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.

[OPEN ACCESS] Carbon aerogels from bacterial nanocellulose as anodes for lithium ion batteries - RSC Advances

Liping Wang, Christina Schütz, German Salazar-Alvarez, and M. Magdalena Titirici
RSC Advances, 2014
DOI: 10.1039/C3RA47853J


Abstract:
Carbon aerogels with large open pores and high surface area are fabricated via pyrolysis of a readily available natural resource, e.g., bacterial nanocellulose (BNC) aerogels. Freeze-drying of the BNC hydrogels is used to preserve the 3D open network structure upon calcination whereas using Fe(III) improves the yield and H/C ratio. These carbon aerogels are explored as anodes in lithium ion batteries where it is shown that they deliver superior capacity retention and rate performance compared to other carbon-based materials.

Macroscopic Control of Helix Orientation in Films Dried from Cholesteric Liquid-Crystalline Cellulose Nanocrystal Suspensions

ChemPhysChem, 2014

DOI: 10.1002/cphc.201400062

Ji Hyun Park; JungHyun Noh; Christina Schütz; German Salazar-Alvarez; Giusy Scalia; Lennart Bergström; Jan P. F. Lagerwall

Abstract:

The intrinsic ability of cellulose nanocrystals (CNCs) to self-organize into films and bulk materials with helical order in a cholesteric liquid crystal is scientifically intriguing and potentially important for the production of renewable multifunctional materials with attractive optical properties. A major obstacle, however, has been the lack of control of helix direction, which results in a defect-rich, mosaic-like domain structure. Herein, a method for guiding the helix during film formation is introduced, which yields dramatically improved uniformity, as confirmed by using polarizing optical and scanning electron microscopy. By raising the CNC concentration in the initial suspension to the fully liquid crystalline range, a vertical helix orientation is promoted, as directed by the macroscopic phase boundaries. Further control of the helix orientation is achieved by subjecting the suspension to a circular shear flow during drying.

Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy

Phys. Rev. B 89, 064402 (2014)
DOI: 10.1103/PhysRevB.89.064402

S. Disch, R. P. Hermann, E. Wetterskog, A. A. Podlesnyak, K. An, T. Hyeon, G. Salazar-Alvarez, L. Bergström, and Th. Brückel

Abstract:

We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Landé factor g=2.05(2) as expected for maghemite (γ-Fe2O3) nanoparticles. A large effective anisotropy field of BA,eff=0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles.