Results Of The Flocculation Property Of Redispersed Microgel Biology Essay

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This chapter describes about the results obtained in the experiment done as per the procedure explained in the chapter 2 and also made discussion of the results (DLS graphs) with each other and compared with other work from the literatures.

3.1 Critical flocculation temperature of poly-NIPAM in multivalent electrolytes.

The critical flocculation temperature (CFT) of poly-NIPAM with multivalent electrolytes was determined using dynamic light scattering technique as per the procedure explained in the session 2.3.5 and results were shown in the table 3.1. The DLS graphs of CFT were plotted, hydrodynamic diameter (nm) in Y-axis and temperature (0C) in X-axis, which are shown in the appendix.

3.1.1 Objective for the determination of CFT.

The study regarding the flocculation property of re-dispersed microgel contains multivalent electrolytes was carried out by maintaining the condition of temperature below CFT.

3.1.2 Results for the CFT experiment.

Sample (3mL)

Critical flocculation temperature, CFT. (0C)

Electrolyte

Concentration.

NaCl

0.1M

34

1M

22

CaCl2

0.1M

34

1M

24

AlCl3

0.1M

32

0.3M

30

Sea water

40%

32

Table 3.1 CFT of poly-NIPAM in multivalent electrolytes.

The CFT experiment of poly-NIPAM revealed that as the concentration or the valency of the electrolytes varied results in a dramatic change in the CFT. The samples such as 0.5% poly-NIPAM having 0.1M NaCl electrolyte and 0.5% poly-NIPAM having 0.1M CaCl2 showed a CFT of 340C while when the concentration changed to 1M showed a CFT of 220C and 240C respectively. As explained in the session 1.5 CFT is the temperature in which the flocculation of the microgels happened due to the disturbance of the steric stabilization. Thus the variation in the CFT in the presence of electrolytes in various concentrations is may be due to some problems in the steric stabilization of the whole system.

3.2 The flocculation property of re-dispersed poly-NIPAM in different electrolytes.

The flocculation properties of re-dispersed microgels were found out with the help of DLS equipment, maintained the conditions and procedures as explained in the session 2.3.6. The DLS graphs were plotted and compared.

3.2.1 Sample A (0.5% poly-NIPAM having 0.1M NaCl electrolyte).

3.2.1.1 DLS graph of sample A.

Graph 3.1 The hydrodynamic diameter vs time of poly-NIPAM having 0.1M NaCl.

The DLS graph 3.1 is explained about the hydrodynamic diameter and the stability of the re-dispersed poly-NIPAM microgel particles having 0.1M NaCl electrolyte over a time period of 7 hours.

3.2.1.2 TEM picture of sample A.

I:\ShanTEM\0-25M NaCl_5000X_0068.jpgI:\ShanTEM\0-25M NaCl_7300X_0006.jpg

Fig.3.1 TEM picture of sample A having magnification of 2000x and 7300x respectively.

3.2.1.3 Result of sample A.

The DLS graph of sample A (graph 3.1) explained that the microgel was stable over a time period of 7 hours having particle size of 482nm ± 6 and was reversible. The TEM picture in 2000x magnification revealed the uniform dispersed microgel particles and in 7300x magnification showed a particle size of sample A (fig.3.1).

3.2.2 Sample B (0.5% poly-NIPAM having 1M NaCl electrolyte).

3.2.2.1 DLS graph of sample B.

Graph 3.2. The hydrodynamic diameter vs time of poly-NIPAM having 1M NaCl.

The hydrodynamic diameter and the stability of the re-dispersed poly-NIPAM microgel having 1M NaCl are explained in the DLS graph 3.2 over a time period of 7 hours.

3.2.2.2 TEM picture of sample B.

I:\ShanTEM\1M NaCl_2000X_0058.jpgI:\ShanTEM\1M NaCl_6000X_0061.jpg

Fig.3.2 TEM picture of sample B having magnification of 3000x and 6000x respectively.

