MatLab R2016b (The MathWorks, Inc.) was also used to implement and extend the phase separation model by Henschke [49]. For all simulations according to the Henschke model, either the sedimentation velocityvsor the initial Sauter mean diameterd3,2(t=0)need to be known. The respective other parameter is calculated from the droplet swarm model. The experimental sedimentation velocity vs,exp in relation to the counter-current bulk phase is determined by the slope of the optically linear part of the sedimentation curve vs,opt,expdivided by 1-φ [48]:
vs,exp=vs,opt,exp
1−φ . (40)
If the initial Sauter mean diameterd3,2(t=0)is unkown, it is determined iteratively with the sedimentation model and the sedimentation velocity. To start the iteration, a value ford3,2(t=0),startneeds to be guessed in the right order of magnitude or derived from experiments. During iteration, the difference between experimental and calculated sedimentation velocity S1 is minimized with the function lsqnonlin which is a least-square solver (Eq. 41, Fig. 24). The maximum number of iterations and function evaluations were set to 104 and the step tolerance to 10−10.
S1=
(︁vs,exp−vs,sim)︁2
vs,exp
. (41)
Since there are several possible solutions ford3,2(t=0), only physically meaningful values (positive real numbers) were used, and thed3,2(t=0) with smallest relatedS1 is chosen. The settling curves can be derived knowingvs
andd3,2(0)and a given fitting parameterrv*. The implementation of the settling curve calculations was directly adapted from the Henschke model [49]. To determine the fitting parameterrv∗a similar method is chosen. The heighthd,exp(t) over time and the total separation time tsep,exp need to be derived from experimental data.
d3,2 (t=0),
S1 stop criterion
d3,2 (t=0),start vs, exp
yes no d3,2 (t=0) function to
minimise
S1
sedimentation d3,2 (t=0) vs, sim lsqnonlin
Fig. 24: Determination of the Sauter mean diameterd3,2(t=0) in MatLab
The starting valuerv,start∗ = 0.02 is chosen with 0.01rv,start∗ as lower and 100 rv,start∗ as the upper boundary.
An error parameterS2 is minimized by comparing the experimental and simulated coalescence curve (Eq. 46, Fig. 25).
S2=
√︄
∑︁N
j=1(hd,sim(t=tj,exph )−hd,j,exp
0 )2
N + (tsep,sim−tsep,exp 2tsep,exp
)2. (42)
Since experimental data only provide discrete values over time, the function interpl is used to interpolate the necessary values for hd,sim. The optimality, function and step tolerance is set to 10−15.
r*v
S2 stop criterion
r*v, start tsep, exp hd, exp
yes no function to
minimise S2
curves lsqnonlin
r*v
r*v tsep,sim
hd,sim
Fig. 25: Determination of the fitting parameterr∗vin MatLab
5 Results and discussion
In this section the results of phase behavior analysis and the developed method for the identification of the phases in agitated 3Φ systems is presented. Furthermore, the experimental and simulated drop size distributions under 2
̄Φ and 3Φ conditions are discussed, followed by a brief description of the emulsion rheology. Furthermore, the experimental phase separation results and the applicability of the Henschke model in microemulsion systems are analyzed.
5.1 Phase behavior and physical properties
The position of the 3Φ area, resulting phase volume fractions and physical properties are important parameters for the application of microemulsion systems as reaction media as well as for the investigation of dispersion and phase separation. The following subsections summarize the main results for systems with Marlipal, Triton X100, Marlophen andC4E2 with different compositions. Furthermore, phase behavior hysteresis in stirred systems is discussed. To identify the phase behavior of the complete microemulsion systems, conductivity measurements were performed during agitation throughout a defined temperature range under atmospheric pressure. The conductivity of the systems is governed by its current continuous phase, which can change with the phase behavior. The electrical conductivity of the single phases is highest in the aqueous phase despite the use of purified water, whereas the organic phase barely does not exhibit a measurable conductivity. The conductivity of the microemulsion phase lies in between [18]. This is exemplary depicted in Figure 26, where the effect of temperature on the respective single phases of a water, 1-dodecene, Marlipal 24/70 system is shown. The phases were separated under 3Φ conditions at T = 88◦C.
