1
|
In-situ SAXS/WAXS investigations of the mechanically-induced phase transitions in semi-crystalline polyamides. POLYMER 2019. [DOI: 10.1016/j.polymer.2019.04.073] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
2
|
Dynamic Structuration of Physical Chitosan Hydrogels. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:12697-12707. [PMID: 29019693 DOI: 10.1021/acs.langmuir.7b02997] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We studied the microstructure of physical chitosan hydrogels formed by the neutralization of chitosan aqueous solutions highlighting the structural gradients within thick gels (up to a thickness of 16 mm). We explored a high polymer concentrations range (Cp ≥ 1.0% w/w) with different molar masses of chitosan and different concentrations of the coagulation agent. The effect of these processing parameters on the morphology was evaluated mainly through small-angle light scattering (SALS) measurements and confocal laser scanning microscopy (CLSM) observations. As a result, we reported that the microstructure is continuously evolving from the surface to the bulk, with mainly two structural transitions zones separating three types of hydrogels. The first zone (zone I) is located close to the surface of the hydrogel and constitutes a hard (entangled) layer formed under fast neutralization conditions. It is followed by a second zone (zone II) with a larger thickness (∼3-4 mm), where in some cases large pores or capillaries (diameter ∼10 μm) oriented parallel to the direction of the gel front are present. Deeper in the hydrogel (zone III), a finer oriented microstructure, with characteristic sizes lower than 2-3 μm, gradually replace the capillary morphology. However, this last bulk morphology cannot be regarded as structurally uniform because the size of small micrometer-range-oriented pores continuously increases as the distance to the surface of the hydrogel increases. These results could be rationalized through the effect of coagulation kinetics impacting the morphology obtained during neutralization.
Collapse
|
3
|
Self-assembly of maltoheptaose-b-PMMA block copolymer systems: 10nm Resolution in thin film and bulk states. Carbohydr Polym 2017; 170:15-22. [PMID: 28521981 DOI: 10.1016/j.carbpol.2017.04.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 04/11/2017] [Accepted: 04/12/2017] [Indexed: 11/29/2022]
Abstract
This paper describes the self-assembly of oligosaccharide-based hybrid block copolymers (BCPs) consisting of maltoheptaose (MH) and poly(methyl methacrylate) (PMMA) into 10nm scale lamellar and cylindrical phases depending on the volume fractions of MH (ϕMH) and the annealing process. Time resolved SAXS study of the BCP bulk samples during thermal annealing indicated that the BCPs phase separate into 10nm scale periodical structures. The solvent vapor annealing induced self-organizations of the BCP into different phases depending on ϕMH and the weight fraction of THF/H2O. BCPs with relatively higher ØMH, MH-b-PMMA3k (ϕMH=0.27) and MH-b-PMMA5k (ϕMH=0.16) self-organized into lamellar phases while the BCP sample with relatively lower ϕMH, MH-b-PMMA9k (ϕMH=0.10), self-organized into cylindrical phase by using THF/H2O=1/4 (w/w). On the other hand, the solvent vapor annealing with larger fraction of THF, i.e. THF/H2O=2/3 (w/w), induced cylindrical phases for MH-b-PMMA3k and MH-b-PMMA5k.
Collapse
|
4
|
Self-Assembly of Amphiphilic Biotransesterified β-Cyclodextrins: Supramolecular Structure of Nanoparticles and Surface Properties. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:7917-7928. [PMID: 28492333 DOI: 10.1021/acs.langmuir.7b01136] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A series of β-cyclodextrin (βCD) amphiphilic derivatives with varying degrees of substitution were prepared by acylating βCDs on their secondary face using thermolysin to catalyze the transesterification. After dissolution in acetone, the βCD-Cn derivatives (n = 8, 10, 12, 14) were nanoprecipitated in water, where they self-organized into structured particles that were characterized using cryo-transmission electron microscopy (cryo-TEM) images and small-angle X-ray scattering (SAXS) data. Two types of morphologies and ultrastructures were observed depending on the total degree of substitution (TDS) of the parent derivative. The molecules with TDS < 5 formed nanospheres with a multilamellar organization, whereas those with TDS > 5 self-assembled into barrel-like (n = 8, 10, 12) or more tortuous (n = 14) particles with a columnar inverse hexagonal structure. In particular, faceted βCD-C14 particles (TDS = 7) appeared to be composed of several domains with different orientations that were separated by sharp interfaces. Ultrastructural models were proposed on the basis of cryo-TEM images and the analysis of the contrast distribution in different projections of the lattice. Complementary compression isotherm experiments carried out at the air-water interface also suggested that differences in the molecular conformation of the series of derivatives existed depending on whether TDS was lower or higher than 5.
