Cleavable surfactants are of interest for several reasons. Above all, the development of surfactants with weak bonds deliberately built into the structure is driven by the need for improved biodegradability of amphiphiles. The breakdown may be catalyzed by enzymes, and biodegradation would be the normal mechanism in sewage plants. Alternatively, the surfactant may degrade by chemical means, e.g., induced by acid, alkali, ultraviolet (UV) light, heat, or ozone. Acid-and alkali-labile surfactants have attracted particular attention, and there is often a compromise between required stability at one stage and ease of breakdown at a subsequent stage. The paper reviews the main routes used to prepare cleavable surfactants and points out advantages and disadvantages of the different approaches. Emphasis is placed on the development during recent years. Cyclic and acyclic acetals, ketals, and ortho esters are the most important types of bonds for the preparation of acid-labile surfactants, whereas alkali-labile amphiphiles usually are based on ester bonds. The ester bond approach has been particularly important for cationic surfactants, and so-called ester quats have rapidly taken a large share of the traditional market for quats. Betaine esters constitute a special class of ester with very pronounced pH dependence. UV-labile surfactants based, for instance, on an azo bond, offer promise for the future.Paper no. S1174 in JSD 3, 81-91 (January 2000). KEY WORDS: Acetal, betaine ester, choline ester, cleavable surfactant, ester quat, isethionate ester, ketal, labile surfactant, ortho ester, UV degradation. SCHEME 17 SCHEME 16amples of environmentally benign amphiphiles. These surfactants, which contain unsaturated bonds, break down easily during ozonization of water, which is a water purification process of growing importance (64).

Rapid thermal chemical vapor deposition of in situ boron-doped polycrystalline silicon-germanium films on silicon dioxide for complimentary-metal-oxide-semiconductor applications

A new class of cleavable surfactants based on the ortho ester link is described. Ortho ester surfactants were synthesized from a short-chain ortho ester, a fatty alcohol, and a poly(ethylene glycol) monomethyl ether. The triple functionality of the ortho ester link results in a mixture of surface-active and nonsurface-active species. Structures were confirmed by 1 H and 13 C nuclear magnetic resonance. Hydrolysis characteristics at pH values ranging from 2 to 8 were determined. It was shown that, after a steep rise, hydrolysis curves flattened out before complete hydrolysis was reached. Ortho ester surfactants hydrolyze more rapidly than corresponding acetal surfactants. Hydrolysis rates are higher for purified samples and at higher temperature, while plateau levels are higher for the purified surfactant mixtures and at lower pH. The origin of these results is discussed. Data also indicate that the hydrolysis mechanism changes with pH. A test of the loss of emulsification capacity for an ortho ester surfactant with time at pH values from 2 to 11.5 and at 22 or 50°C was carried out, showing rapid breaking of the emulsion at mild acid conditions and a requirement of pH ≥ 10 for long-term stability. Surface tension and critical micelle concentration were determined for some of the surfactant mixtures. It was demonstrated that ortho ester surfactants possess excellent biodegradation properties. The new surfactants are promising candidates for use in industrial processes where temporary surfactant action is required.

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A mathematical model of oxidation of SixGe1−x alloys is presented. The growth of SiO2 is simulated in conjunction with the determination of silicon distribution in SixGe1−x using numerical methods. The main feature of the model is the assumption of simultaneous oxidation of germanium and silicon when exposing the SixGe1−x to an oxidizing atmosphere. In accordance with thermodynamics, the GeO2 formed is subsequently reduced by the (free) silicon available at the interface between the growing SiO2 and the remaining SixGe1−x through a reduction reaction. Thus, the enhanced oxidation of silicon in the presence of germanium is modeled as a result of the rapid oxidation of germanium followed by the quick reduction of GeO2 by silicon. The growth of a mixed oxide in the form of either (Si,Ge)O2 or SiO2–GeO2 only occurs when the supply of silicon to the SiO2/SixGe1−x interface is insufficient. A comparison is made between simulation and experiment for wet oxidation (in pyrogenic steam) of polycrystalline SixGe1−x films. It is found that the model gives a good account of the oxidation process. Kinetic parameters, i.e., interfacial reaction rate constant for oxidation of germanium and diffusion coefficient of silicon (germanium) in SixGe1−x, are extracted by fitting the simulation to the experiment.

A series of noncyclic acetal-linked cleavable surfactants were simply prepared by condensation of aldehydes with poly(ethylene glycol) monomethyl ethers. All of the products were characterized by 1H nuclear magnetic resonance. Their hydrophile-lipophile balance, surface tension, cloud point, critical micelle concentration, and foam height were determined. Hydrolysis kinetic studies, followed by gas chromatography, showed that they had higher hydrolytic reactivity in acidic solution than cyclic acetal-linked cleavable surfactants. JAOCS 73, 841-845 (1996).years, have many advantages over ionic surfactants (21). Here a group of nonionic surfactants, derived from poly(ethylene glycol) (PEG) monomethyl ether (MPEGOH) and all having a noncyclic acetal linkage, have been synthesized (Scheme 1, where MW = molecular weight). The hydrolysis kinetics of these surfactants in acidic solution and the fundamental surface-active properties, such as critical micelle concentration (CMC), surface tension, cloud point, and foam height, have been determined.

A new type of cleavable cationic surfactant, based on the ortho ester link, is described. Ortho ester amines with alkyl chain lengths from C 8 to C 16 were synthesized from a short-chain ortho ester, a fatty alcohol, and an amino alcohol. The ortho ester amine was subsequently quaternized with methyl chloride, yielding a cationic surfactant. The structures were confirmed by 1 H and 13 C nuclear magnetic resonance and the surface chemical properties were investigated by measuring both static and dynamic surface tensions. The results were compared to standard n-alkyl trimethyl ammonium bromides. The critical micelle concentrations were found to vary rather widely, whereas the surface tensions in some cases were comparatively low. The short alkyl chain ortho ester quaternaries were found to have low surface tensions at short surface ages and to induce rapid wetting of a hydrophobic surface in dynamic tests. Additionally, the new surfactants were found to hydrolyze rapidly under mild acidic conditions, as measured by both titation and monitoring of the dynamic surface tension. Further, they showed excellent long-term stability at pH 10 in dilute aqueous solutions. The effect of added electrolyte on rate of hydrolysis was also investigated. A marked enhancement in the hydrolysis rate was found when NaBr was added, whereas NaCl did not have the same effect. The new surfactants could potentially be used to provide temporary surfactant action in application areas such as disinfection, fabric care, personal care, chain lubrication, and mineral flotation as well as in textile processes such as dyeing or scouring. a As shown in Scheme 1, x refers to the ethyl substituent, y to the fatty alcohol substituent, and z to the short-chain amine substituent. See text for details. Abbreviation: NMR, nuclear magnetic resonance.FIG. 6. Hydrolysis characteristics for an n-C 10 -trimethylamino ortho ester quat. Bulk surface activity was measured by the bubble pressure method. Temperature was 21 or 50ºC. Surface ages were 3-18 s. Initial concentrations were ca. 1 g/L of solvent-containing product.

PMOSFETs with a Si 0.7 Ge 0.3 channel were fabricated. The intrinsic gain of the Si 0.7 Ge 0.3 channel PMOSFET was compared to a reference Si PMOSFET, and was found to be enhanced by about 20 to 30 % for all gate lengths down to 0.3 m. This enhancement is attributed to an increased effective mobility in the Si 0.7 Ge 0.3 channel. The inclusion of a Si 0.7 Ge 0.3 channel was found to degrade neither the output conductance (g o ) nor the breakdown voltage.