Polyacrylamide, physical properties

In the case of polyacrylamide gels, Stellwagen [367] found that buffer type (TAE vs TBE) did not affect the apparent pore size (21 mn for 10.5% T 5% C to 200 mn for 4.6% r/2% C), although more extreme variations in salt content and buffer physical properties may very likely strongly affect pore structure in polyacrylamide gels. 

Chul, M Phillips, R McCarthy, M, Measurement of the Porous Microstructure of Hydrogels by Nuclear Magnetic Resonance, Journal of Colloid and Interface Science 174, 336, 1995. Cohen, Y Ramon, O Kopeknan, IJ Mizrahi, S, Characterization of Inhomogeneous Polyacrylamide Hydrogels, Journal of Polymer Science Part B Polymer Physics 30, 1055, 1992. Cohen Addad, JP, NMR and Statistical Structures of Gels. In The Physical Properties of Polymeric Gels Cohen Addad, JP, ed. Wiley Chichester, UK, 1996 39. 

Polyacrylamide gels are produced by the copolymerization of acrylamide and the cross-linking agent N,N methylenebisacrylamide. These are supplied by Bio-Rad Laboratories (Bio-Gel P). The Bio-Gel media are available in 10 sizes with exclusion limits ranging from 1800 to 400,000 daltons. Table 3.4 lists the acrylamide gels and their physical properties. 

Freddi, G., Tsukada, M., and Beretta, S. "Structure and physical properties of silk fibroin polyacrylamide blend films". ]. Appl. Polym. Sci. 71(10), 1563-1571 (1999). 

Only a very limited range of measiuements of physical properties has been made, and for dilute and moderately concentrated aqueous solutions of commonly used polymers including carboxymethyl cellulose, polyethylene oxide, carbopol, polyacrylamide, density, specific heat, thermal conductivity, coefficient of thermal expansion and surface tension differ from the values for water by no more than 5-10% [Porter, 1971 Cho and Hartnett, 1982 Irvine, Jr. et al., 1987]. Thermal conductivity might be expected to be shear rate dependent, because both apparent viscosity and thermal conductivity are dependent on structure. Although limited measmements [Loulou et al., 1992] on carbopol solutions confirm this, the effect is small. For engineering design calculations, there will be little error in assuming that all the above physical properties of aqueous polymer solutions, except apparent viscosity, are eqnal to the values for water. 

In addition to solution viscosity, interfacial surface tensions have also been measured as a function of polymer concentration [7]. In general, the polyacrylamides did not significantly change the surface tension of water over the concentration range of interest. On the other hand, the hydroxyethyl celluloses did lower the interfacial surface tension of water by about 5 percent over the concentration range of interest. Other than solution viscosity and surface tension, all other physical properties of the solvent have been assumed to remain unchanged at the very low polymer concentrations used in these experiments. ... 

Despite the sequence identity of PrP and PrP from the same species, they display quite different physical properties. Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy reveal that PrP - is essentially a-helical and devoid of P-pleated sheet structure, whereas the P-pleated sheet content of PrP is -40%, while PrP27-30 contains more than 50 % p-pleated sheet. Procedures that destroy the infectivity of PrP27-30 and PrP (e. g. purification by SDS-polyacrylamide gel electrophoresis or treatment with alkali) also substantially reduce the P-pleated sheet content. It therefore appears that the difference between the normal and disease-causing isoforms of PrP is entirely conformational and related to the respective contents of a-helical structure and P-pleated sheet structure. 

In order to improve the physical properties of paper, especially strength and resistance to erasure, natural polymers, like starches and gums, are added to the stock, as well as cellulose compounds, like carboxy-methyl cellulose, or synthetic polymers, e.g. polyacrylamides and polyamines. Wet-strength resins, such as polyamide resins, are also often added to the stock. Urea-formaldehyde and melamine-formaldehyde resins are no longer in wider use for improving wet strength. 

Some commercially available protein-inert polymers commonly used in microfluidic applications, all of which require permanent surface modification, are polyacrylamide, poly(N-hydroxyethylacrylamide), poly(NJl -di-methylacrylamide) (PDMA), polyvinylpyrrolidone (PVP), poly(vinyl alcohol) (PVA), hydroxyethylceUulose (HEC), and hydroxypropylmethylcellulose (HPMC). To permanently attach protein-resistant materials to the channel surface, high-energy sources, special chemistries, or even strong physical adsorption have been employed to introduce reactive functionalities. After activation, protein-resistant polymers can be anchored via UV-initiated free-radical polymerization. Polymeric materials usually do not have good solvent and heat resistance compared with inorganic materials, and hence it is necessary to take precautions during surface treatment to avoid serious damage to the microstructure or alteration of the physical properties of the bulk material. 

Sodium Dodecy 1 Sulfate Polyacrylamide Gel Electrophoresis is a technique to separate proteins according to their physical properties, such as their molecular weight or their charge at a given pH. If used consecutively, a two-dimensional (2D-PAGE) separation of the protein extract can be achieved. 

Potentially, this direct fluorination process is a new approach to the synthesis of fluorocarbon polymers. Polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyacrylamide, resor phenol formaldehyde resin, and ethylene propylene copolymer have been fluorinated to produce perf1uorocarbon polymers which are structurally similar to the hydrocarbon starting materials and have physical properties similar to known structurally related fluorocarbon polymers obtained by polymerization of fluorocarbon monomers. High yield of fluorocarbon polymers approaching 100 have been obtained. This direct technique used for fluorination of hydrocarbons and polymers is called the LaMar process and has been previously described in connection with the direct fluorination of Lt ver molecular weight species ". ... 

The fluorination of polyacrylamide produced a fluorocarbon polymer with distinctly different physical properties and structure from the parent. There are significant number of molecular units of the proposed structure as evidenced by the carbonyl and nitrogen-fluorine stretches observed in the infrared spectra. It is likely that some of the amide groups have been destructively fluorinated to CF3 groups. This phenomenon has been reported by Attaway, Groth and Bigelow. However, no visible decomposition has occurred in the product which has a very white appearance. 

---