Reversible Stability of Emulsion and Polymer Latex Controlled by Oligochitosan and CO2

The addition of salt to a colloid solution ensures that emulsions can be easily separated into two phases and that polymer latexes can be coagulated. The switchable stability of emulsions and polymer latexes would improve the properties for their current applications. A switchable process of salt addition can be achieved using CO2 and switchable water, and it is a novel, benign approach to achieving a switchable ionic strength in an aqueous solution. However, the problem associated with switchable water is that its additives are all synthetic tertiary amines, most of which are harmful to human beings and the environment. Oligochitosan, as a natural product, can also be used as a switchable water additive. In this paper, a new switchable water system using oligochitosan to change the ionic strength was explored for use in several potential industrial applications. The conductivity of the aqueous solution of oligochitosan (0.2 wt.%) was switched from 0.2 to 331 μS/cm through the addition and removal of CO2. Oligochitosan and CO2 were successfully utilized to reversibly break a crude oil emulsion. Polystyrene (PS) latexes could also be reversibly destabilized; the zeta potential of the PS latex changed between −5.8 and −45.2 mV in the absence and presence of CO2 after oligochitosan was dissolved in the PS latex. The use of oligochitosan is a more environmentally friendly means for reversibly separating colloid solutions.


Introduction
Salt addition is one of the most common post-treatments for emulsions and polymer latexes, where it is used to recover and use hydrophobic material dispersed in the colloids [1]. The addition of common inorganic salt to a colloid solution ensures that emulsions can be easily separated into two phases and polymer latexes can be coagulated. One of the application examples for emulsions is the emulsification of crude oil, which is critical for its pipeline transportation. Crude oil emulsions with low viscosity reduce both cost of delivery and rate of corrosion in the pipeline transportation system. Crude oil and water can be separated at the end of transport through salt addition, and the crude oil that is delivered to the destination could be treated further, such as in a petroleum refinery. For polymer latexes synthesized from emulsion polymerizations, most applications involve obtaining polymer resins or powders from the aggregation of latexes after salt addition, but some applications require a latex form, such as in coatings and adhesives; it is hypothesized that if the redispersion of the polymer powders in water is obtained, it would be helpful to transport latexes in a polymer powder salt addition is that the enhanced ionic strength collapses the electrical double layer of dispersed phases, such as those in emulsion droplets and latex particles, resulting in their aggregation and precipitation based on the DLVO theory which displays the explanation of the stability of colloidal suspension [2]. However, it is difficult to reuse the added inorganic salt [1]. If the added salt possesses reversible properties, the switchable stability of emulsions and polymer latexes could be accomplished.
CO2 responsive materials [3][4][5][6][7][8][9][10] have attracted increasing attention because of their astonishing abilities in various applications, such as commanding the surface activity of surfactants [3], switching the hydrophilicity of substrate surfaces [4], changing the polarity of solvents [6], controlling the stability of polymer latexes [5,[7][8][9] and even dominating the size of hydrogels [10]. The mechanism of CO2 switching involves the reversible reaction of CO2 and switchable groups such as amines [4,5]. The utilization of CO2 as a trigger can generate many switching cycles without the accumulation of any byproduct. Furthermore, CO2 has the advantage of being a cheap, safe, and efficient trigger for switching the properties of CO2 responsive materials [5].
Recently, to improve the process of salt addition, Jessop and coworkers reported a new method called "switchable water," which is an example of a CO2 responsive material [11]. Switchable water is an innovative mixture of water and water-soluble amine, where the removal or addition of CO2 switches the ionic strength of the aqueous solution to expected values [11]. The dissolved watersoluble amine has a very low ionic strength in the absence of CO2. However, after the addition of CO2, the amine is protonated and changed into a bicarbonate salt, which causes the ionic strength to rise sharply. The application of switchable water allows reversible salt addition approaches, which allow the water to be recycled, reducing energy consumption.
