CC BY
5
ISSN 1998-4812
Вестннк EamKHpcKoro yHHBepcHTeTa. 2021. T. 26. №2
425
y^K 541.64
DOI: 10.33184/bulletin-bsu-2021.2.27
DETERMINATION OF THE TYPE OF AGGREGATES IN MIXTURE SOLUTIONS OF SOME POLYMERS
© V. V. Chernova*, M. Yu. Lazdina, A. S. Shurshina, E. I. Kulish
Bashkir State University 32 Zaki Validi Street, 450076 Ufa, Republic of Bashkortostan, Russia.
*Email: my_life82@mail.ru
It was found that when mixing solutions of two polymers, due to the low affinity ofpolymers to each other, there is an increase in the aggregation processes of macromolecules. The type of formed supramolecular structures is determined, first of all, by the nature ofpossible intermolecular interactions between polymers: the preference of polymer1-polymer1 (homoaggregates) or polymer1-polymer2 (heteroaggregates) contacts. It was shown that solutions of polymer mixtures in all studied cases are characterized by a higher degree of aggregation than solutions of individual polymers. For the solutions of mixtures of sodium succinyl chitosan with sodium salt of carboxylcellulose and sodium salt of succinyl chitosan with polyvinyl alcohol, the formation of homoaggregates is characteristic, and for mixtures of chitosan and polyvinyl alcohol, the formation of heteroaggregates is predominant. This is evidenced by the deviations of the intrinsic viscosity values to the lower and higher sides from the additive values, respectively. It was shown that the type of aggregates formed will be one of the determining factors that have a significant effect on the properties of materials formed from polymer solutions.
Keywords: polymer mixtures, aggregation, intrinsic viscosity, homoaggregates, heteroaggregates.
Introduction
It is well known that with the increase in concentration of polymers in solutions, aggregation of macromolecules occurs [1-5]. When two polymers are mixed with each other, the aggregation processes intensify [6-9], which is understandable given the low affinity of different polymers for each other. However, the type of forming supramolecular structures is ambiguous in the case of mixture solutions. The outcome is determined, first of all, by the nature of possible intermolecular interactions between polymers: the preference of polymerl-polymerl (homoaggregates) or polymerl-poly-mer2 (heteroaggregates). It is clear that the type of aggregates formed will be one of the determining factors that have a significant effect on the properties of materials formed from polymer solutions [10-14]. This is possible due to the fact that the film formation process at room temperature occurs rather quickly, which leads the polymer to a nonequilibrium state. In this case, the relaxation processes are so slowed down that the polymer molecules do not come to equilibrium not only during the evaporation of the solvent, but also during the subsequent stay of the film at room temperature. The structure and hence the properties of polymers in such a film are determined by the state of polymer molecules in the initial solution [15-18]. Consequently, by varying the structure formation of polymers in solution, it becomes possible to regulate the physicochemi-cal properties of the material formed from the solution all in all, the aim of this work is definition of the type of aggregates forming in mixture polymer solutions. Physiologically active polymers widely used in biomedical practice were considered as polymers: sodium
salt of chitosan succinyl, sodium salt of carboxymethylcellulose, chitosan, and polyvinyl alcohol.
Experimental
For the study, we took chitosan (ChTS) with MMd 113 kDa, sodium salt of chitosan succinyl (SChTS) with MMd 67 kDa, sodium carboxymethylcellulose (CMC) with Mw 250 kDa, and polyvinyl alcohol (PVA) grade 11/2 with Mw = 35kDa. The degree of substitution of the samples of SChTS for amino groups was 75%. The degree of deacetylation of the initial ChTS samples, from which SChTS were obtained, is 82%. The degree of substitution of CMC is 80%. We used ChTZ and SChTS produced by ZAO "Bioprogress" (Shchelkovo, Russia). CMC brand Blanose CMC 7 MFPH manufactured by Ashland Inc. (France) and PVA produced by Reakhim LLC.
The solvent that we used was 1% acetic acid in the case of ChTS and distilled water in the case of PVA, SChTS, and CMC. Polymer solutions were prepared by stirring on a magnetic stirrer for a day at room temperature.
The intrinsic viscosity of diluted polymer solutions was determined using an Ubbelohde viscometer at a temperature T = (25+1) °C using the Baranov approach [19].
To determine the aggregation index of polymers in solution 8 we used the technique described in detail in [20]. Any deviation of the indicator 8 from the value 8= 1.00 evidences that this system is structured.
Experiments on water sorption by polysaccharide films were carried out at 100 % humidity under thermostated conditions (T = 25 °C). The relative amount of water mt absorbed by the film sample at the
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ХИМИЯ
time t was determined by the gravimetric method by keeping the film samples in a desiccator in water vapor for a certain time t and calculated by the formula: mt = Am/mo, where m0 - initial mass of the film, Amt - the difference between the mass of the film at time t and the initial mass of the polymer in the film.
