CC BY
0UDC 541.64:678.745(088.8)
DOI 10.56525/IWPO6567
IMPACT OF POLYCOMPLEXES
ON STABILITY OF LATEXES
BUSSURMANOVA A.
Caspian University of Technologies and
Engineering named after Sh.Yessenov
Aktau, Kazakhstan
E-mail: akkenzhe.bussurmanova@yu.edu.kz
Abstract. The stability of a positively charged polystyrene latex (PSL) in the presence of a highly charged polyelectrolyte - sodium polyvinylsulfonate (PVA-Na) and electrolytes of various nature was studied. Spectrophotometry and macroelectrophoresis methods have been used to elucidate the mechanism of PSL flocculation with PVA-Na additives and electrolytes, depending on their nature and the order of introducing components into the system. The addition of electrolytes of a certain concentration leads to an improvement in the flocculating effect of the polyelectrolyte. This effect can be explained by the formation of bridges between the functional anionic groups of the polyelectrolyte and di- and trivalent cations of the electrolyte, which leads to compaction of particle aggregates and acceleration of their settling. Such compactization of rigid-chain macromolecules of a highly charged polyelectrolyte in the presence of electrolytes with multiply charged ions leads to the appearance of complex bridges of the type particle - macroion - multiply charged ion - macroion - particle. The effect of inorganic electrolytes on PSL flocculation can be due to two factors: a change in the parameters of the electric double layer of particles and the chemical interaction of electrolyte ions with the functional groups of adsorbed PVA-Na. The action of the first factor can be reduced to compression of the electrical double layer of particles due to an increase in the ionic strength of the medium (concentration mechanism), and a decrease in the charge and potential of particles of the dispersed phase as a result of adsorption of ions on the particle surface (neutralization mechanism).
Key words: polystyrene latex; flocculation; coagulation; electrolytes; stability; hydrodispersion; colloidal systems; optical density; polyelectrolyte; electrophoretic mobility; polymer.
Introduction. Many works are devoted to the study of flocculation of hydrodispersions by water-soluble polymers [1–5]. However, in the literature, insufficient attention has been paid to elucidating the mechanism of action of highly charged polyelectrolytes and their mixtures with inorganic electrolytes of various valences on the stability of model systems.
In this regard, in this work, the task was set to study the effect of a highly charged anionic polyelectrolyte – sodium polyvinylsulfonate (PVS-Na) and its mixture with metal ions of various charges on the stability of positively charged polystyrene latex (PSL).
Materials and research methods. The objects of study are a model hydro dispersion with positively charged particles - polystyrene latex (emulsifier - cetylpyridinium bromide), synthesized according to the procedure [6] and with an average particle diameter of 63.6 nm. Emulsion polymerization of styrene in the presence of an emulsifier - cetylpyridinium bromide - was carried out in a reaction flask with vigorous stirring in a stream of argon. The ratio of styrene : aqueous phase (by volume) was 1:2; initiator - dinitrylazobisisobutyric acid (1% by weight of the monomer); the temperature of the system was 60°C, and the concentration of the emulsifier in the aqueous phase was 2%; the polymerization time was 3 hours. Sodium polyvinylsulfonate (PVS-Na) with a molecular weight of 4900 was used as a highly charged anionic polyelectrolyte. Barium and aluminum chlorides of chemically pure grade were used as electrolytes. .
The stability of colloidal systems in the presence of PVS-Na and their mixtures with electrolytes was judged by the change in the optical density of the system, which was determined on an SF-46 spectrophotometer at a wavelength of 540 (10 nm).
The electrophoretic mobility of the particles was measured by the moving boundary method [7, p. 121-123], and the value of ξ-potential was calculated using the well-known Smolukhovsky formula [7, p. 122], that is, without taking into account the polarization of the electric double layer, the contribution of which under the conditions of our experiments could be in the first approx. The measurement error of (ξ- potential was 1mV.
