Static Light-scattering Measurements Research Articles

Measuring dn/dc for Polysaccharide Microgels of Varying Crosslinking Density

Static light scattering (SLS) is a powerful, noninvasive experimental method that yields the molecular weight (average molecular weight, Mw), the size (radius of gyration, Rg), and the interactions between the scatters (the second virial coefficient, A2). However, proper SLS measurements require determination of the specific refractive index increment (dn/dc) for the samples studied. While tables of dn/dc values are available for various substances, they are not generally available for microgel particles, which in our case are crosslinked chains of an amphiphilic polymer. This paper is focused on measuring dn/dc for microgel samples of varying crosslinking concentrations. Microgel dn/dc values were found to be different from the value of the parent polymer given in literature and found to have a temperature dependence as well as a crosslinker concentration dependence at higher crosslinker concentrations. Using the measured values of microgel dn/dc instead of tabulated parent polymer values on estimates of microgel Mw, Rg, and A2 highlights the importance of direct dn/dc measurements for samples studied by SLS.

A Novel In Silico Monte Carlo Approach to Optimize a PSD Estimation Problem. Generation of Data Fusion Experiment Rules

This article analyzes the performance of combining information from Scanning Electron Microscopy (SEM) micrographs with Static Light Scattering (SLS) measurements for retrieving the so-called Particle Size Distribution (PSD) in terms of experimental features. The corresponding data fusion is implemented using a novel Monte Carlo-based method consisting in a SMF (Sampling-Mapping-Filtering) approach. This approach provides an important reference to assess the strategy of the experiment for this specific problem by means of solving an inverse problem. Furthermore, low levels of volume fraction and a PSD represented by log-normal distributions are considered in order to reduce processing and model errors due to ill-posedness. The prior statistics corresponding to the SEM micrographs have been achieved by means of the Jackknife procedure used as a resampling technique. The likelihood term considers iid normal measurements generated from the Local Monodisperse Approximation (LMA) and also makes use of the same model as forward linear model, in an inversion case known as inverse crime. However, it has been proved that the LMA performs well in practice for low fraction volume systems as considered here. The PSD retrieval is measured in terms of improvement in precision with respect to one of the log-normal parameters in SEM micrographs, i.e., the desirability. Estimates are expressed as a function of a typical system parameter such as polydispersity, as well as experimental variables, i.e., number of particles per micrograph (PPM) and noise level $\varepsilon$ in the SLS measurements. These estimations are then analyzed by means of the Box-Behnken (BB) design and the response surface methodology (RSM) in order to generate a surrogate model from which rules for the optimization of the experiment are made when desirability is maximized. Finally, a Rule-Based System (RBS) is proposed for future use.

Evidence of Long Two-Dimensional Folding Chain Structure Formation of Poly(vinylidene fluoride) in N-Methylpyrrolidone Solution: Total Form Factor Determination by Combining Multiscattering Data.

Very recently, we proposed that poly(vinylidene fluoride) (PVDF) dissolves in a long rectangular column conformation induced by the formation of a two-dimensional folding chain structure in an N-methylpyrrolidone (NMP) solution based on the results obtained from static light scattering (SLS), small- to wide-angle X-ray scattering (S-WAXS), and viscometric experiments. Small- to wide-angle neutron scattering (S-WANS) experiments were able to provide clear decisive evidence for the presence of such a two-dimensional folding chain structure in a deuterated (d)NMP solution of PVDF samples with two different weight average molar masses (Mw) of 100 and 1200 kg mol–1, even under dilute conditions at concentrations less than the overlapping concentrations due to the quite high neutron scattering contrast obtained by using (d)NMP as a solvent. An increase in Mw from 100 to 1200 kg mol–1 substantially increases the particle length and width from L = 80 to 350 nm and w2 = 5.0 to 15 nm, respectively, while the thickness, w1, is maintained at 0.3 nm. Since L is much longer than w2 irrespective of Mw, the particles formed by PVDF molecules in NMP simply behave as long rigid rods in a scattering vector (q) range covered by SLS measurements. A combination study of S-WANS and S-WAXS experiments covering a higher q range with the SLS techniques could clearly reveal increases in both the L and w2 values with increasing Mw.