3.2.2.3 Result of sample B.

The DLS graph of sample B (graph 3.2) explained that the microgel had a particle size of 499nm ± 7, reversible and was stable until the experimental condition of 7 hours. The TEM picture of sample B has been taken in the magnification of 3000x and 6000x respectively and marked the particle size as shown in the fig.3.2.

3.2.3 Sample C (0.5% poly-NIPAM having 0.1M CaCl2 electrolyte).

3.2.3.1 DLS graph of sample C.

Graph 3.3. The hydrodynamic diameter vs time of poly-NIPAM having 0.1M CaCl2

The hydrodynamic diameter and the stability of re-dispersed poly-NIPAM microgel having CaCl2 electrolyte with concentration of 0.1M have studied and plotted on the DLS graph 3.3 over an experimental condition of 7 hours.

3.2.3.2 TEM picture of sample C.

I:\ShanTEM\0-1M CaCl2_2000X_0039.jpgI:\ShanTEM\0-1M CaCl2_6000X_0042.jpg

Fig.3.3 TEM picture of sample C having magnification of 2000x and 6000x respectively.

3.2.3.3 Result of sample C.

The DLS graph 3.3 revealed that the microgel was stable and reversible until the experimental condition period of 7 hours and noticed the particle size of 492nm ± 7. The TEM picture has been taken in the magnification of 2000x and 6000x and marked the particle size (fig.3.3). This picture shows the uniform dispersion of the microgel particles in the colloidal medium.

3.2.4 Sample D (0.5% poly-NIPAM having 1M CaCl2 electrolyte).

3.2.4.1 DLS graph of sample D.

Graph 3.4. The hydrodynamic diameter vs time of poly-NIPAM having 1M CaCl2.

The stability and the hydrodynamic diameter of the re-dispersed poly-NIPAM having 1M CaCl2 has been observed using DLS graph 3.4 over an experimental condition of 7 hours.

3.2.4.2 TEM picture of sample D.

I:\ShanTEM\1M CaCl2_2000X_0076.jpgI:\ShanTEM\1M CaCl2_7300X_0037.jpg

Fig.3.4 TEM picture of sample D having magnification of 2000x and 7300x respectively.

3.2.4.3 Result of sample D.

According to the graph 3.4 of sample D, some changes have been happened to the particle size of the microgels. The particle size of the microgel particle is shown to be 692nm ± 45 and the colloidal medium was unstable until the experimental period of 7 hours. The sample was irreversible as well. The TEM picture (fig.3.4) was taken under the magnification of 2000x and 7300x revealed visually some kind of flocculation and measured the particle size.

3.2.5 Sample E (0.5% poly-NIPAM having 0.1M AlCl3 electrolyte).

3.2.5.1 DLS graph of sample E.

Graph 3.5. The hydrodynamic diameter vs time of poly-NIPAM having 0.1M AlCl3.

The DLS graph of sample E (graph 3.5) put forward the hydrodynamic diameter and the stability of re-dispersed poly-NIPAM microgel having 0.1M AlCl3 electrolyte over a time period of 7 hours.

3.2.5.2 TEM picture of sample E.

I:\ShanTEM\0-1M AlCl3_2000X_0049.jpgI:\ShanTEM\0-1M AlCl3_6000X_0052.jpg

Fig.3.5. TEM picture of sample E having magnification of 2000x and 6000x respectively.

3.2.5.3 Result of sample E.

The DLS graph of sample E (graph 3.5) explained that the particle size of the microgels particles is 516nm ± 6, reversible and stable overt a time period of 7 hours. The TEM picture (fig.3.5) was taken in the magnification of 2000x and 6000x and visualised some kind of changes in the dispersion of the colloidal particles and pointed the size as well.

3.2.6 Sample F (0.5% poly-NIPAM having 0.3M AlCl3 electrolyte).

3.2.6.1 DLS graph of sample F.

Graph 3.6. The hydrodynamic diameter vs time of poly-NIPAM having 0.3M AlCl3.

