Turbidity measurements, phase transitions

To investigate the effect of adding monomeric and dimeric CD on the change of phase transition temperature of the polymers P18 and P19, we performed turbidity measurements at the same polymer concentration as above in the presence of a defined amount of Me-P-CD and CD dimer, respectively (Fig. 25 a,b) [61,62], As reported previously [56-59], we found that addition of Me-p-CD led to cloud points of polymers P18 and P19 of 32°C, which correlates to the LCST of pure poly(NIPAAM). This increase of the cloud points relative to the cloud points of pure P18 and P19 results from the inclusion of the hydrophobic adamantyl units by Me-P-CD. 

The following experiment is conducted to And out the pH at which the polymer will precipitate, and induce drug release from the liposomes, once anchored on the membrane. The phase transition pH is determined at 37°C by measuring the turbidity of the polymer solutions at different pHs. As the polymer undergoes coil-to-globule transition and aggregates, the turbidity of the polymer solution increases. 

The volume phase transition temperature of thermally sensitive particles can be determined using various methods and techniques fluorescence study, light scattering, differential scanning calorimetry, and turbidity measurement. 

It is also possible to use turbidity measurements to evaluate elastic constants (Fig. 5, though elastic constants measured in this way for alkylcyanobiphenyls (nCBs) [25] and mixtures [26] are consistently higher than those determined by Frederiks transition studies. Hakemi [27] measured j, 22 and 33 for 8CB (octylcyano biphenyl) close to the nematic-smectic A phase transition and deduced a value of the critical exponent from the divergence of 22 and 33. 

The volume phase transition of responsive polymers and gels can be monitored by methods based on the measurements of changes in solution and gel properties. The most important are the measurement of turbidity, or optical methods in general, and of transition heats. 

We started from a micellar solution of 100 mM TDMAO and 25 mM SHNC and added 100 mM MF. With time we observed the formation of a lamellar L phase, a vesicular Lv phase, and a vesicular precipitate. This precipitate dissolved to form a vesicular phase, an L phase, and finally again a micellar phase. The hydrolysis of the MF and the resulting phase transitions were observed by measurements of pH, conductivity, turbidity, and by means of freeze-fracture transmission electron microscopy. The microstructures of the phases obtained were compared with the microstructures of the corresponding phases when increasing amounts of HCO2H were mixed with solutions of 100 mM TDMAO and 25 mM SHNC. 

The critical mixture curve is measured in the following manner (Occhio-grosso et al., 1986). At a temperature slightly higher than the UCEP temperature, a vapor-liquid mixture at a fixed overall concentration is compressed to a single phase. The pressure is then isothermally decreased very slowly until the system becomes turbid and a second phase just begins to precipitate. A critical mixture point is obtained if critical opalescence is observed during the transition process and if two phases of equal volume are present when the mixture phase-separates. 

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