## 5 Results
### Measurement by the Pipette with Gap
#### 5.1.3 Vibrational Behavior of the Surface by the Pipette  
To study the vibrational behavior of the surface surrounded by the pipette, the displacement was measured by various laser spot locations inside the pipette. For understanding the influence of the radius of the surface and the stiffness of the sample in this study, two different pipettes and two different mixtures were used in this section--first, by the smaller pipette with 1.25 mm radius. The pipette touches the sample without applying any force on the surface exactly the same as the connected pipette with 0 mN contact force in the previous subsection. The position of the laser spot changed between seven different locations in the area of a circle with a 2.5 mm diameter within the pipette. The displacement amplitude was measured from the laser spots that were positioned in the center of the pipette and by distances of 0.13 mm, 0.15 mm, 0.45 mm, 0.7 mm, 0.6 mm, 0.7 mm and 1.2 mm from the center, and the modulus of elasticity calculated in the frequency range. The measured displacement by the smaller pipette and the corresponding calculated modulus of elasticity in seven laser spot positions are shown in Figure 9a,b respectively. The blue lines in the graphs denote the displacement amplitude measured from the centre of the pipette and the rest of the lines belong to the other locations inside the pipette with the specified distance from the centre. The legend in the graphs denote the distance of the laser spot locations from the centre of the surface within the pipette. As expected from the behaviour of the model which will be discussed in the Section 5.2.6, the displacement in the centre of this pipette (1.25 mm radius) has the highest value with respect to other locations. The calculated modulus of elasticity from the measured displacement has the lowest value in the centre of the pipette as can be expected.  
Figure 8: The measurement results in the two boundary conditions; (**a**) measured excitation pressure; (**b**) measured displacement amplitude; (**c**) calculated modulus of elasticity.  
Second, the position of the laser spot changed between seven different locations in a 3 mm diameter circle on center of the surface surround by the bigger pipette. The diameter of the pipette is 11.5 mm and measurements had been done on the 1:1:0 mixture to examine the effect of mixture stiffness on the results. In this case, the diameter of the surface enclosed by the pipette wall is 11.5 mm, but the laser spot can only move in 3 mm diameter circle in the centre of the enclosed area. Figure 9(c) shows the calculated elastic modulus of the 1:1:0 mixture in the seven different laser spot locations. The mean value and the standard deviation of the calculated modulus of elasticity in the first and the last frequency step are 34.2 kPa, 2.7 kPa and 214 kPa, 5.5 kPa, respectively.  
As is illustrated in the plot (c) of Figure 9, the calculated modulus of elasticity in off-center locations has a lower deviation from the value calculated in the center point, by this bigger pipette with respect to the smaller pipette. Although the laser spot can move in a circle of 2.5 mm diameter in the smaller pipette and in a circle of 3 mm diameter in the bigger pipette which is almost similar, in the first case, the pipette wall restricted the surface in a circle of 3 mm diameter, while the surface is restricted by a diameter of 11.5 mm in the second case. Therefore, a movement in a scale of 100 \(\upmu\)m in the centre of a circle with 11.5 mm diameter in the larger pipette produces less deviation with respect to the smaller pipette. On the other hand, the much lower deviation in the mixture 1:1:0 compared to the 1:1:2 mixture in all the excitation frequency steps is also related to its higher stiffness, which causes of lower amplitude of the generated displacement.