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Nanocellulose is a term referring to a family of cellulosic materials that have at least one of their dimensions in the nanoscale. Examples of nanocellulosic materials are microfibrilated cellulose, cellulose nanofibers or cellulose nanocrystals. Nanocellulose may be obtained from natural cellulose fibers through a variety of production processes. This family of materials possesses interesting properties suitable for a wide range of potential applications.
Micro cellulose (MFC) is a type of nanocellulose that is more heterogeneous than cellulose nanofibers or nanocrystals as it contains a mixture of nano- and micron-scale particles. The term is sometimes misused to refer to cellulose nanofibers instead. [1] [2]
Cellulose nanofibers (CNF), also called nanofibrillated cellulose (NFC), are nanosized cellulose fibrils with a high aspect ratio (length to width ratio). Typical fibril widths are 5–20 nanometers with a wide range of lengths, typically several micrometers.
The fibrils can be isolated from natural cellulose, generally wood pulp, through high-pressure, high temperature and high velocity impact homogenization, grinding or microfluidization (see manufacture below). [3] [4] [5]
Cellulose nanocrystals (CNCs), or nanocrystalline cellulose (NCC), are highly crystalline, rod-like nanoparticles. [6] [7] They are usually covered by negatively charged groups that render them colloidally stable in water. They are typically shorter than CNFs, with a typical length of 100 to 1000 nanometers. [8]
Some cellulose producing bacteria have also been used to produce nanocellulosic materials that are then referred to as bacterial nanocellulose. [9] The most common examples being Medusomyces gisevii (the bacteria involved in the making of Kombucha) and Komagataeibacter xylinus (involve in the fabrication of Nata de coco), see bacterial cellulose for more details. This naming distinction might arise from the very peculiar morphology of these materials compared to the more traditional ones made of wood or cotton cellulose. In practice, bacterial nanocellulosic materials are often larger than their wood or cotton counterparts.
The discovery of nanocellulosic materials can be traced back to late 1940s studies on the hydrolysis of cellulose fibers. [2] Eventually it was noticed that cellulose hydrolysis seemed to occur preferentially at some disordered intercrystalline portions of the fibers. [10] This led to the obtention of colloidally stable and highly crystalline nanorods particles. [11] [12] [13] These particles were first referred to as micelles, before being given multiple names including cellulose nanocrystals (CNCs), nanocrystalline cellulose (NCC), or cellulose (nano)whiskers, though this last term is less used today. [2] Later studies by O. A. Battista showed that in milder hydrolysis conditions, the crystalline nanorods stay aggregated as micron size objects. [14] [15] This material was later referred to as microcrystalline cellulose (MCC) and commercialised under the name Avicel by FMC Corporation. [16]
Microfibrillated cellulose (MFC) was discovered later, in the 1980s, by Turbak, Snyder and Sandberg at the ITT Rayonier labs in Shelton, Washington. [17] [18] [19] This terminology was used to describe a gel-like material prepared by passing wood pulp through a Gaulin type milk homogenizer at high temperatures and high pressures followed by ejection impact against a hard surface. In later work, F. W. Herrick at ITT Rayonier Eastern Research Division (ERD) Lab in Whippany also published work on making a dry powder form of the gel. [20] [19] Rayonier, as a company, never pursued scale-up and gave free license to whoever wanted to pursue this new use for cellulose.[ citation needed ] Rather, Turbak et al. pursued 1) finding new uses for the MFC, including using as a thickener and binder in foods, cosmetics, paper formation, textiles, nonwovens, etc. and 2) evaluate swelling and other techniques for lowering the energy requirements for MFC production. [21] The first MFC pilot production plant of MFC was established in 2010 by Innventia AB (Sweden). [22]
Nanocellulose materials can be prepared from any natural cellulose source including wood, cotton, agricultural [23] or household wastes, [24] algae, [25] bacteria or tunicate. Wood, in the form of wood pulp is currently the most commonly used starting material for the industrial production of nanocellulosic materials.