Collapse
|
5
|
|
6
|
Etude par absorption ultrasonore de la fixation sélective du potassium sur le κ-carraghénane. ACTA ACUST UNITED AC 2017. [DOI: 10.1051/jcp/1983800305] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
7
|
Tuning the Hydrophilic/Hydrophobic Balance to Control the Structure of Chitosan Films and Their Protein Release Behavior. AAPS PharmSciTech 2017; 18:1070-1083. [PMID: 27975192 DOI: 10.1208/s12249-016-0678-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2016] [Accepted: 11/22/2016] [Indexed: 11/30/2022] Open
Abstract
The control over the crystallinity of chitosan and chitosan/ovalbumin films can be achieved via an appropriate balance of the hydrophilic/hydrophobic interactions during the film formation process, which then controls the release kinetics of ovalbumin. Chitosan films were prepared by solvent casting. The presence of the anhydrous allomorph can be viewed as a probe of the hydrophobic conditions at the neutralization step. The semicrystalline structure, the swelling behavior of the films, the protein/chitosan interactions, and the release behavior of the films were impacted by the DA and the film processing parameters. At low DAs, the chitosan films neutralized in the solid state corresponded to the most hydrophobic environment, inducing the crystallization of the anhydrous allomorph with and without protein. The most hydrophilic conditions, leading to the hydrated allomorph, corresponded to non-neutralized films for the highest DAs. For the non-neutralized chitosan acetate (amorphous) films, the swelling increased when the DA decreased, whereas for the neutralized chitosan films, the swelling decreased. The in vitro release of ovalbumin (model protein) from chitosan films was controlled by their swelling behavior. For fast swelling films (DA = 45%), a burst effect was observed. On the contrary, a lag time was evidenced for DA = 2.5% with a limited release of the protein. Furthermore, by blending chitosans (DA = 2.5% and 45%), the release behavior was improved by reducing the burst effect and the lag time. The secondary structure of ovalbumin was partially maintained in the solid state, and the ovalbumin was released under its native form.
Collapse
|
8
|
Tensile Deformation of Bulk Polyamide 6 in the Preyield Strain Range. Micro–Macro Strain Relationships via in Situ SAXS and WAXS. Macromolecules 2017. [DOI: 10.1021/acs.macromol.6b02471] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
9
|
Baff and Rheumatic Autoimmune Disorders: Implications for Disease Management and Therapy. Int J Immunopathol Pharmacol 2016; 20:1-8. [PMID: 17346422 DOI: 10.1177/039463200702000101] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Interest in B-cells has been revived due to the description of new functions. Supporting a role for B-cells in the genesis of autoimmune diseases is the fact that the B-cell activating factor of the TNF ligand family (BAFF) is essential in their physiology. However, in each disease, this is restricted to a subgroup of patients. Based on experiments in mice, and validated in humans, this new cytokine has been highlighted. Excessive production of BAFF alters immune tolerance by rescuing self-binding B-cells. Overexpression in mice leads to autoimmune manifestation, and BAFF levels are elevated in the serum of autoimmune patients. Similar abnormalities occur in chronic lymphocytic leukemia. Recent works suggest that antagonizing the protein (or competing for its receptors) is relevant to the treatment. Advances in our understanding of the BAFF system offers the opportunity to improve our therapeutic approach.