Results and discussion
For all studied polymers, the values of the intrinsic viscosity ([7]) characterizing the size of the individual coil [21], the crossover concentration (C*) separating diluted solutions from semi-diluted [22-24], and the degree of aggregation of macromolecules in solution (S) were determined (tabl. 1).
As can be seen from the data presented in tabl. 1, three out of four studied polymers in the region of large dilutions are solutions of individual molecules. And only PVA macromolecules based on the values of the degree of aggregation S> 1.00 aggregate even in dilute solutions.
Table 1
Some characteristics of polymers in the solvent used
Полимер [tf C* s
ChTS 7.80 0.13 1.00
SChTS 3.2 0.31 1.00
CMC 22.80 0.04 1.00
PVA 0.50 2.0 1.10
Probably, the differences in the degrees of aggregation of these polymers are due to the presence of a charge on the macromolecules of ChTS, SChTS, and CMC. This presence leads to repulsion of macromole-cules from each other and suppresses their tendency to aggregation.
When mixing with each other equally concentrated solutions of SChTS with CMC, SChTS with PVA, and ChTS with PVA, one can expect both the additive behavior of mixed solutions and deviations from additivity due to the rearrangement of the polymer structure in solution. The change in the structure of mixed solutions in comparison with solutions of individual polymers can be indicated, first of all, by the degree of aggregation (3).
From the data presented in fig. 1, it can be seen that all polymer mixtures are aggregated systems for all studied ratios of polymers in the blend.
It should be noted that the values of the degree of aggregation in all cases are greater than the additive values. This indicates an increase in intermolecular interactions in the solutions of mixtures.
The type of structures formed in the solutions of mixtures can be defined by analyzing the characteristic viscosity diagrams. As it can be seen from fig. 2, for the SChTS-CMC and SChTS-PVA systems, a negative deviation of viscosity from the composition of the polymer mixture is observed, which indicates the formation of homoaggregates in the solution of polymer
mixtures. The reason for this is that macromolecules in homoaggregates are characterized by an increased packing density and a smaller size of macromolecular coils.
Ö Ö
n---P____
Уъ ______О"- О
,_______-*—•------- .
20 50 80 ratio of polymers
in the mixture, % vol.
Fig. 1. Dependence of the degree of aggregation 5 of solutions SChTS-CMC (1), SChTS-PVA (2) and ChTS-PVA (3) with a concentration of 0.1 g/dL on the ratio of polymers in the mixture.
ГП] mi
20 50 80 ratio of polymers
in the mixture, % vol.
Fig. 2. Dependence of the intrinsic viscosity of solutions SChTS-CMC (1), SChTS-PVA (2) and ChTS-PVA (3) on the ratio of polymers in the mixture.
For the ChTS-PVA system, the viscosity curve is characterized, on the contrary, by a positive deviation from additivity and, accordingly, by the presence of heteroaggregates in the mixture. Earlier, for the ChTS-PVA system, the formation of heteroaggregates with a reduced packing density was established [25].
mi, g/g mi, g/g
J т я
■ ■
é - - » —0-=—
• • 1
20 50 80 ratio of polymers
in the mixture, % vol.
Fig. 3. Dependence of the amount of water mt absorbed in 24 hours by the film samples SChTS-CMC (1), SChTS-PVA (2) and ChTS-PVA (3) on the ratio of polymers in the mixture.
Thus, mixed compositions of SChTS with PVA and CMC, as well as ChTS with PVA, are structured systems in which the nature of the resulting structures (homo- or heteroassociates) depends on the nature of the polymers. In this case, there is a clear correlation
ISSN 1998-4812
Вестник Башкирского университета. 2021. Т. 26. №2
427
between the type of forming aggregates and the sorption capacity of the films in relation to water vapor. Fig. 3 shows that, in the case of the formation of heteroaggregates in the ChTS-PVA system, the films obtained from solutions of polymer mixtures are characterized by a higher sorption capacity than the films obtained from solutions of individual polymers. On the contrary, in the case of the formation of homoaggregates, mixed films adsorb water to a lesser extent than films of individual polymers.
All in all, the type of forming aggregates determines some of the physicochemical properties of materials formed from solutions.
Conclusions
1. It is shown that solutions of mixtures of polymers in all studied cases are characterized by a higher degree of aggregation than solutions of individual polymers.
2. It was found that the formation of homoaggregates is characteristic of the solutions of the mixtures SChTS-CMC and SChTS-PVA, while the formation of heteroaggregates is predominant for the mixtures of ChTS-PVA. This is evidenced by the deviations of the intrinsic viscosity values to the lower and higher sides from the additive values, respectively.
3. A clear correlation is observed between the type of forming aggregates and the sorption capacity of the films with respect to water vapor.
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Received 15.03.2021.
