Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions

Johan Sundberg, Valentina Guccini, Karl M.O. Håkansson, German Salazar-Alvarez, Guillermo Toriz, Paul Gatenholm

Polymer 75 (2015) 119-124.
DOI: 10.1016/j.polymer.2015.08.035

Highlights:
• Strong cellulose fibers spun from ionic liquid solution.
• Extrusion process simulated in silica based upon rheological measurements.
• Increased DO for fibers regenerated with ethanol stretched at high RH.
• Significant improvement of mechanical properties for re-oriented fibers.
• Mechanical properties comparable to commercially available fibers.

Abstract:
Cellulose is difficult to solubilize and undergoes thermal decomposition prior to melting. In recent years ionic liquids have been evaluated as solvents of cellulose. In the regeneration process the non-solvent governs the resulting material's crystallinity. Water adsorbs to amorphous cellulose, acts as plasticizer and lowers the Tg, hence the degree of crystallinity will affect the potential strain induced reorientation. We prepared regenerated cellulose fibers form ionic liquid using different non-solvents. The influence of shear forces upon cellulose chain alignment during extrusion was simulated in silica based upon rheological measurements. The regenerated fibers had different physical, morphological and mechanical properties. Molecular re-orientation in fibers induced by mechanical strain, at humidities above the Tg, resulted in much improved mechanical properties with the Young's modulus reaching 23.4 ± 0.8 GPa and the stress at break 504.6 ± 51.9 MPa, which is comparable to commercially available cellulose fibers.

[OPEN ACCESS] Rod Packing in Chiral Nematic Cellulose Nanocrystal Dispersions Studied by Small-Angle X-ray Scattering and Laser Diffraction

Christina Schütz, Michael Agthe, Andreas B. Fall, Korneliya Gordeyeva, Valentina Guccini, Michaela Salajková, Tomás S. Plivelic, Jan P. F. Lagerwall, German Salazar-Alvarez, and Lennart Bergström
Langmuir 31 (2015) 6507–6513.
DOI: 10.1021/acs.langmuir.5b00924

Abstract

The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic–anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from ≈15 μm down to ≈2 μm as ϕ increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1° up to 4° as ϕ increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.

[OPEN ACCESS] Fabrication of nanocellulose–hydroxyapatite composites and their application as water-resistant transparent coatings

Mai Ishikawa, Yuya Oaki, Yoshihisa Tanaka, Hideki Kakisawa, German Salazar-Alvarez and    Hiroaki Imai

J. Mater. Chem. B, 2015, Advance Article
DOI: 10.1039/C5TB00927H

Abstract
Nanosized composite rods ~300 nm in length and ~20 nm in width were produced by deposition of 22–77 wt% of a c-axis-oriented hydroxyapatite (HA) on cellulose nanocrystals (CNCs). The CNCs functionalized with sulphonic groups were covered with the HA nanocrystals through controlled nucleation and growth under a moderately supersaturated condition in a solution system based on a simulated body fluid. Water-resistant transparent coatings 2–4 μm thick were obtained via evaporation-induced assembly of CNC–HA nanocomposites by casting their suspension on a glass substrate and the subsequent growth of HA nanocrystals by vapour hydrothermal treatment. The composite coatings exhibited improved mechanical strength compared to that of crustacean exoskeletons, and potential for bone regeneration.

[PhD defence] Christina Schütz – Fabrication of nanocellulose-based materials - Liquid crystalline phase formation and design of inorganic–nanocellulose hybrids

Christina Schütz​ has (literally) nailed her thesis and the dissertation will be on May 29th (See link). The full text of the thesis can be found at DiVA.

[REVIEW] [OPEN ACCESS] Mesocrystals in Biominerals and Colloidal Arrays

Lennart Bergström, Elena V. Sturm (née Rosseeva), German Salazar-Alvarez, and Helmut Cölfen

Accounts of Chemical Research (2015)