0 100 200 300 400 500 600
30 40 50 60 70 80
Electircal conductivityκ[μS/cm]
Temperature T [°C]
aq mi org
α= 0.5 γ= 0.05
Fig. 26: Conductivity of single phases over temperature of a water, 1-dodecene, Marlipal 24/70 system after phase separation at T = 88◦C
To determine the phase behavior of the complete systems, the temperatures are varied so that the measure-ments start within the 2
̄Φ conditions, where the aqueous phase is the continuous one (o/w-emulsion) and the conductivity rises with temperature. In the complete systems, the compositions of the phases constantly change over temperature due to the variations of solubility. This affects the conductivities of the phases, especially in case of the microemulsion phase. Its conductivity does not simply rise with temperature, since the amount of oil in the microemulsion phase increases while the amount of water decreases. Therefore, the microemulsion phase conductivity declines with temperature but still lies in between the values for the aqueous and organic phase. As the temperature reaches the transition to the 3Φ conditions, different effects can occur depending on the continuous phase:
- aq = continuous: κkeeps on rising with temperature,
- org or mi = continuous (phase inversion): κdrastically decreases with temperature towards zero, - mi = continuous (phase inversion): κdecreases slowly with temperature to nearly zero.
In addition to the conductivity measurements, the normalized phase heights after complete separation were used to define the dispersed phase fractions. The phases with large volume fractions more likely become the continuous phase, but exceptions from this rule can occur due to the presence of surfactant in the system and
-3 -2 -1 0 1 2 3
20 30 40 50 60 70 80 90
HLD [-]
Temperature T [°C]
Cc = -1.2 Cc = -0.7
T ≈ 60°C
T ≈ 68°C
variable value
B(S) 0
kdi 0.17 EACN 8.1 Cc -1.2 / -0.7
j(A) 0
ct 0.06 K-1
Fig. 27: Estimated HLD values for water, 1-dodecene, Marlipal 24/70 systems using two different approximations for the surfactant properties Cc
their tendency to follow the Bancroft rule [13], which states that the phase where most of the the surfactant is located more likely becomes the continuous phase. The systems are not expected to achieve thermodynamic equilibrium during experiments. To achieve an equilibrium, samples would need to be kept at a constant temperature for a longer time up to several weeks until the phase compositions are constant. However, this was not aim of the study presented here, since the focus lies on processes which also occur in industrial applications.
5.1.1 Phase behavior in systems with water, 1-dodecene and Marlipal 24/70
The position of the 3Φ temperature interval was calculated with the HLD value for water, 1-dodecene, Marlipal 24/70 systems, although not all necessary parameters for this specific system were found in literature. The Cc of Marlipal was estimated using Cc = -1.2 for aC12E6.5surfactant and Cc = -0.7 for aC14E7surfactant [1]. All values for the calculation and their results are summarized in Figure 27. The optimum formulation at HLD = 0 is reached atTCc=−1.2 ≈68◦C andTCc=−0.7 ≈60◦C, which is lower than the experimental results indicating 3Φ conditions between T = 76 - 92◦C (Figure 28).
Schrader et al. [127] showed, that the application of technical grade instead of pure surfactants can lead to deviations of several degrees Celsius in phase behavior. A comparison of water, 1-dodecene Genapol X080 (r) systems with different purity led to an increase of T = 30 ◦C for the transition from 2
̄Φ to 3Φ conditions.
Furthermore, they reported the development of a 4Φ condition due to the presence of additional components because of impurities like alcohols, surfactants with different degrees of ethoxylation or unconverted ethylene oxide [37, 127]. Since the application of technical grade surfactants is common in industrial processes, the HLD value can not provide an exact position of the optimum formulation if the HLD parameters of the technical grade chemicals are only approximated.
