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Physical Adsorption (physical + adsorption)
Selected AbstractsSurface Polymerization of Hydrophilic Methacrylates from Ultrafine Silica Sols in Protic Media at Ambient Temperature: A Novel Approach to Surface Functionalization Using a Polyelectrolytic Macroinitiator,ADVANCED MATERIALS, Issue 18 2003X. Chen A convenient one-pot synthesis of polymer-grafted nano-sized silica particles using atom transfer radical polymerization (see Figure) is described. Physical adsorption of a cationic macroinitiator allows polymerization of a range of hydrophilic methacrylates. A high degree of coverage of the silica sol particles by the grafted polymer chains was indicated. [source] Functionalized Multi-Wall Carbon Nanotubes for Lipase Immobilization,ADVANCED ENGINEERING MATERIALS, Issue 5 2010I. V. Pavlidis Abstract We examine the immobilization of lipase B from Candida antarctica on functionalized multi-wall carbon nanotubes (MWCNTs) through physical adsorption. MWCNTs functionalized with carboxyl-, amine- and ester- terminal groups on their surface are used as immobilization carriers. Dispersion of the nanotubes and the immobilization procedure take place in aqueous and low-water media. High enzyme loadings are attained, up to 25% of the weight of the carbon nanotubes. These novel biomaterials are characterized though FT-IR and Raman spectroscopy. The MWCNT,lipase bioconjugates exhibit high catalytic activity and increased storage and operational stability. The biomaterials retain more than 55% of their initial activity after 6 months at 4,°C, while they retain approximately 25% of their initial activity after 30 d of incubation in hexane at 60,°C. The catalytic behaviour of the immobilized enzyme depends on the terminal group of the carbon nanotubes, the concentration of the enzyme and the immobilization method employed. [source] Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and FabricationADVANCED MATERIALS, Issue 43 2009Richard L. McCreery Abstract Molecular electronics seeks to incorporate molecular components as functional elements in electronic devices. There are numerous strategies reported to date for the fabrication, design, and characterization of such devices, but a broadly accepted example showing structure-dependent conductance behavior has not yet emerged. This progress report focuses on experimental methods for making both single-molecule and ensemble molecular junctions, and highlights key results from these efforts. Based on some general objectives of the field, particular experiments are presented to show progress in several important areas, and also to define those areas that still need attention. Some of the variable behavior of ostensibly similar junctions reported in the literature is attributable to differences in the way the junctions are fabricated. These differences are due, in part, to the multitude of methods for supporting the molecular layer on the substrate, including methods that utilize physical adsorption and covalent bonds, and to the numerous strategies for making top contacts. After discussing recent experimental progress in molecular electronics, an assessment of the current state of the field is presented, along with a proposed road map that can be used to assess progress in the future. [source] Polyethylene glycol and polyvinyl alcohol as corrosion inhibitors for aluminium in acidic mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007S. A. Umoren Abstract The corrosion inhibition of aluminum in H2SO4 in the presence of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30,60 °C was studied using gravimetric, gasometric, and thermometric techniques. The inhibition efficiency (%I) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PEG and PVA were found to obey Temkin adsorption isotherm at all concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PEG was found to be a better inhibitor than PVA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] EFFECTS OF CO-IMMOBILIZATION OF PECTINASE AND AMYLASE ON ULTRAFILTRATION OF APPLE JUICE SIMULATEJOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2001MARÍA E. CARRÍN ABSTRACT In view of its possible application in apple juice clarification, the potential of co-immobilized pectinase/amylase by physical adsorption on a polysulfone ultrafiltration hollow fiber was examined. Solutions containing different concentrations of pectin and starch were used. The effect of various operational parameters on the production of reducing compounds, mainly galacturonic acid and maltose, was investigated. Results indicated that relative permeate flux, during ultrafiltration of starch-pectin solutions, was up to 35% higher when commercial pectinase and amylase were co-immobilized on a hollow fiber membrane. Although the concentration of reaction products increased up to 50% with the pectin concentration, the same was not verified when the starch content changed from 3.85 to 5.00 mg/mL. However, the reference permeate flux was improved when starch was added to substrate, independently of its concentration. Considering the size of an average starch granule, this increase in permeate flux was attributed to the removal of pectin gel by dragging. Permeate fluxes were comparable for both batch