Littérature scientifique sur le sujet « Nanoparticle-Polymer Suspensions »

To be effective enhanced oil-recovery (EOR) agents, nanoparticles must be stable and be transported through a reservoir. However, the stability of a nanoparticle suspension at reservoir salinity and temperature is still a challenge and how it is affected by reservoir rocks and crude oils is not well understood. In this work, for the first time, the effect of several nanoparticle treatment approaches on the stability of silica nanoparticles at reservoir conditions (in the presence of reservoir rock and crude oil) was investigated for EOR applications. The stability of nanoparticle suspensions was screened in test tubes at 70 °C and 3.8 wt. % NaCl in the presence of reservoir rock and crude oil. Fumed silica nanoparticles in suspension with hydrochloric acid (HCl), polymer-modified fumed nanoparticles and amide-functionalized silica colloidal nanoparticles were studied. The size and pH of nanoparticle suspension in contact with rock samples were measured to determine the mechanism for stabilization or destabilization of nanoparticles. A turbidity scanner was used to quantify the stability of the nanoparticle suspension. Results showed that both HCl and polymer surface modification can improve nanoparticle stability under synthetic seawater salinity and 70 °C. Suspensions of polymer-modified nanoparticles were stable for months. It was found that pH is a key parameter influencing nanoparticle stability. Rock samples containing carbonate minerals destabilized unmodified nanoparticles. Crude oil had limited effect on nanoparticle stability. Some components of crude oil migrated into the aqueous phase consisting of amide-functionalized silica colloidal nanoparticles suspension. Nanoparticles modification or/and stabilizer are necessary for nanoparticle EOR application.

Nanocomposite fibers produced via electrospinning have very large surface area by virtue of their nanometer diameter sizes thereby making them very attractive for various applications such as for adsorption of contaminants from wastewater. In this study, a highly adsorbing nanoparticle, iron-modified montmorillonite was used as filler in the nanocomposite. The effects of polymer solution and suspension properties such as polymer concentration, clay loading, and filler type on the electrospinning of the nanocomposite were investigated using a 2k factorial design of experiment. The types of montmorillonite used were zero valent iron-MMT (ZVIMMT) and iron (III)-MMT (FeMMT). It was found from the SEM images that finer fibers were generated from suspensions with lower polymer concentration in the solution specifically at 5 wt% and from suspensions with ZVIMMT particles as filler. However, a common defect in nanofibers called beads was also observed in the fibers produced from 5 wt% polymer concentration. TEM micrographs confirmed that the ZVIMMT fibers have smaller diameter than the FeMMT fibers. In addition, it was recognized that the layered structure of the clay is still intact after the electrospinning process. The XRD pattern of the fibers revealed that the clay particles were intercalated with the polymer molecules based on the calculated d-spacing. Furthermore, elemental analysis on the bead and string regions of the electrospun fibers confirmed the presence of polymer and montmorillonite particles in both regions.

Polymer nanocomposites based on polyhedral oligomeric silsesquioxanes (POSS) and their solutions and suspensions are promising systems for fundamental research which could potentially utilize self-assembly approach in designing new nanocomposite materials. Numerous applications could benefit from understanding of these systems, for instance polymer solution based paints and varnishes. This work is an initial stage of a study which aim is to link macroscale thermomechanical properties with nanoscale structures found in polymer nanocomposites. To do so, a suitable experimental protocol for preparing differently organized NPs in polymer matrix has to be find first in which both kinetic and thermodynamical parameters should be taken into account, i.e. solution casting has being investigated. The results presented here found differences between nanoparticle induced changes on rheological behavior of polystyrene solution under large amplitude oscillation shear (LAOS). High-affinity OP-POSS NPs seem to interact with PS at low loadings and form stiffened aggregates, whereas low-affinity OM-POSS NPs remained rather uninvolved. Effect of hydrodynamic forces independent of the NPs chemical nature was also observed.