DOI: 10.1021/ar500440b

Abstract

Mesocrystals, which originally was a term to designate superstructures of nanocrystals with a common crystallographic orientation, have now evolved to a materials concept. The discovery that many biominerals are mesocrystals generated a large research interest, and it was suggested that mesocrystals result in better mechanical performance and optical properties compared to single crystalline structures. Mesocrystalline biominerals are mainly found in spines or shells, which have to be mechanically optimized for protection or as a load-bearing skeleton. Important examples include red coral and sea urchin spine as well as bones. Mesocrystals can also be formed from purely synthetic components. Biomimetic mineralization and assembly have been used to produce mesocrystals, sometimes with complex hierarchical structures. Important examples include the fluorapatite mesocrystals with gelatin as the structural matrix, and mesocrystalline calcite spicules with impressive strength and flexibility that could be synthesized using silicatein protein fibers as template for calcium carbonate deposition. Self-assembly of nanocrystals can also result in mesocrystals if the nanocrystals have a well-defined size and shape and the assembly conditions are tuned to allow the nanoparticles to align crystallographically. Mesocrystals formed by assembly of monodisperse metallic, semiconducting, and magnetic nanocrystals are a type of colloidal crystal with a well-defined structure on both the atomic and mesoscopic length scale.

Mesocrystals typically are hybrid materials between crystalline nanoparticles and interspacing amorphous organic or inorganic layers. This structure allows to combine disparate materials like hard but brittle nanocrystals with a soft and ductile amorphous material, enabling a mechanically optimized structural design as realized in the sea urchin spicule. Furthermore, mesocrystals can combine the properties of individual nanocrystals like the optical quantum size effect, surface plasmon resonance, and size dependent magnetic properties with a mesostructure and morphology tailored for specific applications. Indeed, mesocrystals composed of crystallographically aligned polyhedral or rodlike nanocrystals with anisotropic properties can be materials with strongly directional properties and novel collective emergent properties. An additional advantage of mesocrystals is that they can combine the properties of nanoparticles with a structure on the micro- or macroscale allowing for much easier handling.

In this Account, we propose that mesocrystals are defined as “a nanostructured material with a defined long-range order on the atomic scale, which can be inferred from the existence of an essentially sharp wide-angle diffraction pattern (with sharp Bragg peaks) together with clear evidence that the material consists of individual nanoparticle building units”. We will give several examples of mesocrystals and discuss the structural characteristics for biominerals, biomimetic materials, and colloidal arrays of nanocrystals. The potential of the mesocrystal materials concept in other areas will be discussed and future developments envisioned.

[OPEN ACCESS] Origin of the Large Dispersion of Magnetic Properties in Nanostructured Oxides: FexO/Fe3O4 Nanoparticles as a Case Study

M. Estrader, A. López-Ortega, I. V. Golosovsky, S. Estradé, G. Salazar-Alvarez, Ll. López- Conesa, D. Tobia, E. Winkler, J. D. Ardisson, W.A.A. Macedo, M. Vasilakaki, K. N. Trohidou, R. D. Zysler, F. Peiró, L. Bergström, and J. Nogués

Nanoscale (2015)
DOI: 10.1039/C4NR06351A

Abstract:
The intimate relationship in transition-metal oxides between stoichiometry and physiochemical properties makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides.

Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide

Bernd Wicklein, Andraž Kocjan, German Salazar-Alvarez, Federico Carosio, Giovanni Camino, Markus Antonietti, and Lennart Bergström

Nature Nanotechnology 10 (2015) 277–283
DOI:10.1038/nnano.2014.248

Abstract
High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW/m·K, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.

[OPEN ACCESS] Precise control over shape and size of iron oxide nanocrystals suitable for assembly into ordered particle arrays

Erik Wetterskog, Michael Agthe, Arnaud Mayence, Jekabs Grins, Dong Wang, Subhasis Rana, Anwar Ahniyaz, German Salazar-Alvarez and Lennart Bergström

Sci. Technol. Adv. Mater. 15 (2014) 055010
DOI:10.1088/1468-6996/15/5/055010

Abstract
Here we demonstrate how monodisperse iron oxide nanocubes and nanospheres with average sizes between 5 and 27 nm can be synthesized by thermal decomposition. The relative importance of the purity of the reactants, the ratio of oleic acid and sodium oleate, the maximum temperature, and the rate of temperature increase, on robust and reproducible size and shape-selective iron oxide nanoparticle synthesis are identified and discussed. The synthesis conditions that generate highly monodisperse iron oxide nanocubes suitable for producing large ordered arrays, or mesocrystals are described in detail.