PH-Responsive Association Behavior of Biocompatible Random Copolymers Containing Pendent Phosphorylcholine and Fatty Acid.

Well-defined pH-responsive biocompatible random copolymers composed of 2-(methacryloyloxy)ethyl phosphorylcholine and varying quantities of sodium 11-(acrylamido)undecanoate (AaU) (fAaU = 0-58 mol %) were synthesized via reversible addition-fragmentation chain transfer radical polymerization. The pH-responsive association and dissociation behavior of the random copolymers was studied via turbidity, 1H nuclear magnetic resonance relaxation time, dynamic light scattering, static light scattering (SLS), and fluorescence measurements. At basic pH levels, the random copolymers dissolved in water in a unimer state because the AaU units behaved in a hydrophilic manner as a result of the ionization of the pendent fatty acids. The random copolymers with fAaU < 52 mol % associated intramolecularly within a single polymer chain to form unimer micelles at pH 3 because of the protonation of the pendent fatty acids. On the other hand, the random copolymer with fAaU ≥ 52 mol % formed intermolecular aggregates composed of four polymer chains at pH 3, as established by the SLS measurements. The random copolymers displayed the ability to solubilize hydrophobic guest molecules, such as N-phenyl-1-naphthylamine, into the hydrophobic microdomain formed by the pendent dehydrated fatty acids at acidic pHs. At pH 4, 1-pyrememethanol is captured by the random copolymer with fAaU = 52 mol %, and it is released from the random copolymer above pH 9. Furthermore, the mucoadhesive properties of the random copolymer with fAaU = 9 mol % were studied using a surface plasmon resonance technique. The copolymer was adsorbed onto mucin at pH 3; however, the adsorption decreased at pH 7.4.

Temperature Dependence of the Rayleigh Ratio for Toluene: Thermoresponsive Polymers Characterization

AbstractBenzene and toluene are commonly used reference substances for static light scattering (SLS) measurements. However, due to the appearance and wide availability of solid‐state lasers with various wavelengths, there is a need for data on the Rayleigh ratios for references at various wavelengths. Thermoresponsive polymers, which are widely researched now, can have lower critical solution temperature (LCST) values very close to the human body temperature (30–36 °C). Such polymers can be used to develop efficient means for targeted drug delivery. In this paper, we report how to accurately determine the absolute molecular weights of thermoresponsive polymers by the SLS method. This is especially important when the LCST value of a polymer is close to the room temperature (at which SLS measurements are usually taken), which can lead to overestimated results due to the aggregation of macromolecules. So, it is necessary to carefully select the measurement temperature and, accordingly, data are needed on the temperature dependence of the Rayleigh ratios for a reference sample. The Rayleigh ratios and depolarization factors, ρu and ρv, were first determined for toluene within a wide temperature range (10–50 °C). The temperature dependencies of these parameters were shown to be linear in the whole range investigated. Temperature coefficients for the calculation of the Rayleigh ratios at different scattering geometries were obtained. The particular importance of choosing the optimal measurement temperature when determining the molecular weights of thermoresponsive polymers with low values of LCST using the static light scattering method was demonstrated.

PH- and thermo-responsive behavior of PNIPAM star containing terminal carboxy groups in aqueous solutions