Collapse
|
10
|
Hydrothermal Transformation of Wood Cellulose Crystals into Pseudo-Orthorhombic Structure by Cocrystallization. ACS Macro Lett 2016; 5:730-734. [PMID: 35614654 DOI: 10.1021/acsmacrolett.6b00273] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ultrastructural transformation of wood cellulose crystals by hydrothermal treatment was followed by synchrotron and standard X-ray scattering experiments. When treated at 200 °C for 2 h in the presence of an excess of water, a significant sharpening of the equatorial reflections of crystalline cellulose was observed, and the average crystallite size, estimated from the X-ray line broadening, was twice as large as that of untreated wood cellulose. During the treatment, the cellulose structure was converted from the native monoclinic form of cellulose I into a pseudo-orthorhombic system, coined as cellulose I', a transformation occurring only with an excess of water, above 180 °C and after more than half an hour. In situ experiments indicated that the increase of crystallite size was likely due to cocrystallization of individual crystallites rather than to the crystallization of the amorphous domains of cellulose.
Collapse
|
11
|
In situ time-resolved small-angle X-ray scattering observation of the fractal aggregation process in tin alkoxide polymeric solution. J Appl Crystallogr 2016. [DOI: 10.1107/s1600576716000297] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
SnO2 transparent gels have been synthesized from alkoxide precursor in toluene-2-propanol solvents. The chemical reactivity of transition metal alkoxides must be controlled in order to obtain sols and gels. In tin alkoxide based systems, this control can be achieved through complexation by a chelating agent such as acetylacetone. The gelation of the sols has been studied by in situ small-angle X-ray scattering (SAXS) measurements at the European Synchrotron Radiation Facility in Grenoble on the BM02 beamline. After the addition of water, primary particles are created and stick progressively together to form fractal aggregates. The primary particles are continually created during the aggregation process, which causes an evolution of the fractal dimension of the aggregate during gelation. This evolution is similar whatever the chemical composition is, meaning that the aggregation is ruled by one process which has been identified as reaction-limited cluster aggregation. Nevertheless, the final size of the aggregates is dependent on the chemical composition of the sols.
Collapse
|
12
|
In situ SAXS/WAXS investigation of the structural evolution of poly(vinylidene fluoride) upon uniaxial stretching. POLYMER 2016. [DOI: 10.1016/j.polymer.2015.12.041] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
|
13
|
On the strain-induced fibrillar microstructure of polyethylene: Influence of chemical structure, initial morphology and draw temperature. EXPRESS POLYM LETT 2016. [DOI: 10.3144/expresspolymlett.2016.29] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
14
|
Varying the counter ion changes the kinetics, but not the final structure of colloidal gels. J Colloid Interface Sci 2015; 463:137-44. [PMID: 26520820 DOI: 10.1016/j.jcis.2015.10.046] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 10/05/2015] [Accepted: 10/17/2015] [Indexed: 01/12/2023]
Abstract
We show that, while the gelation of colloidal silica proceeds much faster in the presence of added KCl than NaCl, the final gels are very similar in structure and properties. We have studied the gelation process by visual inspection and by small angle X-ray scattering for a range of salt and silica particle concentrations. The characteristic times of the early aggregation process and the formation of a stress-bearing structure with both salts are shown to collapse onto master curves with single multiplicative constants, linked to the stability ratio of the colloidal suspensions. The influence of the salt type and concentration is confirmed to be mainly kinetic, as the static structure factors and viscoelastic moduli of the gels are shown to be equivalent at normalized times. While there is strong variation in the kinetics, the structure and properties of the gel at long-times are shown to be mainly controlled by the concentration of particles, and hardly influenced by the type or the concentration of salt. This suggests that the differences between gels generated by different salts are only transient in time.