Nanocellulose fibrils (MFC and CNFs) may be isolated from the cellulose fibers using mechanical methods that expose the fibers to high shear forces, delaminating them into nano-fibers. For this purpose, high-pressure homogenizers, grinders or microfluidizers can be used.[ citation needed ] This process consumes very large amounts of energy and values over 30 MWh/tonne are not uncommon.[ citation needed ]
To address this problem, sometimes enzymatic/mechanical pre-treatments and introduction of charged groups for example through carboxymethylation or TEMPO-mediated oxidation are used. [26] These pre-treatments can decrease energy consumption below 1 MWh/tonne.[ citation needed ] "Nitro-oxidation" has been developed to prepare carboxycellulose nanofibers directly from raw plant biomass. Owing to fewer processing steps to extract nanocellulose, the nitro-oxidation method has been found to be a cost-effective, less-chemically oriented and efficient method to extract carboxycellulose nanofibers. [27] [28] Functionalized nanofibers obtained using nitro-oxidation have been found to be an excellent substrate to remove heavy metal ion impurities such as lead, [29] cadmium, [30] and uranium. [31]
A chemo-mechanical process for production of nanocellulose from cotton linters has been demonstrated with a capacity of 10 kg per day. [32]
Cellulose nanocrystals (CNC) are formed by the acid hydrolysis of native cellulose fibers, most commonly using sulfuric or hydrochloric acid. Disordered sections of native cellulose are hydrolysed and after careful timing, the remaining crystalline sections can be retrieved from the acid solution by centrifugation and dialysis against water. Their final dimensions depend on the cellulose source, its history, the hydrolysis conditions and the purification procedures. [33] CNCs are commercialised by various companies that use different sources and processes, leading to a range of available products. [34] [35]
Spherical shaped carboxycellulose nanoparticles prepared by nitric acid-phosphoric acid treatment are stable in dispersion in its non-ionic form. [36]
The ultrastructure of nanocellulose derived from various sources has been extensively studied. Techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), wide angle X-ray scattering (WAXS), small incidence angle X-ray diffraction and solid state 13C cross-polarization magic angle spinning (CP/MAS), nuclear magnetic resonance (NMR) and spectroscopy have been used to characterize typically dried nanocellulose morphology.[ citation needed ]
A combination of microscopic techniques with image analysis can provide information on fibril widths, it is more difficult to determine fibril lengths, because of entanglements and difficulties in identifying both ends of individual nanofibrils. [37] [38] [ page needed ] Also, nanocellulose suspensions may not be homogeneous and can consist of various structural components, including cellulose nanofibrils and nanofibril bundles. [39]
In a study of enzymatically pre-treated nanocellulose fibrils in a suspension the size and size-distribution were established using cryo-TEM. The fibrils were found to be rather mono-dispersed mostly with a diameter of ca. 5 nm although occasionally thicker fibril bundles were present. [40] By combining ultrasonication with an "oxidation pretreatment", cellulose microfibrils with a lateral dimension below 1 nm has been observed by AFM. The lower end of the thickness dimension is around 0.4 nm, which is related to the thickness of a cellulose monolayer sheet. [41]
Aggregate widths can be determined by CP/MAS NMR developed by Innventia AB, Sweden, which also has been demonstrated to work for nanocellulose (enzymatic pre-treatment). An average width of 17 nm has been measured with the NMR-method, which corresponds well with SEM and TEM. Using TEM, values of 15 nm have been reported for nanocellulose from carboxymethylated pulp. However, thinner fibrils can also be detected. Wågberg et al. reported fibril widths of 5–15 nm for a nanocellulose with a charge density of about 0.5 meq./g. [42] The group of Isogai reported fibril widths of 3–5 nm for TEMPO-oxidized cellulose having a charge density of 1.5 meq./g. [43]
Pulp chemistry has a significant influence on nanocellulose microstructure. Carboxymethylation increases the numbers of charged groups on the fibril surfaces, making the fibrils easier to liberate and results in smaller and more uniform fibril widths (5–15 nm) compared to enzymatically pre-treated nanocellulose, where the fibril widths were 10–30 nm. [44] The degree of crystallinity and crystal structure of nanocellulose. Nanocellulose exhibits cellulose crystal I organization and the degree of crystallinity is unchanged by the preparation of the nanocellulose. Typical values for the degree of crystallinity were around 63%. [44]
The rheology of nanocellulose dispersions has been investigated. [45] [40] and revealed that the storage and loss modulus were independent of the angular frequency at all nanocellulose concentrations between 0.125% to 5.9%. The storage modulus values are particularly high (104 Pa at 3% concentration) [40] compared to results for CNCs (102 Pa at 3% concentration). [45] There is also a strong concentration dependence as the storage modulus increases 5 orders of magnitude if the concentration is increased from 0.125% to 5.9%. Nanocellulose gels are also highly shear thinning (the viscosity is lost upon introduction of the shear forces). The shear-thinning behaviour is particularly useful in a range of different coating applications. [40]
It is pseudo-plastic and exhibits thixotropy, the property of certain gels or fluids that are thick (viscous) under normal conditions, but become less viscous when shaken or agitated. When the shearing forces are removed the gel regains much of its original state.
