Search results for "surface"
showing 10 items of 9345 documents
Separation studies of amino acids, proteins and enzymes on bonded 1,2-dihydroxy-, 1,2-hydroxylamino-and amino silica packings
1979
1,2-dihydroxy-3-propoxypropyl (HPPS), 1-amino-2-hydroxy-3-propoxypropyl (AHPS) and 1-aminoethyl-3-aminopropyl (AEAPS) silica were synthesized by means of both a surface modification procedure (I) and a bulk modification procedure (II). Method (I) gave a surface concentration, α, of functional groups of 2–3 μmole/m2, whereas method (II) gave values up to 5 μmole/m2. Retention times, peak asymmetries and plate heights of thiamine and ascorbic acid eluted with aqueous buffer solutions ranging from pH 5.3 to 9.2 gave only a±5% variation over periods of 12 hours and more. The recoveries of selected enzymes and proteines examined under static and dynamic conditions were between 60% and 100% depen…
Effect of polystyrene coating on pore, structural and chromatographic properties of silica packings
1990
Abstract A series of mesoporous and macroporous silicas with a mean pore diameter (PD), between 6 and 200 nm were reacted with a copolymer of styrene and vinyl-methyldiethoxysilane. The mass load of coated silicas corresponded to the monolayer capacity of the polymer calculated on the basis of the molecular cross-sectional area, except for the two mesoporous silcias of PD = 6 and 7.5 nm. Depending on the pore size, changes occurred in the specific surface area, as, between the native and the coated product. A comparison of the specific pore volume, νp, of silicas before and after polymer immobilization indicated a major loss of νp for the two mesoporous silicas whereas this effect was much …
Theory-based improvements of continuous polymer fractionation demonstrated for poly(carbonate)
1992
For the first time, a quantitative theoretical analysis (liquid/liquid phase equilibria treated by means of the continuous thermodynamics) of the operating characteristics of continuous polymer fractionation (CPF) was performed. The results of these calculations were compared with data published for CPF of polyethylene. It turned out that the efficiency of the conventional CPF corresponds to approximately two theoretical plates only. For this reason, several improvements, suggested by theoretical considerations, were realized experimentally, for which purpose the system dichloromethane/diethylene glycol/bisphenol-A polycarbonate was chosen. The pulsating sieve-bottom column was replaced by …
Interfacial tension between polymer-containing liquids - Predictability and influences of additives
1999
The first part of the contribution deals with the interfacial tension, σ, of phase-separated polymer solutions in single or mixed solvents and of binary polymer blends as a function of the relative distance to the critical temperature of the system, special attention being paid to the possibilities of theoretical prediction. Two methods are discussed in more detail. One is based on a realistic description of the Gibbs energy of mixing as a function of composition, the second correlates σ with the length of the measured tie line. The second part is devoted to another aspect, namely the effects of additives on the interfacial tension between the coexisting phases of demixed polymer solutions …
Determination of cationic surfactants by capillary zone electrophoresis and micellar electrokinetic chromatography with deoxycholate micelles in the …
2000
Mixtures of the cationic surfactants benzalkonium chloride (BKC) and cetylpyridinium chloride (CPC) were quickly resolved and reproducibly and reliably determined by using background electrolytes (BGEs) containing 80 mM borate, pH 8.5, bile salts and large concentrations of an organic solvent. When the bile salt is present, the separation mechanism changes from capillary zone electrophoresis (CZE) to a mixed micellar electrokinetic chromatography (MEKC)-CZE, with predominant MEKC interactions, which lead to an excellent resolution of all the solutes, including the C12-C18 homologues of BKC and CPC. A BGE containing 50 mM sodium deoxycholate and 30% ethanol for an extreme resolution, or 20% …
t-Curves for n-Hexane
1992
The adsorption and desorption isotherms of n-hexane on powdered alumina and silica have been studied at 25°C over a wide range of relative pressures. Two t-curves for pore structure analysis are proposed, one for alumina (C = 12) and the second for silica (3 ≤ C ≤ 9). The statistical thickness t of the adsorbed n-hexane layer has been drawn as a function of the relative pressure assuming a maximal thickness of 0.55 nm and a mean thickness of 0.42 nm for the monolayer. The results are discussed in relation to previous published data.
Continuous fractionation and solution properties of PIB. II. CPF optimization
1987
The quality of polymer fractionation depends on the choice of the mixed solvent as well as on the particular conditions of operating the continuous countercurrent extraction. With a polyisobutylene (PIB) sample of medium molecular weight Mw = 98,400 g/mol and U = (Mw/Mn) − 1 = 1.4 plus the mixed solvents toluene/2-butanone (TOL/MEK) and n-heptane/2-butanone (HEP/MEK) (both giving comparably good fractionation in equilibrium experiments), possible ways to optimize the CPF were tested. The mixed solvent HEP/MEK turns out to be superior to TOL/MEK for kinetic reasons. Due to the larger gap between its density and that of the pure polymer, the coexisting phases can still move through the column…
Influence of the physical state of water on the barrier properties of hydrophilic and hydrophobic films.
2000
Water transfer through different films, as a function of the physical state of water in contact with the film, the relative humidity difference, and the water vapor pressure difference, was investigated. The films were two synthetic packagings (hydrophobic polyethylene and hydrophilic cellophane) and an edible film. The physical state of water affects water sensitive films, such as cellophane, inducing a higher liquid water transfer due to interactions with the polymer. For hydrophobic polymers, such as polyethylene, neither the physical state of water nor the relative humidity has an influence on the water permeability. In complex system, such as an edible film composed of hydrophilic part…
Hierarchical structure formation of cylindrical brush polymer-surfactant complexes.
2009
The complex formation of cylindrical brush polymers with poly(l-lysine) side chains (PLL) and sodium dodecyl sulfate (SDS) can induce a helical conformation of the cylindrical brush polymer in aqueous solution (Gunari, N.; Cong, Y.; Zhang, B.; Fischer, K.; Janshoff, A.; Schmidt, M. Macromol. Rapid Commun. 2008, 29, 821-825). Herein, we have systematically investigated the influence of surfactant, salt, and pH on the supramolecular structure formation. The cylindrical brush polymers and their complexes with surfactants were directly visualized by atomic force microscopy in air and in aqueous solution. The alkyl chain length (measured by the carbon number, n) of the surfactant plays a key rol…