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Dickson JL, Shah PS, Binks BP, Johnston KP. Steric stabilization of core-shell nanoparticles in liquid carbon dioxide at the vapor pressure. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:9380-9387. [PMID: 15461533 DOI: 10.1021/la048564u] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Nondilute nanoparticle dispersions were stabilized in liquid CO2 at 25 degrees C at pressures as low as the vapor pressure for greater than 30 min. By modifying hydrophilic silica with a trifunctional silylating agent, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxy silane, a cross-linked polymer shell was formed around the silica core. The presence of the shell led to weaker Hamaker interactions between approaching fluoro-silica composite particles and enabled dispersibility at weaker solvent conditions (low pressures) than for metals with larger Hamaker constants. Steric stabilization of the nanoparticles was provided by low-molecular-weight perfluorodecane side chains at the surface of the fluoro-silica composite shell. Compared to polymeric chains, the perfluorodecane side chains are more easily solvated and thus stabilize nanoparticle dispersions in CO2 at much lower pressures, even down to the vapor pressure.
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Affiliation(s)
- Jasper L Dickson
- Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA
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Prestidge CA, Barnes T, Simovic S. Polymer and particle adsorption at the PDMS droplet-water interface. Adv Colloid Interface Sci 2004; 108-109:105-18. [PMID: 15072933 DOI: 10.1016/j.cis.2003.10.015] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Polymer and particle adsorption at the polydimethylsiloxane (PDMS) droplet-water interface has been investigated. Adsorption isotherms and adsorbed layer structure are reported for a range of PEO-PPO-PEO block copolymers, and hydrophilic and hydrophobic silica "nanoparticles". The influence of solution conditions on the adsorption behaviour has indicated the thermodynamics of polymer-droplet and particle-droplet interactions. The influence of droplet cross-linking (deformability) has indicated the role of interfacial penetration in controlling adsorption at the droplet-water interface. The plateau adsorbed amount (Gamma(max)) and adsorbed layer thickness (delta(max)) of PEO-PPO-PEO copolymers are dependent on the copolymer structure and the level of cross-linking within droplets. For a wide range of copolymer structures, Gamma(max) values are in the range 2 to 20 mg m(-2). For delta(max), values range from 2 to 20 nm and are directly proportional to the PEO block length. Droplet cross-linking significantly reduces Gamma and delta values; this is considered to be due to the influence of interfacial penetrability on the adsorbed copolymer conformation. Hydrophilic silica particles adsorb onto PDMS droplets with plateau surface coverages that correspond to their hard sphere radius+double layer thickness, i.e. lateral silica-silica interactions control particle packing. Free energies of adsorption (DeltaG(ads)) are concurrent with a physical adsorption mechanism. Surface coverages, DeltaG(ads) and particle packing at the interface are only weakly influenced by pH, but are significantly influenced by salt addition. Droplet cross-linking reduced particle adsorption only at higher salt concentrations; this was attributed to the increased likelihood of silica particles wetting PDMS. Freeze fracture SEM revealed that individual silica particles are adsorbed at the droplet interface with negligible interfacial aggregation. Densely packed adsorbed particle layers are only observed when the double layer thickness is a few nanometers. Adsorption of hydrophobic particles at the PDMS droplet-water interface is more pronounced (greater adsorbed amounts and DeltaG(ads) values) than for hydrophilic particles and displays a pH dependency in line with 'DLVO behaviour'. The surface coverage values correspond to multiple close packed layers and are significantly influenced by droplet cross-linking, conferring extensive interfacial penetration (confirmed by SEM). Densely packed adsorbed particle layers with interfacial aggregation are observed over a wide range of solution conditions. Interfacial particle saturation occurred at a salt concentration two orders of magnitude less than the critical coagulation concentration (ccc) for silica in water. This phenomenon was observed for both liquid and cross-linked PDMS droplets indicating that particle interaction through the water phase plays a decisive role in particle packing at the interface. SEM indicated the presence of a rigid interfacial crust layer at the salt concentration corresponding to interfacial saturation and a multi-layered interfacial particle wall at salt concentrations >/= ccc. The PDMS droplets under consideration, having inherent colloid stability in the absence of added stabilisers, are an excellent model system for characterising polymer and particle adsorption at the droplet-water interface. The insight gained concerning adsorption thermodynamics at the droplet-water interface is not available from more conventional emulsions.
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Affiliation(s)
- Clive A Prestidge
- Ian Wark Research Institute, The ARC Special Research Centre for Particle and Material Interfaces, University of South Australia, Mawson Lakes, SA 5095, Australia.
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Marrone M, Montanari T, Busca G, Conzatti L, Costa G, Castellano M, Turturro A. A Fourier Transform Infrared (FTIR) Study of the Reaction of Triethoxysilane (TES) and Bis[3-triethoxysilylpropyl]tetrasulfane (TESPT) with the Surface of Amorphous Silica. J Phys Chem B 2004. [DOI: 10.1021/jp036148x] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Michelle Marrone
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
| | - Tania Montanari
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
| | - Guido Busca
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
| | - Lucia Conzatti
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
| | - Giovanna Costa
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
| | - Maila Castellano
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
| | - Antonio Turturro
- Laboratorio di Chimica delle Superfici e Catalisi Industriale, Dipartimento di Ingegneria Chimica e di Processo, Università di Genova, P.le Kennedy, I-16129 Genova, Italy, Istituto per lo Studio delle Macromolecole ISMAC-CNR, Sezione di Genova, Via E. De Marini, 6, I-16149 Genova, Italy, and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso, 31, I-16146 Genova, Italy
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