Collapse
|
15
|
Temperature-Microstructure Mapping of the Initiation of the Plastic Deformation Processes in Polyethylene via In Situ WAXS and SAXS. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b01258] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
16
|
Amorphous Phase Modulus and Micro–Macro Scale Relationship in Polyethylene via in Situ SAXS and WAXS. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b00181] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
17
|
Biophysical Analysis of the Molecular Interactions between Polysaccharides and Mucin. Biomacromolecules 2015; 16:924-35. [DOI: 10.1021/bm501832y] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
|
18
|
Sub-10 nm Scale Nanostructures in Self-Organized Linear Di- and Triblock Copolymers and Miktoarm Star Copolymers Consisting of Maltoheptaose and Polystyrene. Macromolecules 2015. [DOI: 10.1021/ma502295y] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
|
19
|
|
20
|
|
21
|
In-situ SAXS study of the mesoscale deformation of polyethylene in the pre-yield strain domain: Influence of microstructure and temperature. POLYMER 2014. [DOI: 10.1016/j.polymer.2014.02.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
22
|
Hybrid nanocomposites with tunable alignment of the magnetic nanorod filler. ACS APPLIED MATERIALS & INTERFACES 2014; 6:1583-1588. [PMID: 24428247 DOI: 10.1021/am404313s] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
For many important applications, the performance of polymer-anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite (α-FeOOH) nanorods, we produced goethite-poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1-5.5 vol %), we used the orientational order induced by the field in the isotropic phase rather than the spontaneous orientational order of the nematic phase. At the strongest field values (up to 1.5 T), the particles exhibit almost perfect antinematic alignment, as measured by optical birefringence and small-angle X-ray scattering. The results of these two techniques are in remarkably good agreement, validating the use of birefringence measurements for quantifying the degree of orientational order. We also demonstrate that the ordering induced by the field in the isotropic suspension is preserved in the final material after field removal. This work illustrates the interest, for such problems, of considering the field-induced alignment of anisotropic nanoparticles in the isotropic phase, an approach that is effective at low filler content, that avoids the need of controlling the nematic texture, and that allows tuning of the orientation level of the particles at will simply by adjusting the field intensity.
Collapse
|
23
|
Synthesis, Self-Assembly, and Thermal Caramelization of Maltoheptaose-Conjugated Polycaprolactones Leading to Spherical, Cylindrical, and Lamellar Morphologies. Macromolecules 2013. [DOI: 10.1021/ma4019526] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
24
|
In-situ SAXS study and modeling of the cavitation/crystal-shear competition in semi-crystalline polymers: Influence of temperature and microstructure in polyethylene. POLYMER 2013. [DOI: 10.1016/j.polymer.2013.07.055] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
25
|
Spinning of hydroalcoholic chitosan solutions. Carbohydr Polym 2013; 98:50-63. [PMID: 23987316 DOI: 10.1016/j.carbpol.2013.04.070] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Revised: 03/27/2013] [Accepted: 04/23/2013] [Indexed: 11/25/2022]
Abstract
We investigated the spinning of hydroalcoholic chitosan solutions. The dope composition was optimized in order to obtain a continuous alcogel fiber by water evaporation on heating the extruded hydroalcoholic solution. This alcogel fiber was then neutralized in aqueous alkali baths and washed in water to eliminate the residual alcohol and salts before final drying. Depending on the alcohol content in the filament at the neutralization step, on specific alcohol-chitosan interactions and on the nature and concentration of the coagulation base, the process yielded semicrystalline chitosan fibers with different proportions of anhydrous and hydrated allomorphs. Contrarily to the classical annealing method, the formation of mainly anhydrous crystals was obtained without significant molecular weight decrease by neutralizing the polymer in hydrophobic conditions. The control of allomorph content was shown to be related to the hydrophobicity of the solvent (alcohol fraction) at the neutralization step.
Collapse
|
26
|
Electro-induced orientational ordering of anisotropic pigment nanoparticles. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2013; 371:20120257. [PMID: 23459960 DOI: 10.1098/rsta.2012.0257] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The response of anisotropic pigment particle suspensions to externally applied electric fields has been explored for possible application in reflective display technologies. Three different types of pigment particle were suspended in dodecane, using a polymeric stabilizer, and showed Schlieren textures between crossed polarizers at high concentrations (greater than 25-30 wt%), indicating the formation of colloidal nematic phases. Orientational order parameters were determined by X-ray scattering, and the influence of polydispersity on the values is discussed. X-ray scattering measurements also demonstrated a change in the structure factor consistent with the onset of a colloidal nematic phase. In addition, the pigment particles were dispersed into various liquid crystal hosts at low concentrations (less than 5 wt%) with and without the presence of mesogenic mimic stabilizers. However, the influence of these stabilizers on orientational ordering could not be confirmed. The electro-induced ordering determined via scattering was related to the electro-optical response of each suspension using a simple model. The particles in nematic hosts not only showed a high degree of orientational ordering at lower electric field strengths, but also showed a reduction in stability. Although these systems have shown strong orientational ordering, the optical response has been limited by the intrinsic shape of the pigment particles and the distribution of the transition dipoles moments within them. Nevertheless, the feasibility of developing materials for display applications has been demonstrated.
