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A theoretical model describing the association of ionic surfactants into rod-shaped micelles is combined with an approximate formula for the viscosity increase induced by rod-shaped aggregates. It is shown that most of the thermodynamic parameters of the association model can be obtained from viscosity measurements. The approach is applied to micellar solutions of hexadecylpyridinium salts. The pronounced effect of counter-ion concentration on the growth of rod-shaped micelles can be attributed to a slightly higher degree of counter-ion association in the cylindrical part than in the end portions. An attempt is made to explain the finding that the degree of counter-ion association is virtually independent of counter-ion concentration.

Bioassays, including immunoassays, enzyme assays, and assays using enzyme electrodes, and nucleic acid hybridization probes have been the subject of considerable industrial and academic research. New bioassay methods have applications in the medical, chemical, pharmaceutical, and food products industries. Recent US patents and scientific literature on a variety of new bioassay methods are surveyed. A description of these patents and a list of references are given.

Structures formed by self-assembly of α- and β-1-n-octyl-D-glucopyranoside and β-1-n-dodecyl-D-maltoside in water depend upon the configuration at the anomeric center. The β-anomers form aggregates of size comparable to normal ionic micelles, while the α-glucoside is sparingly soluble in water and forms very large, nonspherical assemblies. This contrasting behavior suggests that the head group configuration controls its orientation to the apolar residue and, consequently, the packing of monomers in self-assemblies.The β-anome the latter is evidence of its strong interaction with micellized β-maltoside.

The light-scattering techniques of intensity angular dissymmetry and photon correlation spectroscopy are used to determine the static correlation length, osmotic compressibility, and diffusivity of an oil-in-water microemulsion. The observed temperature dependence of these quantities near a phase separation point qualitatively resembles the critical behavior found for simple fluids and binary mixtures, but with substantially larger values of the critical exponents $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}$.

Using the method of cumulants, we investigate the distribution of diffusion coefficients in polydisperse systems. We consider the intensity weighting for distributions of spherical particles having the same polarizability. Results of computer simulations are presented for a variety of polydisperse situations. Also, comparisons are made between predicted and measure results for mixtures of Dow latex spheres.

A laser doppler velocimeter (LDV) has been designed and constructed for use in measuring ocean water flow velocity in the immediate vicinity of marine organisms anchored inside a water tunnel. The principal innovation reported here is the use of a microprocessor to produce an ’’intelligent’’ instrument which automatically calculates and displays the flow velocity. The resulting electronics design represents a considerable simplification over existing instruments which generally require the use of a separate autocorrelator and/or multi‐channel analyzer (MCA) plus an external minicomputer. The LDV configuration employed is a crossed‐beam design using a 2‐mW He–Ne laser and inexpensive optics. A 48‐channel 1‐bit clipped autocorrelation function is implemented using a modified TTL design reported previously by Chen and co‐workers. A Motorola 6800 micromodule updates the contents of each channel by direct memory access and displays the resulting correlogram on a CRT monitor. The velocity is periodically calcul...

We present calculations for the mean aggregation number and radius of gyration versus the mean hydrodynamic radius for polydisperse distributions of SDS micelles. We also present new measured values for the hydrodynamic radius. These results carry significant implications for the average number of monomers per micelle and for the micellar shape.

Using the method of dynamic light scattering we have measured the diffusion coefficients D of cetyltrimethylammonium hydroxide (CTAOH) micelles as a function of CTAOH and NaOH concentrations at 25°C for 0.01 ≤ [CTAOH] ≤ 0.05 M and 0.02 ≤ [NaOH] ≤ 0.5 M. Substantial enhancements in the diffusivity were observed at low [NaOH] due to the presence of strong intermicellar electrostatic repulsions. We obtained good theoretical fits to the D versus [CTAOH], [NaOH] data over the range 0.01 ≤ [NaOH] ≤ 0.5 M using linear interaction theory (including both thermodynamic and hydrodynamic corrections to D ) with a DLVO-type pair interaction potential. From these fits we obtained estimates of the mean micellar hydrodynamic radius, R h ∼ 23.4 A, and the micellar fractional ionization, α ∼ 0.5.