Figure 28 presents the experimental results of conductivity and corresponding phase volume fractions as a function of temperature for different compositions of water, 1-dodecene and Marlipal 24/70. At the transition from 2
̄Φ, respectively 2̄Φ to 3Φ conditions the separation times were longer than 24 hours. Therefore, all systems which did not separate in a reasonable time interval are indicated by the phase ”mix”. At these temperatures, either 3Φ conditions or 2Φ conditions might occur. The width of the visible 3Φ interval rises with surfactant concentration. Forγ= 0.05, the conductivity drastically declines as soon as the 3Φ conditions are reached which indicates a change from an aqueous to an organic continuous phase. For γ = 0.075 and 0.1 the conductivity declines over a larger temperature range which is a sign for a continuous microemulsion phase, which is supported by the fact that the microemulsion phase volume fraction rises with surfactant concentration. The phase volume fractions within the 3Φ systems significantly vary over temperature for all three system compositions, an increase of the aqueous phase and a decrease of the organic phase volume fraction occurs with rising temperature caused by the changing solubility of the components. At low temperatures, the microemulsion phase consists of high amounts of water and surfactant and smaller amounts of 1-dodecene. With rising temperatures, the water is expelled from the microemulsion phase as the amount of 1-dodecene rises. Extreme changes in phase volume fractions can even lead to a change of the continuous phase in agitated conditions within the 3Φ interval, having severe effects on the drop size distributions and phase separation behavior.
0 0.2 0.4 0.6 0.8 1
74 76 78 80 82 84 86 88 90 mix org mi aq
α= 0.5 γ= 0.1
0 0.2 0.4 0.6 0.8 1
80 82 84 86 88 90 92 94 96
Normalizedphase fractionsφ and electricalconductivityκ[-] mix org mi aq
α= 0.5 γ= 0.05
0 0.2 0.4 0.6 0.8 1
74 76 78 80 82 84 86 88 Temperature T [°C]
mix org mi aq α= 0.5 γ= 0.075
Fig. 28: Normalized phase volume fractions and electrical conductivity in water, 1-dodecene, Marlipal 24-70 systems.
Continuous phases within the 3Φ conditions are: organic forγ = 0.05 and microemulsion forγ = 0.075 andγ= 0.1
0.0001 0.001 0.01 0.1
80 82 84 86 88 90 92 94
Dynamic viscosityη[Pas]
Temperature T [°C]
aq mi org 3φ 2φ
700 800 900 1000 1100
80 82 84 86 88 90 92 94
Densityρ[kg/m³]
Temperature T [°C]
aq mi org
2φ a) 3φ
b)
Fig. 29: a) Dynamic viscosity at constant shear rate of ̇γ= 1000 s−1and b) density for single phases of water, 1-dodecene, Marlipal 24/70 systems. Error bars represent the average standard deviation of the respective phase.
To determine the physical properties, the phases were separated from each other at specific temperatures within the 3Φ interval and the properties of the single phase were analyzed. Thereby, the differences in composition do not have an effect on the physical properties, since the systems always separate into the same phase compositions at the same temperature. The dynamic viscosity of the phases for a constant shear rate of ̇γ= 1000 s−1and the densities are illustrated in Figure 29. For each data point a complete system was prepared and the temperature was raised to 3Φ conditions. Then the systems were separated at the specific temperature indicated on the x-axis and the viscosity of the single phase was measured at the same temperature. The results show an almost constant viscosity of the organic phase over temperature which slightly rises as the 2̄Φ conditions are reached.
The solubility of the surfactant in the organic phase increases with temperature which should induce a rising viscosity, but this effect is barely visible. It might be compensated by the effect of higher temperature that leads to a viscosity reduction. A temperature difference of ∆T = 10◦C leads to a decrease of pure 1-dodecene viscosity by roughly 10% (Appendix A.1, Fig. 87). To compensate this effect, the surfactant concentration in the organic phase needs to rise by 1 - 2% (Appendix A, Fig. 88). The viscosity of the aqueous phase rises from η= 0.17 to 0.7 mPa s which is contrary to the expected effects of rising temperature and reducing surfactant concentration.