Crystalline cellulose has a stiffness about 140–220 GPa, comparable with that of Kevlar and better than that of glass fiber, both of which are used commercially to reinforce plastics. Films made from nanocellulose have high strength (over 200 MPa), high stiffness (around 20 GPa) [46] but lack of high strain[ clarification needed ] (12%). Its strength/weight ratio is 8 times that of stainless steel. [47] Fibers made from nanocellulose have high strength (up to 1.57 GPa) and stiffness (up to 86 GPa). [48]
In semi-crystalline polymers, the crystalline regions are considered to be gas impermeable. Due to relatively high crystallinity, [44] in combination with the ability of the nanofibers to form a dense network held together by strong inter-fibrillar bonds (high cohesive energy density), it has been suggested that nanocellulose might act as a barrier material. [43] [49] [50] Although the number of reported oxygen permeability values are limited, reports attribute high oxygen barrier properties to nanocellulose films. One study reported an oxygen permeability of 0.0006 (cm3 μm)/(m2 day kPa) for a ca. 5 μm thin nanocellulose film at 23 °C and 0% RH. [49] In a related study, a more than 700-fold decrease in oxygen permeability of a polylactide (PLA) film when a nanocellulose layer was added to the PLA surface was reported. [43]
The influence of nanocellulose film density and porosity on film oxygen permeability has been explored. [51] Some authors have reported significant porosity in nanocellulose films, [52] [46] [53] which seems to be in contradiction with high oxygen barrier properties, whereas Aulin et al. [49] measured a nanocellulose film density close to density of crystalline cellulose (cellulose Iß crystal structure, 1.63 g/cm3) [54] indicating a very dense film with a porosity close to zero.
Changing the surface functionality of the cellulose nanoparticle can also affect the permeability of nanocellulose films. Films constituted of negatively charged CNCs could effectively reduce permeation of negatively charged ions, while leaving neutral ions virtually unaffected. Positively charged ions were found to accumulate in the membrane. [55]
Multi-parametric surface plasmon resonance is one of the methods to study barrier properties of natural, modified or coated nanocellulose. The different antifouling, moisture, solvent, antimicrobial barrier formulation quality can be measured on the nanoscale. The adsorption kinetics as well as the degree of swelling can be measured in real-time and label-free. [56] [57]
Owed to their anisotropic shape and surface charge, nanocelluloses (mostly rigid CNCs) have a high excluded volume and self-assemble into cholesteric liquid crystals beyond a critical volume fraction. [58] Nanocellulose liquid crystals are left-handed due to the right-handed twist on particle level. [59] Nanocellulose phase behavior is susceptible to ionic charge screening. An increase in ionic strength induces the arrest of nanocellulose dispersions into attractive glasses. [60] At further increasing ionic strength, nanocelluloses aggregate into hydrogels. [61] The interactions within nanocelluloses are weak and reversible, wherefore nanocellulose suspensions and hydrogels are self-healing and may be applied as injectable materials [62] or 3D printing inks. [63]
Nanocellulose can also be used to make aerogels/foams, either homogeneously or in composite formulations. Nanocellulose-based foams are being studied for packaging applications in order to replace polystyrene-based foams. Svagan et al. showed that nanocellulose has the ability to reinforce starch foams by using a freeze-drying technique. [64] The advantage of using nanocellulose instead of wood-based pulp fibers is that the nanofibrils can reinforce the thin cells in the starch foam. Moreover, it is possible to prepare pure nanocellulose aerogels applying various freeze-drying and super critical CO
2 drying techniques. Aerogels and foams can be used as porous templates. [65] [66] Tough ultra-high porosity foams prepared from cellulose I nanofibril suspensions were studied by Sehaqui et al. a wide range of mechanical properties including compression was obtained by controlling density and nanofibril interaction in the foams. [67] CNCs could also be made to gel in water under low power sonication giving rise to aerogels with the highest reported surface area (>600m2/g) and lowest shrinkage during drying (6.5%) of cellulose aerogels. [66] In another study by Aulin et al., [68] the formation of structured porous aerogels of nanocellulose by freeze-drying was demonstrated. The density and surface texture of the aerogels was tuned by selecting the concentration of the nanocellulose dispersions before freeze-drying. Chemical vapour deposition of a fluorinated silane was used to uniformly coat the aerogel to tune their wetting properties towards non-polar liquids/oils. The authors demonstrated that it is possible to switch the wettability behaviour of the cellulose surfaces between super-wetting and super-repellent, using different scales of roughness and porosity created by the freeze-drying technique and change of concentration of the nanocellulose dispersion. Structured porous cellulose foams can however also be obtained by utilizing the freeze-drying technique on cellulose generated by Gluconobacter strains of bacteria, which bio-synthesize open porous networks of cellulose fibers with relatively large amounts of nanofibrils dispersed inside. Olsson et al. [69] demonstrated that these networks can be further impregnated with metalhydroxide/oxide precursors, which can readily be transformed into grafted magnetic nanoparticles along the cellulose nanofibers. The magnetic cellulose foam may allow for a number of novel applications of nanocellulose and the first remotely actuated magnetic super sponges absorbing 1 gram of water within a 60 mg cellulose aerogel foam were reported. Notably, these highly porous foams (>98% air) can be compressed into strong magnetic nanopapers, which may find use as functional membranes in various applications.
