Barrer unit

In the contact lens field, barrer units are typically used for the oxygen permeabiUty coefficient (Dk). 

The permeability of the membrane is expressed in terms of barrer. The barrer unit is named for R. M. Barrer, who published an early article on the nature of diffusion in a membrane, followed by a widely referenced monograph on diffusion in and through solids (Barrer, 1934, 1951). A barrer is defined as ... 

Fatt, I. (1981) Intern. Contact Lens Clinic 9,76. The Dk/L-values obtained at 35°C and 95% relative humidity are multiplied with the mean film thickness (L) to get Dr-values, which correspond directly to barrer units (=10 cm ml 02/sec ml mmHg). 

The permeability coefficient P is a very characteristic parameter which is often described as a constant intrinsic parameter easily available from simple permeation experiments with membranes of known thickness (using eq. VI - 46). The permeabiliiy coefficient is often given in Barrer units. (lBarrer = lO" cm3(STP).cm.cm. s .ciiikg = 0.76 10 m3(STP).m.m-2.s- .Pa->). 

The dynamic viscosity, or coefficient of viscosity, 77 of a Newtonian fluid is defined as the force per unit area necessary to maintain a unit velocity gradient at right angles to the direction of flow between two parallel planes a unit distance apart. The SI unit is pascal-second or newton-second per meter squared [N s m ]. The c.g.s. unit of viscosity is the poise [P] 1 cP = 1 mN s m . The dynamic viscosity decreases with the temperature approximately according to the equation log rj = A + BIT. Values of A and B for a large number of liquids are given by Barrer, Trans. Faraday Soc. 39 48 (1943). 

Barrer (3) makes similar calculations for the entropies of occlusion of substances by zeolites and reaches the conclusion that the adsorbed material is devoid of translational freedom. However, he uses a volume, area or length of unity when considering the partition function for translation of the adsorbed molecules in the cases where they are assumed to be capable of translation in three, two or one dimensions. His entropies are given for the standard state of 6 = 0.5, and the volume, area or length associated with the space available to the adsorbed molecules should be of molecular dimensions, v = 125 X 10-24 cc., a = 25 X 10-16 cm.2 and l = 5 X 10-8 cm. When these values are introduced into his calculations the entropies in column four of Table II of his paper come much closer together, as is shown in Table I. The experimental values for different substances range from zero to —7 cals./deg. mole or entropy units, and so further examination is required in each case to decide... 

The permeability of gases through membranes is most commonly measured in Barrer, defined as 10-10 cm3(STP)/cm2 s cmHg and named after R.M. Barrer, a pioneer in gas permeability measurements. The term ji/ pio — pit), best called the pressure-normalized flux or permeance, is often measured in terms of gas permeation units (gpu), where 1 gpu is defined as 10 6 cm3(STP)/cm2 s cmHg. Occasional academic purists insist on writing permeability in terms of mol m/m2 s Pa (1 Barrer = 0.33 x 10-15 mol m/m2 s Pa), but fortunately this has not caught on. 

The so-called zone theory of viscosity assumes that the energy of activation may not be localised in two degrees of freedom but (unless EJT is small) be spread over a zone of degrees of freedom, in the liquid, the size of the zone increasing with EJT. This loosens the liquid in the zone as a prerequisite for viscous flow or difiusion. Barrer considered that the equation rj in poise units) ... 

The permeability provides an overall measure of the relative ease of gas permeation through the membrane. An often used unit for the permeability is barrer which is equal to 10 cm (STP)-cm/s-cm -cmHg. 

Li per unit cell, isosteric heats were determined by R. M. Barrer and R. M. Gibbons for 68 Li" 6 Na", calorimetric measurements were made by N. N. Avgul, E. S. Dobrova, and A. V. Kiselev for 40 LL + 25 Na", calorimetric (points) and isosteric (filled curve) heats were obtained by N. N. Avgul, B. G. Aristov, A. V. Kiselev, L. Ya. Kurdyukova, and N. V. Frolova. In the case of GO2 adsorption, the calorimetric heat values coincide with the isosteric. These examples clearly show that the physicochemical constants calculated from experiments (Henry constant, second virial coeflBcient, corresponding heat of adsorption, etc.) are influenced by the zeolite structure and chemical composition. Therefore, it is quite necessary to indicate this composition in the representation and discussion of the thermodynamic results. Uncertain results were often obtained for zeolites having a binding material. 

The common unit of P, is Barrer (IBarrer = 10 10cm3 (STP)-cm/ cm2scmHg = 0.76-10 17m3 (STP) m/m2 s Pa). The ratio P,/l is referred to as the permeance, and its common unit is the gas permeation unit (GPU), which is 10 scm3 (STP)/(cm2 s cmHg). If the downstream pressure is negligible compared with the upstream pressure, the selectivity can be expressed as... 

Researchers in membrane technology have adopted the special permeability unit called the Barrer ... 

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