The increase might also be caused by experimental errors or evaporation of the water during the experiments leading to higher specific surfactant concentrations. A more pronounced dependency on temperature occurs for the microemulsion phase, since the viscosity declines with temperature, covering values from ηmi = 0.00278 to 0.02116 Pa s. This is in accordance with literature predicting a minimum of the viscosity within the 3Φ interval [60]. An increasing microemulsion viscosity is expected to occur near the transition temperature to 2̄Φ conditions, but the temperature gradients during phase separation did not allow for a more detailed analysis in smaller temperature steps between T = 89 - 91◦C. The flow curves of each phase for different compositions
at T = 83◦C are depicted in Figure 30. To avoid evaporation of the fluids caused by the high temperatures, the viscosity was not measured at shear rates below ̇γ= 5s−1 because of increasing time that is necessary to determine reproducible values at low shear rates. The microemulsion phase exhibits Newtonian behavior, which is in accordance with literature. The aqueous excess phase shows a tendency towards shear-thinning behavior which is caused by the presence of surfactant in this phase. No such trend is observed for the organic phase, which is strictly Newtonian, which leads to the conclusion that either the surfactant concentration is low or they do not form distinctive agglomerates within the organic phase. For a given temperature within the 3Φ conditions, the values of α and γ should not affect the physical properties of the phases but only the phase volume fractions, since the systems theoretically separate into phases with the same composition. Although the systems were separated and measured at the same temperature the viscosity values of the phases are not exactly the same in the results presented here, especially in case of the microemulsion phase. This might be caused by temperature gradients during the separation procedure, the lack of a thermodynamic equilibrium.
0.00001 0.0001 0.001 0.01 0.1
5 50 500
Dynamic viscosityη[Pas]
aq mi org α= 0.5 γ= 0.05 a)
5 50 500
Shear rate γ[1/s]
aq mi org
α= 0.5 γ= 0.075 b)
5 50 500
aq mi org
α= 0.5 γ= 0.1 c)
.
Fig. 30: Single phase flow curves of the water, 1-dodecene, Marlipal 24/70 systems with different compositions, separated at T = 83◦C
The densities of the respective phases illustrated in Figure 29b were also determined after separation at a specific temperature. Both aqueous and organic phase inherit an almost constant density over temperature, which leads to the conclusion that the composition does not change within this temperature interval. The density of the microemulsion phase shows a slight increase with a maximum at 86◦C which is not in accordance with the expected changing phase composition. One would rather expect a declining density due to declining water and rising 1-dodecene within the microemulsion phase. The reason for the observed behavior apart from measurement uncertainties is the complex, bicontinuous structure of microemulsion, or the presence of different surfactant species in the technical grade Marlipal 24/70. The same applies for the interfacial tension measurements in Marlipal 24/70 systems, which had high deviations in a range of σ = 0.005 - 1 mN/m and a poor reproducibility. During measurements, turbidity occurred under most conditions which prevented a detailed analysis of the droplet shape. Therefore, the interfacial tension measurements are not depicted here.
5.1.2 Phase behavior in systems with water, 1-dodecene and Marlophen or Triton X100 In systems with Triton X100 and Marlophen similar results were found. A relevant difference to the Marlipal 24/70 systems is the changing position of the 3Φ area. In case of Marlophen NP6 and NP7, the same surfactant concentration ofγmin ≈0.05 is needed to reach the 3Φ conditions around T = 52 - 62◦C. Exemplary results in Triton X100 systems with two different compositions are shown in Figure 31. The minimum surfactant concen-tration isγmin ≈0.15 and the 3Φ interval with reasonable separation times lies in the range of T = 88 - 96◦C.
The conductivity values and phase volume fractions indicate that either the organic or the microemulsion phase is the continuous phases for these compositions. For both compositions the change of dispersed phase frac-tion is less pronounced than in Marlipal 24/70 systems, which might be caused by the more defined molecular structures of these surfactants.
