Quantitative imaging of concentrated suspensions under flow

We review recent advances in imaging the flow of concentrated suspensions, focussing on the use of confocal microscopy to obtain time-resolved information on the single-particle level in these systems. After motivating the need for quantitative (confocal) imaging in suspension rheology, we briefly describe the particles, sample environments, microscopy tools and analysis algorithms needed to perform this kind of experiments. The second part of the review focusses on microscopic aspects of the flow of concentrated model hard-sphere-like suspensions, and the relation to non-linear rheological phenomena such as yielding, shear localization, wall slip and shear-induced ordering. Both Brownian and non-Brownian systems will be described. We show how quantitative imaging can improve our understanding of the connection between microscopic dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of methodology. Submitted for special volume 'High Solid Dispersions' ed. M. Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009); 22 pages, 16 fig

Improved particle size control for the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide

Dispersion polymerization is a well-established method of producing polymer particles that are easily handled and processed. With careful choice of reaction conditions this technique can yield well defined, spherical particles for a wide range of applications. The use of supercritical carbon dioxide (scCO2) as a reaction medium offers a route to performing these syntheses without excessive use of volatile organic solvents and minimizes work-up and disposal steps. However a significant drawback has been the fact that up till now the control of particle size and morphology from CO2 have been limited. This study presents control of particle size and morphology over an unprecedented range for a single stabilizer in scCO2 by coordinating a few simple parameters to tailor the conditions toward different sizes. Further, this study introduces the novel approach in scCO2 of using delayed monomer addition which allows considerable reduction of the batch-to-batch variability as well as reduced agglomeration between particles

The internal structure of poly(methyl methacrylate) latexes in nonpolar solvents

Hypothesis: Poly(methyl methacrylate) (PMMA) latexes in nonpolar solvents are an excellent model system to understand phenomena in low dielectric media, and understanding their internal structure is critical to characterizing their performance in both fundamental studies of colloidal interactions and in potential industrial applications. Both the PMMA cores and the poly(12-hydroxystearic acid) (PHSA) shells of the latexes are known to be penetrable by solvent and small molecules, but the relevance of this for the properties of these particles is unknown. Experiments: These particles can be prepared in a broad range of sizes, and two PMMA latexes dispersed in n-dodecane (76 and 685 nm in diameter) were studied using techniques appropriate to their size. Small-angle scattering (using both neutrons and X-rays) was used to study the small latexes, and analytical centrifugation was used to study the large latexes. These studies enabled the calculation of the core densities and the amount of solvent in the stabilizer shells for both latexes. Both have consequences on interpreting measurements using these latexes. Findings: The PHSA shells are highly solvated (∼85% solvent by volume), as expected for effective steric stabilizers. However, the PHSA chains do contribute to the intensity of neutron scattering measurements on concentrated dispersions and cannot be ignored. The PMMA cores have a slightly lower density than PMMA homopolymer, which shows that only a small free volume is required to allow small molecules to penetrate into the cores. Interestingly, the observations are essentially the same, regardless of the size of the particle; these are general features of these polymer latexes. Despite the latexes being used as a model physical system, the internal chemical structure is complex and must be fully considered when characterizing them

Riboflavin Ameliorates Cisplatin Induced Toxicities under Photoillumination

BACKGROUND: Cisplatin is an effective anticancer drug that elicits many side effects mainly due to induction of oxidative and nitrosative stresses during prolonged chemotherapy. The severity of these side effects consequently restricts its clinical use under long term treatment. Riboflavin is an essential vitamin used in various metabolic redox reactions in the form of flavin adenine dinucleotide and flavin mononucleotide. Besides, it has excellent photosensitizing property that can be used to ameliorate these toxicities in mice under photodynamic therapy. METHODS AND FINDINGS: Riboflavin, cisplatin and their combinations were given to the separate groups of mice under photoilluminated condition under specific treatment regime. Their kidney and liver were excised for comet assay and histopathological studies. Furthermore, Fourier Transform Infrared Spectroscopy of riboflavin-cisplatin combination in vitro was also conducted to investigate any possible interaction between the two compounds. Their comet assay and histopathological examination revealed that riboflavin in combination with cisplatin was able to protect the tissues from cisplatin induced toxicities and damages. Moreover, Fourier Transform Infrared Spectroscopy analysis of the combination indicated a strong molecular interaction among their constituent groups that may be assigned for the protective effect of the combination in the treated animals. CONCLUSION: Inclusion of riboflavin diminishes cisplatin induced toxicities which may possibly make the cisplatin-riboflavin combination, an effective treatment strategy under chemoradiotherapy in pronouncing its antineoplastic activity and sensitivity towards the cancer cells as compared to cisplatin alone

Contrast variation with temperature in light scattering for silica particles in diluted solutions

The contrast variation technique by varying the temperature is applied to a light scattering study of a colloidal dispersion of sphericals silica particles in cyclohexane. It is found that a refractive index variation occurs in the particle and the refractive index at the periphery is higher than at the center of the particle. The inhomogeneity parameter E has a value of 26 nm2

Rapid coagulation of polystyrene latex in a stopped-flow spectrophotometer

With a stopped-flow method the rapid coagulation by electrolyte of several polystyrene latices is measured. By extrapolating back to zero time the initial process of two single particles forming a doublet is observed. We find an average rate constant ifk11 = 6.0 × 10−12 p−1 cm3 sec su−1 at 20°C, where p is the number of particles; this constant is lowered to 4.9 × 10−12 p−1 cm3 sec−1 when we assume that the particle diameters are 5% lower than the Dow values. These values are equal to 56 and 46%, respectively, of the von Smoluchowski values. Using the theory of hydrodynamic interaction, this gives Hamaker constants A = 7.0 × 10−21J or 1.5 × 10−21 J, respectively, in good agreement with theoretical predictions

Preparation of polymethylmethacrylate latices in non-polar media

The dispersion polymerization of methylmethacrylate stabilized by poly(12- hydroxy-stearic acid) in hydrocarbon media has been investigated. Unlike earlier results [7] it was found that stable latex particles can be prepared in the initial monomer concentration range 8.5 % to 34 %. To obtain stable particles varying amounts of stabilizer were used

Preparation and properties of dispersions of colloidal boehmite rods

Dispersions of colloidal boehmite (y-AlOOH) rods (of controllable length) are prepared from alkoxide precursors. A polyisobutene grafting procedure leads to sterically stabilized dispersions. In the organophilic system (L ~ 200 nm ± 50%; D ~ 10 nm ± 25%) an isotropic-nematic phase separation is observed for boehmite volume fractions between 3.8% and 14.6%. The effect of polydispersity on the phase diagram is well predicted qualitatively by Onsager's theory extended to bidisperse mixtures