In the present work, a core-crosslinked poly(N-isopropylacrylamide) (PNIPAM) star polymer with 17 polymer arms was prepared via reversible addition–fragmentation chain transfer (RAFT) radical polymerization. Here, the outer chain end of the PNIPAM arm contained a carboxy group. The pH- and thermo-responsive aggregation behavior of this polymer was studied in aqueous solutions using UV–Vis spectrophotometry, dynamic light scattering, static light scattering (SLS), and transmission electron microscopy (TEM) techniques. By comparing the light scattering intensities of the aggregate and unimer states, the aggregation number was estimated at various pH values below and above the phase transition temperature (Tp); these findings were supported by SLS and TEM measurements. Below the Tp, two star polymer molecules aggregated due to the presence of hydrophobic interactions at pH 4. The star polymer molecule existed as a unimer at pH 5. The arm chains in the unimer state star polymer expanded at pH 10. Above the Tp, the PNIPAM stars were densely aggregated with about 57 polymers at pH 4, whereas six polymers were loosely aggregated at pH 5, and the unimer state polymer shrank at pH 10. This study is useful for understanding the aggregation behavior of stimuli-responsive star polymers.

Cyclophosphazene microgels with adjustable number of crosslinks and deformability by precipitation polycondensation of mono- and bifunctional amines with hexachlorocyclotriphosphazene

Starting from hexachlorocyclotriphosphazene (HCCTP), hexamethylenediamine (HMDA) and 2-dimethylaminoethylamine (DMEN) novel amino-functional cyclomatrix-type poly(organophosphazene) microgels with tunable amount of cross-links were synthesized via precipitation polycondensation in acetonitrile. The synthesis is carried out as a facile one-pot approach in which the microgels' cross-linking density is directly adjusted through the concentration of DMEN acting as reactive diluent. In addition, the influence of different concentrations of DMEN on the cross-linking density of poly(HCCTP-HMDA-DMEN) microgels is investigated through corresponding changes of the microgels' size, degree of swelling, form factor and deformability. To this end, microgels prepared with different ratios of DMEN are thoroughly characterized by means of FTIR spectroscopy, dynamic light scattering (DLS), static light scattering (SLS) and microscopy (FESEM and AFM). The obtained microgels are uniform in size and exhibit high degrees of swelling in water. Our study clearly shows that the microgels' cross-linking density gradually decreases with an increasing concentration of the reactive diluent DMEN. This direct correlation is particularly verified via side-view FESEM micrographs and AFM cross-section profiles, which both reveal an increasing deformability of the microgels with the concentration of DMEN. Results from DLS and SLS measurements support these findings as they reveal an increase of the microgels’ size and degree of swelling, while the form factor (ρ = Rg/Rh) shows a gradual decrease with increasing DMEN concentration. To our knowledge, this study demonstrates for the first time a facile one pot approach for the synthesis of a new class of cyclomatrix-type poly(organophosphazene) microgels with tunable crosslink density providing a functional colloidal toolbox for different applications. © 2001 Elsevier Science. All rights reserved.

Determination of the Rayleigh Ratio with an Uncertainty Analysis by Static Light-Scattering Measurements of Certified Reference Materials for Molecular Weight.

The most important parameter for light-scattering measurements in the Rayleigh scattering region is the Rayleigh ratio, which is necessary to obtain the absolute scattered light intensity from the relative scattered light intensity. The absolute scattered light intensity is directly related to the molar masses of polymers, colloids, biomolecules, and the like. A new Rayleigh ratio was determined by measuring static light scattering from certified reference materials with highly accurate certified values of the molecular weight determined by several other techniques, such as MALDI-TOF mass spectrometry or size-exclusion chromatography. The new Rayleigh ratio can be used for evaluating the uncertainty of the molecular weight of polymers and macromolecules, as measured by light scattering.

Self-Interaction of Human Serum Albumin: A Formulation Perspective.