0 0.2 0.4 0.6 0.8 1
79 84 86 89 92 96 98
mix org mi aq
α= 0.5 γ= 0.2
0 0.2 0.4 0.6 0.8 1
82 84 86 89 92 96 98
Normalized phase fractionsφ and electrical conductivity κ [-]
mix org mi aq
α= 0.5 γ= 0.15
Temperature T [°C]
Temperature T [°C]
Fig. 31: Normalized phase volume fractions and electrical conductivity in water, 1-dodecene, Triton X100 systems.
Continuous phases within the 3Φ conditions are: organic or microemulsion forγ= 0.15 and 0.2
5.1.3 Phase behavior in systems with water, 1-dodecene and C4E2
In addition to these results, the phase behavior of the model system with water, 1-dodecene andC4E2 was also investigated [II, III]. Since the systems separate within several minutes under all conditions, the phase volume fractions were also determined under 2
̄Φ conditions. Figure 32 shows three exemplary compositions leading to different continuous phases within the 3Φ interval.
For α= 0.3,γ = 0.2 (Fig. 32 left) the continuous phase stays the aqueous phase despite the transition from 2̄Φ to 3Φ conditions at T = 80◦C. The abrupt changes of electrical conductivity between T = 87 - 91◦C indicated by the dashed line are caused by large droplets which coalesce in the vicinity of the conductivity probe (cf. section 5.4.2). Apart from these disturbances, the conductivity steadily rises with temperature. For α= 0.5, γ= 0.2 the organic phase volume fraction is the largest one in the system and the organic phase becomes the continuous phase. If the amount of C4E2 is increased to α= 0.5, γ = 0.4 the volume of the microemulsion phase rises and the microemulsion becomes the continuous phase. For two temperatures of this composition (T = 83 + 85◦C) the identity of the lower phase indicated by ”mix” was unclear. This turbid phase was either the aqueous or microemulsion phase. The transition to 3Φ conditions might have caused the formation of extremely small microemulsion droplets which did not yet separate from the aqueous phase (cf. section 5.4.2, [III]). For all three compositions, the variations in dispersed phase fraction are in a range of φ= 1 - 5 %, which is a significant difference to the Marlipal 24/70 system [III] and in accordance to Marlophen and Triton X100, indicating that the composition of the phases is less affected by temperature variation. A summary concerning the effect of αand γon the phase volume fractions at a constant temperature T = 83◦C
0 0.2 0.4 0.6 0.8 1
35 55 70 77 79 83 87 91 95
Normalized phase fractionsφ and electrical conductivity κ [-] org mi aq
α= 0.3 γ= 0.2
0 0.2 0.4 0.6 0.8 1
23 40 60 76 79 83 86 80 93 95 org
mi aq
α= 0.5 γ= 0.2
0 0.2 0.4 0.6 0.8 1
25 45 65 75 79 83 87 91 95 org
mi aq streaks α= 0.5 γ= 0.4
Temperature T [°C]
mix
Fig. 32: Normalized phase volume fractions and electrical conductivity in water, 1-dodecene,C4E2systems. Continuous phases within the 3Φ conditions are: aqueous forα= 0.3γ = 0.2 (left) [III], organic for α= 0.5,γ = 0.2 (middle) [II, III] and microemulsion forα= 0.5,γ= 0.4 (right) [III]
α 0.3 0.4 0.5 0.5 0.5 0.5 0.5 0.5 γ 0.2 0.2 0.175 0.2 0.225 0.34 0.37 0.4 0
0.2 0.4 0.6 0.8 1
org mi aq T = 83°C
System composition
continuous continuous continuous continuous
continuous continuous
continuous
continuous
Normalied phase fractionsφ[-]
Fig. 33: Interface heights after complete separation for systems with water, 1-dodecene and C4E2 [III] [114]
0 1 2 3 4
20 40 60 80 100
Interfaical tension σ[mN/m]
Temperature T [°C]
aq/org mi/org aq/mi
2φ 3φ
α= 0.5 γ= 0.2
0.2 0.4 0.6 0.8 1 1.2
78 82 86 90 94
Interfaical tension σ[mN/m]
Temperature T [°C]
Fig. 34: Experimental interfacial tensions as a function of temperature in water, 1-dodecene, C4E2 systems. Error bars are not depicted in the left diagram to ensure greater clarity (cf. [III])
is depicted in Figure 33 [III] [114]. Increasing α shifts the ratio of organic to aqueous phase towards larger organic phase fractions, whereas a rising γ increases the volume fraction of the microemulsion phase. These results offer the possibility to directly control which phase becomes the continuous one, as is described in more detail in [III] and section 5.4.2.
