| 1. |
- Caggiano, N.J., et al.
(författare)
-
Local Chain Alignment via Nematic Ordering Reduces Chain Entanglement in Conjugated Polymers
- 2018
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 51:24, s. 10271-10284
-
Tidskriftsartikel (refereegranskat)abstract
- Chain entanglements govern the dynamics of polymers and will therefore affect the processability and kinetics of ordering; it follows that through these parameters chain dynamics can also affect charge transport in conjugated polymers. The effect of nematic coupling on chain entanglements is probed by linear viscoelastic measurements on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and poly((9,9-dioctylfluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) with varying molecular weights. We first verify the existence of nematic phases in both PFTBT and PCDTBT and identify nematic-isotropic transition temperatures, TIN, between 260 and 300 °C through a combination of differential scanning calorimetry, polarized optical microscopy, temperature-dependent X-ray scattering, and rheology. In addition, both PCDTBT and PFTBT show a glass transition temperature (Tg) and TIN, whereas only PFTBT has a melting temperature Tm of 260 °C. Comparing the molecular weight dependence of TIN with theoretical predictions of nematic phases in conjugated polymers yields the nematic coupling constant, α = (550 ± 80 K)/T + (2.1 ± 0.1), and the long-chain limit TIN as 350 ± 10 °C for PFTBT. The entanglement molecular weight (Me) in the isotropic phase is extracted to be 11 ± 1 kg/mol for PFTBT and 22 ± 2 kg/mol for PCDTBT by modeling the linear viscoelastic response. Entanglements are significantly reduced through the isotropic-to-nematic transition, leading to a 10-fold increase in Me for PFTBT and a 15-fold increase for PCDTBT in the nematic phase.
|
|
| 2. |
|
|
| 3. |
- Kapuscinski, Martin, et al.
(författare)
-
Temporal Evolution of Superlattice Contraction and Defect-Induced Strain Anisotropy in Mesocrystals during Nanocube Self-Assembly
- 2020
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:5, s. 5337-5347
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding and controlling defect formation during the assembly of nanoparticles is crucial for fabrication of self-assembled nanostructured materials with predictable properties. Here, time-resolved small-angle X-ray scattering was used to probe the temporal evolution of strain and lattice contraction during evaporation-induced self-assembly of oleate-capped iron oxide nanocubes in a levitating drop. We show that the evolution of the strain and structure of the growing mesocrystals is related to the formation of defects as the solvent evaporated and the assembly process progressed. Superlattice contraction during the mesocrystal growth stage is responsible for the rapidly increasing isotropic strain and the introduction of point defects. The crystal strain, quantified by the Williamson-Hall analysis, became more anisotropic due to the formation of stress-relieving dislocations as the mesocrystal growth was approaching completion. Understanding the formation of the transformation of defects in mesocrystals and superlattices could assist in the development of optimized assembly processes of nanoparticles with multifunctional properties.
|
|
| 4. |
|
|
| 5. |
- Kapuscinski, Martin, et al.
(författare)
-
Two-Stage Assembly of Mesocrystal Fibers with Tunable Diameters in Weak Magnetic Fields
- 2020
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 20:10, s. 7359-7366
-
Tidskriftsartikel (refereegranskat)abstract
- Controlling the morphology and crystallographic coherence of assemblies of magnetic nanoparticles is a promising route to functional materials. Time-resolved small-angle X-ray scattering (SAXS) was combined with microscopy and scaling analysis to probe and analyze evaporation-induced assembly in levitating drops and thin films of superparamagnetic iron oxide nanocubes in weak magnetic fields. We show that assembly of micrometer-sized mesocrystals with a cubic shape preceded the formation of fibers with a high degree of crystallographic coherence and tunable diameters. The second-stage assembly of aligned cuboidal mesocrystals into fibers was driven by the magnetic field, but the first-stage assembly of the oleate-capped nanocubes was unaffected by weak magnetic fields. The transition from 3D growth of the primary mesocrystals to the second stage 1D assembly of the elongated fibers was related to the size and field dependence of isotropic van der Waals and directional dipolar interactions between the interacting mesocrystals.
|
|
| 6. |
|
|
| 7. |
- Munier, Pierre, et al.