In the present study, small-angle X-ray scattering (SAXS) and static light scattering (SLS) have been used to study the solution properties and self-interaction of recombinant human serum albumin (rHSA) molecules in three pharmaceutically relevant buffer systems. Measurements are carried out up to high protein concentrations and as a function of ionic strength by adding sodium chloride to probe the role of electrostatic interactions. The effective structure factors (Seff) as a function of the scattering vector magnitude q have been extracted from the scattering profiles and fit to the solution of the Ornstein–Zernike equation using a screened Yukawa potential to describe the double-layer force. Although only a limited q range is used, accurate fits required including an electrostatic repulsion element in the model at low ionic strength, while only a hard sphere model with a tunable diameter is necessary for fitting to high-ionic-strength data. The fit values of net charge agree with available data from potentiometric titrations. Osmotic compressibility data obtained by extrapolating the SAXS profiles or directly from SLS measurements has been fit to a 10-term virial expansion for hard spheres and an equation of state for hard biaxial ellipsoids. We show that modeling rHSA as an ellipsoid, rather than a sphere, provides a much more accurate fit for the thermodynamic data over the entire concentration range. Osmotic virial coefficient data, derived at low protein concentration, can be used to parameterize the model for predicting the behavior up to concentrations as high as 450 g/L. The findings are especially important for the biopharmaceutical sector, which require approaches for predicting concentrated protein solution behavior using minimal sample consumption.

Assembly Kinetics of Vimentin Tetramers to Unit-Length Filaments: A Stopped-Flow Study

Intermediate filaments (IFs) are principal components of the cytoskeleton, a dynamic integrated system of structural proteins that provides the functional architecture of metazoan cells. They are major contributors to the elasticity of cells and tissues due to their high mechanical stability and intrinsic flexibility. The basic building block for the assembly of IFs is a rod-like, 60-nm-long tetrameric complex made from two antiparallel, half-staggered coiled coils. In low ionic strength, tetramers form stable complexes that rapidly assemble into filaments upon raising the ionic strength. The first assembly products, “frozen” by instantaneous chemical fixation and viewed by electron microscopy, are 60-nm-long “unit-length” filaments (ULFs) that apparently form by lateral in-register association of tetramers. ULFs are the active elements of IF growth, undergoing longitudinal end-to-end annealing with one another and with growing filaments. Originally, we have employed quantitative time-lapse atomic force and electron microscopy to analyze the kinetics of vimentin-filament assembly starting from a few seconds to several hours. To obtain detailed quantitative insight into the productive reactions that drive ULF formation, we now introduce a “stopped-flow” approach in combination with static light-scattering measurements. Thereby, we determine the basic rate constants for lateral assembly of tetramers to ULFs. Processing of the recorded data by a global fitting procedure enables us to describe the hierarchical steps of IF formation. Specifically, we propose that tetramers are consumed within milliseconds to yield octamers that are obligatory intermediates toward ULF formation. Although the interaction of tetramers is diffusion controlled, it is strongly driven by their geometry to mediate effective subunit targeting. Importantly, our model conclusively reflects the previously described occurrence of polymorphic ULF and mature filaments in terms of their number of tetramers per cross section.

Physicochemical Characteristics of Chitosan–TiO2 Biomaterial. 1. Stability and Swelling Properties

The surface and electrokinetic properties of chitosan–TiO2 biomaterial have been investigated. Both carbohydrate polymer and titanium dioxide demonstrate unique physicochemical properties appropriate for biotechnological applications. However, the changing stability of such systems restricts its usage. Improved stability can be controlled by environmental parameters, process conditions, or modifying TiO2 structure. Antibacterial chitosan was used because its protective barrier can retard ripening, water loss, as well as destruction of products. The concentrations of compounds and solution pH were varied. Static and dynamic light-scattering measurements make evident the relationship between the state of aggregation of the suspensions and the stability. The chitosan–TiO2 system is characterized by improved physicochemical properties in comparison with base TiO2 as an effect of electrosteric stability. Stable material was obtained with the precisely selected compounds ratio, proved by Fourier transform infra...

Green-to-Red Electrochromic Fe(II) Metallo-Supramolecular Polyelectrolytes Self-Assembled from Fluorescent 2,6-Bis(2-pyridyl)pyrimidine Bithiophene.