Although switchable water can be used in green chemistry, some studies have demonstrated that switchable water with tertiary amines is not an asset in relieving toxic effects in comparison to common compounds or methods [12]. One of the main targets of green chemistry is developing environmentally friendly compounds that can replace existing chemicals and alleviate their negative influence on nature and humans. Therefore, effort should be committed to lessening the existing toxicity of switchable water additives. Because all of the switchable water additives are amines, which are the CO2-switchable groups, we considered whether it would possible to select a natural amine as a candidate for a switchable water additive rather than an artificial or synthetic one. Although alkaloids [13] and nucleobases [14] would be great choices, only oligochitosan [15] was selected in our research. This was because oligochitosan is more common and cheaper, and its molecular structure with polyhydroxy groups shows that it should be more water soluble than the former two. Oligochitosan is an amino sugar and one of the most abundant monosaccharides (Scheme 1). It is produced commercially through the hydrolysis of chitosan and is one of the most common dietary supplements [16]. There is no doubt that oligochitosan is healthy and safe for both humans and the environment. Herein, we propose a new switchable water additive, oligochitosan, whose aqueous solution has a low ionic strength in the absence of CO2. However, after the introduction of CO2, these charged amine species increase the ionic strength of the solution. The ionic strength can be controlled through the addition and removal of CO2. In addition to testing the conductivity to confirm the reversibility, oligochitosan was added to a crude oil emulsion and polystyrene (PS) latex. This proved that Scheme 1. Molecular structure of oligochitosan. The repeating number n is located in a range from 0 to 18.
Herein, we propose a new switchable water additive, oligochitosan, whose aqueous solution has a low ionic strength in the absence of CO 2 . However, after the introduction of CO 2 , these charged amine species increase the ionic strength of the solution. The ionic strength can be controlled through the addition and removal of CO 2 . In addition to testing the conductivity to confirm the reversibility, oligochitosan was added to a crude oil emulsion and polystyrene (PS) latex. This proved Polymers 2018, 10, 1352 3 of 10 that oligochitosan acted as a switchable water additive in colloid solutions, and those mixtures had reversible stability through multiple switching cycles.

Preparation of Polystyrene Latex
Styrene (15 mL), AIBN (0.1 g), and SDS (0.5 g) were mixed in deionized water (50 mL). The mixture was stirred continuously at 400 rpm under a N 2 atmosphere for 30 min. The polymerization started and the reaction was controlled at 75 • C for 7 h.

Persistency Tests of Target Colloid Solutions Triggered by CO 2
The target colloid solutions included a crude oil emulsion and PS latex. The crude oil emulsion was produced by mixing crude oil (20.0 g), water (50.0 mL), and SDS (1.0 g). The PS latex was used immediately after polymerization.
The target colloid solution was then destabilized by the continuous sparging of CO 2 (90 mL·min −1 ) through the solution within 20 min at 25 • C. Then, the target colloid solution was allowed to separate into two phases. To homogenize the separate phases into a stable colloidal solution again, N 2 (90 mL·min −1 ) was sparged into the solution for 20 min to release the CO 2 through shaking by hand [16]. The flow rate of the CO 2 and N 2 was monitored by a flowmeter.
The desired amount of oligochitosan was added to one of the target solutions stored in a glass vial using a magnetic stir bar. The emulsion was bubbled with CO 2 (90 mL·min −1 ) for 20 min with stirring. Later, the unstable colloid solution was sparged with N 2 (90 mL·min −1 ) for 20 min to remove the CO 2 .

Characteristics
The conductivities of the solutions containing oligochitosan were tested using a conductivity meter (FE30, Mettler Toledo, Columbus, OH, USA) with a quartz conductivity probe at 25 ± 0.5 • C.
The molecular weight of the polymer was measured using gel permeation chromatography (GPC) apparatus (Waters, Milford, MA, USA) equipped with a Waters 1515 pump. During the experiments, pure tetrahydrofuran was selected as the eluent.