Figure 34 shows the interfacial tensions of a water, 1-dodecene, C4E2 system over temperature. The expected minimum ofσaq/organd a reduction ofσmi/orgwith temperature in accordance with literature can be observed [60] (cf. also Fig. 13). The reproducibility of the experimental results for the aq/mi interface was poor due to a turbidity of the liquids and small droplet sizes, respectively satellite drops which also occurred for the non-ionic surfactants and disturb the definition of the droplet shape. The interfacial tensions σaq/mi could not be determined at all temperatures and the resulting average experimental error of ±0.2 mN/m is high in comparison to the interfacial tension values, leading to a relative error in the range of ≈20 - 50%. To analyze how the changing solubilities affect the composition of each phase, the respective mass fractions of water, 1-dodecene andC4E2 in the phases were determined using Karl-Fischer-Titration and gas chromatography. The complete systems were brought to T = 20/40/60◦C (2
̄Φ conditions) and to T = 83◦C (3Φ conditions), separated from each other and analyzed [V] (Figure 35). The aqueous phase mainly consists of water andC4E2, whereas the amount of 1-dodecene is lower than 1 wt.%. The C4E2 concentration decreases with temperature by 26 wt.%. The value at T = 60◦C might be an outlier from this trend. In the organic phase less than 1 wt.% of water is present and the amount ofC4E2increases with temperature by≈12 wt.%. Comparing the composition of all three phases at T = 83◦C (Fig. 35, right) shows that the microemulsion phase has the largest amount ofC4E2, but only a small amount of oil in the range of 1-2 wt.%. This temperature represents the conditions in the lower part of the 3Φ temperature interval. The amount of oil is expected to increase with temperature while the water content decreases. The aqueous excess phase mainly consists of water and C4E2, the organic
0 20 40 60 80 100
20 40 60 83
Massfractionx [wt.%]
Temperature T [°C]
1-dodecene C4E2 water
0 20 40 60 80 100
20 40 60 83
Massfractionx[wt.%]
Temperature T [°C]
1-dodecene C4E2 water
0 20 40 60 80 100
aq mi org
Massfractionx[wt.%]
Phase 1-dodecene C4E2 water
aq
org
T = 83°C
Fig. 35: Mass fractions of water, 1-dodecene and C4E2 (α= 0.5, γ = 0.2) in the aqueous (left) and organic (middle) phase for different temperatures. Composition of each phase at T = 83◦C under 3Φ conditions (right) [V]
700 800 900 1000 1100
20 30 40 50 60 70 80
Densityρ[kg/m³]
Temperature T [°C]
aq (exp) aq (calc) org (exp) org (calc) mi (exp) mi (calc)
0.0001 0.001 0.01
20 30 40 50 60 70 80
Dynamic viscosityη[Pas]
Temperature T [°C]
aq (exp) aq (art) org (exp) org (art) mi (exp) mi (art)
a) b)
Fig. 36: a) Directly measured densities of the phases (exp) and calculated densities (calc) using the phase composition measurements and densities of the single components, Right: Directly measured dynamic viscosities (exp.) and the values for artificial phases (art) mixed using the composition results ( ̇γ= 1000 s−1)
excess phase of 1-dodecene and C4E2. Due to the low solubility, the amount of 1-dodecene, respectively water in these phases can be neglected. To validate this quantification, knowledge of these compositions was used to estimate the density of the phases by using the percentages of water, 1-dodecene andC4E2 and their respective pure component density at T = 83◦C (cf. App. A.1, Fig. 87) while neglecting possible excess volume of the mixtures.