(författare)
-
Assembly of cellulose nanocrystals and clay nanoplatelets studied by time-resolved X-ray scattering
- 2021
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 17:23, s. 5747-5755
-
Tidskriftsartikel (refereegranskat)abstract
- Time-resolved small-angle X-ray scattering (SAXS) was used to probe the assembly of cellulose nanocrystals (CNC) and montmorillonite (MNT) over a wide concentration range in aqueous levitating droplets. Analysis of the SAXS curves of the one-component and mixed dispersions shows that co-assembly of rod-like CNC and MNT nanoplatelets is dominated by the interactions between the dispersed CNC particles and that MNT promotes gelation and assembly of CNC, which occurred at lower total volume fractions in the CNC:MNT than in the CNC-only dispersions. The CNC dispersions displayed a d proportional to phi(-1/2) scaling and a low-q power-law exponent of 2.0-2.2 for volume fractions up to 35%, which indicates that liquid crystal assembly co-exists and competes with gelation.
|
|
| 8. |
- Munier, Pierre, 1993-, et al.
(författare)
-
Rheo-SAXS study of shear-induced orientation and relaxation of cellulose nanocrystal and montmorillonite nanoplatelet dispersions
- 2022
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 18:2, s. 390-396
-
Tidskriftsartikel (refereegranskat)abstract
- The development of robust production processes is essential for the introduction of advanced materials based on renewable and Earth-abundant resources. Cellulose nanomaterials have been combined with other highly available nanoparticles, in particular clays, to generate multifunctional films and foams. Here, the structure of dispersions of rod-like cellulose nanocrystals (CNC) and montmorillonite nanoplatelets (MNT) was probed using small-angle X-ray scattering within a rheological cell (Rheo-SAXS). Shear induced a high degree of particle orientation in both the CNC-only and CNC:MNT composite dispersions. Relaxation of the shear-induced orientation in the CNC-only dispersion decayed exponentially and reached a steady-state within 20 seconds, while the relaxation of the CNC:MNT composite dispersion was found to be strongly retarded and partially inhibited. Viscoelastic measurements and Guinier analysis of dispersions at the shear rate of 0.1 s−1 showed that the addition of MNT promotes gel formation of the CNC:MNT composite dispersions. A better understanding of shear-dependent assembly and orientation of multi-component nanoparticle dispersions can be used to process materials with improved mechanical and functional properties.
|
|
| 9. |
|
|
| 10. |
- Segad, Mo, et al.
(författare)
-
Ca/Na Montmorillonite: Structure, Forces and Swelling Properties.
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:8, s. 5782-5790
-
Tidskriftsartikel (refereegranskat)abstract
- Ca/Na montmorillonite and natural Wyoming bentonite (MX-80) have been studied experimentally and theoretically. For a clay system in equilibrium with pure water, Monte Carlo simulations predict a large swelling when the clay counterions are monovalent, while in presence of divalent counterions a limited swelling is obtained with an aqueous layer between the clay platelets of about 10 A. This latter result is in excellent agreement with X-ray scattering data, while dialysis experiments give a significantly larger swelling for Ca montmorillonite in pure water. Obviously, there is one "intra-lamellar" and a second "extra-lamellar" swelling. Montmorillonite in contact with a salt reservoir containing both Na(+) and Ca(2+) counterions will only show a modest swelling unless the Na(+) concentration in the bulk is several orders of magnitude larger than the Ca(2+) concentration. The limited swelling of clay in presence of divalent counterions is a consequence of ion-ion correlations, which reduce the entropic repulsion as well as give rise to an attractive component in the total osmotic pressure. Ion-ion correlations also favor divalent counterions in a situation with a competition with monovalent ones. A more fundamental result of ion-ion correlations is that the osmotic pressure as a function of clay sheet separation becomes nonmonotonic, which indicates the possibility of a phase separation into a concentrated and a dilute clay phase, which would correspond to the "extra-lamellar" swelling found in dialysis experiments. This idea also finds support in the X-ray scattering spectra, where sometimes two peaks corresponding to different lamellar spacings appear.
|
|
| 11. |
- Segad, Mo, et al.