The surface tension was determined with the Wilhelmy plate technique via a surface tensiometer (Krüss K100). Several series of constant surface tension data were obtained at 25.0 ± 0.5 • C. Pure water was used to continuously dilute stock aqueous solutions of surfactants, and the surface tension at each concentration was determined by averaging three measurements [17]. To calculate the critical micelle concentration (CMC) values, a plot was drawn to show the linear portions of the surface tension against the logarithm of the concentration, with the CMC data acquired from the x-value of the inflection point in the plot. A Malvern Mastersizer 2000 (size range of 0.05-2000 nm) was utilized to determine the particle size. A Zetasizer Nano ZS (Malvern Instruments, Malvern, UK) was used to measure the zeta potential of the polymer particles [16].
A Hitachi H600 transmission electron microscope (TEM, Hitachi, Tokyo, Japan) was operated at an accelerating voltage of 75 kV for microscopic observations of the polymer particles [18].
The viscosity of polymer latexes, emulsions and crude oil was tested with an MCR 302 rotational rheometer (Anton Paar, Graz, Austria) equipped with a Searle-type concentric cylinder geometry (CC27).
The value of pH was measured by a Sartorius PB-10 basic pH meter.

CO 2 -Switchable Properties of Oligochitosan
The molecular structure of oligochitosan is shown in Scheme 1. Oligochitosan has no tertiary amines but has primary amine groups, which can also react reversibly with CO 2 . The combination of CO 2 and amines can be described by several different mechanisms. The consolidation of CO 2 and tertiary amines causes the formation of bicarbonate. However, the reaction of primary and secondary amines with CO 2 is based on a different mechanism. CO 2 can directly react with primary and secondary amines to produce carbamates through the composition of zwitterionic intermediates [19]. Scheme 2 depicts the CO 2 reaction mechanisms with primary and tertiary amines. In the presence of CO 2 in a water solution, the primary amine groups of oligochitosan can be protonated and charged.
Polymers 2018, 10, x FOR PEER REVIEW 4 of 10 A Hitachi H600 transmission electron microscope (TEM, Hitachi, Tokyo, Japan) was operated at an accelerating voltage of 75 kV for microscopic observations of the polymer particles [18].
The viscosity of polymer latexes, emulsions and crude oil was tested with an MCR 302 rotational rheometer (Anton Paar, Graz, Austria) equipped with a Searle-type concentric cylinder geometry (CC27).
The value of pH was measured by a Sartorius PB-10 basic pH meter.

CO2-Switchable Properties of Oligochitosan
The molecular structure of oligochitosan is shown in Scheme 1. Oligochitosan has no tertiary amines but has primary amine groups, which can also react reversibly with CO2. The combination of CO2 and amines can be described by several different mechanisms. The consolidation of CO2 and tertiary amines causes the formation of bicarbonate. However, the reaction of primary and secondary amines with CO2 is based on a different mechanism. CO2 can directly react with primary and secondary amines to produce carbamates through the composition of zwitterionic intermediates [19]. Scheme 2 depicts the CO2 reaction mechanisms with primary and tertiary amines. In the presence of CO2 in a water solution, the primary amine groups of oligochitosan can be protonated and charged. Scheme 2. Mechanisms for reaction of CO2 with (a) primary and (b) tertiary amines. Reprinted from [19], with permission from Elsevier 2011.
The conductivity of oligochitosan (0.2 wt.%) in an aqueous solution was tested at 25 ± 0.5 °C for two cycles of switching the sparging of CO2 and N2. The continuous sparging of CO2 caused the solutions to become saturated with CO2. The bubbling of N2 ensured the removal of CO2, and the resultant neutralization of the zwitterionic intermediate salts was accelerated. Figure 1 displays the conductivity measurement results after the alternate bubbling of CO2 and N2. The conductivity of the aqueous solution of oligochitosan was enhanced from 0.2 to 331 μS/cm through 20 min of the CO2 bubbling process. It decreased to its original value after the N2 bubbling. The unprotonated oligochitosan turned into a carbamate salt in the presence of water and CO2. It is obvious that the aqueous solutions of oligochitosan had considerable switchability because there were primary amine groups in their molecular structures (Figure 1).

