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Microphase segregation w u r s in certain solidsolution binary mixtures of n-alkanes at room temperature. The kinetics of segregation for the mixtures C28H/C36D, C2gH/CWD, and C3OH/C3bD have been studied at molar concentration ratios of 4:1, 1:4, and 1:l. During the demixing, the mixture maintains a lamellar, highly crystalline orthorhombic subcell structure that is very similar to that of the pure odd-numbered n-alkanes. The average domain sizes of the segregated components of mixtures, in which one component is hydrogenated and the other deuterated, were determined from the band splitting observed for the infrared-active methylene-scissors band. The range of domain sizes that can be monitored extends from single isolated chains to aggregates of the order of 100-150 chains. Curves obtained from plotting log L against log r, where L is the average lateral dimension of the domains and t is time, are nonlinear. However, for mixtures of a given concentration ratio the curves vary in shape with chain length in a systematic way so as to correspond to different segments of a common (S-shape) curve. The relative rates of segregation for the different mixtures are, as expected, very sensitive to the chain-length difference between the two components. The rate increases dramatically as the chain-length difference increases. In the earlier stages of demixing, the rates for the 1:4 mixtures are generally greater than those for the 4:l mixtures, suggesting that partial v a d e a play an important role in the early-stage kinetics. An asymmetry in the domain sizes of the two mponents is found in the 1:l mixtures, espcjally in the C B~/ C~~~ mixture. This asymmetry indicates that the domains of the longer chains are more compact than those of the shorter chains.

The first zeolite structure (ITQ-40) that contains double four (D4) and double three (D3) member ring secondary building units has been synthesized by introducing Ge and NH 4 F and working in concentrated synthesis gels. It is the first time that D3-Rs have been observed in a zeolite structure. As was previously analyzed [Brunner GO, Meier, WM (1989) Nature 337:146-147], such a structure has a very low framework density (10.1 T∕1,000 Å 3 ). Indeed, ITQ-40 has the lowest framework density ever achieved in oxygen-containing zeolites. Furthermore, it contains large pore openings, i.e., 15-member rings parallel to the [001] hexagonal axis and 16-member ring channels perpendicular to this axis. The results presented here push ahead the possibilities of zeolites for uses in electronics, control delivery of drugs and chemicals, as well as for catalysis.double three-rings in zeolites | low framework density zeolites | germanosilicate zeolites T here is an increasing interest in the synthesis of zeolites with low framework density and extra-large pores (>12 tetrahedral atoms). The preparation of such materials will increase the use of zeolites in catalysis (1, 2) while further expanding their possibilities in microelectronics by preparing materials with low values of the high-frequency dielectric constant, or for uses related with controlled delivery of chemicals and diagnostic treatment (3, 4).In 1989, Brunner and Meier performed a topological analysis on synthesized zeolites and aluminophosphates with four-connected frameworks (5). They found that when the frameworks were grouped as a function of the smallest ring present in the structure, the minimum framework density calculated for each of the groups decreases with the smallest ring size. These results suggested that one way of preparing low framework density zeolites could be to build structures with four-and three-rings. Following this suggestion and the recognition that several beryllium-containing natural zeolites, such as lovdarite and nabesite, have three-rings in their structures, Cheetham et al. (6) prepared a large pore (14 × 8 × 8) zeolite with Be that contains three-rings. Previously, Davis et al. considered using zinc as a framework cation to promote the formation of three-rings, and while three zincosilicates containing three-rings were subsequently synthesized, none of them contain extra-large pores (7-9). Later, we have shown by theoretical and experimental work, that Ge has a directing effect toward the formation of double four-rings (D4Rs) (10, 11), and the presence of these secondary building units (SBUs) has allowed the synthesis of several large and extra-large pore zeolites (12-15). Among those, Instituto de Tecnologia Química number 33 (ITQ-33) contains D4Rs and three-ring units in the structure and has a low framework density (12.3 T∕1;000 Å 3 ). Very recently, an interrupted zeolite with a three-dimensional mesoporous channel system (ITQ-37) has been presented (16), which contains D4Rs and has the lowest framework density reported (10.3 T∕1000...

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