5.3 Influence of the polymer on the internal structure of the
line is a fit according to the TEUBNER-STREYapproximation. The scattering patterns of the polymer containing microemulsions are shifted to higher I(q) values for clarity. As can be seen in figure 5.13, neither the position of the maximum qma x nor the general shape of the peak is influenced significantly by the added polymers ofS2except F108.
The results of the data analysis using the TEUBNER-STREY approximation of the resulting scattering intensities is given in table 5.4 for S2 and in table 5.5 for S3. As described before, in the poly-mer containing samples a polypoly-mer content ofτ = 0.05 was chosen. The domain size d remains almost constant for the observed samples atγ=0.25, 0.30 and 0.35. For F108 only one sample was measured atγ=0.25, higher surfactant content leads to the formation of lamellar phases. For the correlation length a slight increase with increasing PEO content of the polymer at higherγvalues can be assumed. In the case of F108 theξvalue is reduced toξSAX S≈4.8 nm.
For the pure microemulsion system atα=0.5,δ=0.0875 andγin the range ofγ=0.25 to 0.35, domain sizes ofd=11.1−17.7nmand correlation length ofξ=5.5−6.7nmwere calculated from fits with the TS-formula. As shown in table 5.3, these parameters are in the typical range for sugar surfactant based microemulsion systems.
Table 5.3: Comparision of the results of the TS-Analysis in the system water/Lanol 99/C12/14G1.3/ n-pentanol at constantα=0.5andδ=0.0875with examples of sugar surfactant based microemulsions using n-pentanol as cosurfactant found in the literature. a RME = rapeseed methyl ester; b SANS measurements, water replaced by D2O;c Please note that in this work a different batch of C12/14G1.3 was used.
system α γ δ ξ/nm d/nm ref.
Lanol 99/C12/14G1.3 0.5 0.25 to 0.35 0.0875 6.7 to 5.5 17.7 to 11.1 RMEa/C12/14G1.3 0.5 0.299 0.07 4.7 to 4.4 14.4 to 14.1 [16]
RME/C12/14G1.3 b 0.5 0.29 to 0.30 0.07 4.7 to 4.4 13.4 to 12.8 [15]
C6H12/C8/10G1.3 b 0.5 0.15 to 0.23 0.06 7.9 to 6.5 22.2 to 13.5 [7]
Lanol 99/C12/14G1.3 b,c 0.5 0.24 to 0.34 0.0825 5.6 to 4.7 18.6 to 9.7 [7]
Series 2
With respect to the error bars, the addition of the polymer only leads to small changes in the struc-tural sizes of the microemulsions. Only F108, the largest polymer with an average molecular mass of approximately 14600 g·mol−1differs significantly from the other samples. The domain size d of the pure microemulsion at γ= 0.25 is around 17.7 nm, the domain size upon addition of L101 -P105 is slightly increased, as the amount of surfactant available is reduced. This effect is rather small, as the changes in d are within the error bars. Otherwise for F108 the domain size dF108 = 20.2 nm.
Table 5.4: Results of the TS-Analysis of the SAXS-data in the system water/Lanol 99/C12/14G1.3(S2) /n-pentanol at constantα=0.5andδ=0.0875.
γ=0.25 γ=0.30 γ=0.35 d /nm ξ/nm d/nm ξ/nm d /nm ξ/nm
pure 17.7 6.7 13.4 5.7 11.1 5.5
L101 18.0 6.4 13.9 6.2 11.5 5.8
P103 18.1 5.9 13.7 6.1 11.3 6.0
P104 17.8 6.5 13.6 6.5 11.3 6.3
P105 17.7 6.7 13.6 6.2 11.3 6.3
F108 20.2 4.8 lamellar
This increase of the domain size in the F108 containing system is an indication of the change in the internal structure of the microemulsion. Further increase of the surfactant and the polymer amount toγ≥30 leads to the formation of lamellar structures, the bicontinuous phase is not longer observed. At γ = 0.25ξ varies slightly around 6.5 nm, only for P103 lower values are reached.
At higherγvalues the addition of triblock copolymers leads to a slight increase of the correlation length. The effect is rather small, atγ=0.30 and 0.35 the increase is in the range of 0.4 to 0.9 nm , with the tendency of a larger effect for the more hydrophilic polymers.
This effect, shown forγ=0.35 in figure 5.14 is comparable to the results BYELOVet al. reported for microemulsion systems containing homo and diblock copolymers. For the diblock copolymers they observed an increase ofξwhile the domain sized was not influenced[2].
The same observation is made for the bending rigidityκT S, calculated from the fit parameters of the
0 10 20 30 40 50 5,0
5,5 6,0 6,5 7,0 10,0 10,5 11,0 11,5 12,0
d
d,/nm
PEO content / wt%
Figure 5.14: d and ξ calculated from the scattering patterns in the system water / Lanol 99 / C12/14G1.3(S2)/n-pentanol at constantα=0.5,γ=0.35,δ=0.0875andε=0.05. The resulting length scales are plotted versus the PEO content in the polymers. Upon addition of F108 lamellar phases occurred atγ=0.35, therefore no sample containing F108 was measured. Within the error bars, d is not increased compared to the pure system, whileξincreases upon polymer addition.