Reversible Emulsion
Emulsification is a competent approach for diminishing the viscosity of crude oil. The issues encountered in pipeline transportation could be solved if the crude oil emulsions had CO2 switchability. Crude oil emulsions that have lower viscosity with CO2 switchable surfactants could be prepared for transport and the crude oil and water could be detached after transporting through the removal or addition of CO2. If the surface activity of common surfactants in aqueous solution Scheme 2. Mechanisms for reaction of CO 2 with (a) primary and (b) tertiary amines. Reprinted from [19], with permission from Elsevier 2011.
The conductivity of oligochitosan (0.2 wt.%) in an aqueous solution was tested at 25 ± 0.5 • C for two cycles of switching the sparging of CO 2 and N 2 . The continuous sparging of CO 2 caused the solutions to become saturated with CO 2 . The bubbling of N 2 ensured the removal of CO 2 , and the resultant neutralization of the zwitterionic intermediate salts was accelerated. Figure 1 displays the conductivity measurement results after the alternate bubbling of CO 2 and N 2 . The conductivity of the aqueous solution of oligochitosan was enhanced from 0.2 to 331 µS/cm through 20 min of the CO 2 bubbling process. It decreased to its original value after the N 2 bubbling. The unprotonated oligochitosan turned into a carbamate salt in the presence of water and CO 2 . It is obvious that the aqueous solutions of oligochitosan had considerable switchability because there were primary amine groups in their molecular structures (Figure 1). the electrostatic repulsion among the intermolecular head groups of the SDS surfactants [22]. After the CO2 was removed with N2, the CMC value reverted to its original state, because the charged oligochitosan was converted to its neutral form and could not decrease the electrostatic repulsion among the head groups of the SDS surfactants. Consequently, the aqueous solution with dissolved SDS possessed a switchable surface tension behavior, with the help of the CO2 and oligochitosan, which acted as a switchable organic salt.

Reversible Emulsion
Emulsification is a competent approach for diminishing the viscosity of crude oil. The issues encountered in pipeline transportation could be solved if the crude oil emulsions had CO 2 switchability. Crude oil emulsions that have lower viscosity with CO 2 switchable surfactants could be prepared for transport and the crude oil and water could be detached after transporting through the removal or addition of CO 2 . If the surface activity of common surfactants in aqueous solution could be reversibly modified by switchable water and CO 2 , then an emulsion stabilized by such surfactants could have reversible stability controlled by the switchable water and CO 2 . Figure 2 presents data for the surface tension and critical micelle concentration (CMC). The aqueous solutions contained sodium dodecyl sulfate (SDS) and lecithin in the absence and presence of the switchable water additive, oligochitosan, and/or CO 2 . The observed CMC value for SDS showed a good match with the literature values [20]. It was proven that neutral oligochitosan could not change the surface tension and CMC values. The CMC of the pure SDS aqueous solution in the presence of CO 2 was marginally lower than the value under air because the ionization of the oligochitosan by the CO 2 dissolved in the water produced carbamate ions, which decreased the surface tension [21,22]. However, the combination of CO 2 and oligochitosan ensured the appearance of the organic salt and consequently enhanced the ionic strength, resulting in a decrease in the CMC of SDS ( Figure 2). The presence of CO 2 increased the ionic strength of the solution, which decreased the electrostatic repulsion among the intermolecular head groups of the SDS surfactants [22]. After the CO 2 was removed with N 2 , the CMC value reverted to its original state, because the charged oligochitosan was converted to its neutral form and could not decrease the electrostatic repulsion among the head groups of the SDS surfactants. Consequently, the aqueous solution with dissolved SDS possessed a switchable surface tension behavior, with the help of the CO 2 and oligochitosan, which acted as a switchable organic salt.