(författare)
-
Microstructural and Swelling Properties of Ca and Na Montmorillonite: (In Situ) Observations with Cryo-TEM and SAXS
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:13, s. 7596-7601
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of pure sodium and calcium smectite clays with platelet sizes on the order of a few hundred nanometers were characterized using a combination of cryo-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). With monovalent sodium counterions the clay is dispersed as individual platelets, as seen by cryo-TEM, that order into a nematic phase. From SAXS a one-dimensional swelling of the day in water is observed with the characteristic spacing h(s) = delta/phi(c), where h(s) is the separation between the platelets, delta = 1 nm is the effective platelet thickness, and phi(c) is the clay volume fraction in the sample. In calcium montmorillonite, on the other hand, cryo-TEM images dearly show the presence of tactoids, where the platelets have aggregated into stacks with a periodic spacing of 2 nm. From imaging a large number of tactoids the distribution function f(N) far the number of platelets per tactoid was estimated, and the average number (N) approximate to 10. The characteristic 2 nm spacing as well as the small number of platelets per tactoid was also confirmed by SAXS. The present study demonstrates that cryo-TEM, with carefully prepared specimen, is a very useful technique to characterize clay dispersions, particularly in aggregated systems.
|
|
| 12. |
- Segad, Mo
(författare)
-
Microstructure determination of IQ-WB clays: a direct procedure by small-angle X-ray scattering
- 2013
-
Ingår i: Journal of Applied Crystallography. - 1600-5767. ; 46, s. 1316-1322
-
Tidskriftsartikel (refereegranskat)abstract
- An accurate characterization of the microstructure of raw and pure homoionic clays from Wadi Bashira in Iraq (IQ-WB) has been carried out experimentally, using small-angle X-ray scattering (SAXS) and dynamic light scattering. The structures of lamellar IQ-WB dispersions were identified by these techniques and by complementary free swelling and dialysis experiments. SAXS measurements were used to resolve the characteristic distance, h(s), between individual platelets in Na IQ-WB and between platelets inside tactoids formed in Ca clays. The tactoids in raw and Ca IQ-WB have well formed lamellar structures where h(s) = 1.9 nm. The average lateral size, < D >, of a platelet is determined to be a few hundred nanometres. Analysis of the SAXS peaks, based on the Scherrer relation, revealed a small difference in the average number of platelets per tactoid, < N > = 6-9, depending on platelet size and the concentrations of divalent counter-ions. It was also found that the average tactoid size can be estimated from an empirical relation as follows: < N > similar or equal to delta + alpha < D >, where delta is a constant and alpha the slope.
|
|
| 13. |
- Segad, Mo
(författare)
-
Synchrotron X-ray Scattering and Monte Carlo Simulations of Structure and Forces in Silicate Nanoplatelet Dispersions
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clays are the world’s most widely used natural material, however, little is known regarding the microstructure as well as the forces involved in clay-water interactions, and their influence on the swelling properties. The utilization of clay platelets is nowadays a key in a number of biological and industrial applications e.g. nuclear waste management. Bentonites from different natural sources and pure Na/Ca montmorillonite platelets have been studied experimentally and theoretically. Small angle X-ray scattering (SAXS), dynamic light scattering (DLS), nuclear magnetic resonance (NMR), X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM) and Cryogenic-TEM were applied to provide direct information about the structure of dry clays as well as clay platelets in equilibrium with a bulk solution of given ionic composition, temperature and pH. Monte Carlo (MC) simulations have been used to predict the osmotic pressure of montmorillonite dispersions. The swelling behavior is mainly regulated by counterion valency and surface charge density. Divalent counterions and high surface charge density lead to a limited swelling, while monovalent counterions favor a large swelling. This thesis has also investigated the aggregation of nanoplatelets in clay-water systems, in order to understand the effect of platelet size on the structure and swelling behavior. A new twist on aggregation phenomenon is that, really small platelets (~ 20 nm) do not form a tactoid, whereas larger platelets give rise to larger tactoids. The platelet size controls the aggregation and microstructure of silicate platelets into tactoids following an empirical relation as: N ≃ δ + α Deff, where N is the number of platelets per tactoid, Deff is the effective diameter of platelets, δ and α are constants.
|
|
| 14. |
- Segad, Mo, et al.