The structure and properties of metallo-supramolecular polyelectrolytes (MEPEs) self-assembled from rigid 2,6-bis(2-pyridyl)pyrimidine and the metal ions FeII and CoII are presented. While FeL1-MEPE (L1 = 1,4-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]benzene) is deep blue, FeL2- and CoL2-MEPE (L2 = 5,5'-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]-2,2'-bithiophene) are intense green and red in color, respectively. These novel MEPEs display a high extinction coefficient and solvatochromism. Ligand L2 shows a high absolute fluorescence quantum yield (Φf = 82%). Viscosity and static light-scattering measurements reveal that the molar masses of these MEPEs are in the range of 1 × 108 g/mol under the current experimental conditions. In water, FeL1-MEPE forms a viscous gel at 20 °C (c = 8 mM). Thin films of high optical quality are fabricated by dip coating on transparent conducting indium tin oxide (ITO) glass substrate. Optical, electrochemical, and electrochromic properties of the obtained MEPEs are presented. Green to red and blue to colorless electrochromism is observed for FeL2-MEPE and FeL1-MEPE, respectively. The results show that the electrochromic properties are affected by the ligand topology. The Fe-MEPEs show a reversible redox behavior of the FeII/FeIII couple at 0.86 and 0.82 V versus Fc+/Fc and display an excellent redox cycle stability under switching conditions. FeL2-MEPE in its oxidized state exhibits a broad absorption band covering the near-IR region (ca. 1500 nm) due to the ligand-to-metal charge transfer transition originating due to charge delocalization in the bithiophene spacer.

Bayesian approach to the inverse problem in a light scattering application

In this article, static light scattering (SLS) measurements are processed to estimate the particle size distribution of particle systems incorporating prior information obtained from an alternative experimental technique: scanning electron microscopy (SEM). For this purpose we propose two Bayesian schemes (one parametric and another non-parametric) to solve the stated light scattering problem and take advantage of the obtained results to summarize some features of the Bayesian approach within the context of inverse problems. The features presented in this article include the improvement of the results when some useful prior information from an alternative experiment is considered instead of a non-informative prior as it occurs in a deterministic maximum likelihood estimation. This improvement will be shown in terms of accuracy and precision in the corresponding results and also in terms of minimizing the effect of multiple minima by including significant information in the optimization. Both Bayesian schemes are implemented using Markov Chain Monte Carlo methods. They have been developed on the basis of the Metropolis–Hastings (MH) algorithm using Matlab® and are tested with the analysis of simulated and experimental examples of concentrated and semi-concentrated particles. In the simulated examples, SLS measurements were generated using a rigorous model, while the inversion stage was solved using an approximate model in both schemes and also using the rigorous model in the parametric scheme. Priors from SEM micrographs were also simulated and experimented, where the simulated ones were obtained using a Monte Carlo routine. In addition to the presentation of these features of the Bayesian approach, some other topics will be discussed, such as regularization and some implementation issues of the proposed schemes, among which we remark the selection of the parameters used in the MH algorithm.

Effect of end-group modification, hydrophilic/hydrophobic block ratio and temperature on the surface, associative and thermodynamic behaviour of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers in aqueous media

This study describes the surface, micellar, associative and thermodynamic properties of four diblock oxyethylene (E)/oxybutylene (B) copolymers with different hydrophilic block ends and various hydrophilic/hydrophobic ratios in aqueous media. The copolymers were denoted DE40B18, TE40B18, E56B19 and E56B7. The aqueous polymer solutions at various concentrations and temperatures were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements were employed to detect the critical micelle concentration (CMC) as well as to calculate the surface-active and thermodynamic parameters of adsorption at the air/water interface. CMC values were also used to calculate the enthalpy of micellization (∆H0mic), free energy of micellization (∆G0mic) and entropy of micellization (∆S0mic). Similarly, various thermodynamic parameters for adsorption at the air/water interface were also deduced. Dynamic light scattering (DLS) was used to obtain the hydrodynamic radii (rh) and volumes (υh) of the micelle at different temperatures, and hence the hydrodynamic expansion parameter (δh) was also estimated. Likewise, static light-scattering measurements enabled us to determine various parameters of the copolymer micelles, such as the weight-average molar mass (Mw), association number (Nw), thermodynamic radius (rt), thermodynamic volume (υt), anhydrous volume (υa) and the thermodynamic expansion parameter (δt). Various thermodynamic and micellar parameters obtained from light scattering show that the micelles formed are spherical in shape and have rather soft interaction potentials at low temperature but become harder at higher temperature. Based on the different experimental results obtained, it can be said that various surface, micellar and thermodynamic parameters are dependent not only on the temperature and solution conditions but also on the hydrophobic/hydrophilic ratio and the end-group composition of the polymer. Modification of the hydrophilic end group of the polymer prominently affects various micellar properties. This effect can be assigned to the difference in polarity and the intermicellar charge effect.

