The transport of engineered nanoparticles in porous media is of interest in numerous applications including electromagnetic imaging of subsurface reservoirs, enhanced oil recovery, and CO 2 sequestration. A series of poly(2-acrylamido-2methyl-1-propanesulfonic acid-co-acrylic acid) (poly(AMPS-co-AA)) random copolymers were grafted onto iron oxide (IO) nanoparticles (NPs) to provide colloidal stability in American Petroleum Institute (API) standard brine (8 wt/wt % NaCl and 2 wt/wt %CaCl 2 , anhydrous basis). A combinatorial approach, which employed grafting poly(AMPS-co-AA) with wide ranges of compositions onto platform amine-functionalized IO NPs via a 1-ethyl-3-(3-(dimethylamino)propyl)carbondiimidecarbondiimide (EDC) catalyzed amidation, was used to screen a large number of polymeric coatings. The ratio of AMPS/AA was varied from 1:1 to 20:1 to balance the requirements of particle stabilization, low adsorption/retention (provided by 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS)), and permanent attachment of stabilizer (provided by acrylic acid (AA)). The resulting nanoparticles remained stable in aqueous suspension despite the extremely high salinity conditions and exhibited low adsorption on silica microspheres. Greater than 91% of applied IO-NP mass was transported through columns packed quartz sand, and the mobility of IO NP increased by ca. 6% when the AMPS to AA ratio was increased from 1:1 to 3:1, consistent with batch adsorption data. In both static batch reactor and dynamic column tests, the observed attachment of IO NPs was attributed to divalent cation (Ca 2+ ) mediated bridging and hydrophobic interactions. Collectively, the rapid, high throughput combinatorial approach of grafting and screening (via batch adsorption) provides for the development of high mobility NPs for delivery in various porous media under high salinity conditions.

In subsurface imaging and oil recovery where temperatures and salinities are high, it is challenging to design polymer-coated nanoparticles with low retention (high mobility) in porous rock. Herein, the grafting of poly­(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylic acid) (poly­(AMPS-co-AA)) on magnetic iron oxide nanoparticles was sufficiently uniform to achieve low adsorption on model colloidal silica and crushed Berea sandstone in highly concentrated API brine (8% NaCl and 2% CaCl2 by weight). The polymer shell was grafted via amide bonds to an aminosilica layer, which was grown on silica-coated magnetite nanoparticles. The particles were found to be stable against aggregation in American Petroleum Institute (API) brine at 90 °C for 24 h. For IO nanoparticles with ∼23% polymer content, Langmuir adsorption capacities on colloidal silica and crushed Berea Sandstone in batch experiments were extremely low at only 0.07 and 0.09 mg of IO/m2, respectively. Furthermore, upon injection of a 2.5 mg/mL IO suspension in API brine in a column packed with crushed Berea sandstone, the dynamic adsorption of IO nanoparticles was only 0.05 ± 0.01 mg/m2, which is consistent with the batch experiment results. The uniformity and high concentration of solvated poly­(AMPS-co-AA) chains on the IO surfaces provided electrosteric stabilization of the nanoparticle dispersions and also weakened the interactions of the nanoparticles with negatively charged silica and sandstone surfaces despite the very large salinities.

Recently, there has been a signifi cant interest in the fabrication of patterned polymer surfaces because of potential applications in surface-based technologies such as microfl uidic devices, chemical/biosensors, platforms for tissue engineering, etc. [ 1 ] To date, polymer brushes are widely used in patterning surfaces due to their robustness, broad range of chemical and mechanical properties, and ability to modify surface properties, [ 2 ] and thus an ideal surrogate for self-assembled monolayers (SAM)s. Despite the numerous applications of patterned polymer surfaces, there have been a limited number of strategies reported toward the formation of laterally well-defi ned binary composition patterned brushes. [ 3 ] Most of the methods used involve expensive, tedious and complex lithographic techniques, [ 4 ] which limits their practical applications. Another material of high interest are conducting polymers, which are a versatile class of organic materials with electrical, optical, and electrochemical properties that are easily modifi ed by design and synthesis. They are useful as display materials, semi-conductors, electrochromic devices, fl uorescent materials, non-linear optical materials, electromagnetic shielding, and various types of industrial coatings for anti-corrosion and anti-static purposes. [ 5 ] Due to their unique properties, conducting polymers [ 6 ] are also being exploited in making 2D nano/microstructured arrays because of the many applications such as photonic crystals, diffraction gratings, biosensors, and surface-enhanced Raman scattering (SERS). [ 7 ] The electropolymerization technique endows several advantages -ease in control of thickness and lateral dimension of the pattern, site-directed patterning, and deposition over large surface areas onto various conducting substrates. One unique electrodeposition approach is by template-assisted electropolymerization, which has remained largely unexplored for 2D patterning. To our knowledge, this is the fi rst report on binary composition patterned surfaces combining a conducting polymer and a polymer brush via a simple approach of colloidal template-assisted electropolymerization followed by growing the polymer brush, using surface initiated atom transfer radical polymerization (SI-ATRP). This study is also the fi rst account on dual patterned inverse colloidal crystals (in a single layer assembly) of electrodeposited conducting polymer and an SI-ATRP initiator. The generic method reported here should be useful for making different types of binary patterned surfaces using different combinations of polymer brushes, conducting polymers, and self-assembled monolayers. The importance of such combinations may be found in redox-active ( π -conjugated polymer-based) stimuli-responsive polymer brushes and modulation of electro-optical properties simultaneous with changes in solvent swelling properties (polymer brushes), dependent on the binary composition and mode or size of patterning.The protocol for stepwise patterning of binary patterned polymer su...

A facile “grafting through” approach was developed to tether tunable quantities of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as well as zwitterionic poly([3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide) (PMPDSA) homopolymer onto iron oxide (IO) nanoparticles (NPs). In this case, homopolymers may be grafted, unlike “grafting to” approaches that often require copolymers containing anchor groups. The polymer coating provided steric stabilization of the NP dispersions at high salinities and elevated temperature (90 °C) and almost completely prevented adsorption of the NPs on silica microparticles and crushed Berea sandstone. The adsorption of PAMPS IO NPs decreased with the polymer loading, whereby the magnitude of the particle-surface electrosteric repulsion increased. The zwitterionic PMPDSA IO NPs displayed 1 order of magnitude less adsorption onto crushed Berea sandstone relative to the anionic PAMPS IO NPs. The ability to design homopolymer coatings on nanoparticle surfaces by the “grafting through” technique is of broad interest for designing stable dispersions and modulating the interactions between nanoparticles and solid surfaces.

Single-molecule fluorescence spectroscopy is employed to reveal 3-dimensional details of the mechanisms underpinning ion transport in a polyelectrolyte thin film possessing polymer-brush nanoscale order. The ability to resolve fluorescence emission over three discrete polarization angles reveals that these ordered materials impart 3-dimensional orientation to charged, diffusing molecules. The experiments, supported by simulations, report global orientation parameters for molecular transport, track dipole angle progressions over time, and identify a unique transport mechanism: translational diffusion with restricted rotation. Generally, realization of this experimental method for translational diffusion in systems exhibiting basic orientation should lend itself to evaluation of transport in a variety of important, ordered, functional materials.