Rubber membrane

Chambers A and B are separated by an elastic rubber membrane whose motion in response to pressure differences is transmitted to the needle N. Variations in the pressure difference can then be followed by observing the displacement of the point of the needle. Initially chamber A and the capillary are filled to the desired pressure by opening cocks and C, ... 

If you blow up a balloon, energy is stored in it. There is the energy of the compressed gas in the balloon, and there is the elastic energy stored in the rubber membrane itself. As you increase the pressure, the total amount of elastic energy in the system increases. 

However, there seems to be some drawback in the solubility or dispersibility of ion-sensing material in silicone rubber. This is mainly because silicone rubber does not contain a large quantity of plasticizer as the membrane solvent, in which neutral carriers can be dissolved easily, unlike in plasticized-PVC ion-sensing membranes. This issue is serious, especially with silicone-rubber membranes containing neutral carriers that show high crystallinity. Valinomycin, a typical ionophore, seems applicable to silicone-rubber-based K" -selec-tive electrodes [7,8,12-14]. Conventional crown-ether-based neutral carriers are also quite soluble in silicone rubber. 

FIG. 4 Selectivity comparison among silicone-rubber-membrane Na -ISFETs based on calixarene neutral carriers (1), (2), and (5). 

FIG. 6 Time-course changes of potential response for silicone-rubber-membrane Na+-selective electrodes based on neutral carriers (5), (2), and bis(12-crown-4) on changing Na concentration from 1 X 10 to 3 X 10 M. (From Ref. 22.)... 

Foly(dimethylsiloxane) (silicone rubber) membranes are fabricated by hydrolysis of alkox-ysilyl terminal groups of silicone-rubber precursors [oligo(dimethylsiloxane) derivatives and crosslinking agents], followed by condensation. Covalent bonding of neutral carriers carrying an alkoxysilyl group to silicone rubber is, therefore, feasible by simple reaction of the silicone-rubber precursor with alkoxysilylated neutral carriers, as schematically shown in Scheme 1 [44]. 

SCHEME 1 Mechanism for chemical modification of poly(dimethysiloxane) (silicone rubber) membranes with ion-sensing active material. 

FIG. 11 Potential response of Na+-selective electrodes based on silicone-rubber membranes modified chemically by triethoxysilylated calix[4]arene (8) (O) without anion excluder ( ) with TFPB ( ) modified chemically by triethoxysilylated tetraphenylborate (9) as well. (From Ref. 44.)... 

Applicability in biological ion assay is an important factor for biocompatible potentio-metric ion sensors. Attempts were made to determine Na" " concentrations in human blood sera by using silicone-rubber membrane Na+-ISFETs based on (5) [Fig. 17(a)] [29]. The found values for Na concentration in undiluted, 10-fold diluted, and 100-fold diluted serum samples are in good agreement with the Na" " calibration plots. Even in the undiluted serum samples, only a slight potential shift was observed from the calibration. This indicates that the calixarene-based silicone-rubber-membrane Na+-ISFETs are reliable on serum Na assay. For comparison with the silicone-rubber membrane, Na -ISFETs with corresponding plasticized-PVC membrane containing (2) or (5) were also tested for the Na assay. The found values of Na" " concentration... 

The Na -selective electrodes based on silicone-rubber membranes modified chemically by (8) and (9), were also investigated for Na assay in control serum and urine [22]. The found values for the Na concentrations in both of the serum and urine samples are in good agreement with their corresponding actual values with a relative standard deviation of about 1%. These results suggest that the Na -selective electrodes based on silicone-rubber membranes modified chemically by calix[4]arene neutral carrier (8) are reliable on assay in human body fluid. 

Carefully check the rubber membrane to be used to be sure it has no tiny pinholes through which the acid could leak. Fasten the membrane over the top of the container completely and securely, but leaving a pocket in the membrane deep enough to hold a spoonful or so of liquid. See Figure 16. 

