Adsorption and Thermogravimetric Studies of Mesoporous Silica Coated with Siloxane Polymer

Adsorption Behaviour of Tween80 on Graphite

Techniques including thermogravimetry (TG), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were applied to characterize the adsorption behaviour of Tween80 on graphite. TG is a suitable method for determining the amount of Tween80 adsorbed since it is not restricted by the large amount of solvent adsorbed in this disperse system. The results indicate that TG may provide an alternative method for measuring the amount adsorbed in some disperse systems in which there are significant differences between the thermal behaviours of the adsorbate, adsorbent and solvent.

The adsorption isotherms of Tween80 were of the Langmuir type, with the adsorbed amount attaining a maximum value at temperatures between 30°C and 50°C. XPS and FT-IR measurements were used to provide detailed information about the functional group shift. In addition, AFM images indicated that the adsorption of Tween80 has a considerable influence on the topography of graphite, with the adsorbate being adsorbed preferentially on the step defect sites at the edge of the graphite crystal.

Synthesis of Polymer-Mesoporous Silica Nanocomposites

Polymer nanocomposites show unique properties combining the advantages of the inorganic nanofillers and the organic polymers. The mesoporous silica nanofillers have received much attention due to their ordered structure, high surface area and ease for functionalization of the nanopores. To accommodate macromolecules, the nanopores lead to unusually intimate interactions between the polymer and the inorganic phase, and some unusual properties can be observed, when compared with nonporous fillers. Whereas many review articles have been devoted to polymer/nonporous nanofiller nanocomposites, few review articles focus on polymer/mesoporous silica nanocomposites. This review summarizes the recent development in the methods for synthesizing polymer/mesoporous silica nanocomposites based on the papers published from 1998 to 2009, and some unique properties of these composites are also described.

Adsorption of organic molecules on silica surface

The adsorption behaviour of various organic adsorbates on silica surface is reviewed. Most of the structural information on silica is obtained from IR spectral data and from the characteristics of water present at the silica surface. Silica surface is generally embedded with hydroxy groups and ethereal linkages, and hence considered to have a negative charged surface prone to adsorption of electron deficient species. Adsorption isotherms of the adsorbates delineate the nature of binding of the adsorbate with silica. Aromatic compounds are found to involve the pi-cloud in hydrogen bonding with silanol OH group during adsorption. Cationic and nonionic surfactants adsorb on silica surface involving hydrogen bonding. Sometimes, a polar part of the surfactants also contributes to the adsorption process. Styryl pyridinium dyes are found to anchor on silica surface in flat-on position. On modification of the silica by treating with alkali, the adsorption behaviour of cationic surfactant or polyethylene glycol changes due to change in the characteristics of silica or modified silica surface. In case of PEG-modified silica, adsolubilization of the adsorbate is observed. By using a modified adsorption equation, hemimicellization is proposed for these dyes. Adsorptions of some natural macromolecules like proteins and nucleic acids are investigated to study the hydrophobic and hydrophilic binding sites of silica. Artificial macromolecules like synthetic polymers are found to be adsorbed on silica surface due to the interaction of the multifunctional groups of the polymers with silanols. Preferential adsorption of polar adsorbates is observed in case of adsorbate mixtures. When surfactant mixtures are considered to study competitive adsorption on silica surface, critical micelle concentration of individual surfactant also contributes to the adsorption isotherm. The structural study of adsorbed surface and the thermodynamics of adsorption are given some importance in this review.

Study of influence on the surface energy heterogeneity of multiwalled carbon nanotubes after the adsorption of poly(acrylic acid)

The heterogeneity of the surface energy of multiwalled carbon nanotubes (MWNTs) before and after the adsorption of poly(acrylic acid) (PAA) at 77 K was investigated by a nitrogen probe adsorption technique in a wide range of pressures. The adsorption energy distributions (AEDs) were calculated from the low-pressure data of isotherms (i.e., the data of submonolayer adsorption) using the regularization method. Based on the AED, two types of dominant energetic surfaces are identified and assigned to the graphite-like carbon and disordered carbon or defects in the pure MWNTs, respectively. While the adsorption amount of PAA is raised, a significant decrease in the contribution of higher-energy surface in AEDs is observed for those PAA-adsorbed MWNTs. It is thus demonstrated that PAA prefers interacting with higher-energy surfaces to lower-energy surfaces in MWNTs. Nitrogen probe adsorption measurements including low-pressure data are shown to be a feasible and effective tool to characterize the heterogeneity of structure and surface properties of porous materials.