Polyelectrolyte Dimensions

Ikecise direct experimental determinations of polyelectrolyte dimensions under 0 conditions in aqueous media have been carried out... 

Ionic interactions (repulsive or attractive) can also dramatically alfect HDV. For charged polymers, ionic effects often dominate behavior, especially in aqueous solutions. Theoretical treatments for predicting polyelectrolyte dimensions and phase behavior are discussed by Barrat and Joanny (3) scaling theory for charged polymers is reviewed by Dobrynin, Colby, and Rubinstein (4). 

These outlined expressions have proven to be a robust approach to predicting polyelectrolyte dimensions for varying linear charge density and ionic strength conditions [8,12,42],... 

The linearity of L with N is maintained at the theta point. Relative to Eq. 5, the chains have shrunk by a factor of (a/d),/3 but the linear variation indicates that the chains are still distorted at the theta point and characteristic dimensions do not shrink through a series of decreasing power laws as do free chains [29-31]. Experimentally, Auroy [25] has produced evidence for this linearity even in poor solvents. Pincus [32] has recently applied this type of analysis to tethered polyelectrolyte chains, where the electrostatic interactions can produce even stronger stretching effects than those that have been discussed for good solvents. Tethered polyelectrolytes have also been studied by others [33-35],... 

From the physics point of view, the system that we deal with here—a semiflexible polyelectrolyte that is packaged by protein complexes regularly spaced along its contour—is of a complexity that still allows the application of analytical and numerical models. For quantitative prediction of chromatin properties from such models, certain physical parameters must be known such as the dimensions of the nucleosomes and DNA, their surface charge, interactions, and mechanical flexibility. Current structural research on chromatin, oligonucleosomes, and DNA has brought us into a position where many such elementary physical parameters are known. Thus, our understanding of the components of the chromatin fiber is now at a level where predictions of physical properties of the fiber are possible and can be experimentally tested. 

The molecular characterization of polyelectrolytes in general, and of DADMAC polymers in particular is complicated for several reasons. First, in aqueous solution the individual properties of the macromolecules are dominated by Coulom-bic interactions. Therefore, the resulting polyelectrolyte effects have to be suppressed through the addition of low molecular electrolyte, such as NaCl. The increase of the ionic strength results in a decrease of the chain stiffness of the polyelectrolyte molecules (see Sect. 5). The chains then revert to the coil dimensions of neutral macromolecules in dilute solutions. However, problems may still arise, particularly since the mode of action of these effects is quite different in various characterization methods [27]. 

Successful assembly requires matching features of the template, meaning that wavelength and height have to be of the same dimensions. Additionally, adhesion of particles and surface must be avoided by weak repulsive forces. In this context, polyelectrolyte multilayer-wrinkles are particularly useful, as the wettability of the multilayer is determined by the part of the layer adjacent to the film/solution or film/air interface respectively, while the elastic properties are determined by the total film [84], Thus, elastic constants can be adjusted largely independent from wettability properties. 

A negative photoresist, SU-8 (Microchem), was used in the microreactor mold process for preparing the PDSM-E microreactors. When exposed to ultraviolet light, material may be removed via a wet etching process leaving high-definition features in micrometer dimensions. Additionally, a microreactor has been constructed in silicon onto which layer-bylayer self-assembled polyelectrolytes and enzymes are deposited. This system is being used for comparison with the PDMS-E system performance. 

Only if an inert electrolyte like NaCl is added, the strong electrostatic interactions are increasingly screened and the highly expanded polyelectrolyte coils start to shrink. Eventually the unperturbed dimensions are approached at high enough concentrations of inert salt [18-20]. In such cases, phase separation occurs if this inert salt level is surpassed [21-23]. The latter phenomena has been denoted as salting out of polyelectrolytes, or alternatively, as H-type precipitation, because the concentration of inert salt required to cause precipitation of the polyelectrolyte is high and independent of the polymer concentration [23]. 

The present review deals mainly with two examples of polyelectrolyte phase behavior as discussed above. As an example for an H-type precipitation, the solution properties of polyvinylpyridinium chains are monitored as function of added inert salt. Here, we focus on the determination of the effective charge density and of the solvent quality parameter which are supposed to play a central role for the understanding of polyelectrolyte solution without specific counterion interactions. The second system under investigation comprises the interaction of polyacrylic acid with alkaline earth cations which exhibit very specific interactions, thus representing an example for type L-precipitation. Here the coil dimensions close to the phase boundary are compared to those close to type H-precipitation with inert added salt. 

It was already noted in previous studies, that added salt affects the micellar structure only above a certain value of the salt concentration cs. In studies of PtBS-PSSNa block copolymers a dependence of the brush dimension on the added salt concentration appeared above cs=0.01 mol/1. The thickness of a free-standing black films drawn from a diblock polyelectrolyte solution exhibited a steady drop above ionic strengths of 0.2 mol/1 [39]. 

Glass slides with the dimensions of 76 x 26 x 1 mm were used as supports for the multilayers. The slides were thoroughly cleaned by a mixture of sulfuric acid and potassium dichromate at 80 °C for about 2 hours in an ultrasonic bath prior to the films deposition. The initial concentration co of polyelectrolytes in the solution was 1 x 10 2 mole of the repeating units per liter. The pH value of the solution was about 6. Adsorption was carried out at room temperature in open glass beakers of 100 mL without stirring for 20 min. After every deposition step, the glass slides were rinsed three times for 1 min with Millipore Milli-Q water. The substrate was not dried between the adsorption steps. 

Abstract In this paper we report on AFM force spectroscopy measurements on hollow polymeric spheres of colloidal dimensions made from polyelectrolyte multilayers of polyal-lylamine and polystyrenesulfonate in water. We find that the shells show a linear force-deformation characteristic for deformations of the order of the shell wall thickness. This experimental outcome is discussed in terms of analytical results of continuum mechanics, in particular the scaling behaviour of the shell spring constant with wall thickness, shell radius and speed of the deformation is analysed. The experimental results agree well with the predictions of Reissner for thin shells and allow... 

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