Abstract During the past decade submicron and nanoparticles have aroused a wide interest and gained new applications due to their high surface area and strength. Grinding with a wet stirred media mill is usually the last process step before the submicron or nanoparticles are added to an application, and the step where the final particle size distribution is achieved. Since stirred media milling is an energy-intensive process, energy efficiency should be optimized. This can be done by determining the optimum operational parameters for the mill and using the highest possible solids concentration. The solids concentration can be increased by controlling particle-particle interactions with stabilization chemicals, e.g. polymers. This thesis concerns parameters and grinding aids affecting the particle size distribution and suspension stability of the aqueous submicron grinding of calcium carbonate (CaCO3) and titanium dioxide (TiO2) in stirred media mills. TiO2 particles are aggregates produced via a bottom-up method, while CaCO3 are primary mineral particles produced by a top-down method. The most energy efficient grinding of TiO2 to a 300 nm particle size with the narrowest possible particle size distribution was obtained with the lowest stress energy, implying the smallest grinding medium size. It was observed that electrosteric stabilization with sodium polyacrylates was effective for TiO2, and sodium polyacrylate with a molecular weight of 12500 g/mol was found to be the most effective for reducing the viscosity of the suspension. As with TiO2, electrosteric stabilization with sodium polyacrylates was also found to be effective for CaCO3, but in this case sodium polyacrylate with a lower polydispersity index was more effective, showing a better stabilization potential in micron and submicron grinding and reducing the viscosity and particle size to a greater extent. Nanogrinding experiments were performed for a CaCO3 suspension with low PDI sodium polyacrylate and it was found to be possible to obtain a particle size of 26 nm, smaller than any size previously reported when grinding CaCO3
Tiivistelmä Viimeisen kymmenen vuoden aikana alle yhden mikrometrin partikkelit ovat herättäneet kiinnostusta ja niille on kehitetty uusia sovelluksia niiden suuren pinta-alan ja lujuuden ansiosta. Ultrahienojauhatus märkähelmimyllyllä on useimmiten viimeinen prosessivaihe ennen partikkelien lisäämistä sovelluskohteeseen ja siinä saavutetaan partikkelien lopullinen partikkelikokojakauma. Helmimyllyjauhatuksen energiankulutus minimoidaan etsimällä optimioperointiparametrit kullekin jauhatusprosessille ja käyttämällä korkeinta mahdollista suspension kuiva-ainepitoisuutta. Suspension kuiva-ainepitoisuutta voidaan nostaa hallitsemalla partikkelien välisiä vuorovaikutuksia stabilointiaineilla, kuten polymeereillä. Tässä väitöskirjassa tutkittiin operointiparametrien ja jauhatusapuaineiden vaikutusta titaanidioksidin (TiO2) ja kalsiumkarbonaatin (CaCO3) partikkelikokojakaumaan ja lietteen stabiilisuuteen submikronijauhatuksessa. Tutkitut TiO2-partikkelit olivat aggregaatteja, jotka oli valmistettu sulfaattiprosessilla saostamalla, ja tutkitut CaCO3-partikkelit olivat primäärisiä mineraalipartikkeleita. TiO2-partikkeleille saavutettiin energiatehokkain jauhatus ja samalla toivottu partikkelikokojakauma, eli mediaani 300 nm ja mahdollisimman kapea jakauma, pienillä helmillä, jotka aiheuttavat partikkeleihin pienimmän puristusenergian. Elektrosteerinen stabilointi käyttämällä natriumpolyakrylaatteja stabilointiaineena havaittiin tehokkaaksi menetelmäksi hallita TiO2-partikkelien välisiä vuorovaikutuksia. Natriumpolyakrylaatti, jonka molekyylimassa oli 12500 g/mol, oli tehokkain TiO2-partikkeleille alentaen suspension viskositeettiä eniten. Myös CaCO3-partikkeleille elektrosteerinen stabilointi natriumpolyakrylaatteja käyttäen oli tehokkain stabilointimenetelmä. Myös natriumpolyakrylaattien polydispersiteetti-indeksin vaikutusta tutkittiin CaCO3-suspensioille. Tulokset osoittivat matalan polydispersiteetti-indeksin olevan tehokkaampi alentaen viskositteettia ja pienentäen partikkelikokoa tehokkaammin kuin natriumpolyakrylaatti, jolla oli korkeampi polydispersitetti-indeksi. Tämän vuoksi natriumpolyakrylaatti, jolla oli matala polydispersiteetti-indeksi, valittiin nanojauhatuskokeisiin. Kokeissa CaCO3-partikkelit saatiin jauhettua 26 nm kokoon, joka on pienin koskaan aiemmin jauhamalla saavutettu koko CaCO3-partikkeleille