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

A. López-Ortega, M. Estrader, G. Salazar-Alvarez, A.G. Roca, J. Nogués
Physics Reports, 2014, accepted manuscript
DOI: 10.1016/j.physrep.2014.09.007

Abstract:
The applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural-morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of prospective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed.

[OPEN ACCESS] Probing planar defects in nanoparticle superlattices by 3D small-angle electron diffraction tomography and real space imaging

Arnaud Mayence, Dong Wang, German Salazar-Alvarez, Peter Oleynikov and Lennart Bergström
Nanoscale, 2014, Accepted Manuscript
DOI: 10.1039/C4NR04156A

Abstract
We demonstrate how the acquisition and processing of 3D electron diffraction data can be extended to characterize structural features on the mesoscale, and show how lattice distortions in superlattices of self-assembled spherical Pd nanoparticles can be quantified using small-angle electron diffraction tomography (3D SA-EDT). Transmission electron microscopy real space imaging and 3D SA-EDT reveals a high density of stacking faults that was related to a competition between fcc and hcp arrangements during assembly. Information of the orientation of the stacking faults was used to make analogies between planar defects in the superlattices and Shockley partial dislocations in metallic systems.

Oriented aggregation of lepidocrocite and impact on surface charge development

Philipp A. Kozin, German Salazar-Alvarez, and Jean-François Boily

Langmuir 30 (2014) 9017–9021

DOI: 10.1021/la500507e

Abstract

The impact of lepidocrocite (γ-FeOOH) nanoparticle aggregation on mineral surface charge development was resolved in aqueous solutions of NaCl and NaClO4. Synthetic rod-like particles exhibiting charged edge (100) and neutrally/low-charged (010) faces self-aggregated in salt-free solutions. Aggregation was notably imaged by high-resolution transmission electron microscopy, and inferred by decreases in N2(g)-B.E.T. specific surface area from 94 m2/g to 77 m2/g after 12 months, and to 66 m2/g after 33 months storage. Potential determining (H+, OH–) ions loadings in the 4–11 pH range were unchanged only if the particles remained aggregated in NaCl but only if they were disaggregated in NaClO4. These differences, alongside molecular simulations and experimental ion loadings resolved in other studies from our group, point to important controls on background electrolyte ion identity on the aggregation and charge development in lepidocrocite. These results may apply further to other mineral surfaces of comparable surface (hydr)oxo populations.

[Summer school] Organic–inorganic hybrids and composites: from basic understanding to functional materials

The Chalmers Soft Matter Graduate School is organizing a summer school on “Organic–inorganic hybrids and composites: from basic understanding to functional materials”.  Please find attached the announcement. The summer school will take place between 2-5 of september lunch to lunch and it will be held in Djurönäset in the Stockholm archipelago (www.djuronaset.com).

Scope:
Organic–inorganic hybrids and composites have been playing a major role in research and society in recent years. Traditionally, organic–inorganic hybrids have had a focus on the polymeric matrix filled with relatively passive inorganic components. In parallel, with increased interest in alternatives to fossil fuels, there has been a strong move towards the fabrication of functional materials based on biopolymers that can be extracted from renewable sources. Hybrids and composites based on biopolymers are an ideal component for the fabrication of multifunctional materials in combination with various useful inorganic nanomaterials as they can combine impressive properties with environmentally benign and energy efficient production routes.
This course aims to give the participants an understanding of the properties of the organic and inorganic components, preparation methods, characterisation techniques and also examples of functional hybrid materials.

Topics that will be covered:
• Biopolymers: Properties of biopolymers (cellulose, chitin, DNA, proteins) in solutions and dispersions, JL.
• Bionanomaterials: Types of bionanomaterials, sources and isolation methods, GSA
• Nucleation and assembly: i) Nucleation and growth of inorganic materials, ii)Colloidal processing and assembly of hybrids, LB
• Optical characterisation: Polarised light microscopy, JL
• Morphological characterisation: Electron microscopy and X-ray scattering, GSA
• Surface characterisation: Catechols as model systems, DRM
• Interfacial characterisation: Solid state NMR, DL
• Mechanical characterisation: Tensile, flexural, compression testing and fracture toughness measurements, RL
• Bioinspired composites: High performance composites, RL

Lecturers:

