Solute-polymer interaction

PCB ADSORPTION. PCBs are practically insoluble in water because of a very weak solute-water interaction PCBs will have a strong solute-polymer interaction if a polymer such as styrene-divinyl-benzene is used water will have a weak interaction with styrene-divinylbenzene thus, conditions for effective adsorption are present. Therefore, large volumes of water can be passed through a column packed with a styrene-divinylbenzene polymer, and the PCBs will be adsorbed (partitioned) efficiently. 

PCB DESORPTION. PCBs are very soluble in a number of organic solvents. Because acetone is very effective in displacing the water from the pores of the polymer, it will be used in this example of desorption. A fairly strong interaction of acetone with the styrene-divinylbenzene surface can be predicted because acetone and benzene are miscible solvents. Consequently, a small amount of acetone will desorb the PCBs because strong solvent-solute and solvent-polymer interactions override the strong solute-polymer interaction. This desorption, commonly called elution, does not occur during the adsorption process because the matrix water is a poor eluent dictated by its weak interaction with hydrophobic polymers. 

Karim, K. A. Bonner, D. C., "Thermodynamic Interpretation of Solute-Polymer Interactions at Infinite Dilution," J. Appl. Polym. Sci., 22, 1277 (1978). 

Absorption of a solute liquid or vapor into a polymer film can profoundly affect the viscoelastic behavior of the polymer. The magnitude of this effect depends on the nature of the solute/polymer interactions and on the amount of solute absorbed. The solute/polymer interactions can range fttun simple dispersion to hydrogen-bonding and other specific interactions. The extent of absorption can be described by the partition coefficient, AT, which quantifies the thermcxlynamic distribution of the solute between two phases (K = coiKentration in polymer divided by die concentration in the liquid or vapor phase in contact with the polymer). It has long been known that acoustic wave devices can be used to probe solubility and partition coefficients (53,67). Due to the relevance of these topics to chemical sensors, more comprehensive discussions of these interaction mechanisms and the significance of the partition coefficient are included in Chapter 5. 

Alternative methods of determining exist. In one method (86) particulate polymer Is stirred In a closed container which contains a dilute A-B solution. The change In free solution solute concentration monitored over a period of time Indicates the magnitude of the solute-polymer Interaction and yields a value of... 

Solution-diffusion transport mechanism When the feed contacts the membrane, the solutes (denoted i in Fig. 3.6-10) adsorb on and subsequently absorb in the membrane surface by solute-polymer interactions (Fig. 3.6-lOA). Preferential solute-polymer interactions imply that the solvating power of the polymer is higher for the solutes than for the bulk solvent. 

For polymers with high degree of crystallinity, stiff and inflexible chains, and strong cohesive force, type-111 sorption isotherm is observed. In this case, solnte-solute interactions are stronger than solute-polymer interactions resulting in clnstering of solute molecules. 

Journal of Biomaterials Science Polymer Edition 10,No.l2,1999, p.1289-302 FTIR SPECTROSCOPIC INVESTIGATION AND MODELLING OF SOLUTE/POLYMER INTERACTIONS IN THE HYDRATED STATE Am Ende M T Peppas N A Purdue University... 

The solubility of a polymer depends on the solvent-solute (polymer) interactions, which must be greater than the solute-solute and solvent-solvent interactions. A polymer can be solubilised by a solvent with similar solubility parameters if certain polymer-solvent interactions are present between them. Polymers with flexible chemical linkages such as -0-/-S- or linear structures, have a better solubility than polymers with rigid linkages such as -N=N-, -C=C-, -C=N-, aromatic, heterocyclic, ladder or cross-linked structures. Similarly, amorphous and flexible polymers have better solubility than crystalline or rigid polymers. 

To establish whether the values of X j or Xfj agree with those obtained from equilibrium absorption at25°C, x 2(cxp)> such values were determined for a serie-s of polydimethylsiloxane-hydrocarbon systems (Table 5.2) [22]. In all the cases the values of Xfj are higher than those of X g and in very good agreement with values of Z 2(exp) proving that gas-chromatographic data reflect the equilibrium solute-polymer interactions. 

The effect of the I, location on calculated retention diagrams under identical conditions of solute-polymer interaction and film thickness is... 

The Flory-Huggins solute-polymer interaction parameter may be also calculated from activity coefficients [16,39]. In the case of pure solvents the equation is ... 

In dilute polymer solutions, hydrodynamic interactions lead to a concerted motion of tire whole polymer chain and tire surrounding solvent. The folded chains can essentially be considered as impenneable objects whose hydrodynamic radius is / / is tire gyration radius defined as... 

Q are the absorbance and wavenumber, respectively, at the peak (center) of the band, p is the wavenumber, and y is the half width of the band at half height. Liquid band positions ate usually shifted slightly downward from vapor positions. Both band positions and widths of solute spectra are affected by solute—solvent interactions. Spectra of soHd-phase samples are similar to those of Hquids, but intermolecular interactions in soHds can be nonisotropic. In spectra of crystalline samples, vibrational bands tend to be sharper and may spHt in two, and new bands may also appear. If polarized infrared radiation is used, both crystalline samples and stressed amorphous samples (such as a stretched polymer film) show directional effects (28,29). 

Water-soluble pAM neutral polymer interacts with ions of the solution through the complex formation between amide groups and hydrated ions. 

The range of semi-dilute network solutions is characterised by (1) polymer-polymer interactions which lead to a coil shrinkage (2) each blob acts as individual unit with both hydrodynamic and excluded volume effects and (3) for blobs in the same chain all interactions are screened out (the word blob denotes the portion of chain between two entanglements points). In this concentration range the flow characteristics and therefore also the relaxation time behaviour are not solely governed by the molar mass of the sample and its concentration, but also by the thermodynamic quality of the solvent. This leads to a shift factor, hm°d, is a function of the molar mass, concentration and solvent power. 

It is known that polymer dynamics is strongly influenced by hydrodynamic interactions. When viewed on a microscopic level, a polymer is made from molecular groups with dimensions in the angstrom range. Many of these monomer units are in close proximity both because of the connectivity of the chain and the fact that the polymer may adopt complicated conformations in solution. Polymers are solvated by a large number of solvent molecules whose molecular dimensions are comparable to those of the monomer units. These features make the full treatment of hydrodynamic interactions for polymer solutions very difficult. 

Temperature-sensitive polymers, depending on polymer structure and polymer-polymer interactions, generally exhibit two behaviors, lower critical solution temperature (LCST) [31] and upper critical solution temperature (UCST). Phase diagrams for these behaviors are presented in Figure 9. 

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