Clearly, the surface tension of an SDS aqueous solution can be significantly changed by the CO 2 trigger after the addition of oligochitosan. Furthermore, the response of the surface tension is reversible. The surface tension of an SDS aqueous solution containing oligochitosan was measured at 25 ± 0.5 • C for two cycles of alternating CO 2 and N 2 bubbling (Figure 3). The N 2 was sparged to facilitate the removal of CO 2 from the aqueous solution and the subsequent neutralization of the carbamate salts. Figure 3 shows the changeable surface tension and pH value during two cycles of alternating CO 2 and N 2 bubbling. The surface tension decreased from 34.9 to 31.0 mN·m −1 after the addition of CO 2 for 20 min. The pH value changed between 7.2 and 5.6 in the CO 2 /N 2 bubbling cycles. It returned to the original value after bubbling N 2 through the aqueous solution.  Clearly, the surface tension of an SDS aqueous solution can be significantly changed by the CO2 trigger after the addition of oligochitosan. Furthermore, the response of the surface tension is reversible. The surface tension of an SDS aqueous solution containing oligochitosan was measured at 25 ± 0.5 °C for two cycles of alternating CO2 and N2 bubbling (Figure 3). The N2 was sparged to facilitate the removal of CO2 from the aqueous solution and the subsequent neutralization of the carbamate salts. Figure 3 shows the changeable surface tension and pH value during two cycles of alternating CO2 and N2 bubbling. The surface tension decreased from 34.9 to 31.0 mN·m −1 after the addition of CO2 for 20 min. The pH value changed between 7.2 and 5.6 in the CO2/N2 bubbling cycles. It returned to the original value after bubbling N2 through the aqueous solution. The results obtained for the switching ability of the oligochitosan show that switching behaviors should also be possible for an emulsion with dissolved oligochitosan. To prove the ability of the oligochitosan and SDS in relation to emulsion stability, a crude oil-in-water emulsion (with a weight ratio of 0.8:1) was prepared using oligochitosan (0.2 wt.% compared to water) and SDS (0.012 mol·L −1 ). Under these circumstances, the SDS with neutral oligochitosan was shown to be an impressive emulsifying agent. The reason for stable emulsion is due to the diffuse electrical double layer surrounding the emulsion droplets, where the inner layer is composed of SDS adsorbed on the surface of droplets and the outer layer is composed of sodium ions, which are attracted to the surface charge. Without CO2, the neutral oligochitosan does not adversely influence the electrical double layer. Figure 4 shows that after CO2 sparging for 20 min, the crude oil-in-water emulsion was stable for more than 36 h. However, in the presence of CO2, oligochitosan reacted by CO2 to obtain the charged oligochitosan, increasing the ionic strength, collapsing the electrical double layer, and allowing the droplets to aggregate together. The stability of the emulsion declined sharply through the addition of salt because of the charged oligochitosan due to CO2, and the emulsion droplets coalesced over 20 min (Figure 4). Both phases were completely apparent after a further 20 min. However, if N2 was sparged into the mixture containing the two phases of the crude oil/water to induce the removal of CO2, the primary amine groups of oligochitosan transformed back into their neutral form, and a stable emulsion could be prepared with subsequent stirring.