The micellar diffusivity, measured by quasielastic light scattering, is described by a simple phenomenological expression for a variety of surfactants over a range of surfactant concentrations and temperatures at low salt concentration where electrostatic interactions dominate. This universal expression contains the low order perturbations to the micellar diffusivity in the absence of interactions. The dominant correction scales with the ratio of surfactant to salt concentrations and results from repulsive electrostatic interactions, screened by the added salt ions. By fitting experimental data to this expression, we obtain the Stokes–Einstein micellar radius and a relative measure of the micellar ionization fraction.

Quasi-elastic light scattering measurements have been performed on aqueous solutions of CTAB (cetyltrimethylammonium bromide). Theoretic fits to the measured diffusion coefficients at low NaBr were obtained by using the generalized Stokes-Einstein equation expanded to first order in the surfactant concentration (including both thermodynamic and hydrodynamic terms), with a pair-interaction potential taken from Dlvo theory. Good fits are obtained at low NaBr concentrations by assuming a constant micellar radius for each temperature and assuming that the remaining parameters (aggregation number, fractional ionization, and Hamaker coefficient) are independent of temperature. This procedure yields an unambiguous value for the fractional ionization alpha for CTAB micelles: alpha = 0.22. The limits of validity of the theoretic fitting procedure (previously applied by Corti and Degiorgio to the system sodium n-dodecyl sulfate (SDS) + NaCl) are discussed. 65 references.

The diffusion coefficient and correlation radius associated with the droplet particles in oil-in-water microemulsions (CTAB, octane, butanol, NaBr and water) were determined by dynamic light scattering- Unlike the case of CTAB micelles, there is a maximum in the correlation radius versus temperature plot.

The cationic surfactant dodecyl ammonium chloride (DAC) undergoes a one- to two-fluid phase transition with decreasing temperature T at constant [NaCl]. In the case of [DAC]= 0.025M, there is phase separation in the region T ≳ 16°C provided that [NaCl] ≳ 0.23M. Below [NaCl] ∼ 0.23M the apparent micellar hydrodynamic radius Rh aPP, determined by dynamic light scattering from the diffusion coefficient D, increases with decreasing T. This behavior is typical of a variety of ionic micellar systems in the presence of added salt and has been ascribed to micellar growth (e.g. SDS + NaCl). However, with DAC + NaCl for [NaCl] > 0.23M, there may be an additional mechanism which causes Rh aPP to increase greatly with decreasing T -- i.e., critical-type fluctuations at the approach to a phase boundary. This behavior is qualitatively similar to that observed for nonionic micelles and micro- emulsions. In these systems the decrease in D (i.e. increase in Rh app) upon the approach to a cloud point or phase boundary is believed to be due to long-range correlated diffusion of micelles/droplets of basically unchanging size. Hence, the diffusivity results for DAC + NaCl at [NaCl] > 0.23M may be due to either micellar growth or critical-type behavior, or a combination of the two.

Using the method of dynamic light scattering, we have determined the diffusion coefficients of micelles in aqueous solution as a function of surfactant and salt concentrations for three related systems: CTAB (C16H33N(CH3)3Br) + NaBr, MyTAB(C14H29N(CH3)3Br) + NaBr and CTACl(C16H33N(CH3)3Cl) + NaCl. For each system there is a well-defined salt concentration below which the micellar diffusivity increases linearly with surfactant concentration. In this low-salt region, in which the net intermicellar interaction is repulsive, we have obtained good fits to the diffusivity data using linear interaction/DLVO theory. From this procedure we have determined the “minimum-sphere” micellar radius as a function of temperature as well as estimates of the micellar fractional ionization α and the Hamaker constant A for the above systems as well as for SDS(C12H25SO4Na) + NaCl. Hence, by this approach one is able to relate variations in these physical parameters to subtle changes in surfactant composition (e. g. alkyl chain length) and counterion properties. Interestingly, significant micellar growth apparently commences at the salt concentration at which the net intermicellar interaction shifts from repulsive to attractive.

