Van Der Waals Attraction Between Macroscopic Bodies

A general dispersion formula is derived, which represents the dispersion energy between two bodies A and B by their macroscopic screened fluctuation fields. These fluctuation fields are calculated exactly in the case of half-spaces and spheres. In the case of half-spaces the Lifshitz dispersion formula is obtained. The dispersion energy between spheres is found to vary as 1/d for separations d small compared with the radii and to be proportional to 1/d⁶ for separations d large compared with the radii. The effect of layers adsorbed on the surfaces of the spheres on the dispersion energy is calculated. The dielectric properties of the adsorbed layers predominate over those of the bulk material for separations d smaller than the layer thickness.     

Anaerobic Adhesive Cure Mechanism-II

Anaerobic adhesives are single-component acrylic adhesives which cure rapidly at or below room temperature when air is excluded, but they remain in an uncured stage over a long time when they are exposed to an adequate supply of air. Thus, anaerobic adhesives are widely used in retaining compounds for nuts and bolts, in sealants, and for impregnation. Recently, anaerobic adhesives have also been used in electrical and electronic applications because of their fast room temperature cure capability and their convenience.     

Anaerobic Adhesive Cure Mechanism-I

Anaerobic adhesives are single-component acrylic adhesives which cure rapidly at or below room temperature when air is excluded, but they remain in an uncured stage over a long time when they are exposed to an adequate supply of air. Thus, anaerobic adhesives are widely used in retaining compounds for nuts and bolts, in sealants, and for impregnation. Recently, anaerobic adhesives have also been used in electrical and electronic applications because of their fast room temperature cure capability and their convenience.¹     

Anaerobic Adhesive Cure Mechanism-I

Anaerobic adhesives are single-component acrylic adhesives which cure rapidly at or below room temperature when air is excluded, but they remain in an uncured stage over a long time when they are exposed to an adequate supply of air. Thus, anaerobic adhesives are widely used in retaining compounds for nuts and bolts, in sealants, and for impregnation. Recently, anaerobic adhesives have also been used in electrical and electronic applications because of their fast room temperature cure capability and their convenience.¹     

Polymerization kinetics of acrylonitrile by oxidation: Reduction system using potassium persulfate/ascorbic acid in an aqueous medium

The kinetics of acrylonitrile polymerization initiated by free radicals formed in situ in a potassium persulfate/ascorbic acid redox system was investigated in an aqueous sulfuric acid medium in the temperature range of 40–70°C. The rate of polymerization and the rate of the disappearance of potassium persulfate were measured. A kinetic scheme involving the production of initiating radicals from the oxidation of ascorbic acid by potassium persulfate ions and termination exclusively by the interaction of chain radicals with persulfate ions is proposed. The effects of some water‐miscible organic solvents on the rate of polymerization were investigated. The temperature dependence of the rate was studied. A possible mechanism consistent with the experimental data is proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

p‐Acetylbenzylidene triphenylarsonium ylide initiated radical polymerization of methyl acrylate

Polymerization of methyl acrylate (MA), initiated by p‐acetyl benzylidene triphenylarsonium ylide (p‐ABTAY) in dioxan at (60 ± 1)°C for 1 h, follows nonideal kinetics (R_p ∝ [I]^0.21[M]^1.40) due to primary radical termination as well as degradative chain transfer reaction. The polymerization proceeded upto 20.49% conversion without gelation and results in the polymer of high molecular weight 98,000. The overall activation energy and the value of k_p²/k_t are 14 kJ mol^–1 and 18.75 × 10^–6 L mol^–1 s^–1, respectively. The ylide dissociates to form phenyl radical, which initiates the polymerization of MA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Graft copolymerization of poly(methyl methacrylate) with some alkyl methacrylates by atom transfer radical polymerization method and thermal properties

The preparation of graft copolymers of poly(methyl methacrylate) with some alkyl methacrylates were carried out via atom transfer radical polymerization method catalyzed by CuCl/2,2′-bipyridine and using a macroinitiator, poly[(methyl methacrylate)-co-(3,5-bis(chloroacetoxy)phenyl methacrylate)], including an amount of 1 mol % having α-halogeno carbonyl group in the side groups. Although the number-average molecular weights of a graft copolymer series of n-butyl methacrylate (n-ButMA) ended at different times increased from 55,700 to 99,500, the polydispersities decreased from 1.85 to 1.39 with time. The thermal degradation kinetics of macroinitiator and a two-armed graft copolymer of n-ButMA with this macroinitiator, PMMA-g-PnButMA: 4% (by mol), were carried out at different heating rates by thermogravimetric analysis and the results were compared. Using both the Flynn–Wall–Ozawa and Kissinger methods, the decomposition activation energies for macroinitiator were determined as 168 and 162 kJ/mol, respectively; they were also calculated as 233 and 239 kJ/mol for PMMA-g-PnButMA: 4%. The solid state thermodegradation mechanisms of both macroinitiator and PMMA-g-PnButMA: 4% are R₁-type mechanism, a phase boundary-controlled reaction, and F₁-type mechanism, a random nucleation with one nucleus on the individual particle, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012