Results and Discussion. It is known [8-10] that the coagulation of negatively charged sols by anionic polymers occurs only in the presence of a certain electrolyte concentration, especially multivalent cations. At the same time, the concentration of metal ions causing coagulation in the presence of polymers is much less than that necessary for coagulation in the absence of a polymer. The authors suggested that anionic polymers form complexes with multivalent cations, and then these complexes are adsorbed on the surface of particles, and subsequent coagulation is caused by the binding of individual particles into polymer chains in the form of bridges. The effect of electrolytes on the flocculation of dispersions by polyelectrolytes is also due to changes in the electrical and geometric parameters of polyions and the electrical surface characteristics of the particles themselves [1, 9-11]. This significantly affects the amount of adsorption and the structure of the adsorption layers of polyions [9-11] and, accordingly, the conditions of flocculation. Therefore, in this work, an attempt was made to elucidate the conditions and mechanism of PSL flocculation with sodium polyvinylsulfonate, as well as the effect of multivalent cations on this process.
In Fig.1. shows the change in the optical density of PSL depending on the concentration of PVS-Na at a fixed concentration of sodium chloride, which is much lower than its coagulating concentration.
Figure 1 - Dependence of the optical density of positively charged polystyrene latex (PSL) on the concentration of sodium polyvinylsulfonate. 1- in the absence of NaCI; 2 – in the presence of 4⸱10-3 mol/L NaCI. The mass fraction of PSL in the system was 0.014%
The maxima on curves A - f (CPVS-Na) characterize the formation of floccules at a certain concentration of PVS-Na, and a further decrease in the optical density corresponds to the stabilization region of the system. As can be seen from the figure, effective flocculation of PSL with sodium polyvinylsulfonate is observed in the presence of small amounts of sodium chloride. The enhancement of flocculation at certain ratios of the anionic polyelectrolyte and monovalent electrolyte is mainly associated with an additional decrease in the aggregative stability of latex due to compression of the electric double layer and a decrease in the charge and potential of the particles [1, 2].
On fig. 2 and 3 show the kinetic curves of PSL flocculation with a mixture of PVS-Na and electrolytes at fixed concentrations of PVS-Na, below its flocculating concentration (Fig. 2.) and above its stabilizing concentration (Fig. 3.) depending on the increasing concentration of electrolytes.
Figure 2 - PSL flocculation kinetics depending on the order of adding components to the system. The concentration of PVS-Na in the system is 6.84⸱10-5 mol/L
1 - PVS-Na-BaC12; 2 - PSL-PVS-Na-BaC12; 2' - PSL-PVS-Na-AlC13; 3 – PVS-Na-BaCl2-PSL; 3' - PVS-Na-А1С13-PSL; 4 - PSL-А1С13 - PVS-Na; 4' - PSL-BaС12 -PVS-Na
Figure 3 - PSL flocculation kinetics depending on the order of adding components to the system. The concentration of PVS-Na in the system is 3.42⸱10-4 mol/L.
1 - PVS-Na - A1C13; 2 - PSL - PVS-Na - A1C13; 2' - PSL - PVS-Na - BaC12; 3 - PVS-Na - А1С13 - PSL; 3' - PVS-Na - ВаС12 - PSL; 4 – PSL - А1С13 - PVS-Na; 4' - PSL-BaС12 -PVS-Na
As follows from these figures, the addition of electrolytes of a certain concentration leads to an improvement in the flocculating effect of the studied polyelectrolyte, which is expressed in the appearance of maxima on the curves. This reduces the dose of polyelectrolyte, which is necessary to achieve a certain degree of flocculation, at the same time, the expansion of the flocculation zone occurs, which manifests itself the higher the valence of the coagulating electrolyte ion. This effect can be explained by the formation of bridges between the functional groups of the anionic (OSO group) polyelectrolyte and di- and trivalent cations (Ba2+, A13+), which leads to compaction of particle aggregates and acceleration of their settling. Such compactization of rigid-chain macromolecules of a highly charged polyelectrolyte in the presence of electrolytes with multiply charged ions leads to the appearance of complex bridges of the type particle - macroion - multiply charged ion - macroion - particle.
The effect of inorganic electrolytes on PSL flocculation can be due to two factors: a change in the parameters of the double electrical layer (DEL) of particles and the chemical interaction of electrolyte ions with the functional groups of adsorbed PVA-Na. The action of the first factor can be reduced to compression of the DEL of particles due to an increase in the ionic strength of the medium (concentration mechanism), and a decrease in the charge and potential of the particles of the dispersed phase as a result of adsorption of ions on the particle surface (neutralization mechanism).