We studied dispersion state and dynamics of polymer grafted nanoparticle in photopolymer matrix nanoparticle-polymer blend- and their thermal and rheological properties. While thinking about a nanoparticle-polymer blend, the first question comes in is the dispersion state of nanoparticle in polymer. Especially in case of a blend film, dispersion of nanoparticle is very crucial in deciding its properties. It is still a challenging problem to get the dispersed blend even after 30 years of its invention. So, we started our work with the investigation of nanoparticle dispersion in polymer melt film and its evolution with time at high temperature. Eventually we studied the dynamics of nanoparticle in polymer melts at high temperature and the rheological and thermal properties of these blends. In chapter 1, I have provided the introductory discussion about polymer’s conformation, dynamics etc. Polymer grafted nanoparticle dispersion and its dynamical behaviour in polymer matrix has been discussed in this chapter briefly. The experimental techniques used for this work have been explained in chapter 2. It is well known that preparation process of a blend film has a significant contribution to the final dispersion state of nanoparticle. A good practice to prepare such blend films is to anneal the film after it spincoated on a hard substrate. The purpose is to remove the trapped solvent as well as removing the unstable/meta-stable state achieved by sudden freezing of the polymers during spincoating. It was observed that the dispersion state of nanoparticle is improved after annealing. We study this evolution of dispersion at annealing temperature using in-situ X-ray scattering measurement and presented in chapter 3. We found super-diffusive in-plane and very slow out of plane motion of polystyrene grafted gold nanoparticle (PGNP) in polystyrene (PS) matrix at high temperature (T>Tg). The PGNP dispersion becomes homogeneous throughout the film which is otherwise a segregated film. After cooling down to room temperature, even though a partial reversal of the segregation occurs, the final dispersion state is better than that before annealing. We have shown a method of capturing the well dispersed state (the high temperature dispersion state) of PGNP at room temperature. In chapter 4 we presented the study of PGNP dynamics in the polymer melt film at high temperature where the particles are expected to be almost homogeneously dispersed as we found in the previous observations. Anomalous relaxation dynamics is observed leading to an unusual temperature dependence of effective viscosity of the film and the anomaly increases under confinement. The observed anomalous behaviour could be explained in terms of the hydrodynamic slip experienced by the PGNP while the system has a dewetting PGNP-polymer interface. We estimated approximate slip length at the PGNP-polymer interface as a function of temperature and thickness. The slip length diverges at low temperature. Thickness dependent study reveals an increase of slip length under confinement resulting in a stronger anomaly for thinner films. Slip length at a polymer melt-polymer grafted wall interface (flat interface) as well as polymer melt-polymer grafted spherical particle interface (spherical interface) has been calculated by varying temperature and miscibility parameter, f (f=ratio of grafted and matrix chain molecular weight) using molecular dynamics simulations. A good agreement established between the simulation and the observed experimental results. In associated with the interface slip, the PGNP-polymer interface layer seems to have an effective interface viscosity which is different from bulk polymer viscosity. A strong wave vector dependent hydrodynamic interaction between PGNPs was indicated by the observed temperature and wave vector dependent short time diffusion coefficient. This phenomenon could be explained in terms of the full slip boundary condition at the PGNP-polymer interface. It is not surprising that the properties, e.g. thermal, rheological properties would get affected by the dispersion of PGNP as well as their dynamics. In chapter 5 we explored rheological propertis of nanoparticle-polymer blend film such as viscosity using force-distance spectroscopy for different miscibility parameters, f and temperature. A reduction in the viscosity of the blend film was observed with respect to its pristine polymer film for a smaller f value. The deviation of blend film viscosity from pristine polymer film viscosity reduces with increase in f. The extent of the viscosity reduction for smaller f increases towards lower temperature. Further, we have studied demixing temperature of a two component polymer blend system (Polystyrene (PS)/Poly (vinyl methyl ether) (PVME) blend) getting influenced by the presence of PGNP dispersed in it. When the grafted chain length is much higher than the matrix PS chain, the demixing temperature gets increased, while the grafted chain length is much smallerthan matrix PS leads almost no change. The PGNPs are observed to be present inthe PVME phase while the grafted PS chains are too short compared to the matrix PS chains and in opposite case while grafted chain is larger compared to matrix PSchains, the PGNPs are located at the PS matrix Rheological property of the PGNP suspensions in presence of linear PS chains hasbeen studied using diffusing wave spectroscopy and presented in chapter 6. A change in frequency dependence of viscous modulus was observed in a case where the linear PS chain is much longer than the grafted PS chains with increasing concentrations of PS linear chains indicating a shear thickening behaviour at higher linear PS concentrations. Presence of shorter linear chains do not show any such change in frequency dependence. To investigate about the observed shear thickening, dynamic light scattering measurement were performed on these samples. A large shrinkage of nanoparticlecorona in presence of large linear chains was observed which could lead to the observed shear thickening behaviour. The shorter linear chains inter-penetrate into the grafted chains resulting in a swelling of nanoparticle grafts. Comparatively lower resultant viscosity observed for shorter chains possibly due to the faster mobility of shorter chains penetrating into the grafts. Finally in chapter 7, I summarize my thesis work and express my future work plan.

