Current optical data storage (ODS) technologies use onephoton-absorption processes to write data by locally changing the optical properties of the medium. [ 1 , 2 ] Since the lateral dimensions of spots that can be written are near the diffraction limit, signifi cant capacity increases require new approaches such as storage in three dimensions. DVDs, which comprise up to four individually addressable storage layers, exemplify the potential of this concept, but the complexity of producing and using multilayer systems increases with the number of layers. In bulk materials, changes can be confi ned in the third dimension via nonlinear optical processes, such as two-photon absorption (TPA). [3][4][5][6] We have developed a novel ODS system that relies on the optically-induced switching of the aggregation state and fl uorescence of a TPA dye in a polymer matrix. Welldefi ned, ∼ 3 × 3 × 6 μ m-large voxels were written with single focused laser pulses and read by confocal laser scanning microscopy. Such ODS systems are easily produced and promise a storage capacity of up to several Tbytes on a DVD-size disk, which is ∼ 100× higher than that of current commercial ODS technologies. [ 6 , 7 ] The optical changes considered for rewritable and write-once read-many three-dimensional (3D) ODS storage media based on TPA include reversible and irreversible photo chemical reactions such as photoisomerizations, [8][9][10] photo-induced dimerizations, [ 11 , 12 ] photodecompositions, [ 13 , 14 ] and photopolymerizations. [15][16][17] Fluorescent photochromic systems have attracted particular interest, because the exploitable photophysical processes are fast, effi cient, and reversible. [18][19][20] However, it has been challenging to create fl uorescent photochromic materials, which combine high stability, high fl uorescence quantum yield, and large TPA cross-section. We here demonstrate a novel approach to 3D ODS materials, which relies on the switching of the aggregation state of an excimer-forming fl uorescent dye with an appreciable TPA cross-section in an inert host polymer.We have previously reported a range of materials, which change their fl uorescence and/or absorption properties upon exposure to heat, [21][22][23] chemicals, [ 24 ] or mechanical forces, [25][26][27] on account of reversible or irreversible stimulusinduced changes of the aggregation state of the dye molecules. We surmised that such changes could be induced in small volumes by TPA-induced local heating and therefore explored a melt-processed blend of poly(ethylene terephthalate glycol) (PETG) and 1.1% w/w of 1,4-bis( α -cyano-4-octadecyloxystyryl)-2,5-dimethoxybenzene [ 22 , 23 ] (C18-RG, Figure 1 a) as TPAaddressable ODS medium. C18-RG was selected on account of its signifi cant changes in absorption and emission spectra upon aggregation/dissociation, its high thermal and photochemical stability, and, as demonstrated here, its appreciable TPA cross-section. PETG was chosen as the matrix due to its glassy nature and transparency in the relevant op...

Clay aerogels, ultra low density materials made via a simple freeze-drying technique, have shown much promise in broad applications because of their low densities, often in the same range as silica aerogels (0.03-0.3 g/cm(3),) but suffering from low mechanical strength. A bioinspired approach to mineralize an active polymer/clay aerogel composite is inspected, showing marked improvement of the mechanical properties with increasing modification. Further property improvement was achieved using a layer-by-layer approach to produce alternate layers of polymer and silica on the surface.

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S P O N T A N E O U S ignition properties of combustible materials, particularly fuels and hydrocarbons, have been an important area of combustion research for over 50 years. This interest in spontaneous ignition is based on the important role which this phenomenon plays in the fire hazard in the handling and storage of combustibles, the performance of various types of combustion engines, and the elucidation of oxidation and combustion mechanisms of fuels, hydrocarbons, and related substances.The spontaneous ignition temperature (SIT) of a substance is defined as that lowest temperature a t which the substance will ignite in air without the aid of a spark or flame. Based on the thermal theory of ignition and on classical reaction-rate theory, spontaneous ignition temperature can be regarded as that temperature to which a combustible mixture must be raised so that the rate of heat evolved by the exothermic oxidation reactions of the system will just overbalance the rate a t which heat is lost to the surroundings. However, the criterion that is usually taken to indicate ignition-i.e., visible and/or audible combustion observed under ordinary laboratory conditions-is quite subjective. Also, the spontaneous ignition temperature of a substance should be a quantity related to some characteristic chemical property of the material, yet its experimentally determined value is markedly dependent on the method and apparatus employed for its determination. I n a recent monograph, Mullins (1 7) reviews this subject, including the importance, definition, and meaning of spontaneous ignition and spontaneous ignition temperature and describes numerous methods for its determination and the factors which influence results.Earlier work on the effects of oxygen concentration ( 2 , 12-14) indicated that it would be of interest to study spontaneous ignition in finer detail using better instrumentation with particular emphasis on preignition behavior. A static system was chosen for its simplicity and to make temperature-time measurements. An inherent fault of such a system is the problem of uniform gas mixing after introducing the hydrocarbon sample. This problem should be minimized by discharging the sample as a fine spray and by a long time delay before ignition occurs.The general purpose of this investigation was to study the influence of chemical structure on the spontaneous ignition processes. Specifically, the influence of chain length, chain branching, unsaturation, and of cyclic and aromatic structures on the preignition processes was examined by measuring internal gas temperature and oxygen consumption.I n addition to minimum ignition temperature in air for cool-or hot-flame ignition, minimum reaction temperature, preignition temperature range, temperature rise, and oxygen consumption a t ignition were useful. A correlation between these values and ease of oxidation and ignition was noted. The findings were as follows: I n general, decreasing chain length, addition of methyl groups, unsaturation, and particularly, chain branchin...

3D Optical data storage is demonstrated in co‐extruded multilayer films using organic materials. Co‐extrusion is able to produce films on a much larger scale at a much lower cost than current methods. The material compatibility and mechanical flexibility allow for new data formats with higher capacities to be realized.