Of fluidity

Butadiene—Methacrylic Acid Ionomers. Carboxyl groups can readily be introduced into butadiene elastomers by copolymerization, and the effects of partial neutralization have been reported (63—66). The ionized polymers exhibit some degree of fluidity at elevated temperatures, but are not thermoplastic elastomers, and are very deficient in key elastomer properties such as compression set resistance. 

Flussigkeits-. liquid, fluid, hydraulic, hydrostatic. -bad, n. liquid bath, -dichtemesser, m. hydrometer, -druck, m. pressure of a liquid, hydrostatic pressure, -ffirderung, /. conveyance of liquids, -gemisch, n. mixture of liquids, liquid mixture, -grad, m. degree of fluidity viscosity. -gradmesser, m. viscosimeter. -Unse, /. (Micros.) immersion objective, -mass, n. liquid measure, -menge. 

An ATE requires high lubrication performance, high levels of oxidation stability to withstand the locally high operating temperatures, a degree of fluidity that ensures... 

A state of fluidity and thus of translational mobitity in a membrane may be confined to certain regions of membranes under certain conditions. For example, protein-protein interactions may take place within the plane of the membrane, such that the integral proteins form a rigid matrix—in contrast to the more usual situation, where the hpid acts as the matrix. Such regions of rigid protein matrix can exist side by side in the same membrane with the usual lipid matrix. Gap junctions and tight junctions are clear examples of such side-by-side coexistence of different matrices. 

Liquid crystal sounds like a contradiction. Liquids are fluid, their molecules continually changing places in a manner that is not particularly well organized. Crystals are immobile, their molecules locked into fixed positions that form regular patterns. Yet, not only does this unusual combination of fluidity and regular patterns exist, it plays important roles in biological organisms. 

Gruszecki, W.I. and K. Strzalka. 1991. Does the xanthophyll cycle take part in the regulation of fluidity of the thylakoid membrane. Biochim. Biophys. Acta 1060 310-314. 

Clarke RJ, Kane DJ (1997) Optical detection of membrane dipole potential avoidance of fluidity and dye-induced effects. Biochim Biophys Acta Biomembr 1323(2) 223-239... 

Tab. 8.1. Main fluorescence techniques for the determination of fluidity (from Valeur, 1993)...

The serious drawback of the methods of evaluation of fluidity based on intermolecular quenching or excimer formation is that the translational diffusion can be perturbed in constrained media. It should be emphasized that, in the case of biological membranes, problems in the estimation of fluidity arise from the presence of proteins and possible additives (e.g. cholesterol). Nevertheless, excimer formation with pyrene or pyrene-labeled phospholipids can provide interesting in-... 

Fig. 8.3. Excimer-forming bifluorophores for the study of fluidity. 1 ,co-di-(l-pyrenyl)-propane 2 a,co-di-(l-pyrenyl)-methylether 3 10,10 -diphenyl-bi s-9-anth ryl methyloxide (DIPHANT) 4 meso-2,4-di-(N-carbazolyl) pentane.

Bifluorophoric molecules consisting of two identical fluorophores linked by a short flexible chain may form an excimer. Examples of such bifluorophores currently used in investigations of fluidity are given in Figure 8.3. 

The various fluorescence-based methods for the determination of fluidity and molecular mobility are summarised in Table 8.1. Attention should be paid to the comments indicated in the last column. 

Two main types of viscometers are suitable for the determination of the viscosity of a polymer melt The rotation viscometer (Couette viscometer, cone-plate viscometer) and the capillary viscometer or capillary extrusiometer. The latter are especially suitable for laboratory use since they are relatively easy to handle and are also applicable in the case of high shear rates. With the capillary extrusiometer the measure of fluidity is not expressed in terms of the melt viscosity q but as the amount of material extruded in a given time (10 min). The amount of ex-trudate per unit of time is called the melt index or melt flow index i (MFI). It is also necessary to specify the temperature and the shearing stress or load. Thus MFI/2 (190 °C)=9.2 g/10 min means that at 190 °C and 2 kg load, 9.2 g of poly-... 

Unsaturated fatty acid chains do not pack together in the bUayer as tightly as saturated fatty acid chains these properties contribute to different degrees of fluidity of membranes of different lipid composition. 

Lateral Mobility(Fluidity) of Sulfonate A and B Micelles. The ratio of excimer to monomer fluorescence intensity of pyrene had previously been used to measure the fluidity of biological membranes (8). The ease of excimer formation was correlated with the fluidity of the membrane. The same principle may be applied to the measurement of fluidity in inverted micelles. To this end, we used three pyrene carboxylic acid probes of varying chain length PVA, PNA and... 

Lateral Mobility in Alkarylsulfonate Micelles. In order to make a valid comparison of fluidity between sulfonates A and B, the micellar sizes should be comparable. This condition is required so that equal population of pyrene moieties between the two sulfonate systems can be assumed. Alternatively, the requirements might be met if they have equal aggregation numbers. If the above-mentioned (See Section A under "Results") assumptions regarding polar core composition are reasonable, the condition for equal probe population between the two sulfonate micelles can still be reasonably approximated. 

About 10 years ago Wayne Hubbel and I examined the fluidity of a large variety of membranes using spin labels. Excitable membranes were very fluid by our criteria the most rigid membrane we ever studied was the purple membrane supplied to us by Walter Stoeckenius, which was like concrete on our scale of fluidity. At that time I felt that this membrane could only translocate electrons or protons, because of this rigidity (see Ref. 31 in my report and earlier references contained therein). 

Since the phospholipids have cis-unsaturated fatty acid components there is a certain amount of fluidity to the bilayer. You can picture a sea of lipids moving in a transverse motion across the inside and outside faces. Note that the exterior of the membrane is composed of the polar portions of the biolipids while the interior of the membrane is highly nonpolar. 

Cells regulate their lipid composition to achieve a constant membrane fluidity under various growth conditions. For example, bacteria synthesize more unsaturated fatty acids and fewer saturated ones when cultured at low temperatures than when cultured at higher temperatures (Table 11-2). As a result of this adjustment in lipid composition, membranes of bacteria cultured at high or low temperatures have about the same degree of fluidity. 

Latent Caloric, or IIeat of Fluidity.—Black asserted, many years ago, that fluidity was owing to the chemioal combination of matter with a certain amount of heat, whjoh could not be detected by the thermometer. To this he applied the tarm heat of fluidity, or latent heal, assuming that heat, by its chemical combination... 

Figure 4. Relation of fluidity (Gieseler) to some petrographic parameters...

---