Valuable information on the mechanism of PSL flocculation with sodium polyvinylsulfonate and multivalent electrolytes can be obtained from electrophoresis data, which are presented in Fig. 4.
Figure 4 - Changes in the electrokinetic potential of PSL particles on the concentration of electrolytes and on the order of introducing components into the system. The concentration of PVS-Na in the system in all cases is equal to 3.42⸱10-4 mol/L
1 - PSL - PVS-Na - A1C13; 2 - PSL - PVS-Na - BaC12; 3 - PSL - BaC12 -PVS-Na; 4 - PSL - A1C13 - PVS-Na.
As expected, the addition of an electrolyte to the latex, and then a polyelectrolyte, leads to a stronger decrease in ξ-potential of PSL particles, that is, the neutralization mechanism prevails. In the reverse order of introducing components into the system, PSL flocculation occurs at values of ξ-particle potential higher than in the first case. In this process, the concentration mechanism of flocculation plays a dominant role. Apparently, for the systems studied by us, the influence of the second factor, that is, the formation of chemical compounds between polyvalent cations and the OSO group of polyions adsorbed on particles, is more important. This leads to the formation of rapidly sedimenting complex aggregates: particle - macroion - particle.
The effect of the order of introduction of an inorganic electrolyte and PVS-Na into a dispersed system, as well as the duration of contact of each of them with particles of the dispersed phase, on the particle settling rate is considered. As can be seen from Fig. 2, 3, the change in the duration of contact of particles with electrolyte from 2 to 60 min. has practically no effect on the sedimentation properties of the system, whereas with an increase in the duration of its interaction with PVS-Na, the sedimentation rate noticeably increases. In all likelihood, the preliminary introduction of an electrolyte into the latex leads to a decrease in the electrical parameters of the DEL of the initial particles, and the addition of PVS-Na leads to the flocculation of the already astabilized dispersion. When these reagents are introduced in the reverse order, the binding of PVA-Na molecules by multivalent ions both in solution and in the adsorption layer, accompanied by a change in the adsorption equilibrium of PVA-Na - solid phase, and the orientation of segments of macromolecules on the surface, apparently become of primary importance. This process occurs in time, which is reflected in curves 2-4 in Figure 2.3. However, when multiply charged ions are added to a solution of polyelectrolytes, sedimentation of the coagulated polyions themselves can be observed [1, 10]. For example, in [1], it was found that when starch interacts with calcium salts, a sparingly soluble compound is formed due to the binding of the cation to the functional groups of the polyelectrolyte. This phenomenon is usually observed in the interaction of weakly acidic or weakly basic polyelectrolytes with multivalent ions, both cations and anions [10]. The shape of the macromolecules is also important. It is known that with a slightly bent shape of macromolecules, better binding of particles occurs, leading to the formation of larger and stronger floccules [1, 8, 9, 11, 12].
In the case under consideration, there is a change in the conformation or shape of the macromolecules of a highly charged polyelectrolyte. This is confirmed by viscometric data, which are illustrated in Fig.5.
Figure 5 - Dependence of the specific viscosity of PSL (1), PVS-Na (2) and PSL - PVS-Na mixture (3) on the concentration of barium chloride. The concentration of PVS-Na in the system is 6.84⸱10-5 mol/L
It follows from this figure that the aggregation of highly diluted monodisperse PSL is more clearly observed in the PSL - PVS-Na - BaCl2 ternary system (curve 3), i.e., in the flocculation (coagulation) region, the viscosity of the system reaches its maximum value, and a further decrease in the viscosity of the system is due to the onset of stabilization of PSL particles or precipitation of larger aggregates [9]. As for the change in viscosity for the PSL - BaC12 and PVS-Na - BaC12 systems, it also has an extreme character. Here, the increase in the viscosity of the system can be associated with the formation of small PSL aggregates as a result of slow coagulation with BaCl2 electrolyte, and in the absence of PSL, BaCl2 complexation with PVS-Na occurs. This contributes to a slight increase in the viscosity of the system.
