Experimental methods bulk measurements

Now it is known that this is not true for all substances the examples of cadmium, sodium chloride, and potassium chloride were cited in Section III. A, where the lack of wetting behavior led to an experimental method for measuring ffj,. If, however, this result is assumed to hold true, then the calculation reduces to a calculation of and a separate calculation or measurement of ff( . Skapski then estimates the difference in energy of the bonds broken to form the solid-vapor and liquid-vapor interfaces from the enthalpy of fusion of the bulk solid and the volume change on melting, and adds to it a small estimated contribution from the entropy change in the outer layer of the liquid and of the solid. The result is... 

Various terms have been used to characterize the water associated with cellulose fibers. Bound water, imbibed water, water of constitution, adsorbed water, fiber saturation point are some of the terms that have been used to describe the water in pulps and papers. The origin of each term can be traced to either theoretical considerations or to the experimental method of measurement. Bound water has been the most popular term used to describe the associated water. Bulk water or free water is that portion of water not associated (or not bound) with the fibers. Two measurement techniques may not yield identical values of bound water. 

Although there are only three principal sources for the analytical signal—potential, current, and charge—a wide variety of experimental designs are possible too many, in fact, to cover adequately in an introductory textbook. The simplest division is between bulk methods, which measure properties of the whole solution, and interfacial methods, in which the signal is a function of phenomena occurring at the interface between an electrode and the solution in contact with the electrode. The measurement of a solution s conductivity, which is proportional to the total concentration of dissolved ions, is one example of a bulk electrochemical method. A determination of pH using a pH electrode is one example of an interfacial electrochemical method. Only interfacial electrochemical methods receive further consideration in this text. 

The liquid-liquid interface is not only a boundary plane dividing two immiscible liquid phases, but also a nanoscaled, very thin liquid layer where properties such as cohesive energy, density, electrical potential, dielectric constant, and viscosity are drastically changed along with the axis from one phase to another. The interfacial region was anticipated to cause various specific chemical phenomena not found in bulk liquid phases. The chemical reactions at liquid-liquid interfaces have traditionally been less understood than those at liquid-solid or gas-liquid interfaces, much less than the bulk phases. These circumstances were mainly due to the lack of experimental methods which could measure the amount of adsorbed chemical species and the rate of chemical reaction at the interface [1,2]. Several experimental methods have recently been invented in the field of solvent extraction [3], which have made a significant breakthrough in the study of interfacial reactions. 

Conventional bulk measurements of adsorption are performed by determining the amount of gas adsorbed at equilibrium as a function of pressure, at a constant temperature [23-25], These bulk adsorption isotherms are commonly analyzed using a kinetic theory for multilayer adsorption developed in 1938 by Brunauer, Emmett and Teller (the BET Theory) [23]. BET adsorption isotherms are a common material science technique for surface area analysis of porous solids, and also permit calculation of adsorption energy and fractional surface coverage. While more advanced analysis methods, such as Density Functional Theory, have been developed in recent years, BET remains a mainstay of material science, and is the recommended method for the experimental measurement of pore surface area. This is largely due to the clear physical meaning of its principal assumptions, and its ability to handle the primary effects of adsorbate-adsorbate and adsorbate-substrate interactions. 

Powder flow is most frequently thought of as relevant to formulation development, and there are numerous references attempting to correlate any one of a number of measures of powder flow to the manufacturing properties of a formulation [34—40]. In particular, the importance of physical properties in affecting powder flow has been well documented. Research into the effect of the mechanical properties on powder flow has, however, been very limited. It is, of course, important to be able to determine and quantitate the powder flow properties of formulations. It is of equal importance, however, to determine the powder flow characteristics of bulk drug early in the development process (preformulation phase). Often, the preformulation or formulation scientist is constrained by time, materials, and manpower. Yet certainly the preformulation studies carried out should be meaningful. Well-defined experimental methods and procedures should be used the information generated should be reproducible and permit useful predictions to be made. 

A perfect prototype of an ideally cation-permselective interface is a cathode upon which the cations of a dissolved salt are reduced. Experimental polarization curves measured on metal electrodes fit the theory very closely. Since in dimensional units the limiting current is proportional to the bulk concentration, the polarization measurements on electrodes may serve for determining the former. This is the essence of the electrochemical analytical method named polarography. (For the theory of polarographical methods see [28]—[30].)... 

The liquid-liquid interface formed between two immissible liquids is an extremely thin mixed-liquid state with about one nanometer thickness, in which the properties such as cohesive energy density, electrical potential, dielectric constant, and viscosity are drastically changing from those of bulk phases. Solute molecules adsorbed at the interface can behave like a 2D gas, liquid, or solid depending on the interfacial pressure, or interfacial concentration. But microscopically, the interfacial molecules exhibit local inhomogeneity. Therefore, various specific chemical phenomena, which are rarely observed in bulk liquid phases, can be observed at liquid-liquid interfaces [1-3]. However, the nature of the liquid-liquid interface and its chemical function are still less understood. These situations are mainly due to the lack of experimental methods required for the determination of the chemical species adsorbed at the interface and for the measurement of chemical reaction rates at the interface [4,5]. Recently, some new methods were invented in our laboratory [6], which brought a breakthrough in the study of interfacial reactions. 