Lennart Bergström (Stockholm University)
Jan Lagerwall (University of Luxembourg)
Danielle Laurencin (Institute Charles Gerhardt of Montpellier, France)
Rafael Libanori (ETH, Zurich, Switzerland)
Daniel Ruiz-Molina (Institut Català de Nanociència i Nanotecnologia, Spain)

German Salazar-Alvarez (Stockholm University)

Registration: 
To apply to the summer school send an email to Christina Schütz (christina.schuetz@mmk.su.se) not later than July 28, 2014. The number of participants is limited to 30 and there is a priority to those students enrolled in the “Soft Matter Graduate School”at Chalmers University (www.chalmers.se/soft/); other students and participants are accepted on a first come, first serve basis. The summer school is free of charge for all students doing their PhD at a Swedish university. For students abroad and other participants, the fee is 6000 SEK (incl. accommodation and all meals; excl. VAT).

Schedule and examination:

time\date	Tuesday 2nd	Wednesday 3rd	Thursday 4th	Friday 5th
9-11.30		Nucleation and assembly	Surface characterisation	Project presentations
11.30-13.00	Arrival and lunch	Lunch	Lunch	Lunch and departure
13.00-15	Biopolymer dispersions and solutions	Optical characterisation	Interfacial characterisation
15-17	Bionanomaterials	Morphological characterisation	Mechanical characterisation
17-18	Free time
18-20	Dinner	School dinner	Dinner
20-21	Project assignments		Bioinspired composites

The students are expected to work actively during the course and the participants will receive material to study in advance. During the course there will be individual assignments and individual presentations. We recommend that students after completing the course will be given 3 ECTS.


Contact:
• German Salazar-Alvarez (course leader) (german@mmk.su.se)
• Christina Schütz (registration and practical issues) (christina.schuetz@mmk.su.se) 

Postdoctoral fellowship in 3D electron microscopy studies of nanoparticles and nanoparticle arrays

Re. SU FV-1248-14. Last application date: 2014-05-09.

Stockholm University, a modern university with a multicultural environment, is one of the world’s top 100 higher education institutes. Here more than 60,000 students and 5,000 staff are active within science, the humanities and the social sciences. Stockholm is a cultural hub and economic centre, with many green areas and surrounded by water, making it an ideal place in which to enjoy a relaxed and exciting student life.

         MMK is a leading institution in materials synthesis and structure characterization. We have recently obtained a large grant for the project “3D Electron Microscopy for Nanostructure Research (3DEM- NATUR)” from the Knut and Alice Wallenberg Foundation. The 3DEM-NATUR project aims at developing new transmission electron microscopy methods to obtain 3D structural information for studying atomic and mesoscopic arrangements in solids, on surfaces and at interfaces. More information about the 3DEM-NATUR project can be found at http://www.mmk.su.se/page.php?pid=945.

         We are interested in studying nanoparticles and self-assembled nanoparticle arrays using various 3-dimensional transmission electron microscopy (TEM) techniques. Techniques involve the recently developed Rotation Electron Diffraction (RED) method and other EM techniques such as electron tomography, and STEM‐HAADF, STEM‐EELS and electron holography may also be applied.

Assessment criteria

The candidate must have obtained a PhD degree in chemistry, physics, materials science or other relevant field no more than three years prior the application deadline, unless there are special circumstances that should be taken into account. These might be illness, parental leave, union duties or similar. The applicant should have excellent English language skills, both oral and written communication.

         Proven experience in TEM and nanoparticle synthesis is essential. Experience in nanoparticle assembly and crystallography is desirable.

Terms of employment

The scholarship is for one year with the possibility of one-year extension. The preferred starting date is 4th of August 2014.

Stockholm University strives to be a workplace free from discrimination and offers equal opportunities to everyone.

More information
For further information about the position, please contact German Salazar-Alvarez, telephone +46-(0)8-163942 or german@mmk.su.se

Application

The application should be written in Swedish or English and contain:

    – Cover letter describing the interest and skills of the applicant

    – CV with publication list (including DOI),

    – Copy of PhD degree certificate,

    – Contact information for 2 reference persons

Welcome with your application, marked with the reference number SU FV-1248-14, no later than 9 May, 2014 by e-mail to: registrator@su.se.

Applications that are submitted electronically should be in Word (.doc/.docx) or PDF format. Please include the reference number SU FV-1248-14 also in the message line.