Collapse
|
27
|
Control of 10 nm scale cylinder orientation in self-organized sugar-based block copolymer thin films. NANOSCALE 2013; 5:2637-41. [PMID: 23443358 DOI: 10.1039/c3nr00332a] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The present paper describes the orientational control of 10 nm scale cylinders in sugar-based block copolymer thin films by simply varying the composition of the annealing co-solvent. The affinity of the block copolymer to the solvent vapor could be systematically adjusted in this way.
Collapse
|
28
|
Effect of Enzyme Concentration of the Morphology and Properties of Enzymatically Triggered Peptide Hydrogels. Biomacromolecules 2013; 14:1403-11. [DOI: 10.1021/bm4000663] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
|
29
|
Sub-10 nm Nano-Organization in AB2- and AB3-Type Miktoarm Star Copolymers Consisting of Maltoheptaose and Polycaprolactone. Macromolecules 2013. [DOI: 10.1021/ma3026578] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
30
|
10 nm Scale Cylinder-Cubic Phase Transition Induced by Caramelization in Sugar-Based Block Copolymers. ACS Macro Lett 2012; 1:1379-1382. [PMID: 35607110 DOI: 10.1021/mz300543u] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To date, the feature size of microphase separation in block copolymers has been downsizing to 10 nm scale. However, morphological control for such a small feature is still a challenging task. The present Letter discusses a phase transition in a natural/synthetic "hybrid" block copolymer system based on an oligosaccharide and poly(ε-caprolactone) via thermal annealing. Time-resolved small-angle X-ray scattering investigation as a function of temperature indicated the phase transition from hexagonally close-packed cylinder to body-centered cubic at 10 nm scale. Atomic force microscope images of the block copolymer thin films annealed at different temperatures clearly confirmed the existence of these morphologies. The driving force of this phase transition (from cylinder to cubic) is the change of volume fraction of the block copolymer due to thermal caramelization.
Collapse
|
31
|
Effect of peptide and guest charge on the structural, mechanical and release properties of β-sheet forming peptides. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:16196-206. [PMID: 23088490 DOI: 10.1021/la303328p] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The effect of peptide charge on the self-assembly, gelation behavior, and model drug release profiles has been explored here for three octa-peptides, VEVKVEVK (VEK2), VKVKVEVK (VEK3), and VEVEVKVE (VEK1), that carry a net charge of 0, +2, and -2 at neutral pH, respectively. Transparent, self-supporting hydrogels were found to form above a critical concentration when the peptide charge modulus was >1 and this was independent of the sign of the charge. TEM, SAXS, and shear rheology revealed that there were no differences in hydrogel structure or mechanical properties when the peptides were at the same concentration and carried the same charge modulus. All peptides were found to form dense fibrillar networks formed by β-sheet rich single fibers where lateral aggregation of the fibers occurred and increased with decreasing charge modulus. Such behavior was found to correlate with an increase in hydrogel mechanical properties, demonstrating that fiber lateral aggregation is inextricably linked with the mechanical properties of these hydrogels. Two hydrophilic model drug molecules, namely napthol yellow (NY) and martius yellow (MY), were subsequently incorporated within the VEK1 and VEK3 hydrogels at pH 7 and although they did not effect the self-assembly of the peptide at a molecular level, they did effect the level of lateral fiber aggregation observed and, therefore, the mechanical properties of the hydrogels. The release of each molecule from the hydrogels was monitored over time and shown to be controlled by Fickian diffusion where the diffusion rate, D, was dependent on the ratio between the overall effective charges carried by the peptide, i.e., the fibrillar network, and the overall charges carried by the guest molecules, but independent from the hydrogel concentration and mechanical properties within the ranges investigated. This work highlights the possibility of controlling the rate of release of small drug molecules by manipulating the charges on the guest molecules as well as the charged state of the self-assembling peptide.
