Charges, electrical

The charge on the electrospinning liquid jet prrmarrly resides on its strrface (Feng 2002 Hohman et al. 2001a Spivak and Dzenis 1999). Typical surface charge densities can be calculated from the feed rate of solution, polymer concentration, and the current flow I across the gap. 

Where the collector plate is grounded through an ohmic resistance, the current can be estimated from the measured potential drop across the resistance. If the volumetric feed rate of polymer solution is Q, fiien conservation of mass and charge (assuming no adventitious losses in charge from the jet) require 

Assuming constant acceleration of a jet of uniform diameter He, J.-H., et al. (2007c) obtained the following scaling relationship for the radius r of the jet  

As the jet extends and reduces in diameter, the surface charge density, as well as the force with which the jet is attracted by the collector, also increase. 

Theron and colleagues (Theron et al. 2001) expressed the volume and surface charge densities in terms of 7, Q, and d as follows  

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M.p. 103°C. Noradrenaline is released in the adrenal medulla with adrenaline, and also at the sympathetic nerve endings. Its release from a nerve fibre is followed by binding to a receptor molecule on the next nerve or muscle fibre, probably causing a change in the electrical charge of the receptor-cell membrane. Biosynthetically it normally serves as a precursor for adrenaline. 

Apolar stationary phases having no dipolar moments, that is their center of gravities of their positive and negative electric charges coincide. With this type of compound, the components elute as a function of their increasing boiiing points. The time difference between the moment of injection and the moment the component leaves the column is called the retention time. 

An fuel-air mixture explosion can be initiated by a sudden discharge of static electricity. Yet, while flowing in systems, a fluid develops an electrical charge which will take as long to dissipate as the fluid is a poor conductor. The natural electrical conductivity of jet fuel is very low, on the order of a few picosiemens per meter, and it decreases further at low temperature. 

The influence of electrical charges on surfaces is very important to their physical chemistry. The Coulombic interaction between charged colloids is responsible for a myriad of behaviors from the formation of opals to the stability of biological cells. Although this is a broad subject involving both practical application and fundamental physics and chemistry, we must limit our discussion to those areas having direct implications for surface science. 

The discussion focuses on two broad aspects of electrical phenomena at interfaces in the first we determine the consequences of the presence of electrical charges at an interface with an electrolyte solution, and in the second we explore the nature of the potential occurring at phase boundaries. Even within these areas, frequent reference will be made to various specialized treatises dealing with such subjects rather than attempting to cover the general literature. One important application, namely, to the treatment of long-range forces between surfaces, is developed in the next chapter. 

When a battery (or a generator or other power supply) outside the system drives current, i.e. a flow of electric charge, tlirough a wire that passes tlirough the system, work is done on the system ... 

Millikan R A A new modification of the cloud method of determining the elementary electrical charge and the most probable value of that charge Phil. Mag. 19 209-28... 

The major class of plate-like colloids is tliat of clay suspensions [21]. Many of tliese swell in water to give a stack of parallel, tliin sheets, stabilized by electrical charges. Natural clays tend to be quite polydisperse. The syntlietic clay laponite is comparatively well defined, consisting of discs of about 1 nm in tliickness and 25 nm in diameter. It has been used in a number of studies (e.g. [22]). 

If < 1, then binding is anticooperative, for example when an electrically charged particle adsorbs at an initially neutral surface the accumulated charge repels subsequent arrivals and makes their incorjDoration more difficult [58]. 

Ernest O. Lawrence, inventor of the cyclotron) This member of the 5f transition elements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A.E. Larsh, and R.M. Latimer. A 3-Mg californium target, consisting of a mixture of isotopes of mass number 249, 250, 251, and 252, was bombarded with either lOB or IIB. The electrically charged transmutation nuclei recoiled with an atmosphere of helium and were collected on a thin copper conveyor tape which was then moved to place collected atoms in front of a series of solid-state detectors. The isotope of element 103 produced in this way decayed by emitting an 8.6 MeV alpha particle with a half-life of 8 s. 

The three particles that make up atoms are protons, neutrons, and electrons. Protons and neutrons are heavier than electrons and reside in the "nucleus," which is the center of the atom. Protons have a positive electrical charge, and neutrons have no electrical charge. Electrons are extremely lightweight and are negatively charged. They exist in a cloud that surrounds the atom. The electron cloud has a radius 10,000 times greater than the nucleus. 

Quantity of electricity, electric charge Q Retarded van der Waals constant B,P... 

After being formed as a spray, many of the droplets contain some excess positive (or negative) electric charge. Solvent (S) evaporates from the droplets to form smaller ones until, eventually, ions (MH+, SH+) from the sample M and solvent begin to evaporate to leave even smaller drops and clusters (S H n = 1, 2, 3, etc.). Later, collisions between ions and molecules (Cl) leave MH+ ions that proceed into the mass analyzer. Negative ions are formed similarly. 

Additional ionization is effected by including radioactive substances or plasma or glow discharges in the evaporation chamber or by electrical charging of the nebulizer. Such techniques are also discussed in Chapters 8 and 11. 

A solution of an analyte in a solvent can be sprayed (nebulized) from an electrically charged narrow tube to give small electrically charged droplets that desorb solvent molecules to leave ions of the analyte. This atmospheric-pressure ionization is known in various forms, the one most relevant to this section being called electrospray. For additional detail, see Chapters 8, 9, and 11. 

The Z-spray inlet causes ions and neutrals to follow different paths after they have been formed from the electrically charged spray produced from a narrow inlet tube. The ions can be drawn into a mass analyzer after most of the solvent has evaporated away. The inlet derives its name from the Z-shaped trajectory taken by the ions, which ensures that there is little buildup of products on the narrow skimmer entrance into the mass spectrometer analyzer region. Consequently, in contrast to a conventional electrospray source, the skimmer does not need to be cleaned frequently and the sensitivity and performance of the instrument remain constant for long periods of time. 

A hexapole assembly of rods (poles) is built similarly to the quadrupole, but now there are three sets of opposed rods evenly spaced around a central axis. The hexapole cannot act as a mass filter by applying a DC field and is used only in its all-RF mode. It is therefore a wide band-pass filter and is used to collimate an ion beam. (Like-charged particles repel each other, and an electrically charged beam will tend to spread apart because of mutual repulsion of ions unless steps are taken to reduce the effect.)... 

In the ion source, substances are converted into positive or negative ions having masses (m, mj,, m ) and a number (z) of electric charges. From a mass spectrometric viewpoint, the ratio of mass to charge (m,/z, m2/z,, m /z) is important. Generally, z = 1, in which case, m/z = mj,... 

An electron carries one unit of negative electrical charge (Figure 46.2). Its mass is about 1/2000 that of a proton or neutron. Therefore, very little of the mass of an atom is made from the masses of the electrons it contains, and generally the total mass of the electrons is ignored. For example, an atom of iron has a mass of 56 atomic units (au also called Daltons), of which only about 0.02% is due to the 26 electrons. Thus an iron atom (Fe ) is considered to have the same mass as a doubly charged cation of iron (Fe " ), even though there is a small mass difference. 

The electron carries one negative electric charge and has a mass only 1/2000th that of a proton. 

The neutron carries zero electric charge and has a unit atomic mass. Its actual mass is about 10 to 10... 

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