Salt Concentration Change

In the Rubner group, a controUed etching of PAA/PAH PEMs was investigated in NaCl solutions where the PEM thickness decreases to a fixed value depending on the initial film thickness and salt concentration [110]. The dissolution of PEMs 

The degree of ionization of weak polyelectrolytes such as PAA and PAH depends on the pH of their solutions. The linear charge density on the weak polyelectrolyte backbones in the assembled films is a function of pH. Therefore, the electrostatic interaction within weak PEMs can be easily tuned and excess charge can be created by varying the environment pH. Although the bulk weak PEMs fabricated at certain deposition pH does not carry excess charge, the fraction of charged parts in 

7 /-flyer-by-/.flyerSe -/Assemfa/eof Multilayer Stimuli-Responsive Polymeric Films 

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Protein poorly retained Increase salt concentration. Change salt to one that increases the surface tension. Change pH towards the isoelectric point of the protein. Change stationary phase to one with smaller hydrocarbon- aceous moieties and/or lower ligate density, i.e. reduce phase ratio. 

Formation of H-bonding between synthetic polymers is used as a way to improve compatibility in blends. Interesting examples of switching from closed to open assemblies are the reversible transformation of the structure of folic acid 3 into linear ribbon-like aggregates (by salt concentration changes),and of cyclic octapep-tides into linear chains (by UV radiation). 

Surface functionalization is an extremely important field of science as the surface properties significantly affect the application of solid materials. Development on specific surface characteristics is thus always of importance and need, and has seen growing interest in recent years. One such surface property of recent interest is the reversible response of the materials to stimulants like temperature, pH, salt concentration changes, etc. Generation of this property on the surface of the materials leads to functionalized materials in which their nature, e.g., hydrophobicity or hydrophilicity, can be finely controlled by enviroiunental stimulants like temperature, salt, pH, etc. This property translates the use of these materials in a number of applications, like temperature-controlled adsorption and desorption of biomolecules, temperature-controlled drug delivery processes, etc. 

In addition to the commonly used synthetic polymers such as pNIPAM and poly(N-vinylcaprolactam) (PVCL), elastin-like polymers were introduced as thermoresponsive polymers for affinity precipitation (Shimazu et al., 2003). An elastin-like polymer consists of the repeating penta-peptide, Val-Pro-Gly-Xaa-Gly (Xaa being any amino acid except proline). It undergoes reversible phase transition under temperature or salt concentration changes similar to pNIPAM (Shimazu et a/., 2003). An elastin-like polymer was used as a terminal tag for the facilitation of recombinant protein purification as attaching it to the hydrolase enzyme improves its purification. Purification, in excess of 1300-fold was achieved after two cycles of reversible changes of elastin-like polypeptide conformation precipitation induced by environmental changes (Shimazu et al., 2003). 

Refractive Index. The effect of mol wt (1400-4000) on the refractive index (RI) increment of PPG in ben2ene has been measured (167). The RI increments of polyglycols containing aUphatic ether moieties are negative drj/dc (mL/g) = —0.055. A plot of RI vs 1/Af is linear and approaches the value for PO itself (109). The RI, density, and viscosity of PPG—salt complexes, which maybe useful as polymer electrolytes in batteries and fuel cells have been measured (168). The variation of RI with temperature and salt concentration was measured for complexes formed with PPG and some sodium and lithium salts. Generally, the RI decreases with temperature, with the rate of change increasing as the concentration increases. 

Bromley and co-workers (36) have calculated the minimal energy of separation of water from seawater containing 3.45 wt % salt, at 25°C, to be 2.55 kj/(kg fresh water) for the case of 2ero fresh water recovery (infinitesimal concentration change) and 2.91 kj/(kg fresh water) for the case of 25% fresh water recovery. is, however, severalfold smaller than the energy necessary for water desalination ia practice. 

In preparing any of the above for use in columns, the dry powder is evacuated, then mixed under reduced pressure with water or the appropriate buffer solution. Alternatively it is stirred gently with the solution until all air bubbles are removed. Because some of the wet powders change volumes reversibly with alteration of pH or ionic strength (see above), it is imperative to make allowances when packing columns (see above) in order to avoid overflowing of packing when the pH or salt concentrations are altered. 

The fluorescent compound F, a luciferin, emits blue light (Amax 476 nm Fig. 3.2.4) in the presence of molecular oxygen and the protein P, a luciferase. In the luminescence reaction, F is changed into an oxidized form (structure 8, Fig. 3.2.6). The luminescence reaction is highly sensitive to pH, with a narrow optimal range around pH 7.8 (Fig. 3.2.2) the optimum salt concentration is 0.15 M for NaCl... 

Table II summarizes analytical data for dissolved inorganic matter in a number of natural water sources (J3, 9, J 9, 20, 21). Because of the interaction of rainwater with soil and surface minerals, waters in lakes, rivers and shallow wells (<50m) are quite different and vary considerably from one location to another. Nevertheless, the table gives a useful picture of how the composition of natural water changes in the sequence rain ->- surface water deep bedrock water in a granitic environment. Changes with depth may be considerable as illustrated by the Stripa mine studies (22) and other recent surveys (23). Typical changes are an increase in pH and decrease in total carbonate (coupled), a decrease in 02 and Eh (coupled), and an increase in dissolved inorganic constituents. The total salt concentration can vary by a factor of 10-100 with depth in the same borehole as a consequence of the presence of strata with relict sea water. Pockets with such water seem to be common in Scandinavian granite at >100 m depth.

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