TS- approximation. Only for the samples with the highest surfactant content and hence the highest polymer content related to the overall mass, the bending rigidity is slightly increased.
Among the seriesS2 polymers the composition of the polymers changes. Therefore the variation of the size of the PEO- and PPO-blocks changes the solubility of the polymer in the water and oil phase. These changing solubilities at γ = 0.25 lead to different polymer concentrations at the interface, resulting in larger variations ind andξ. At higher surfactant and polymer concentration this effect is reduced as water and oil phase are saturated.
0 10 20 30 40 50 60 70 80 90 10
12 14 16 18 20
= 0.25
= 0.30
= 0.35
d/nm
PEO content / wt%
0 20 40 60 80
4,6 4,8 5,0 5,2 5,4 5,6 5,8 6,0 6,2 6,4 6,6 6,8
= 0.25
= 0.30
= 0.35
/nm
PEO content / wt%
Figure 5.15: Results of the TS analysis forS2: top domain size d plotted versus PEO content of the polymer (0 for pure system). Except F108 (80 wt% PEO), the domain size does not change within the error bars upon polymer addition. bottom: correlation lengthξplotted versus PEO content. At lowγ values no clear trend is observed, with increase ofγ,ξrises with PEO content of the polymer. For F108 atγ=0.25 theξvalue is significantly lowered.
Series 3
Applying the highly effective polymers of the series S3 changes the phase behaviour of the mi-croemulsion systems dramatically. The SAXS experiments were again performed atγ=0.25, 0.30 and 0.35. The F108 containing microemulsion shows an extended lamellar phase atγvalues above γ=0.28, so only the sample atγ=0.25 was measured. For similar reasons no data is available for F88 atγ=0.35.
Table 5.5: Results of the TS-Analysis of the SAXS-data in the system water/Lanol 99/C12/14G1.3(S3) /n-pentanol at constantα=0.5andδ=0.0875.
γ=0.25 γ=0.30 γ=0.35 d in nm ξin nm d in nm ξin nm d in nm ξin nm
pure 17.7 6.7 13.4 5.7 11.1 5.5
F38 19.3 5.6 14.4 5.4 11.6 5.1
F68 18.7 6.2 14.4 5.5 11.6 4.9
F88 19.2 5.6 14.6 4.9 lamellar
F108 20.2 4.8 lamellar
The influence of the large hydrophilic polymers on the internal structure of the microemulsion is completely different compared to the observations with the less efficient polymers of seriesS2. While with S2 the domain size did not show significant changes and only at high γ values ξincreased upon polymer addition. All of theS3 polymers increase d and reduceξ. This is a result of the H.
growing structure sizes, as 5% less surfactant is available to form the internal film. The same effect is observable within the seriesS2, but in case of theS3polymers the increase of d is constantly higher andd Hrising from F68 to F108 atγ=0.25. At higherγvalues the overall surfactant content in the microemulsion is higher, reducing this effect. As shown in figure 5.16, among the highly efficient polymers (F68 to F108) d rises with the molecular weight of the polymer, while the correlation lengthξis reduced. In SAXS experiments we are only able to see the water domains and the polar headgroups of the sugar surfactants due to their higher electron densities compared to the oil phase [4]. This may be a result of a swelling of the water phase due to the large hydrophilic PEO chains.
This effect might be superimposed by the rendering of the water domains by the soluble polymers.
But as the effect is higher with the heavy polymers applied, which additionally show an extended
formation of lamellar phases at higher surfactant content, we expect the amphiphilic polymers being part of the internal surfactant film. Interestingly, the highest effects are reached with less molecules, as the mass fraction of the added polymer remains equal while the molecular mass increases from 8400g/molfor F68 to 14600g/molin case of F108.
0 2 4 6 8 10 12 14 10
11 12 13 14 15 16 17 18 19 20 21
= 0.25
= 0.30
= 0.35
L
d/nm
m W
/ kg mol -1
L F88 F108
F38 F68
0 2 4 6 8 10 12 14
4,0 4,5 5,0 5,5 6,0 6,5 7,0
= 0.25
= 0.30
= 0.35
nm
m W
/ kg mol -1
L
L F108 F88
F38 F68
Figure 5.16: Results of the TS analysis for seriesS3. top: Domain size d plotted versus the mass mW of the Pluronic polymer. In all cases the polymers increase the domain size compared to the pure system.
bottom: Correlation length ξplotted versus the molar mass mW of the used Pluronic polymer. The correlation length of the samples containing Pluronics is shorter than in the pure system.