Collapse
|
32
|
Tubulin posttranslational modifications as regulators of microtubule-based functions in cells. Cilia 2012. [PMCID: PMC3555722 DOI: 10.1186/2046-2530-1-s1-p17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
|
33
|
|
34
|
Chitosan-based nanocapsules: physical characterization, stability in biological media and capsaicin encapsulation. Colloid Polym Sci 2012. [DOI: 10.1007/s00396-012-2669-z] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
|
35
|
Oligosaccharide/silicon-containing block copolymers with 5 nm features for lithographic applications. ACS NANO 2012; 6:3424-3433. [PMID: 22456229 DOI: 10.1021/nn300459r] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Block copolymers demonstrate potential for use in next-generation lithography due to their ability to self-assemble into well-ordered periodic arrays on the 3-100 nm length scale. The successful lithographic application of block copolymers relies on three critical conditions being met: high Flory-Huggins interaction parameters (χ), which enable formation of <10 nm features, etch selectivity between blocks for facile pattern transfer, and thin film self-assembly control. The present paper describes the synthesis and self-assembly of block copolymers composed of naturally derived oligosaccharides coupled to a silicon-containing polystyrene derivative synthesized by activators regenerated by electron transfer atom transfer radical polymerization. The block copolymers have a large χ and a low degree of polymerization (N) enabling formation of 5 nm feature diameters, incorporate silicon in one block for oxygen reactive ion etch contrast, and exhibit bulk and thin film self-assembly of hexagonally packed cylinders facilitated by a combination of spin coating and solvent annealing techniques. As observed by small angle X-ray scattering and atomic force microscopy, these materials exhibit some of the smallest block copolymer features in the bulk and in thin films reported to date.
Collapse
|
36
|
Reorientation of cellulose nanowhiskers in agarose hydrogels under tensile loading. Biomacromolecules 2012; 13:850-6. [PMID: 22295902 DOI: 10.1021/bm201764y] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Agarose hydrogels filled with cellulose nanowhiskers were strained in uniaxial stretching under different humidity conditions. The orientation of the cellulose whiskers was examined before and after testing with an X-ray laboratory source and monitored in situ during loading by synchrotron X-ray diffraction. The aim of this approach was to determine the process parameters for reorienting the cellulose nanowhiskers toward a preferential direction. Results show that a controlled drying of the hydrogel is essential to establish interactions between the matrix and the cellulose nanowhiskers which allow for a stress transfer during stretching and thereby promote their alignment. Rewetting of the sample after reorientation of the cellulose nanowhiskers circumvents a critical increase of stress. This improves the extensibility of the hydrogel and is accompanied by a further moderate alignment of the cellulose nanowhiskers. Following this protocol, cellulose nanowhiskers with an initial random distribution can be reoriented toward a preferential direction, creating anisotropic nanocomposites.
Collapse
|
37
|
Influence of monovalent ions on density fluctuations in hydrothermal aqueous solutions by small angle X-ray scattering. J Chem Phys 2012; 136:044515. [PMID: 22299899 DOI: 10.1063/1.3679021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Synchrotron small angle X-ray scattering measurements on water and alkaline bromine aqueous solutions (XBr, with X = Li, Rb, or Cs) were carried out from ambient to supercritical conditions. The temperature was increased from 300 to 750 K along several isobars between 24 and 35 MPa. The correlation length and the structure factor were extracted from the data following the Ornstein-Zernike formalism. We obtained experimental evidence of the shift of the critical point and isochore and their dependence on the ions concentration (0.33 mol/kg and 1.0 mol/kg). We also observed that the size of the density fluctuations and the structure factor increase with the presence of the ions and that this effect is positively correlated with the atomic number of the cation. These behaviors were compared with ZnBr(2) and NaCl systems from the literature.
Collapse
|
38
|
|
39
|
Kinetics of the Formation of 2D-Hexagonal Silica Nanostructured Materials by Nonionic Block Copolymer Templating in Solution. J Phys Chem B 2011; 115:11330-44. [DOI: 10.1021/jp200213k] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
40
|
Structure of Micelles of a Nonionic Block Copolymer Determined by SANS and SAXS. J Phys Chem B 2011; 115:11318-29. [DOI: 10.1021/jp200212g] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
41
|
SAXS study of phase separation process in the SiO 2-SnO 2nanostructured materials. Acta Crystallogr A 2011. [DOI: 10.1107/s0108767311089963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
|
42
|
Aqueous suspensions of natural swelling clay minerals. 1. Structure and electrostatic interactions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:5562-5573. [PMID: 21476528 DOI: 10.1021/la2001255] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10(-3) M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order.