The heat of permeation of chlorine in a silicone rubber membrane is —3 to — 5 kcal mol-1 while that of nitrogen is 1.0-1.5 kcal mol-1. Separation of these gases therefore is helped by low temperature. The flux of chlorine actually increases as temperature is lowered, reflecting the increased sorption. The flux of nitrogen decreases, reflecting the lower diffusivity. 

J. Pick, K. Toth, E. Pungor, M. Vasak, and W. Simon, A potassium-selective silicone-rubber membrane electrode based on neutral carrier, Anal Chim Acta 64, 477-480 (1973). 

Zeolite-filled silicone rubber membranes part 1. Membrane preparation and pervaporation results. 

Jia and coworkers prepared thin-film composite zeolite-filled silicone rubber membranes by a dip-coating method [82]. The membranes have a thin silicalite-1/ silicone rubber mixed-matrix selective layer on top of a porous polyetherimide support. 

Hennepe, H.j.C., Bargeman, D., Mulder, M.H.V., and Smolders, C.A. (1987) Zeolite-filled silicone rubber membranes part 1. membrane pervaporation and pervaporation results. J. Membr. Sd., 35 (1), 39-55. 

The University of California field stations have dealt with dilute pesticide waste disposal on an experimental basis by using lined soil evaporation beds. The beds typically are 20 x 40 x 3 ft pits lined with a butyl rubber membrane and back filled with 12 to 18 Inches of sandy loam soli. Figure 1 Is a cross secton of such a bed. Used containers and spray equipment are washed on an adjacent concrete slab the wastewater drains Into a sedimentation box for trapping particulates, followed by a distribution box In the bed. From the distribution box, the dilute pesticide solutions run underneath the soli surface through leach lines made of 4 Inch perforated PVC pipe. The system Is designed so that water moves up through the soli by capillary action and evaporates off the surface. 

Figure 5.8 — Probe-type sensor based on continuous circulation of a stream containing an acid-base indicator for the batch determination of COj in sea water, (a) Reagent delivery capillary, (d) Reagent exit capillary, (c) Optical fibre from source, (d) Optical fibre to detector, (e) White silicone rubber membrane. (/) White silicone sealant, (g) Epoxy resin, (/i) 0-ring. (/) Sensor housing. (/) Optical cable. (Reproduced from [12] with permission of the American Chemical Society).

Recently developed blood oxygenators are disposable, used only once, and can be presterilized and coated with anticoagulant (e.g., heparin) when they are constructed. Normally, membranes with high gas permeabilities, such as silicone rubber membranes, are used. In the case of microporous membranes, which are also used widely, the membrane materials themselves are not gas permeable, but gas-liquid interfaces are formed in the pores of the membrane. The blood does not leak from the pores for at least several hours, due to its surface tension. Composite membranes consisting of microporous polypropylene and silicone rubber have also been developed. 

The term surface tension is tied to the concept that the surface stays under a tension. In a way, this is similar to a rubber balloon, where also a force is required to increase the surface area of its rubber membrane against a tension. There is, however, a difference while the expansion of a liquid surface is a plastic process the stretching of a rubber membrane is usually elastic. 

We start by describing an important phenomenon If in equilibrium a liquid surface is curved, there is a pressure difference across it. To illustrate this let us consider a circular part of the surface. The surface tension tends to minimize the area. This results in a planar geometry of the surface. In order to curve the surface, the pressure on one side must be larger than on the other side. The situation is much like that of a rubber membrane. If we, for instance, take a tube and close one end with a rubber membrane, the membrane will be planar (provided the membrane is under some tension) (Fig. 2.4). It will remain planar as long as the tube is open at the other end and the pressure inside the tube is equal to the outside pressure. If we now blow carefully into the tube, the membrane bulges out and becomes curved due to the increased pressure inside the tube. If we suck on the tube, the membrane bulges inside the tube because now the outside pressure is higher than the pressure inside the tube. 

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