Light‐Induced Surface Modification of Natural Plant Microparticles: Toward Colloidal Science and Cellular Adhesion Applications

Playing an instrumental role in the life of plants, pollen microparticles are one of the most fascinating biological materials in existence, with abundant and renewable supply, ultrahigh durability, and unique, species‐specific architectural features. Aside from their biological role, pollen microparticles also demonstrate broad utility as functional materials for drug delivery and microencapsulation, and increasingly for emulsion‐type applications. As natural pollen microparticles are predominantly hydrophobic, developing robust surface functionalization strategies to increase surface hydrophilicity would increase the range of colloidal science applications, including opening the door to interfacing microparticles with biological cells. This research investigates the extraction and light‐induced surface modification of discrete pollen microparticles from bee‐collected pollen granules toward achieving functional control over the responses elicited from discrete particles in colloidal science and cellular applications. Ultraviolet–ozone treatment is shown to increase the proportion of surface elemental oxygen and ketones, leading to increased surface hydrophilicity, enhanced particle dispersibility, tunable control over Pickering emulsion characteristics, and enhanced cellular adhesion. In summary, the findings demonstrate that light‐induced surface modification improves the functional properties of pollen microparticles, and such insights also have broad implications across materials science and environmental science applications.     

The carbonization of colloidal polyaniline nanoparticles to nitrogen‐containing carbon analogues

The carbonization of nanostructures afforded by conducting polymers represents a new route to the preparation of functional nanostructured carbons. The exposure of colloidal polyaniline particles stabilized with poly(N‐vinylpyrrolidone) or silica nanoparticles at 650 °C in inert atmosphere led, in both cases, to nitrogen‐containing carbonaceous materials with specific surface areas of 200 and 205 m² g^?1, respectively, and conductivities of 8.3 × 10^?7 and 1.9 × 10^?10 S cm^?1, respectively. The latter material contained 77 wt% of silica. The original particulate nanostructure of the samples was preserved after carbonization. The carbon‐to‐nitrogen atomic ratio was 7.2 and 7.9; the nitrogen content in the carbonized polyaniline–poly(N‐vinylpyrrolidone) particles was 10.8 wt%. Thermogravimetric analysis in air revealed their stability to be up to 500 °C. This is comparable with commercial multi‐wall carbon nanotubes, which have similar areas of application. The nitrogen‐containing carbons are potentially useful as supports for catalysts and in applications where carbon of higher hydrophilicity would be of benefit. Copyright © 2010 Society of Chemical Industry     

Layered double hydroxide platelets exfoliation into a water‐based polyester

Nitrate layered double hydroxide (LDH) phase Zn₂Al(OH)₆(NO₃)·2H₂O is successfully exfoliated in the presence of polyester under mild conditions using water as essential solvent and at room temperature under air. From small angle X‐ray scattering spectroscopy a total exfoliation is found to be achieved using up to 10 wt % LDH, while intercalated polymer nanocomposite structures largely extended up to 14 nm are observed for loading ranging from 10 to 20 wt %. The process is found to be explained by the diffusion of the polymer chain into the interlayer host structure. Starting from an initial value of 0.89 nm, ≈3, 7, 10, 14, and 20 nm transient interleaved nanostructures are formed without any carbonate uptake. The collective gap distance is certainly due to a defined number of polymer chains diffusing into the LDH interstices. Similarly, starting from an aqueous polyester solution highly concentrated in LDH nitrate phase up to 50% w.w, successive dilutions yield platelet exfoliation, thus rendering a smooth chemistry process attractive for potential applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Better Sintering through Green-State Deformation Processing