In the presence of CO2, oligochitosan is a charged polymer, whose rheology would have an The results obtained for the switching ability of the oligochitosan show that switching behaviors should also be possible for an emulsion with dissolved oligochitosan. To prove the ability of the oligochitosan and SDS in relation to emulsion stability, a crude oil-in-water emulsion (with a weight ratio of 0.8:1) was prepared using oligochitosan (0.2 wt.% compared to water) and SDS (0.012 mol·L −1 ). Under these circumstances, the SDS with neutral oligochitosan was shown to be an impressive emulsifying agent. The reason for stable emulsion is due to the diffuse electrical double layer surrounding the emulsion droplets, where the inner layer is composed of SDS adsorbed on the surface of droplets and the outer layer is composed of sodium ions, which are attracted to the surface charge. Without CO 2 , the neutral oligochitosan does not adversely influence the electrical double layer. Figure 4 shows that after CO 2 sparging for 20 min, the crude oil-in-water emulsion was stable for more than 36 h. However, in the presence of CO 2 , oligochitosan reacted by CO 2 to obtain the charged oligochitosan, increasing the ionic strength, collapsing the electrical double layer, and allowing the droplets to aggregate together. The stability of the emulsion declined sharply through the addition of salt because of the charged oligochitosan due to CO 2 , and the emulsion droplets coalesced over  (Figure 4). Both phases were completely apparent after a further 20 min. However, if N 2 was sparged into the mixture containing the two phases of the crude oil/water to induce the removal of CO 2 , the primary amine groups of oligochitosan transformed back into their neutral form, and a stable emulsion could be prepared with subsequent stirring.
Polymers 2018, 10, x FOR PEER REVIEW 7 of 10 the emulsion of crude oil had the much lower viscosity than the unemulsified crude oil. The addition of oligochitosan did not influence the viscosity of the emulsion; all the stable emulsions had similar viscosities, ranging from 2.1 to 2.5 mPa·s, including the emulsion that was reformed after N2 sparging and hand shaking.  It was reported that the alternate CO2/N2 bubbling could be utilized to switch an emulsion into two phases, supplying the possibility to trigger the emulsion phase behavior within the oil reservoir by playing with CO2 injection [23]. Thus, in the same way, the stabilizing property of the emulsion with oligochitosan was switched off and on through the addition and removal of CO2, and it has the potential to be used in the switchable emulsification of crude oil and water. In future, our group will focus on how oligochitosan and CO2 affect the combination of non-ionic surfactants and anionic surfactants, as their mixture is used more widely in the real application, such as crude oil recovery.

Switchable Salt Addition of Polystyrene Latex
A transmission electron microscope (TEM) was used to observe the initial and aggregated PS latexes. The left image in Figure 6 shows a TEM image of particles in the initial PS latex where neutral oligochitosan was dissolved. The TEM image shows that the mean diameter of the particles was approximately 200 nm, and that the oligochitosan had no influence on the PS latex. The right image The phase separation appears with the addition of CO 2 (center). However, a stable emulsion is reformed after sparging N 2 and hand shaking (right).
In the presence of CO 2 , oligochitosan is a charged polymer, whose rheology would have an impact on colloid systems [23][24][25]. Figure 5 demonstrates the viscosity of oligochitosan aqueous solutions with or without CO 2 . The solutions of oligochitosan (0-2 wt.%) have a viscosity similar to water, namely around 1.2 mPa·s. The reason for this is, as a kind of oligomer, oligochitosan has a low molecular weight. The viscosity of crude oil in this experiment was about 27 mPa·s at 25 ± 0.5 • C, and the emulsion of crude oil had the much lower viscosity than the unemulsified crude oil. The addition of oligochitosan did not influence the viscosity of the emulsion; all the stable emulsions had similar viscosities, ranging from 2.1 to 2.5 mPa·s, including the emulsion that was reformed after N 2 sparging and hand shaking.   It was reported that the alternate CO2/N2 bubbling could be utilized to switch an emulsion into two phases, supplying the possibility to trigger the emulsion phase behavior within the oil reservoir by playing with CO2 injection [23]. Thus, in the same way, the stabilizing property of the emulsion with oligochitosan was switched off and on through the addition and removal of CO2, and it has the potential to be used in the switchable emulsification of crude oil and water. In future, our group will focus on how oligochitosan and CO2 affect the combination of non-ionic surfactants and anionic surfactants, as their mixture is used more widely in the real application, such as crude oil recovery.