The DLS graph 3.6 disclosed about the hydrodynamic diameter of 0.5% poly-NIPAM having 0.3M AlCl3 electrolyte over a time period of 7 hours.

3.2.6.2 TEM picture of sample F.

I:\ShanTEM\0-3M AlCl3_2000X_0044.jpgI:\ShanTEM\0-3M AlCl3_6000X_0047.jpg

Fig.3.6 TEM picture of sample F having magnification of 2000x and 6000x respectively.

3.2.6.3 Result of sample F.

The DLS graph 3.6 revealed that the hydrodynamic diameter of the microgel particles was 586nm ± 11, reversible and stable over a time period of 7 hours. The TEM picture (fig.3.6) visualised in the magnification of 2000x and 6000x that the particles were not uniformly dispersed and measured the particle size.

3.2.7 Sample G (0.5% poly-NIPAM having 40% ASTM sea water).

3.2.7.1 DLS graph of sample G.

Graph 3.7 The hydrodynamic diameter vs time of poly-NIPAM having 40% ASTM sea water.

The DLS graph 3.7 represents the hydrodynamic diameter of re-dispersed poly-NIPAM microgel particles having 40% ASTM sea water over a experimental condition of 7 hours.

3.2.7.2 TEM picture of sample G.

I:\ShanTEM\40% Sea Water 50C_2000X_0069.jpgI:\ShanTEM\40% Sea Water 50C_6000X_0072.jpg

Fig.3.7 TEM picture of sample G having magnification of 2000x and 6000x respectively.

3.2.7.3 Results of sample G.

The DLS graph 3.7 concluded that the hydrodynamic diameter of the microgel particle size was 499nm ± 16 and shows stability for an experimental period of 7 hours. This sample was reversible. The TEM picture (fig.3.7) was taken in and visualised in the magnification of 2000x and 6000x that the particles are dispersed uniformly in the medium and measured the size of the particle.

3.2.8 Sample H (0.5% poly-NIPAM having 40% sea water from another laboratory).

3.2.8.1 DLS graph of sample H.

Graph 3.8 The hydrodynamic diameter vs time of poly-NIPAM having 40% ASTM sea water prepared at another laboratory.

The DLS graph 3.8 having the same composition of microgel and sea water as that of sample G but conducted in another laboratory maintaining the same condition of this project, shows a wide range in particle size of re dispersed poly-NIPAM.

3.2.8.2 TEM picture of sample H.

I:\ShanTEM\40% Sea Water_3000X_0077.jpgI:\ShanTEM\40% Sea Water_6000X_0026.jpg

Fig.3.8 TEM picture of sample H having mafgnification of 3000x and 6000x respectively.

3.2.8.3 Result of sample H.

The DLS graph 3.8 disclosed an incredible increase in the particle size of 12μm ± 2, and was unstable over a time period of 7 hours. In addition to, the sample was irreversible and flocculated with very high rate. The TEM picture (fig.3.8) were taken in the magnification of 3000x and 6000x and visualised, shows some kind of flocculation and measured the particle size.

3.3 Discussion and inference.

The critical flocculation temperature of the poly-NIPAM having multivalent electrolytes was found out as explained in the session 3.1, and the results were plotted in the table 3.1. This experiment disclosed that as concentration of the electrolyte increases results in a dramatic decrease in the CFT of the microgels. When the concentration of NaCl electrolyte and CaCl2 become 1M, then the CFT went down to 220C and 240C respectively (session 3.1.2). While according to the study of Rasmusson et al (2004), as the concentration of the NaCl increase to 0.1M then the CFT decreases linearly with increase in temperature, but such type of changes haven't divulged in this CFT experiment (session 3.1.2).

In the mean time the valency of the electrolytes also cause some effects in the CFT of the poly-NIPAM microgel. In the session 3.1.2, the CFT of the samples having 0.1M NaCl and 0.1M CaCl2 was 340C while the sample contains 0.1M AlCl3 shows the CFT of 320C. That means a decrease in 20C.

The above eight DLS graphs were compared each other and its findings could be summarised in the following table 3.2.

