Reinforcement planar

During the last two decades micro/nanocellulose-reinforced composites have been the subject of intensive research and a number of review papers have appeared covering this work [14, 17, 19, 24, 53, 173,174], Nanocellulose either in CNC or NFC form will result in varying reinforcement of nanocomposites. Also, different types of nanocellulose can be used in various forms of reinforcement, including distributed reinforcements, planar reinforcements, or continuous networked structures. 

Fibrous Composites. These composites consist of fibers in a matrix. The fibers may be short or discontinuous and randomly arranged continuous filaments arranged parallel to each other in the form of woven rovings (coUections of bundles of continuous filaments) or braided (8). In the case of chopped strand mat the random arrangement is planar. In whisker (needle-shaped crystals or filaments of carbon and ceramics) reinforced materials the arrangement is usually three-dimensional and the resulting composites are macroscopically homogeneous. 

The most recent theoretical study, by Alhrichs and co-workers, deals with the di(phosphino)carbene Id and (phosphino) (phosphonio)carbenes Ie,f.16 The optimized geometry of the di(phosphino)carbene Id is weakly bent (PCP angle 160.5°) and highly unsymmetrical Only one of the phosphorus centers (P1) is in a planar environment, and it is much more closely bonded to the carbenic center than the other one (P1C 1.533 and P2C 1.765 A). The atomic charges (P1 +1.0, C -0.8, P2 +0.6) indicate that the short P bond is a double bond reinforced by Coulombic attraction, while the nature of the molecular orbitals revealed a slight delocalization of the carbene lone pair into the low-lying a (P-N) orbitals of the two phosphino substituents. The distortion from the symmetrical structure can be viewed as a second-order Jahn-Teller effect. 

The deshielded 31P and 13C NMR chemical shifts observed for 41-43 ( 31P +130, 13C +76, /PC 85 Hz) are consistent with the presence of a P = C double bond and positive charge development at phosphorus these spectroscopic data are in fact very similar to those observed for the methylenephosphonium salt 40.59,6° This similarity is reinforced by the X-ray analysis of the gallium adduct 42 (Fig. 4) (i) The phosphorus and carbon atoms adopt a trigonal planar geometry, (ii) there is a twist angle between the two planes of 34.1°, and (iii) the phosphorus-carbon bond distance is rather short (1.61 A). 

Trisubstituted carbon-centred radicals chemically appear planar as depicted in the TT-type structure 1. However, spectroscopic studies have shown that planarity holds only for methyl, which has a very shallow well for inversion with a planar energy minimum, and for delocalized radical centres like allyl or benzyl. Ethyl, isopropyl, tert-butyl and all the like have double minima for inversion but the barrier is only about 300-500 cal, so that inversion is very fast even at low temperatures. Moreover, carbon-centred radicals with electronegative substituents like alkoxyl or fluorine reinforce the non-planarity, the effect being accumulative for multi-substitutions. This is ascribed to no bonds between n electrons on the heteroatom and the bond to another substituent. The degree of bending is also increased by ring strain like in cyclopropyl and oxiranyl radicals, whereas the disubstituted carbon-centred species like vinyl or acyl are bent a radicals [21]. 

This conclusion is reinforced by Yu et al. [4] in the portion of their model that addressed planarization behavior. They argued that spatial selectivity is determined by the dimensions and behavior of the pad asperities. From geometry, a pad asperity of radius jS cannot enter a trench of width w and depth if w is below some critical value... 

Over the last decade advances have occurred very rapidly in the area identified as composite materials. In general, a composite material is the combination of any two or more materials, one of which has superior mechanical properties but is in a difficult to use form (e.g. fiber, powder, etc.). The superior component is usually the reinforcement while the other component serves as the matrix in which the reinforcement is dispersed. The resultant composite is a material whose properties are near those of the reinforcement element but in a form which can be easily handled and can easily function as a structural element. Included in this definition are all of the reinforced materials including particulate, fiber, flake and sheet reinforcements. Adhesive joints for, example, would be a planar or two dimensional composite 1). 

One of the more useful criteria for "aromatic" character is derived from nmr chemical shifts. It is known that the protons of benzene are found at a lower field than ordinary olefinic protons, and it has been attributed to the ring current in the Ti-system which will reinforce the applied field at the protons. This has found confirmation in the observation that protons placed over an aromatic ring will be shifted upfield.39 A particularly striking effect is found with the planar cyclooctadecanonaene in which the outer hydrogens have an unusually large downfield shift (8 9.28) and the inner hydrogens have a remarkably large upfield shift (8 -2.99).40... 

Binding of urea to metal ions may be reinforced and coordination through the N atom may be favored even for 3d metal ions by incorporating the urea moiety in a chelate arrangement. A -(2-Pyridylmethyl)urea was found to bind either as an N,0-chelate (45) or as an N,N-chelate (46), depending on the metal ion, which is most likely due to the different bond angles and the preferred chelate ring sizes in tetrahedral zinc(ll) or square-planar copper(ll) (107). 

Some polychlorinated biphenyls, especially their non-planar para-hydroxylat-ed metabolites also possess estrogenic activity [126,135,140]. These metabolites have a higher estrogenic potency than their parent compounds. Some co-planar polychlorinated biphenyls (PCB 77 and PCB 126) have been shown in vivo to have estrogenic as well as antiestrogenic activities, probably solely through hydroxy metabolites (NIH shift to para). This reinforces the European view that EDCs can only be confirmed in intact animals. It is also known that some hydroxylated metabolites of polycyclic aromatic hydrocarbons (PAHs), e.g. 3,9-dihydroxybenzo[a]anthracene, show estrogenic activity [141 -143]. 

Methyl-3,5-diphenyl-l//-thiopyran 1-oxide forms red air-stable complexes with carbonyls of chromium, molybdenum and tungsten. (78CB1709). X-Ray diffraction measurements on these compounds confirm the non-planarity of the thiabenzene oxide nucleus and reinforce the evidence for high inversion barriers at sulfur. These complexes are found in isomeric forms with either the sulfur-oxygen bond axial to the half-chair conformation adopted by the ring, or the S- methyl group axial the complexes cannot be interconverted. 

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