Induction Bonding

Induction Curing Adhesives. Typically one-component epoxy adhesive systems are used for induction bonding of structural parts. However, two-component adhesives have also been used. The properly designed induction cured adhesive should provide the following application and performance properties ... 

Plastic Adhesives Dielectric Welding Induction Bonding Mechanical Fastening Solvent Welding Spin Welding Thermal Welding Ultrasonic Welding... 

Suwanwatana W, Yarlagadda S, and Gillespie J W Jr. (2006) Hysteresis heating based induction bonding of thermoplastic composites, Compos Sci Technol 66 1713-1723. 

Unlike the case for metals, secondary bonds are of great importance in polymers. These bonds are much weaker than covalent bonds, but for even moderate chain length polymers these bonds have a significant impact on the molecular and bulk properties of these materials. These intermolecular bonds are based on electrostatic interactions and are due to either attractions between permanent dipoles, quadmpoles, and other multipoles, or between a permanent multipole and an induced charge on a second molecule (or moiety, in the case of a polymer), or between transient multipoles. All such secondary bonds can be considered van der Waals forces, but many texts use van der Waals to denote induced and/or transient multipole interactions only. The induced interaction is sometimes referred to as polarization, or sometimes induction bonding. The transient interaction is very weak and is known as dispersion or London dispersion forces, and arises from electrostatic interactions between two molecules due to temporary inhomogeneous electron density distributions in the outermost electron shells of these molecules. 

The polarizing influence of an electronegative atom decreases with the number of inteiwening rr-bonds. This is called the inductive effect and is indicated in Figure 3-6b by a progression of 6 symbols, (t is generally accepted that the inductive effect is attenuated by a factor of 2-3 by each intervening bond. The inductive ctlcct is not... 

The underlying principle of the PEOE method is that the electronic polarization within the tr-bond skeleton as measured by the inductive effect is attenuated with each intervening o -bond. The electronic polarization within /r-bond systems as measured by the resonance or mesomeric effect, on the other hand, extends across an entire nr-system without any attenuation. The simple model of an electron in a box expresses this fact. Thus, in calculating the charge distribution in conjugated i -systems an approach different from the PEOE method has to be taken. 

The knowledge base is essentially two-fold on one hand it consists of a series of procedures for calculating all-important physicochemical effects such as heats of reaction, bond dissociation energies, charge distribution, inductive, resonance, and polarizability effects (.see Section 7.1). The other part of the knowledge base defines the reaction types on which the EROS system can work. 

There is little evidence for the operation in reactions of the inducto-meric effect, the time-dependent analogue of the inductive effect. This may be so because the electrons of the delocalized system, and are thus not so susceptible to the demands of the reagent. 

The greater positive character hence the increased acidity of the O—H proton of 2 2 2 tnfluoroethanol can be seen m the electrostatic potential maps displayed m Figure 1 8 Structural effects such as this that are transmitted through bonds are called indue tive effects A substituent induces a polarization m the bonds between it and some remote site A similar inductive effect is evident when comparing acetic acid and its trifluoro derivative Trifluoroacetic acid is more than 4 units stronger than acetic acid... 

Inductive effects depend on the electronegativity of the substituent and the num ber of bonds between it and the affected site As the number of bonds increases the inductive effect decreases... 

The strength of an acid depends on the atom to which the proton is bonded The two mam factors are the strength of the H—X bond and the electronegativity of X Bond strength is more important for atoms m the same group of the periodic table electronegativity is more important for atoms m the same row Electronegative atoms elsewhere m the molecule can increase the acidity by inductive effects... 

Recall from Section 115 that effects that are transmitted by the polarization of u bonds are called inductive effects... 

Attack at the meta position leads to a more stable intermediate than attack at either the ortho or the para position and so meta substitution predominates Even the inter mediate corresponding to meta attack however is very unstable and is formed with dif ficulty The trifluoromethyl group is only one bond farther removed from the positive charge here than it is m the ortho and para intermediates and so still exerts a significant although somewhat diminished destabilizing inductive effect... 

The decreased shielding caused by electronegative substituents is primarily an inductive effect and like other inductive effects falls off rapidly as the number of bonds between the substituent and the proton increases Compare the chemical shifts of the pro tons m propane and 1 mtropropane... 

Closely related to the inductive effect and operating in the same direction is the field effect In the field effect the electronegativity of a substituent is communicated not by successive polarization of bonds but via the medium usually the solvent A substituent m a molecule polarizes surrounding solvent molecules and this polarization is transmit ted through other solvent molecules to the remote site... 

Induced dipole/mduced dipole attraction (Section 2 17) Force of attraction resulting from a mutual and complemen tary polanzation of one molecule by another Also referred to as London forces or dispersion forces Inductive effect (Section 1 15) An electronic effect transmit ted by successive polanzation of the cr bonds within a mol ecule or an ion... 

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