(393w) Exploring the Dispersibility of Gold Nanoparticles in DMSO Using Gas-Expanded Liquid Systems

Nanoparticles exhibit very unique and highly size-dependent magnetic, mechanical, chemical, electronic, and optical properties.  Thus, it is necessary to develop technologies to produce monodisperse samples of nanoparticles in order to exploit these size-dependent properties in various applications.  Our group has developed a technique that enables the separation of nanoparticles into different size ranges by manipulating the thermophysical properties of a solvent/antisolvent mixture in a gas expanded liquid system (GXL).  GXLs have solvent strength and transport properties that are intermediate to those of liquids and gases which can be controlled by pressure variations, and these properties can be utilized for nanoparticle separation applications.  In our lab, GXLs have been successfully used for this purpose to size-selectively separate alkyl-capped metal nanoparticles and semiconductor quantum dots dispersed in organic solvents.  Ongoing research in our lab is centered on using this GXL separation technique to size-selectively separate metal nanoparticles that have been stabilized by non-polar ligands with different structures (linear and branched) and dispersed in a variety of non-polar alkyl solvents (linear and branched).  However, it is desired to understand the versatility of the GXL nanoparticle size-selective separation process using other molecules, such as polar and organosulfur compounds, in order to gain a better understanding of general nanoparticle dispersibility behavior in these solvents.  Thus, an alternative means of nanoparticle stabilization and subsequent size-selective separation has been developed by dispersing the nanoparticles in a functional solvent, such as dimethyl sulfoxide (DMSO). Interestingly in some cases, DMSO can adequately serve as both the ligand and solvent for nanoparticle systems.  It has been reported in the literature and observed in our lab that a sufficient amount of CO₂ can diffuse into DMSO to create a GXL for nanoparticle precipitation from DMSO.  Preliminary precipitation experiments have been undertaken to determine whether a CO₂ gas expanded DMSO system may be used to size-selectively separate gold nanoparticles by tuning the applied CO₂ pressure.  Initial results from UV-vis spectroscopy analysis indicate that the DMSO molecule alone may not be able to sufficiently stabilize the gold nanoparticles long enough to successfully perform precipitation experiments using the GXL technique.  To gain more control over gold nanoparticle dispersibility in these unique DMSO-GXL systems, alternative stabilizing agents, such as fatty acids found naturally in animals and vegetables, have been added to the DMSO nanoparticle system.  In each case, UV-vis spectroscopy is used to understand the gold nanoparticle/DMSO/fatty acid ligand system by measuring the absorbance of the gold nanoparticles as a function of the applied CO₂ pressure.  Furthermore, a cascaded vessel apparatus can be used to perform size-selective separations of the gold nanoparticle dispersions from DMSO using GXL.  Comparisons will be made to gold nanoparticles that have been size-selectively separated from the traditional non-polar solvent/ligand systems in order to demonstrate the versatility of using DMSO as an alternative solvent for nanoparticle systems.