New studies on gum ghatti (Anogeissus latifolia) part 5: The conformational properties of gum ghatti

The conformational properties of gum ghatti and its fractions were investigated using high performance size exclusion chromatography (HPSEC) coupled with multiple detectors, static light scattering (SLS) and dynamic light scattering (DLS) methods. The measured Mark–Houwink equation parameters α (0.5 < α < 0.8) indicated a random coil conformation of four fractions: F50 was more rigid than the other fractions, whereas F65 exhibited a loosely extended chain that is close to a spherical conformation. DLS and SLS measurements in aggregate free (0.5 M NaOH) solution further confirmed the conformational properties. The high positive A2 value of each fraction indicated that 0.5 M NaOH solution is a good solvent for gum ghatti. The values of Rg and Rh decreased with molecular weight in the order of F80, F65 and F50. The less branched fraction F50 (ρ = 1.694) has a random coil conformation in 0.5 M NaOH solution, whereas F65 and F80 exhibited random coil close to spherical conformation due to their highly branched structure.

Regulation of Acetate Kinase Isozymes and Its Importance for Mixed-Acid Fermentation in Lactococcus lactis

Acetate kinase (ACK) converts acetyl phosphate to acetate along with the generation of ATP in the pathway for mixed-acid fermentation in Lactococcus lactis. The reverse reaction yields acetyl phosphate for assimilation purposes. Remarkably, L. lactis has two ACK isozymes, and the corresponding genes are present in an operon. We purified both enzymes (AckA1 and AckA2) from L. lactis MG1363 and determined their oligomeric state, specific activities, and allosteric regulation. Both proteins form homodimeric complexes, as shown by size exclusion chromatography and static light-scattering measurements. The turnover number of AckA1 is about an order of magnitude higher than that of AckA2 for the reaction in either direction. The Km values for acetyl phosphate, ATP, and ADP are similar for both enzymes. However, AckA2 has a higher affinity for acetate than does AckA1, suggesting an important role under acetate-limiting conditions despite the lower activity. Fructose-1,6-bisphosphate, glyceraldehyde-3-phosphate, and phospho-enol-pyruvate inhibit the activities of AckA1 and AckA2 to different extents. The allosteric regulation of AckA1 and AckA2 and the pool sizes of the glycolytic intermediates are consistent with a switch from homolactic to mixed-acid fermentation upon slowing of the growth rate.

Accuracy of Protein Size Estimates Based on Light Scattering Measurements

There are two types of light scattering measurements: static light scattering (SLS) and dynamic light scattering (DLS). The SLS method is used to estimate the molecular weight (MW) of particles by measuring the time-averaged intensity of light scattered by the particles, whereas the DLS method is used to estimate the diffusion coefficient of particles by observing the time-correlation of scattered light intensity. These techniques have recently been applied to the investigation of the aggregation, denaturation and folding, and complex formation of proteins in solution. However, the accuracy of protein size measurement by light scattering is poorly understood. In the present study, we carried out the size measurements of five globular proteins by SLS and DLS at a detection angle of 90。 and compared these data to measurements made by size exclusion chromatography (SEC). The difference (%) between the MW estimated from each method and the MW calculated from the amino acid sequence (namely the calibration residual error) was regarded as an index of measurement accuracy. The averaged calibration residual errors were 5.2 and 4.7 for SEC and SLS measurements, respectively. For the DLS measurements, the extrapolation of the apparent hydrodynamic radii to a protein concentration of zero may effectively eliminate the interparticle and hydrodynamic interactions and significantly reduced the averaged calibration residual error to 4.8%. Our results suggested that the size of globular proteins can be estimated using light scattering measurements with an accuracy equivalent to that of SEC.