Abstract Nanoparticle additives, with their anomalous thermal conductivity, have attracted attention in research and industry as a novel mode of enhancing the heat transfer mediums. Most studies conducted on nanoparticle suspensions in liquids, pastes, or composites at present have relied on constitutive relations using properties of the bulk substance and of the nanoparticle to explain the effective thermal conductivity. In order to utilize nanoparticles in real world engineering applications, chemical functionalization of the surface of the nanoparticle is frequently employed, either to suspend in liquid applications or to stabilize in arrays. In this study, we have sought to explain the underlying mechanisms of thermal conductivity enhancement taking into consideration the nanoscale effects, such as phonon transport in the nanoparticle coupled with vibrational modes of the surface functional molecules, in order to tailor the functional groups not only for suspension stability but also for minimizing Kapitza resistance at the surface of the nanoparticle. Density functional theory simulations in SIESTA and equilibrium transport theory analysis via GOLLUM2 were used in tandem to evaluate the thermal transport at the nanoparticle to surface ligand junction. By treating the nanoparticle surface and the polymer or acid coating as distinct homogeneous substrates, a model for thermal conductivity becomes more tractable.

Direct write (DW) technology offers a simple method of rapid manufacturing technology for printing electronic, optoelectronic devices, and complex functional devices. The key component of DW technology is the functional inks, which are colloidal suspensions of functional nanoparticles in various solvents such as aerosol or liquid form. With a DW approach, patterns or structures can be easily deposited on flexible substrates such as paper, plastics, and composites, once the solvent volatilizes or is driven off via conventional, laser, or microwave sintering. In this work, polymer-assisted silver (Ag) nanoinks were synthesized by silver salt and polymer in the water solution at relatively high silver precursor concentrations and relatively low concentration of polymers. The silver nanoparticle dispersion and morphology was examined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the size of Ag nanoparticles was in nanoscale (∼20 nm) with a narrow distribution of Ag nanoparticle sizes. The viscosity and thermal properties of synthesized silver nanoinks were characterized to determine their applicability and the lifetime. It has been shown that the synthesized silver nanoink can be printed on a flexible plastic substrate or glass substrate. The morphology of the Ag nanoink line printed on the substrate was observed by optical microscopy and scanning electron microscopy (SEM) to understand the relationship between the microstructure and wettability. Uniaxial tension tests of silver nanoink line on a Kapton film indicate that the ink can be stretched ∼20% without failure. The resistance of silver nanoink line printed on the Kapton films was also measured by four probe conductivity measurement system to assess the electrical performance. The resistivity is about 7.5 × 10−5 Ω-cm by thermal treatment at 250°C for 30 min, which is about half that of bulk silver (1.6 × 10−6 Ω-cm). Overall, the performance of the synthesized silver nanoink is comparable to a commercially available ink with lower Ag weight content at relatively low cost.

Abstract Nanoparticle-included polymeric composite coatings with preferential nanoparticle alignment and oriented structures show improved functional and structural properties than randomly oriented structures, suitable for broad applications in microelectronics, automobile, defense, and space missions. Traditionally used techniques, such as drop-casting, chemically modified surfaces, and external fields, have been used for self-assembly but with several disadvantages, such as material limitations. Thus, there is a need to develop a new approach for generating hierarchical nanoparticle structures. Our unique processing is based on advanced additive manufacturing with a colloidal suspension-based deposition approach for layer-by-layer deposition of anisotropic nanoparticles. Leveraging the colloidal deposition technique, these anisotropic nanoparticles were deposited onto the 3D printed substrates with designed patterning. The presence of micropatterns generates selective nanoparticle distribution and assembly along with hydrodynamic forces to initiate the region-specific microscale patterning and nanoscale alignment of 1D and 2D nanoparticles. The polymer and nanoparticle composite film showed different deposition morphologies (e.g., straight or wavy films). In addition, the influence of nanoparticle deposition morphology on functional properties was investigated. This novel technique shows the potential to scale up microelectronics production by 3D printing electronic structures, including interdigitated devices, supercapacitors, fuel cells, and circuits.