(författare)
-
Tactoid Formation in Montmorillonite
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:48, s. 25425-25433
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of Ca montmorillonite contain small clusters of clay platelets, often named "tactoids". In these tactoids, the platelets are arranged parallel to each other with a constant spacing of 1 nm. We have used small-angle X-ray scattering (SAXS) to determine the average number of platelets per tactoid, < N >. We found that this number depends on the platelet size, with larger platelets yielding larger tactoids. For a dispersion in equilibrium with a mixed electrolyte solution, the tactoid size also depends on the ratio of divalent to monovalent cations in the reservoir. Divalent counterions are strongly favored in this competition and will accumulate in the tactoids. In dispersions of pure sodium montmorillonite, that are equilibrated with a mixture of Na+ and Ca2+ cations, the Na+ cations initially cause a repulsion between the platelets, but the divalent ions rapidly replace the monovalent ones and lead to the formation of tactoids, typically within less than one hour based on the divalent to monovalent ratio. This cation exchange as well as tactoid formation can be semiquantitatively predicted from Monte Carlo simulations.
|
|
| 15. |
- Thuresson, Axel, et al.
(författare)
-
Flocculated Laponite-PEG/PEO dispersions with monovalent salt, a SAXS and simulation study.
- 2016
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 466, s. 330-342
-
Tidskriftsartikel (refereegranskat)abstract
- It is well-known that clay can form lamellar structures i.e. tactoids, and recently it has been shown that the tactoid formation is dependent on the platelet diameter. To the authors knowledge, no tactoid formation has been observed for montmorillonite platelets with a diameter less than 60nm. In this study, small angle X-ray scattering in combination with coarse-grained modeling and molecular dynamics simulations have been utilized to study the sediment of Laponite-polyethylene glycol/polyethylene oxide (PEG/PEO) at elevated salt concentrations (150mM-1M). Laponite consists of platelets with a diameter of 25nm and it is known to have a relatively monodisperse size-distribution. At pH 10, the face of the platelets has a strong negative charge, whereas the rim is slightly positive. Here we show that it is possible to induce tactoids for Laponite if two constraints are fulfilled: (1) addition of high amount of salt such as NaCl, and (2) addition of a neutral polymer such as PEG. The role of the salt is to screen the repulsive interactions between the platelets and the role of the polymer is to bridge the platelets together: hence the loss in configurational entropy of the polymer is counteracted by the gain in attractive polymer-platelet interaction. As the concentration of NaCl and/or PEG increases, the Bragg peak becomes sharper, which is an indication of that larger tactoids are formed. Comparison between Laponite and montmorillonite shows that the interlayer distance between the platelets increases linearly with an increased Debye screening length for both type of clays, whereas the structure peaks of Laponite are broader compared to the montmorillonite. We argue that the main reason to the latter is due to the size of the platelets: (i) smaller platelets are less rotationally restricted and (ii) the effect of positive edge charges is larger when the platelets are smaller, which results in more irregular aggregates. In absence of the polymer, montmorillonite form tactoids above ∼0.3MNaCl whereas Laponite does not. Even though the model used is simple, we find qualitative agreement between experiments and simulations, which verifies that the underlying physics for tactoid formation is captured.
|
|
| 16. |
- Tsironi, Ifigeneia, et al.
(författare)
-
Brine rejection and hydrate formation upon freezing of NaCl aqueous solutions
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:14, s. 7625-7632
-
Tidskriftsartikel (refereegranskat)abstract
- Studying the freezing of saltwater on a molecular level is of fundamental importance for improving freeze desalination techniques. In this study, we investigate the freezing process of NaCl solutions using a combination of X-ray diffraction and molecular dynamics simulations (MD) for different salt-water concentrations, ranging from seawater conditions to saturation. A linear superposition model reproduces well the brine rejection due to hexagonal ice Ih formation and allows us to quantify the fraction of ice and brine. Furthermore, upon cooling at T = 233 K, we observe the formation of NaCl center dot 2H(2)O hydrates (hydrohalites), which coexist with ice Ih. MD simulations are utilized to model the formation of NaCl crystal hydrates. From the simulations, we estimate that the salinity of the newly produced ice is 0.5% mass percent (m/m) due to ion inclusions, which is within the salinity limits of fresh water. In addition, we show the effect of ions on the local ice structure using the tetrahedrality parameter and follow the crystallite formation using the ion coordination parameter and cluster analysis.
|
|
