Dependence on molar mass

In order to achieve the best efficiency the SEC column should be operated at optimized operating parameters. The most important ones are flow rate [cf. van Deemter equation for band-broadening effects (21)], sample viscosity (depends on molar mass and concentration of the sample), and injection volume (7). 

In a previous paper [24] the viscoelastic properties of polyacrylamide homopolymers in solution were discussed in dependence on molar mass, concentration, solvent quality and shear rate. Considering these data a simple equation was developed for the r 0-M-c relationship. 

Up to 100 vortices can be observed at one time, dependent on molar mass, concentration and shear rate. The vortices are seen to rotate about their own axis at the same time moving in the direction of shear. Vortices were seen up to the highest achievable shear rate g=1000 s-1. Decreasing or increasing the shear rate has little or no influence on the generation of vortices. They appear or disappear in a few seconds. The vortices are not caused by air or vapour bubbles. Vortices were also observed in a solution to which a surfactant had been added, and the onset... 

The polymers are easily soluble in polar solvents like TFIF, DMAc, and DMSO, indicating that the solubility is enhanced by the large number of polar end groups and the branched structure. It is fully amorphous with a glass transition temperature between 90 and 110 C,depending on molar mass. 

The ratio of 6.8 for the two peak areas from stochastic TDFRS is close to the value of 5.9 as expected from the concentration ratio and the refractive index increments of the two PS, which depends on molar mass due to end-group effects. The thermal diffusion coefficient DT= 1.12 x 10 7 cm2 (sK) l is in excellent agreement with the value found previously in our laboratory [36]. 

About 40 different grades of regular butyl rubbers are available [63], depending on molar mass (Afv 3-6-105, polydispersity MW M 3-5) and on unsaturation level. For 0.7 mol% of isoprene the molar mass of subchain in the cross-linked rubber is =8000, and =2500 for the highest level (2.2%), which is much more than in polydienes or natural rubber networks. They are shared in two main families characterized by their range of Mooney viscosity, typically ML(I + 8)(100°C) 41-57 and 60-80. 

Escape of a gas through a small hole (or assembly of microscopic holes) into a vacuum Depends on molar mass and temperature of gas... 

Activated carbon surface area 1000 to 1500 m /g pore volume 0.6 to 0.8 cmVg, temperature <540°C loading very dependent on molar mass of target solute, solubility in the carrier liquid, and pH. Example loading 0.01 kg organic molar mass 100/kg dry solid. The value varies with the (molar mass). ... 

The reason for this dependence on molar mass is the same as for effusion rates lighter molecules have higher molecular speeds than heavier molecules, so they move farther in a given amount of time. 

In the heterosphere, a stratification of gases depending on molar masses, occurring by action of diffusion and gravitation, may be observed. It is possible to recognize 4 layers [10-20] as follows ... 

The technique is based on the principle that molecules, under the influence of a centrifiig field, distribute accor rtg to size perpendicularly to the axis of rotation. This sedimentation process is dependent on molar mass. The polymer is detected with index of refraction measurernents or interferometry. There are two approaches m obtain MM avoages fixim the measurements sedimentation equilibrium and sedimentation velodty [26]. 

Activated carbon surface area 1000 to 1500 m /g pore volume 0.6 to 0.8 cm /g, temperature < 540 °C loading very dependent on molar mass of target solute, solubility in the carrier liquid and pH. Example loading 0.01 kg organic molar mass 100/kg dry solid. The value varies with the molar mass . Carbon usage expressed as kg carbon required/m liquid increases with increase in the TOC in the feed and depends on the type of species present. A gross approximation is that 1 kg/m is required for 300 mg TOC/L with n = 1.0 for the range 200-30000 TOC, mg/L. acid treated clay surface area 225 to 300 m /g. 

As this subchapter is devoted to solvent activities, only the monodisperse case will be taken into account here. However, the user has to be aware of the fact that most LLE-data were measured with polydisperse polymers. How to handle LLE-results of polydisperse polymers is the task of continuous thermodynamics, Refs. Nevertheless, also solutions of monodisperse polymers or copolymers show a strong dependence of LLE on molar mass of the polymer, or on chemical composition of a copolymer. The strong dependence on molar mass can be explained in principle within the simple Flory-Huggins %-function approach, please see Equation [4.4.61]. 

In homopolymers, physical properties are to some extent dependent on molar mass. Class transition temperature and various mechanical properties will increase with molar mass and eventually reach some sort of plateau value. The same is of course tme for a (statistical) copolymer, but in the case of a copolymer there is an additional degree of freedom. The copolymer composition may have a significant influence on maaoscopic properties. If the homopolymers of the two monomers in a copolymer have different Tg values, the Tg value of a statistical copolymer will fie in between the two homopolymer values. More or less, the same holds tme for other properties, such as hardness and elasticity modulus. All of this is tme if the copolymer has a narrow CCD. If the CCD is broader or even bimodal, phase separation may occur. This will lead to a much more complex situation, where the properties are a function not just of the overall chemical composition, but also of the phase morphology as was indicated in Section 6.12.3.1. An additional complication can be introduced if the copolymer chains contain a gradient as explained in Section 6.12.7. 

The general aim of all experiments is to measme solvent activities in polymer solutions over the complete concentration range and for all desired temperatiues (and pressures). Additionally, the dependence on molar mass of the polymer has to be taken into account. As is clear from all explanations above, there is no really universal method to fulfill all piuposes. 

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