The most convenient method to measure bulk density is to fill the particles into a known volume container (usually cylindrical), level the surface, and weigh the particles in the container. The bulk density is calculated by the mass of the particles divided by the volume that can be read from the scale of the measuring cylinder. In order to minimize experimental errors, the container should be ideally at least 1L in volume, and the ratio of length and diameter should be about 2 1. Also it is recommended to leave the sample for approximately 10 min to achieve an equilibrium volume (density) value before making readings. 

The experimental methods used to study Fen spin crossovers include measurement of bulk magnetic susceptibility, vibrational spectroscopy (because M—L bond strengths differ appreciably between the HS and LS states), crystallography, and Mossbauer spectroscopy. 

Still another major operation in analysis is measurement, which may be carried out by physical, chemical, or biological means. In each of these three areas a wide range in techniques is available. For example, titrimetry is the most common of the chemical methods of measurement, and spectroscopy the most widely used of the available physical methods. In most analytical studies the bulk of the effort is directed to an examination of the theoretical background, experimental limitations, and applications of various techniques of measurement. Since methods of analysis are usually defined in terms of the final measurement step, the impression is often given that this stage constitutes the entire subject of analytical chemistry. Even though the measurement aspect deserves much attention, it should be remembered that the preliminary steps of definition of the problem, sampling, and separation are also critical to the overall process. 

Electrical methods. The electrical methods of measuring temperature are based on two facts, firstly, that the resistance of a conductor varies with the temperature, and secondly, that the electromotive force which is produced at a point of contact between two different metals or alloys is hkewise a function of the temperature. If, therefore, we close a circuit consisting of two wires of different metals, so that there are two joints in the circuit where two metals meet, a current will flow in general so long as these joints are not at the same temperature. If the temperature of the one joint is known, a measurement of the electromotive force enables us to determine the temperature of the other. On account of the great sensibility of electrical measurements, it is possible to measure very small differences of temperature by either of these methods. They have the further advantage over the first and second methods, that we are enabled by their means to measure very high and very low temperatures in a most convenient manner. The small bulk occupied by a thermocouple is often important from an experimental point of view, and for this reason thermocouples are preferable in some cases to all other forms of thermometer. 

Possibly the most typical property of a liquid-fluid interface is that it cannot be autonomous it only exists as the boundary between two adjacent bulk fluids. Any movement or flow in an interface will cause some corresponding motion in the adjacent bulk phases and vice versa. To identify interfacial (excess) rheological properties, measured rheological properties of the system have to be divided into two parts, one attributable to the interface and one to the bulk. Such a division is always somewhat arbitrary and may depend on the experimental method used. 

One of the most useful experimental methods to be applied to protein adsorption in recent years is the radiotracer technique (Mura-matsu, 1973). Proteins labeled with, 31I and 125I (Brash et al., 1974) and [14C]acetyl derivatives of proteins (Phillips et al., 1975) have been used as tracers. As well as measuring adsorption directly, this method has the great advantage that it can detect exchange between interface and bulk even when the total amount adsorbed does not vary. A technique that has been used to obtain independent measurements of the amount of protein adsorbed by measuring film thickness is ellipsometry (Trurnit, 1953). 

For details on the experimental procedures and analyses, including pitfalls, the reader is referred to the mentioned reviews and in particular the work in [73,74], We treat below a simplified case. In practice, it is found that the application of these methods to polymers often leads to overestimates of moduli compared to bulk measurements. This deviation and other effects have been largely attributed to neglected viscoelastic effects [45],... 

Effective diffusivities in porous catalysts are usually measured under conditions where the pressure is maintained constant by external means. The experimental method is discussed in Sec. 11-2 it is mentioned here because under this condition, and for a binary counterdiffusing system, the ratio is the same regardless of the extent of Knudsen and bulk... 

We have been searching for experimental methods that can measure surface viscosities as low as 10 10 g/sec or measure the collisional dynamics that should correspond to the Mann-Cooper model. To qualify, the experimental method must respond to dilute monolayers having densities less than 1014 mojecules/cm2. From our experience with the ESR spin label technique for measuring bulk viscosity effects in ultrathin films (8),... 

Velocity and concentration profiles are two important parameters often needed by the operator of slurry handling equipment. Several experimental techniques and mathematical models have been developed to predict these profiles. The aim of this chapter is to give the reader an overall picture of various experimental techniques and models used to measure and predict particle velocity and concentration distributions in slurry pipelines. I begin with a brief discussion of flow behavior in horizontal slurry pipelines, followed by a revision of the important correlations used to predict the critical deposit velocity. In the second part, I discuss various methods for measuring solids concentration in slurry pipelines. In the third part, I summarize methods for measuring bulk and local particle velocity. Finally, I review models for predicting solids concentration profiles in horizontal slurry pipelines. 

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