Therefore, in our case, the optimal ratio of PVS-Na functional groups and multivalent electrolytes probably leads to better binding of PSL particles, and these macromolecules are more flexible and easily subject to conformational change. To exclude the hydrolysis of aluminum chloride, the experiments were carried out at pH = 3 of the medium, similar results, that is, the formation of salt bonds of LaCI3 with sodium polystyrene sulfonate, were obtained by the authors of [9]. Since the aggregative stability of colloids varies over a wide range, for the selection of flocculants it is necessary to have substances capable of adsorbing on the surface of particles at different rates and recharging them. In [11], a model of the kinetics of flocculation of polymer-containing disperse systems was proposed. At the same time, to estimate the rate of dispersion destabilization for polyethyleneimine (PEI), the adsorption rate constant (Kad) was chosen, and for the Al(NO3)3 electrolyte, the coagulation rate constant (Kc). It is shown that the aggregative stability of disperse systems when oppositely charged polyelectrolytes are introduced into them depends on the ratio of the coagulation and adsorption rate constants and passes through a minimum depending on their ratio. Usually, rapidly adsorbing electrolytes are effective for destabilizing very stable disperse systems. Systems with intermediate aggregative stability require slowly adsorbing substances, which led to the widespread use of polyelectrolytes for this purpose. As an example, in [11], the efficiency of destabilization of aqueous suspensions of a negatively charged zinc-sulfide phosphor under the action of Al(NO3)3 and a cationic polyelectrolyte - PEI with MW = 2⸱104. Certain amounts of Al(NO3)3 and polyelectrolyte were introduced into this suspension, and a day after equilibrium was reached, the dispersion of the suspension was determined by sedimentation analysis. It turned out that the total number of particles in the suspension treated with PEI is less than in the case of Al(NO3)3. In this case, PEI is a more effective suspension destabilizer than Al(NO3)3, since the ratio of Kad/Kc constants is lower for PEI than for Al(NO3)3. As shown by the authors of [11], if the aggregative stability of the initial suspension is reduced, i.e., the coagulation rate constant is increased, then it can be expected that, at a constant adsorption rate constant, the Kad/Kc ratio decreases and the efficiency of this flocculant decreases. Indeed, with the preliminary introduction of 1 mol/L Al(NO3)3 into the system, which makes it less stable compared to the initial one, and the subsequent addition of PEI, the flocculating ability of the latter decreases. The simulation of the adsorption-coagulation process has shown that the ratio of constants Kad/Kc makes it possible to evaluate the effectiveness of one or another flocculant (ionic polyelectrolytes) for a particular disperse system and serves as a criterion for their selection.
Conclusion. Under the action of an anionic polyelectrolyte and a monovalent electrolyte on the PSL, due to the compression of the electrical double layer and the decrease in the charge and potential of the particles, with a decrease in the aggregative stability of the latex, flocculation increases. When inorganic electrolytes act on PSL flocculation, the parameters of the DEL of the particles change and the electrolyte ions chemically interact with the functional groups of adsorbed PVS-Na. When changing the parameters of the double electric layer (EDL) of particles, the DEL of particles is compressed due to an increase in the ionic strength of the medium (concentration mechanism), and the charge and potential of particles of the dispersed phase decrease as a result of adsorption of ions on the surface of particles (neutralization mechanism).
With an increase in the viscosity of the system, small PSL aggregates are formed as a result of slow coagulation with electrolyte, and in the absence of PSL, complex formation of electrolyte and polyelectrolyte occurs.
Thus, the possibility of stability control with the help of additives of a highly charged polyelectrolyte and inorganic electrolytes containing multivalent coagulating ions has been shown.