The calculated results and the experimental densities received by a direct analysis of the phases are summarized in Figure 36a. Although some deviations can be seen for the aqueous phase and organic phase, the results are in good agreement. The same holds true for the dynamic viscosities of the phases, as shown in Figure 36b. The experimental viscosity results for the single phases are compared to the viscosity of artificial phases that were mixed using the previously determined mass fractions. Although again some deviations for the aqueous phase occur, the values of the organic and microemulsion phase are in good agreement.
5.1.4 Hysteresis effects
If the systems are continuously stirred while enhancing the temperature from 2
̄Φ to 3Φ conditions, the phase inversion occurs at a specific temperature with a good reproducibility of ±1◦C. However, if the temperature is reduced from 3Φ towards 2
̄Φ conditions, a hysteresis effect can be observed, as is shown in Figure 37a for a system with Triton X100 and Figure 37b for C4E2.
In case of Triton X100, the phase inversion during heating from an o/w emulsion (2
̄Φ) to an organic continuous phase (3Φ) occurs at higher temperatures than the reserved inversion during cooling. The deviation is around
0 0.2 0.4 0.6 0.8 1
80 85 90 95 100
Nomralizedelectricalconducitivtyκ[-]
Temperature T [°C]
Heating Cooling
0 0.2 0.4 0.6 0.8 1
50 60 70 80 90 100
Nomralizedelectricalconducitivtyκ[-]
Temperature T [°C]
Heating Cooling
C4E2 α = 0.5 γ= 0.2 Triton X100
α = 0.5 γ= 0.2
2φ 3φ 2φ
3φ
a) b)
Fig. 37: Hysteresis of the phase inversion in a) Triton X100 systems and b) C4E2 systems. Images show droplets of C4E2 systems under the schematically illustrated phase conditions
60 70 80 90 100
0 0.1 0.2 0.3 0.4
Temperature T [°C]
Amount of surfactant γ[-]
Marlipal 24/70 Triton X100 C4E2
Fig. 38: Measured borders of the 3Φ area (data points) for water, 1-dodecene systems with either Marlipal 24/70, Triton X100 orC4E2 [II, III] [114]. The colored areas roughly depict the position of the 3Φ areas.
∆T≈2◦C. In systems with Marlipal and Marlophen, the temperature deviations were even smaller than with Triton X100. The systems with C4E2 change from an o/w emulsion (2
̄Φ) to a 3Φ condition with multiple emulsion droplets while enhancing the temperature. Details about the identification of the phases and multiple emulsions are provided in section 5.2 and 5.4.2.1 of this thesis. During cooling these multiple emulsions vanish, but an organic continuous phase is present even at room temperature which can be verified using the droplet appearance and the low conductivity. Paul et al. [109] reported a similar hysteresis in conductivity and in phase separation time in these systems, but were not able to provide details on the dispersion type since they did not have the possibility to apply an in-situ imaging technique. As depicted in Figure 37 on the endoscope images, the reason for the deviations in phase separation times are the different initial droplet sizes and another type of dispersion. It is, however, unclear if the dispersed phase during cooling consist of both microemulsion and aqueous droplets or only of aqueous droplets. If the stirring is stopped, the systems separate into two phases.
A subsequent restart of the agitation leads to the expected 2
̄Φ conditions with an o/w emulsion. Therefore, the dispersion conditions in microemulsion systems can be metastable under the condition that stirring is not stopped. A more detailed analysis of this effect may be advantageous for process control, since dispersions with some surfactants seem to be less sensitive to changes in temperature than others. On the other hand, the unexpected behavior might cause problems with phase separation.
5.1.5 Summary of phase behavior results in water, 1-dodecene, surfactant systems
Figure 38 summarizes the phase behavior results with the different surfactants by showing the experimental 3Φ boundaries as data points. The colored areas very roughly indicate the positions of the respective 3Φ systems.
It should be noted that to determine the complete phase behavior, a significantly higher amount of samples