Aqueous colloidal suspensions of alumina were processed in the dispersed state and the flocculated state by controlling the double-layer interactions between the particles. Repulsive particle forces led to high packing densities but the green bodies were mechanically so weak that they were unable to retain their shape (the dispersed case). Attractive forces led to good green strength but the packing density was low and the particles were agglomerated (the flocculated case). The agglomerated structure of the flocced specimens could be fragmented by mechanical deformation of the green compact; the deformation was carried out under a superimposed hydrostatic pressure of less than 1 MPa. The flow stess of the flocculated structures depended on the deformation rate, and on the magnitude of the superimposed hydrostatic pressure. The flow stress was 2.5 kPa at a strain rate of 0.1 s⁻¹. Deformation processing of the flocced structures increased the green (relative) density from 0.51 to 0.62. The sintering behavior of underformed and deformation-processed flocced structures was studied. Deformation-processed green bodies sintered more rapidly and yielded a final grain size that was smaller and more uniform than that obtained from the undeformed specimens. The ability to homogenize and densify the packing of flocculated structures by deformation processing suggests new opportunities in green-state processing, for example (i) uniform mixing of more than one kind of particle or particles and fibers, and (ii) net shape forming by injection molding or extrusion, without the use of organic binders.     

Effects of pH and temperature on the sorption of sodium dodecyl sulfate by cellulose acetate/polyaniline blend membranes

Cellulose acetate/polyaniline (PANi) blends show a selective response to the presence of sodium dodecyl sulfate (SDS). Such detection can be monitored by visible absorption spectroscopy. In this article, we show how this is dependent on the pH and temperature. At pH 2, the redshift of the maximum absorbance wavelength of blend films is essentially dependent on hydrochloric acid; however, at pH 3, this effect clearly decreases, and at pH values between 4 and 6, the alteration of the blend color depends only on SDS. The selective detection of SDS is faster with a higher percentage of PANi in the blend. At 25°C, the mechanism of sorption is essentially Fickian for short times, but this changes at higher temperatures, and at temperatures of 40°C and higher, the sorption kinetics show an initial time lag in which no visible response from the blend to SDS is detected. The response rate of blends to SDS detection increases with the temperature and PANi content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The Ultrafiltration of Very Dilute Colloidal Gold Suspensions

The ultrafiltration behaviour of very dilute colloidal suspensions has been investigated in terms of transmembrane pressure and pH in a batch cell with and without stirring using PM30 and SKIP membranes.For small (10 nm) colloidal gold particles the unstirred flux was higher than the stirred. An increase in concentration polarization due to the lack of stirring shields the electrostatic repulsion between particles, resulting in aggregation of particles that are retained at the membrane surface. This loosely packed layer can be responsible for the higher flux in the unstirred condition. For large (50 nm) gold particles, greater flux was achieved in stirred condition due to the decrease in concentration polarization.While the SKIP membranes showed a complete retention for larger colloidal gold particles, for smaller particles the retention was complete after around 1 minute. The PM30 membrane completely retained colloidal gold particles of both sizes.Lower flux with higher flux decline was obtained for the smaller colloidal gold particles compared to the larger ones. The cross section micrographs show that the larger sol forms a less densely packed deposit layer on the membrane surface. Changing the pH of the colloidal gold suspension resulted in a substantial change to the flux and retention. However the level of local ionic concentration at the membrane surface appears to be of utmost importance as it affects the degree of colloidal aggregation and packing of the deposit layer, thus influencing flux and retention.Analysis of the filtration data coupled with electron microscopy showed that cake filtration was the dominant mechanism during the course of ultrafiltration as well as microfiltration of very dilute colloidal gold suspensions.     

Synthesis and characterization of PNIPAM/PS core/shell particles

Crosslinked, monodisperse PNIPAM particles were synthesized by precipitation polymerization. The particle size was measured by dynamic light scattering (DLS), capillary hydrodynamic fractionation (CHDF), and transmission electron microscopy (TEM). Two different polymerization methods were used to prepare PNIPAM/PS core/shell particles, both above and below the volume phase transition temperature (VPPT) using either a semibatch or seeded semibatch polymerization process. In both processes, uniform “raspberry” structures were obtained in which polystyrene formed small domains on the surface of the PNIPAM particles. The resulting core and shell structure was confirmed by temperature‐dependent particle size and density gradient experiments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010