The technique of intensity correlation light-scattering spectroscopy has been used to accurately determine the extent of physical swelling of lysozyme, ribonuclease, and chymotrypsinogen produced by thermal denaturation. The change in hydrodynamic radius is deduced from direct measurements of the diffusion coefficient, carried out in the temperature range 20° to 70°C at various values of pH in the range 1.0 to 3.0 at ionic strengths of from 0.01 M to 0.2 M. An average radius increase of 18% is observed for lysozyme and ribonuclease, with an estimate of 26% for chymotrypsinogen. Analysis of the pH dependence of the transition temperature leads to the conclusion that the lysozyme charge increases by approximately +2e during unfolding. We have applied this value of the charge increase along with the 18% average radius increase to estimate the electrostatic contribution to the free-energy change for denaturation of lysozyme. The results are consistent with the experimental observation that the transition temperature is nearly independent of ionic strength.

The size, shape and structure of the micellar aggregates formed from ionic surfactants are believed to be influenced by a variety of variables1’2. These include the surfactant composition (hydrocarbon “chain length” and headgroup species) and molarity; the counterion species and concentration; and finally temperature and pressure. Pioneering studies of micelle size as a function of temperature and salt concentration have been made using the powerful technique of quasi-elastic light scattering spectroscopy by Benedek’s group at MIT3–5, Corti and Degiorgio6,7, and others8,9.

The homogeneous fluorescent immunoassay described above allows one to measure the brightness of fluorescently tagged carrier particles that are suspended in a background of free, unbound fluorescent sources. We have demonstrated the feasibility of our technique using a gentamicin competitive assay as well as idealized model systems. We have seen that the fluctuation-correlation method is able to discriminate against free background sources because each fluorescing particle in solution contributes to the correlation peak [Eq. (4)] with a weighting equal to the square of its respective intensity. Hence, a few very bright sources contribute disproportionately to the "signal" relative to many weak ones. To take advantage of this property, one would therefore design an assay that uses relatively larger carrier particles, each of which is capable of binding on the order of 10(3) to 10(4) tagged antibodies or antigens. Unfortunately, the nonlinear dependence of the correlation peak on the brightness of the fluorescing species causes the technique to be perturbed by carrier particle aggregation; the apparent bound fluorescence intensity increases with the extent of aggregation. The latter may be an unavoidable consequence of performing assays using raw blood serum, for example. The ultimate usefulness of this method will depend on its sensitivity and speed when applied to "real" assays of clinical significance. These characteristics will be influenced by a number of technical details. Given our limited experience with the method thus far, it would appear that its principal drawback is its relatively slow speed. In order to decrease the time needed for a reliable measurement, one must average the random fluctuations in the fluorescent intensity to zero more quickly. In principle, this can be accomplished by decreasing the shot noise by collecting a larger fraction of the fluorescent light, and increasing the sampling rate. The method requires rather complicated instrumentation; it is by no means clear that this level of complexity is justified given the realistic level of sensitivity that will be obtained by this technique.

Using the technique of dynamic light scattering, we have examined the effect of interactions (predominantly electrostatic repulsions) on micellar diffusion coefficients, D, for two related cationic surfactants, CTAOH (C16H33N(CH3)30H) and CTACl (C16H33N(CH3)3C1), under conditions of little-to-moderate micellar growth -- 0 to 0.5M electrolyte and 0.01 to 0.05M surfactant at 25°C -- where variations in D are due primarily to changes in intermicellar interactions. We obtained systematic plots of D vs [surfactant] with positive slopes and common diffusivities, Do, extrapolated to the cmc. Diffusivities increase with decreasing [electrolyte] due to inadequate screening of the intermicellar Coulombic repulsions. With no added electrolyte D exceeds Do by a factor of almost 5 at 0.05M surfactant. Plots of D vs [surfactant] are linear for CTAOH with [NaOH] ≥ 0.03M and for CTAC1 with [NaCl] ≥ 0.01M. At lower [electrolyte] the curvature of the D vs [surfactant] plots is due to screening by anions dissociated from the micelle. Following Corti and Degiorgio we applied linear interaction theory to the D vs [surfactant], [electrolyte] plots, taking into account theormodynamic and hydrodynamic corrections to D, using the DLVO pair interaction potential, which is overwhelmingly repulsive in dilute electrolyte.