Switchable Salt Addition of Polystyrene Latex
A transmission electron microscope (TEM) was used to observe the initial and aggregated PS It was reported that the alternate CO 2 /N 2 bubbling could be utilized to switch an emulsion into two phases, supplying the possibility to trigger the emulsion phase behavior within the oil reservoir by playing with CO 2 injection [23]. Thus, in the same way, the stabilizing property of the emulsion with oligochitosan was switched off and on through the addition and removal of CO 2 , and it has the potential to be used in the switchable emulsification of crude oil and water. In future, our group Polymers 2018, 10, 1352 8 of 10 will focus on how oligochitosan and CO 2 affect the combination of non-ionic surfactants and anionic surfactants, as their mixture is used more widely in the real application, such as crude oil recovery.

Switchable Salt Addition of Polystyrene Latex
A transmission electron microscope (TEM) was used to observe the initial and aggregated PS latexes. The left image in Figure 6 shows a TEM image of particles in the initial PS latex where neutral oligochitosan was dissolved. The TEM image shows that the mean diameter of the particles was approximately 200 nm, and that the oligochitosan had no influence on the PS latex. The right image in Figure 6 confirms that the particles aggregate into clusters, demonstrating that the stability of the latex particles was destroyed by the charged oligochitosan. in Figure 6 confirms that the particles aggregate into clusters, demonstrating that the stability of the latex particles was destroyed by the charged oligochitosan. For further confirmation of the TEM findings, the particle size distribution and the surface potential of the nanoparticles were appraised using static light scattering (SLS) and ζ-potential measurements. Figure 7 introduces and analyzes the particle sizes of the PS latexes under different situations at 25 °C. The SLS measurements showed that the diameter of the particles dispersed in the aqueous sample were 242 nm on average, or approximately 10-30 nm larger than the values estimated from the TEM images. This disparity is a result of the disparity between the measurement methods: SLS is used to analyze the particle size of an aqueous solution, and TEM is only used to examine dry particles. The PS latex had an initial zeta potential of −45.2 mV, suggesting that there were many SDS molecules with negative charges located near the surface of the PS particles. The electrical double layers of the particles were not influenced by the dissolved oligochitosan. However, in the presence For further confirmation of the TEM findings, the particle size distribution and the surface potential of the nanoparticles were appraised using static light scattering (SLS) and ζ-potential measurements. Figure 7 introduces and analyzes the particle sizes of the PS latexes under different situations at 25 • C. The SLS measurements showed that the diameter of the particles dispersed in the aqueous sample were 242 nm on average, or approximately 10-30 nm larger than the values estimated from the TEM images. This disparity is a result of the disparity between the measurement methods: SLS is used to analyze the particle size of an aqueous solution, and TEM is only used to examine dry particles. in Figure 6 confirms that the particles aggregate into clusters, demonstrating that the stability of the latex particles was destroyed by the charged oligochitosan. For further confirmation of the TEM findings, the particle size distribution and the surface potential of the nanoparticles were appraised using static light scattering (SLS) and ζ-potential measurements. Figure 7 introduces and analyzes the particle sizes of the PS latexes under different situations at 25 °C. The SLS measurements showed that the diameter of the particles dispersed in the aqueous sample were 242 nm on average, or approximately 10-30 nm larger than the values estimated from the TEM images. This disparity is a result of the disparity between the measurement methods: SLS is used to analyze the particle size of an aqueous solution, and TEM is only used to examine dry particles. The PS latex had an initial zeta potential of −45.2 mV, suggesting that there were many SDS molecules with negative charges located near the surface of the PS particles. The electrical double layers of the particles were not influenced by the dissolved oligochitosan. However, in the presence of CO2, the oligochitosan turned into carbamate salt, which caused the ionic strength to increase and