Lamellar units

FIG. 7 Structures of various liquid-crystalline phases of membrane lipids. (A) Normal hexagonal phase (Hi) (B) lamellar phase (C) inverted hexagonal phase (Hu). Cubic phases consisting of (D) spherical, (E) rod-shaped, and (F) lamellar units. The hydrocarbon regions are shaded and the hydrophilic regions are white. (Reprinted by permission from Ref. 11, copyright 1984, Kluwer Academic Publishers.)... 

SSL is water dispersible and forms hexagonal II mesophases at temperatures above 45 °C at pH 5.0. If neutralized to pH6.5-7.0 in water, SSL forms lamellar mesophases which can be diluted to form stable dispersions of lamellar units (Krog, 1975). Calcium stearoyl lactylate is less water dispersible, but more soluble in oils and fats than the sodium salt. Calcium stearoyl lactylate was originally developed in the USA as a dough conditioner more than two decades ago and it is still used in yeast doughs, but only to a minor extent compared to sodium stearoyl lactylate, which is one of the major dough conditioners for yeast-raised bakery products in the USA. 

The effect of different types of comonomers on varies. VDC—MA copolymers mote closely obey Flory s melting-point depression theory than do copolymers with VC or AN. Studies have shown that, for the copolymers of VDC with MA, Flory s theory needs modification to include both lamella thickness and surface free energy (69). The VDC—VC and VDC—AN copolymers typically have severe composition drift, therefore most of the comonomer units do not belong to crystallizing chains. Hence, they neither enter the crystal as defects nor cause lamellar thickness to decrease, so the depression of the melting temperature is less than expected. 

Copolymers of vinyUdene chloride and methyl acrylate have been studied by x-ray techniques (75). For example, the long period (lamellar thickness) for an 8.5 wt % methyl acrylate copolymer was found to be 9.2 nm by smaH-angle x-ray scattering. The unit cell is monoclinic, with a = 0.686 and c = 1.247 nm by wide-angle x-ray scattering. 

The dichloride 8.21a forms fragile, lamellar crystals with a golden colour. The X-ray structure reveals a layered arrangement of hexameric units formed by linking three ( BuNTeCl2)2 dimers by chloride bridges. The reaction of 8.21a with potassium tert-butoxide yields... 

Another type of fibril substructure in PET fibers, besides the microfibrillar type already discussed, is the lamellar substructure, also referred to as the lateral substructure. The basic structural unit of this kind of substructure is the crystalline lamella. Formation of crystalline lamellae is a result of lateral adjustment of crystalline blocks occurring in neighboring microfibrils on the same level. Particular lamellae are placed laterally in relation to the axis of the fibrils, which explains the name—lateral substructure. The principle of the lamellar substructure is shown in Fig. 2. 

A very recent application of the two-dimensional model has been to the crystallization of a random copolymer [171]. The units trying to attach to the growth face are either crystallizable A s or non-crystallizable B s with a Poisson probability based on the comonomer concentration in the melt. This means that the on rate becomes thickness dependent with the effect of a depletion of crystallizable material with increasing thickness. This leads to a maximum lamellar thickness and further to a melting point depression much larger than that obtained by the Flory [172] equilibrium treatment. 

Structured laundry liquids are currently available in Europe and were recently introduced in the United States [50,51]. These products typically contain high levels of surfactants and builder salts, as well as enzymes and other additives. In the presence of high ionic strength, the combination of certain anionic and nonionic surfactants form lamellar liquid crystals. Under the microscope (electron microscope, freeze fracturing) these appear as round droplets with an onion-like, multilayered structure. Formation of these droplets or sperulites permits the incorporation of high levels of surfactants and builders in a pourable liquid form. Stability of the dispersion is enhanced by the addition of polymers that absorb onto the droplet surface to reduce aggregation. 

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