Properties

Re-dispersed poly-NIPAM having

NaCl (Na+)

CaCl2 (Ca2+)

AlCl3 (Al3+)

40% ASTM sea water.

0.1M

1M

0.1M

1M

0.1M

0.3M

Size (hydrodynamic diameter)

482nm

± 6

499nm

± 7

492nm

± 7

692nm

± 45

516nm

± 6

586nm

± 11

499nm

± 16

CFT (0C)

34

22

34

24

32

30

32

Reversible

YES

YES

YES

NO

YES

YES

YES

Stable over time. (7 hrs)

YES

YES

YES

NO

YES

YES

YES

Table 3.2 The flocculation behaviour of 0.5% poly-NIPAM in multivalent electrolytes.

By discussing the eight DLS graphs and the TEM pictures, it was clearly understood that some changes has happened in the particle size of poly-NIPAM having 1M CaCl2 (session 3.2.4.3), poly-NIPAM having 0.3M AlCl3 (session 3.2.6.3) and also in the graph having 40% ASTM sea water prepared in another laboratory (session 3.2.8.3). Some changes have been expected in the graph 3.7 but nothing shown by the DLS.

The sample A containing 0.5% poly-NIPAM and 0.1M NaCl was noticed as stable over a time period of 7 hours and its particle size was 482nm ± 6 (session 3.2.1.3) and its CFT was 340C as described in the table 3.2. While the concentration of the NaCl increased from 0.1M to 1M (sample B), there shows a dramatic decrease in the CFT, but remains stable and the particle size, 499nm ± 7 was almost nearer to the particle size of sample A (session3.2.2.3 and table 3.2). The sample C (0.5% poly-NIPAM having 0.1M CaCl2) also displayed the same property of sample A (session 3.2.3.3). The samples (A, B and C) exhibit reversible property as well as shown in the table 3.2.

The flocculation property of the re-dispersed microgel has varied when the concentration of the CaCl2 increased to 1M, sample D. As described in the session 3.2.4.3, the particle size of the microgel gets increased to 692nm ± 45 and was unstable under the experimental period of 7 hours. In addition to this the CFT gets reduced to 240C and more over this sample was irreversible (table 3.2).

The samples (E and F), 0.5% poly-NIPAM having 0.1M AlCl3 and 0.5% poly-NIPAM having 0.3M AlCl3 respectively, were stable until the experimental condition of 7 hours and reversible also. While the sample F exhibit a higher particle size, 586nm ± 11 comparing with the sample E, 516nm ± 6 and shows a CFT of 300C and 320C respectively (table 3.2).

Some changes has been expected in the sample G (0.5% poly-NIPAM having 40% ASTM sea water), but shows very similar to the samples contain 0.1M NaCl and 0.1M CaCl2 (A and C) as clear in the table 3.2 having particle size 499nm ± 16, when compared to the sample H (0.5% poly-NIPAM having 40% ASTM sea water from another laboratory).

The very important thing disclosed by sample H is its higher particle size, 12μm ± 2 (table 3.2). This means, something is happened in the surface charge of the particle and might flocculate each other and converted to large lumps of particles. This sample was irreversible and unstable until the experimental period of 7 hours as described in the session 3.2.8.3.

The CaCl2 and AlCl3 are multivalent electrolytes having charges of +2 and +3 respectively. As the concentration of these multivalent electrolytes, the charges of these electrolytes might affect the electrostatic repulsion of the microgel particles. Since at higher temperatures, the colloidal stability of the microgels are due to the electrostatic repulsion (due to the surface charges) of particles. When the concentration of the positive ions increases which may leads to the binding of microgel particles together and to form bigger size particles. This enhances in the flocculation of the microgel particles. As the particle size of a colloidal medium increases, the stability gets disturbed.

Some studies reveals that presents of smaller concentrations electrolytes enhances the stability of the microgels. According to Liu et al (2008) the concentration of 0.2M NaCl in the microgel intensified the stability of the colloidal system.

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