Entanglement threshold

Like PEO-LiCl04, a 6 1 crystalline compound is formed but, in this instance, the weakened interactions between polymer chains [18] contributes to the lowest melting point for any PEO-salt crystalline complex. A eutectic with composition 0 Li = 11 1 forms, provided the PEO molecular chain length is beyond the entanglement threshold [31]. For lower molecular weights, the 6 1 compound dose not crystallize in the presence of excess PEO and a crystallinity gap exists over the range 6 l < 0 Li < 12 1 [26]. 

An interesting class of polymer matrices widely employed for CSE consists of temperature-dependent, viscosity-adjustable polymer solutions that are filled into the capillary at one temperature at low viscosities and are used in separation at another temperature at entanglement threshold concentrations and higher viscosities. Such viscosity-adjustable polymers are termed thermoresponsive... 

Let us consider a homopolymer of initial molar mass Mn0 (molar mass of the monomer unit m0) and a critical molar mass (entanglement threshold... 

The mechanism of separation with linear polymers is as follows. At a certain polymer concentration known as the entanglement threshold, the individual polymer strands begin to interact with each other, leading to a meshlike structure within the capillary. This allows DNA separation to take place. Many of the common polymers are cellulose derivatives, such as hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, and methylcellulose. Other applicable polymers include linear polyacrylamide, polyethylene oxide, agarose, polyvinyl pyrrolidone, and poly-N. Ar-dimethylacrylamide. High-resolution separation up to 12,000 bp has been reported using entangled polymer solutions. 

When plotting the log of the reduced mobility vs. the log of the molecular mass of the analyte the typical sigmoidal curves known from DNA analysis are also obtained. The concentration of the sieving polymer has to be beyond its entanglement threshold concentration c. A typical plot is shown in Fig. 10, where different concentrations of dextran T 2000 have been added to the running buffer. Also included are the reduced mobilities of the PSS in the plain buffer. As can be seen, the sieving properties are improved with increasing dextran concentra-... 

Fig. 1 Illustration of flexible polymers in dilute solution ic < c ), entanglement threshold (c = c ), and semidilute solution (c > c ) regimes, as well as cross-linked chain. One chain is drawn as a thick line for easier visualization. The small circle in the semidilute solution regime represents the blobs of size 4-Source From The separation matrix, in Analysis of Nucleic Acids by Capillary Electrophoresis ...

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