Determination of solvation layer thickness by a magnetophotonic approach.
ABSTRACT Derjaguin-Landau-Verwey-Overbeek (DLVO) theory fails in explaining the superior stability of colloid particles in aqueous suspensions under conditions of high ionic strengths where electrostatic forces are effectively screened. Accumulating evidence shows that the formation of a thin rigid layer of solvent molecules in the vicinity of a colloidal particle surface provides an additional repulsive interaction when the interparticle distance is reduced to several nanometers. The effective determination of the thickness of the solvation layer however remains a challenge. Here, we demonstrate a simple yet powerful magnetophotonic technique that can be used to study the thickness of the solvation layers formed on the colloidal silica surface in various polar solvents. A relationship between the hydrogen-bonding ability of the solvents and the thickness of solvation layer on colloidal silica surfaces has been identified; this observation is found to be consistent with the previously proposed hydrogen-bonding origin of the solvation force.
- SourceAvailable from: Jianguo Guan[Show abstract] [Hide abstract]
ABSTRACT: The first steric-repulsion-based magnetically responsive photonic crystals (MRPCs) is constructed by synthesizing uniform superparamagnetic polyvinylpyrrolidone-coated Fe3 O4 colloidal nanocrystal clusters. The color tunable range of the MRPCs can not only cover almost the entire visible specztrum in solvents of diverse polarities, but also is insusceptible to ionic strength or pH values, facilitating the practical applications of MRPCs.Advanced Materials 02/2014; 26(7):1058-1064. · 15.41 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Understanding nanoparticle diffusion within non-Newtonian biological and synthetic fluids is essential in designing novel formulations (e.g. nanomedicines for drug delivery, shampoos, lotions, coatings, paints, etc.), but is presently poorly defined. This study reports the diffusion of thiolated and PEGylated silica nanoparticles, characterized by small angle neutron scattering, in solutions of various water-soluble polymers such as poly(acrylic acid) (PAA), poly(N-vinyl pyrrolidone) (PVP), poly(ethylene oxide) (PEO) and hydroxyethylcellulose (HEC), probed using NanoSight nanoparticle tracking analysis. Results show that the diffusivity of nanoparticles is affected by their dimensions, medium viscosity and in particular by specific interactions between nanoparticles and the macromolecules in solution; strong attractive interactions such as hydrogen bonding hamper diffusion. The water-soluble polymers retarded diffusion of thiolated particles in the order: PEO > PVP > PAA > HEC whereas for PEGylated silica particles retardation was in the order: PAA > PVP = HEC > PEO. In the absence of specific interactions with the medium, PEGylated nanoparticles exhibit enhanced mobility compared to their thiolated counterparts despite some increase in their dimensions.Langmuir 12/2013; · 4.38 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Nano-tribological properties of surface-adsorbed, brush-like copolymers of poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) and poly(L-lysine)-graft-dextran (PLL-g-dextran) have been investigated in aqueous viscous solvent mixtures by means of colloid-probe lateral force microscopy. Lateral forces for PEG/dextran brushes have been measured as a function of shear velocity in aqueous mixtures of glycerol and ethylene glycol (EG), which are highly miscible with water, but are poor solvents for hydrophilic PEG and dextran chains. Prior to the friction measurements on polymer brushes, a nano-scale Stribeck curve was obtained on a bare silica surface in the selected aqueous co-solvent mixtures. The Stribeck curve for bare surfaces indicates the existence of a surface-solvating thin film due to the adsorption of hydrated ions, preventing direct silica-silica contact in the boundary-lubrication regime. A clear transition to the hydrodynamic regime could be seen at high speeds for solvents with higher viscosities. The polymer brushes, however, show a shear-thinning effect with increasing shear speed and a combined influence of polymer film and solvent viscosity on the measured friction forces. The formation of an interfacial fluid-film is shown to shift the hydrodynamic regime of hydrated brushes to a lower value of Uη. The correlation between the structural configuration and the corresponding frictional properties of the polymer brushes upon changing solvent quality is discussed.Langmuir 07/2013; · 4.38 Impact Factor