and permeate recycling operations. [source] Formulation pH modulates the interaction of insulin with chitosan nanoparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2002Zengshuan Ma Abstract Previous studies on chitosan-insulin nanoparticles have reported diverse encapsulation efficiency and insulin release profiles despite similar formulation and preparation procedures. This study examined the efficiency and mechanism of association of insulin with chitosan nanoparticles in the pH range of 2.3 to 6.3. Nanoparticles of 237 to 235 nm were prepared by ionotropic gelation of chitosan with tripolyphosphate counterions. Insulin was quantified by an RP-HPLC method. The insulin association efficiency (AE) spanned a broad range from 2 to 85%, and was highly sensitive to formulation pH. Highest AE was measured at insulin loading concentrations,,,4.28 U/mL and pH 6.1, close to the pI of native insulin and the pKa of chitosan. This association, attributed to physical adsorption of insulin through hydrophobic interactions with chitosan, was labile, and the associated insulin rapidly and completely released by dilution of the nanoparticles in aqueous media of pH 2 to 7.4. AE obtained at pH 5.3 was less than half that measured at pH 6.1 at corresponding insulin concentration, but the association at pH 5.3 appeared to be based on stronger interactions, because the release of insulin was pH-dependent and recovery was less than 25% even upon disintegration of the chitosan matrix. Interaction of insulin with the chitosan nanoparticles rendered the protein more susceptible to acid and enzymatic hydrolyses, the effects being more predominant in nanoparticles prepared at pH 5.3 than at pH 6.1. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1396,1404, 2002 [source] Equilibrium and heat of adsorption of phosphine on CaCl2 -modified molecular sieveASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Qiongfen Yu Abstract Adsorption characteristics of the virgin and CaCl2 -immersed molecular sieves at 298 K were investigated to select the adsorbent with high adsorption capacity to phosphine. Adsorption isobars and adsorption isotherms over the phosphine partial pressure and temperature ranged 0 , 1000 Pa and 298 , 343 K were measured. The adsorption equilibrium data for phosphine at various temperatures were fitted to Langmuir and Freundlich isotherm models and their isosteric heats of adsorption were determined by the Clausius-Clapeyron equation. It was found the Freundlich was more suitable for description of phosphine adsorption process through calculating average absolute relative error, and the fitted result about Langmuir model showed the heterogeneous characteristics of modified adsorbent. The isosteric heat of adsorption was about 15 kJ/mol, which indicated adsorptive phosphine removal performance may be a dominant of physical adsorption being easy for desorption. The isosteric heat of adsorption decreased with an increase of the surface loading on CaCl2/5A, which means that CaCl2/5A molecular sieve had an energetically heterogeneous surface. The present study confirmed that the CaCl2/5A molecular sieves would be one of the candidates for separation and recycle of phosphine. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Accurate control of oxygen level in cells during culture on silicone rubber membranes with application to stem cell differentiationBIOTECHNOLOGY PROGRESS, Issue 3 2010Daryl E. Powers Abstract Oxygen level in mammalian cell culture is often controlled by placing culture vessels in humidified incubators with a defined gas phase partial pressure of oxygen (pO2gas). Because the cells are consuming oxygen supplied by diffusion, a difference between pO2gas and that experienced by the cells (pO2cell) arises, which is maximal when cells are cultured in vessels with little or no oxygen permeability. Here, we demonstrate theoretically that highly oxygen-permeable silicone rubber membranes can be used to control pO2cell during culture of cells in monolayers and aggregates much more accurately and can achieve more rapid transient response following a disturbance than on polystyrene and fluorinated ethylene-propylene copolymer membranes. Cell attachment on silicone rubber was achieved by physical adsorption of fibronectin or Matrigel. We use these membranes for the differentiation of mouse embryonic stem cells to cardiomyocytes and compare the results with culture on polystyrene or on silicone rubber on top of polystyrene. The fraction of cells that are cardiomyocyte-like increases with decreasing pO2 only when using oxygen-permeable silicone membrane-based dishs, which contract on silicone rubber but not polystyrene. The high permeability of silicone rubber results in pO2cell being equal to pO2gas at the tissue-membrane interface. This, together with geometric information from histological sections, facilitates development of a model from which the pO2 distribution within the resulting aggregates is computed. Silicone rubber membranes have significant advantages over polystyrene in controlling pO2cell, and these results suggest they are a valuable tool for investigating pO2 effects in many applications, such as stem cell differentiation. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | |||||||||||||