Calcium concentrations of a large number of cataractous human lenses and nine normal human lenses were measured by atomic absorption spectroscopy. The mean concentration of calcium in cataractous lenses is 2–13 times higher than the mean calcium concentration of the normal lenses. In considering individual lenses, however, a large number of cataractous lenses contain either less or equivalent calcium concentrations than are present in normal lenses. The Calcium distributions in both the water-soluble and water-insoluble protein fractions isolated from yellow and brown cataracts were also determined. While some aggregate fractions of yellow lenses are calcium rich, no clearcut differences in the mean calcium concentrations of the remaining protein fractions could be established.

The method of quasi-elastic light-scattering spectroscopy was used to establish quantitatively the concentration of high mmolecular weight (HMW) aggregates present in the normal human intact lens as a function of age. The concentration of HMW proteins increases monotonically with age. HMW proteins are absent in the infant lens, but represent 3% of the total soluble lens protein at age 60 years. The percent concentration of HMW proteins measured in intact lenses of various ages by quasi-elastic light scattering is in striking agreement with values determined biochemically.

We have investigated the influence of dilute tertiary amyl alcohol (t-AmOH) on micellar size and charge by dynamic light scattering using two related surfactant/salt systems: CTABr (C16H33N(CH3)3-Br) + NaBr, and CTAC1 (C16H33)N(CH3)3C1) + NaCl. These were chosen because of their contrasting sensitivity to added salt with respect to micellar growth. For CTABr there is substantial growth at 25°C for [NaBr] > 0.05M, whereas for CTAC1 there is negligible growth below [NaCl] ∼ 1M. We measured the micellar diffusion coefficient D as a function of [surfactant] and [salt] at 25°C over the range 0.25% ≤ [t-AmOH] ≤ 7% (w/w) , approaching the solubility limit of t-AmOH in water, ca. 11%. We focused our attention on relatively low salt concentrations, where interlicellar interactions are predominantly repulsive and micellar growth is either small-to-moderate (CTABr) or negligible (CTAC1). For the CTACl-related ternary system we applied linear interaction theory (with a DLVO-type pair potential) to estimate the hydrodynamic radius Rh and fractional ionization a, from fits to D vs [surfactant] for various [salt]. Over the range of t-AmOH investigated, in general Rh decreases and a increases somewhat with increasing [t-AmOH], consistent with previous findings in the literature.

We have measured the infrared and far infrared absorption spectrum of powders, films and single crystals of (TTF) (TCNQ) at temperatures above and below the metal‐semiconductor transition at 58°K. At all temperatures there is a broad and extremely intense (α ∼ 105 cm−1) absorption band centered at ∼ 2800 cm−1 (∼ .35eV), which is polarized along the conducting axis of this pseudo‐one‐dimensional conductor. We identify this absorption as the “charge transfer band”, which is associated with intra‐band transitions, i.e. within the lowest occupied bands of both TCNQ− and TTF+. The peak energy of this absorption is shifted down from the ∼1.1eV value of most other simple TCNQ− salts, presumably due to the reduction of the on‐site coulomb interaction by the polarizability of TTF+.

The nature of the spin‐cluster (“multi‐magnon”) excitations which have been observed in CoCl2·2H2O at liquid helium temperatures is reviewed. Using the far infrared laser lines of HCN and DCN, the authors measured the spin‐cluster resonance linewidths as a function of sample temperature and found excellent agreement to a simple exponential broadening law with a single characteristic energy independent of cluster size. It seems possible that the optic phonon which intersects the Ising “fan” of excitations is playing the dominant role in the relaxation mechanism giving rise to the T‐dependent energy widths.