviker at 298 K: 1) DAC; 2) Silica; 3) DAC-silica (40:60); 4) DAC-silica (50:50); 5) DAC-silica (60:40)
On the base of carrying out investigations the following conclusions were made:
Sorption of water steams by initial DAC, silica, their mechanical mixtures and nanocompositions of different compositions has been investigated;
Thermodinamical parameters of interaction such as the middle free energy of mixing and Gibbs energy in systems polymer-water have been determined;
Figure 4. Isotherms of sorption of water steams by nanocompositions DAC-silica in coordinates of equation De Bur-Zviker at 298 K: 1) DAC-silica
(40:60); 2) DAC-silica (40:60)+LA.; 3) DAC-silica (50:50); 4) DAC-silica (50:50)+LA; 5) DAC-silica (60:40); 6) DAC-silica (60:40)+LA
With using of theory Branauer-Emmet-Teller the values of "water surface" of investigated samples were determined; such parameters as nanomolecular layer, radius of porouses and total volume of porouses were calculated;
By theory De Bur-Zwiker values of "real" sorption didn't complicated by capillary condensation and clasterization of water for different investigated samples were determined.
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