Interlamellar thickness

Figure 21 Plot of thickness values as a function of molecular weight for linear polyethylene fractions quenched to —78°C. (A), crystallite thickness, Lc (O), interlamellar thickness, La ( ), interfacial thickness, Lb. Reprinted with permission from Ref. [277]. Copyright 1990 American Chemical Society.

PVDF/PMMA 0-75% PMMA interlamellar thickness amorphous layer SAXS [Ullmann and Wendorff, 1985]... 

Table 6.9 Long Period L (nm), Lamellar Thickness 1 (nm), and Amorphous Interlamellar Thickness /a (nm) of Pure iPP and iPP/HOCP Blends Isothermally Crystallized and Annealed.

Fig. 4.41. Plot of thicknesses in Angstrom units against weight-average molecular weight for linear polyethylene fractions quenched to 78 °C. A crystallite core thickness Lc o interlamellar thickness La interfacial thickness Lb. Reproduced from [228]. Copyright 1990, American Chemical Society.

The interlcunellar water content calculated on the basis of a 8.6 A interlamellar thickness and the above mentioned apparent density of 0.36 kg-dm is 120 cm NPT). The experimental values. Table I, are expected to be decreased by 1) interstratification between collapsed and open lamellar ii) variable heights of the pillars, sometimes too small to allow the efficient packing of H 0 molecules and iii) different types of ordering of the pillars within the Interleunellar space. Some of these effects must influence the time of preheating at 300°C, in Al(La)-CLH and the temperature of preheating of Al-CLM. 

Figure 8.6. A diagrammatic view of a semicrystalline polymer showing both chain folding and interlamellar entanglements. The lamellae are 5-50 nm thick (after Windle 1996).

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The molecular size and the cross-sectional area of coumarine 1 were calculated to be 3.2x10.4x7.5 (A) and 78 A, respectively. From the data of observed d-spacings and the calculated molecular size, three possibilities for the conformation of coumarine molecules could be proposed. In the dl-type [shown in Fig. 5(a)], since the thickness of one aluminosilicate layer was about 9.6 A, the full clearance space was estimated to be about 3.6 A. This value was almost equal to the thickness of the planar coumarine molecule. Therefore, it was considered that coumarine molecules were "flat" on the silicate surfaces and covered each exchangeable cation site without any overlap. In the dh-type [shown in Fig. 5(b,c)], the measured d-spacing was 18.5 A, so that the interlamellar spacing was evaluated to be about 8.9 A, in which the coumarine... 

The observed equilibrium thickness represents the film dimensions where the attractive and repulsive forces within the film are balanced. This parameter is very dependent upon the ionic composition of the solution as a major stabilizing force arizes from the ionic double layer interactions between any charged adsorbed layers confining the film. Increasing the ionic strength can reduce the repulsion between layers and at a critical concentration can induce a transition from the primary or common black film to a secondary or Newton black film. These latter films are very thin and contain little or no free interlamellar liquid. Such a transition is observed with SDS films in 0.5 M NaCl and results in a film that is only 5 nm thick. The drainage properties of these films follows that described above but the first black spot spreads instantly and almost explosively to occupy the whole film. This latter process occurs in the millisecond timescale. 

Figure 1. Computer simulation of the formation of clay tactoid by a process of aggregation of lCr particles. Ration length to thickness 9/1. In the three topmost diagrams each rectangle endorses a portion of the tactoid shown enlarged below, df is represented by the thickness of the line enclosing the sheets in contact. Adapted from ref. 6. N.B. With respect to the next section, the molar fraction xi consists of the water in the interlamellar space and in the closed spaces within the tactoid. The molar fraction xb is in a 10 A thick layer on the external contour of the tactoid.

As already indicated, the surface area of the dry clay appeared to be about 50m2g-1. The platy particles (the tactoids) were therefore about 20 layers thick during the first stage of water sorption, the particles were split into smaller tactoids of around six clay platelets (surface area of 105 m2 g-1). The external dimensions at p/p° > 0.25 remained fairly constant, but the interlamellar sorption was accompanied by swelling and the development of an accessible internal area (possibly as high as... 

An important result is the coincidence of the temperature of the main phase transition determined for the water-ethanol dispersion by DSC (see below) with the temperature of the steep change in the foam bilayer thickness (23°C). Within the range from 22 to 23°C the foam bilayer thickness variation is similar to that of the interlamellar distance in water dispersions of DMPC [443]. These facts show that both in the bulk phase and in the foam bilayer a chainmelting phase transition occurs which is characterised by a sharp shift in the number of gauche conformations of carbon-carbon bonds [430,444]. 

The thickness transition at 13°C is an interesting experimental observation. It is in contrast to the pretransition in water dispersions of DMPC, for which the interlamellar spacing decreased with the fall of temperature [443], the foam bilayer thickness increases in the range of this transition upon cooling. 

It is well known that the main phase transition is due to the melting hydrocarbon tails of amphiphile molecules [430,436], The average number of gauche conformations for each DMPC molecule is about 7 in the liquid-crystalline state [444], In view of this the thickness of the hydrocarbon layers of a foam bilayer can be estimated to be h = 1.13 nm. Then for the liquid-crystalline state of the foam bilayer, the thickness of the polar inner layers is (i2 = 3.5 nm and the total thickness of the foam bilayer is h = 5.7 nm. These values are relevant to the liquid-crystalline state of the foam bilayers (24-30°C) and are shown in Table 3.14. The value obtained for the thickness of the DMPC foam bilayer in the liquid-crystalline state seems reasonable when compared with the value of the interlamellar distance in the liquid crystalline DPPC-water-alcohol dispersions [445], extrapolated to high ethanol concentrations. 

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