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Бусурманова Ақкенже Чаншарқызы
Химия ғылымдарының кандидаты, «Жаратылыстану ғылымдары» кафедрасының қауымдастырылған профессор м.а., Ш.Есенов атындағы Каспий технологиялар және инжиниринг университеті, Ақтау, Қазақстан
ПОЛИКОМПЛЕКСТЕРДІҢ ЛАТЕКСТЕРДІҢ ТҰРАҚТЫЛЫҒЫНА ӘСЕРІ
Аңдатпа. Жоғары зарядталған полиэлектролит – натрий поливинилсульфонаты (Na-ПВС) және әртүрлі табиғаттағы электролиттер болған кезде оң зарядталған полистирол латексінің (ПСЛ) тұрақтылығы зерттелді. Na-ПВС қоспалары мен электролиттермен PSL флокуляциясының механизмін анықтау үшін спектрофотометрия және макроэлектрофорез әдістері олардың табиғатына және компоненттерді жүйеге енгізу тәртібіне байланысты қолданылды. Белгілі бір концентрациядағы электролиттердің қосылуы полиэлектролиттің флокуляциялық әсерінің жақсаруына әкеледі. Бұл әсерді полиэлектролиттің функционалды аниондық топтары мен электролиттің екі және үш валентті катиондары арасында көпірлердің түзілуімен түсіндіруге болады, бұл бөлшектер агрегаттарының тығыздалуына және олардың шөгуінің жылдамдатылуына әкеледі. Көп зарядталған иондары бар электролиттердің қатысуымен қатты зарядталған полиэлектролиттің қатты тізбекті макромолекулаларының осылай тығыздалуы бөлшек – макроион – көп зарядталған ион – макроион – бөлшек типті күрделі көпірлердің пайда болуына әкеледі. Бейорганикалық электролиттердің ПСЛ флокуляциясына әсері екі факторға байланысты болуы мүмкін: бөлшектердің электрлік қос қабатының параметрлерінің өзгеруі және электролит иондарының адсорбцияланған Na-ПВС функционалдық топтарымен химиялық әрекеттесуі. Бірінші фактордың әрекеті ортаның иондық күшінің жоғарылауы (концентрация механизмі) есебінен бөлшектердің электрлік қос қабатының қысылуына және дисперсті фаза бөлшектерінің заряды мен потенциалының төмендеуіне дейін төмендеуі мүмкін. бөлшектердің бетіндегі иондардың адсорбциялануының нәтижесі (бейтараптандыру механизмі).
Түййінді сөздер: полистирол латекс; флокуляция; коагуляция; электролиттер; тұрақтылық; гидродисперсия; коллоидтық жүйелер; оптикалық тығыздық; полиэлектролит; электрофоретикалық қозғалғыштық; полимер.
Бусурманова Аккенже Чаншаровна
Кандидат химических наук, и.о.ассоц.профессора кафедры «Естественные науки», Каспийский университет технологии и инжиниринга им. Ш. Есенова, г. Актау, Казахстан
ВЛИЯНИЕ ПОЛИКОМПЛЕКСОВ НА СТАБИЛЬНОСТЬ ЛАТЕКСА
Аннотация. Изучена устойчивость положительно заряженного полистирольного латекса (ПСЛ) в присутствии сильнозаряженного полиэлектролита - поливинилсульфоната натрия (ПВС-Na) и электролитов различной природы. Методами спектрофотометрии и макроэлектрофореза выяснен механизм флокуляции ПСЛ добавками ПВС-Na и электролитов в зависимости от их природы и порядка внесения компонентов в систему. Добавка электролитов определенной концентрации, приводит к улучшению флокулирующего действия полиэлектролита. Этот эффект можно объяснить образованием мостиков между функциональными анионными группами полиэлектролита и двух - и трехвалентными катионами электролита, которое приводит к уплотнению агрегатов частиц и ускорению их оседания. Такая компактизация жесткоцепных макромолекул сильнозаряженного полиэлектролита в присутствии электролитов с многозарядными ионами приводит к возникновению сложных мостиков типа частица - макроион - многозарядный ион - макроион - частица. Действие неорганических электролитов на флокуляцию ПСЛ может быть обусловлено двумя факторами: изменением параметров двойного электрического слоя частиц и химическим взаимодействием ионов электролита с функциональными группами адсорбированного ПВС-Na. Действие первого фактора может сводиться к сжатию двойного электрического слоя частиц за счет увеличения ионной силы среды (концентрационный механизм), и снижению заряда и потенциала частиц дисперсной фазы в результате адсорбции ионов на поверхности частиц (нейтрализационный механизм).
Ключевые слова: полистирольный латекс; флокуляция; коагуляция; электролиты; стабильность; гидродисперсия; коллоидные системы; оптическая плотность; полиэлектролит; электрофоретическая подвижность; полимер.