Collapse
|
43
|
Nano-organization of amylose-b-polystyrene block copolymer films doped with bipyridine. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:4098-4103. [PMID: 21395269 DOI: 10.1021/la104936k] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
This paper discusses the self-assembly of rod-coil amylose-b-polystyrene (Mal-b-PS) block copolymer thick and thin films. The nano-organization falls in an interdomain spacing d of about 10 nm, much smaller than flexible-flexible petrol block copolymer systems. Additionally, hydrogen-bonding interactions between carbohydrate rods (amylose) and 4',4-bipyridine (bipy) molecules induces phase transitions. Indeed, adding bipy in maltooctadecaose-block-polystyrene (Mal18-b-PS) copolymers results, at room temperature, in the formation of a lamellar phase having Mal18 bipy-rich nanodomains instead of hexagonal close-packed (HCP) of cylinders made of Mal18, whereas a coexistence of Mal7bipy-rich cylindrical and spherical nanodomains are formed from maltoheptaose-b-polystyrene (Mal7-b-PS) copolymers instead of a poorly organized array of Mal7-based cylinders. On heating, the Mal7bipy-b-PS system shows more rich phase behavior as compared to the Mal7-b-PS one due to weakening of hydrogen bonding with temperature. Such a system is of great interest in developing active layers in light-emitting diodes (LEDs) or in photovoltaic cells to realize devices with an optimal structure, that is, having large interface area and domain size with similar exciton diffusion length (10 nm).
Collapse
|
44
|
Phase-Separation Kinetics and Mechanism in a Methylcellulose/Salt Aqueous Solution Studied by Time-Resolved Small-Angle Light Scattering (SALS). MACROMOL CHEM PHYS 2011. [DOI: 10.1002/macp.201000697] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
45
|
Structure of Polyelectrolytes with Mixed Monovalent and Divalent Counterions: SAXS Measurements and Poisson−Boltzmann Analysis. Macromolecules 2011. [DOI: 10.1021/ma102226v] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
46
|
|
47
|
Nanostructured Films Made from Zwitterionic Phosphorylcholine Diblock Copolymer Systems. Macromolecules 2011. [DOI: 10.1021/ma1029554] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
48
|
Micron range morphology of physical chitosan hydrogels. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:17495-17504. [PMID: 20879755 DOI: 10.1021/la102907u] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Physical chitosan hydrogels are potential biomaterials for several biomedical applications, such as wound healing, tissue repair, and drug delivery. Controlling the microstructural organization of chitosan gels is one of the keys for monitoring the physical, mechanical, and biological properties. As a result, the main objective of the present work was to explore the microstructural organization of chitosan hydrogels in relation with the processing conditions of gelation. For this purpose, different gelation routes were studied, that is, chitosan solution neutralization of an aqueous or hydroalcoholic solution and neutralization of an alco-gel. Overall, the resulting morphology after processing was determined by the medium viscosity during neutralization and the nature and concentration of the base. The effect of these processing parameters on the morphology was evaluated mainly through small angle light scattering (SALS) measurements including in situ measurements during chitosan neutralization. As a result, we reported different bulk microstructures consisting in 200-400 nm aggregates (primary particles) agglomerated into micrometer range clusters or arranged into more organized structures, that is, forming microchannels (4-6 μm). We thus established a qualitative and quantitative relation between supramolecular morphology and gelation conditions of chitosan hydrogels.
Collapse
|
49
|
New Insights on the Strain-Induced Mesophase of Poly(d,l-lactide): In Situ WAXS and DSC Study of the Thermo-Mechanical Stability. Macromolecules 2010. [DOI: 10.1021/ma101430c] [Citation(s) in RCA: 191] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
|
50
|
New Insight on Initiation of Cavitation in Semicrystalline Polymers: In-Situ SAXS Measurements. Macromolecules 2010. [DOI: 10.1021/ma101042d] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|