Light scattering and surface tensiometric studies of tip-modified PEO-PBO diblock copolymers in water

The micellar and associative properties of four diblock copolymers, Me2N(CH2)2OE79B34 (denoted DE80B34), I−Me3N+(CH2)2OE79B34 (denoted TE80B34), I−Me3N+(CH2)2OE48B22 (denoted TE49B22), and HO(CH2)2OE62B22 (denoted E62B22), in aqueous solution and at various concentrations and temperatures, were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements enabled the critical micelle concentration (CMC) to be determined at different temperatures, and thus the enthalpy of micellization (ΔHomic), the free energy of micellization (ΔGomic), and the entropy of micellization (ΔSomic) to be ascertained. Dynamic and static light-scattering measurements allowed the micellar parameters to be calculated and the extent of hydration of the copolymer micelle to be obtained qualitatively. The experimental results provided by these techniques are discussed in the terms of the variation in the hydrophilic to hydrophobic (E/B) ratio and end-group modification. Micellar parameters such as the weight-average molar mass (Mw), the association number (Nw), the thermodynamic radius (rt), and the hydrodynamic radius (rh) obtained from light-scattering data show that the micelles formed by the conventional EmBn and dimethylamino-tipped (DEmBn) copolymers are harder than those of trimethylammonium-tipped (TEmBn) copolymers. This difference in micellar properties is considered to be due to differences in polarity and charge effect at the hydrophilic ends of the tip-modified copolymers. The high value of rh for DEmBn and TEmBn copolymers as compared to E62B22 is an indication of micellar aggregation.

Electric field induced cloudy–clear transitions in micellar solutions of a block copolymeric amphiphile

We report observations of cloudy–clear transitions, triggered by electric fields, in micellar solutions of a poly(oxy ethylene/propylene)–poly(dimethylsiloxane) based triblock amphiphile dissolved in silicone oil (DC245). Initial studies showed complete clarification of a cloudy 2% solution at ambient temperature when subjected to a uniform electric field of ∼5 kV cm−1. Static Light Scattering measurements showed that the clarification was associated with a significant reduction in the size of the micellar aggregate from ca. 200 nm to 50 nm. Field strength studies at varying temperatures established the potency of the effect at 1 kV cm−1 field equivalent to a 1 K decrease in temperature. The observed effect was qualitatively different from the electric field induced macroscopic pattern formations, or self assembled domain rotations or mesogen alignment phenomena; and quantitatively far more impactful than the minor shifts in phase boundaries reported earlier. Although the mechanistic underpinning of the observed field effect has yet to be established, the optical switchability of the solutions could be exploited for various electro-optical applications such as displays, and optical filters. The work also opens up the possibilities of using electric fields for manipulating micellar solubilization or creating tunable templates for nano-material synthesis.

Crystal structure of thermosensitive gel spheres of poly(N-isopropylacrylamide) in the deionized aqueous suspension as studied by the static light-scattering measurements

Static light-scattering measurements of deionized suspensions of the thermosensitive gels of poly(N-isopropylacrylamide) with various degrees of cross-linking and sizes were made at 20 and 40 °C. Sharp scattering peaks are observed in the scattering curve, and they were attributed to the face-centered cubic (fcc) and/or body-centered cubic lattices (bcc) in the distribution of gel spheres. The fcc and bcc crystal structures formed in the stable and unstable conditions, respectively, i.e., the former formed more favorably at high sphere concentrations and/or low temperatures. The closest intersphere distances were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. These experimental results emphasize the important role of the extended electrical double layers in the crystallization of gel spheres, though the contribution of the double layers in gel systems is weak compared with that in the typical colloidal spheres.