Nanocelluloses can stabilize emulsions and foams by a Pickering mechanism, i.e. they adsorb at the oil-water or air-water interface and prevent their energetic unfavorable contact. Nanocelluloses form oil-in-water emulsions with a droplet size in the range of 4-10 μm that are stable for months and can resist high temperatures and changes in pH. [70] [71] Nanocelluloses decrease the oil-water interface tension [72] and their surface charge induces electrostatic repulsion within emulsion droplets. Upon salt-induced charge screening the droplets aggregate but do not undergo coalescence, indicating strong steric stabilization. [73] The emulsion droplets even remain stable in the human stomach and resist gastric lipolysis, thereby delaying lipid absorption and satiation. [74] [75] In contrast to emulsions, native nanocelluloses are generally not suitable for the Pickering stabilization of foams, which is attributed to their primarily hydrophilic surface properties that results in an unfavorable contact angle below 90° (they are preferably wetted by the aqueous phase). [76] Using hydrophobic surface modifications or polymer grafting, the surface hydrophobicity and contact angle of nanocelluloses can be increased, allowing also the Pickering stabilization of foams. [77] By further increasing the surface hydrophobicity, inverse water-in-oil emulsions can be obtained, which denotes a contact angle higher than 90°. [78] [79] It was further demonstrated that nanocelluloses can stabilize water-in-water emulsions in presence of two incompatible water-soluble polymers. [80]
A bottom up approach can be used to create a high-performance bulk material with low density, high strength and toughness, and great thermal dimensional stability: cellulose nanofiber plate (CNFP). Cellulose nanofiber hydrogel is created by biosynthesis. The hydrogels can then be treated with a polymer solution or by surface modification and then are hot-pressed at 80 °C. The result is bulk material with excellent machinability. “The ultrafine nanofiber network structure in CNFP results in more extensive hydrogen bonding, the high in-plane orientation, and “three way branching points” of the microfibril networks”. [81] This structure gives CNFP its high strength by distributing stress and adding barriers to crack formation and propagation. The weak link in this structure is bond between the pressed layers which can lead to delamination. To reduce delamination, the hydrogel can be treated with silicic acid, which creates strong covalent cross-links between layers during hot pressing. [81]
The surface modification of nanocellulose is currently receiving a large amount of attention. [82] Nanocellulose displays a high concentration of hydroxyl groups at the surface which can be reacted. However, hydrogen bonding strongly affects the reactivity of the surface hydroxyl groups. In addition, impurities at the surface of nanocellulose such as glucosidic and lignin fragments need to be removed before surface modification to obtain acceptable reproducibility between different batches. [83]
Processing of nanocellulose does not cause significant exposure to fine particles during friction grinding or spray drying. No evidence of inflammatory effects or cytotoxicity on mouse or human macrophages can be observed after exposure to nanocellulose. The results of toxicity studies suggest that nanocellulose is not cytotoxic and does not cause any effects on inflammatory system in macrophages. In addition, nanocellulose is not acutely toxic to Vibrio fischeri in environmentally relevant concentrations. [84]
Despite intensified research on oral food or pharmaceutical formulations containing nanocelluloses they are not generally recognized as safe. Nanocelluloses were demonstrated to exhibit limited toxicity and oxidative stress in in vitro intestinal epithelium [85] [86] [87] or animal models. [88] [89] [90]
The properties of nanocellulose (e.g. mechanical properties, film-forming properties, viscosity etc.) makes it an interesting material for many applications. [91]
In the area of paper and paperboard manufacture, nanocelluloses are expected to enhance the fiber-fiber bond strength and, hence, have a strong reinforcement effect on paper materials. [94] [95] [96] Nanocellulose may be useful as a barrier in grease-proof type of papers and as a wet-end additive to enhance retention, dry and wet strength in commodity type of paper and board products. [97] [98] [99] [100] It has been shown that applying CNF as a coating material on the surface of paper and paperboard improves the barrier properties, especially air resistance [101] and grease/oil resistance. [101] [102] [97] It also enhances the structure properties of paperboards (smoother surface). [103] Very high viscosity of MFC/CNF suspensions at low solids content limits the type of coating techniques that can be utilized to apply these suspensions onto paper/paperboard. Some of the coating methods utilized for MFC surface application onto paper/paperboard have been rod coating, [98] size press, [102] spray coating, [104] foam coating [105] and slot-die coating. [101] Wet-end surface application of mineral pigments and MFC mixture to improve barrier, mechanical and printing properties of paperboard are also being explored. [106]
Nanocellulose can be used to prepare flexible and optically transparent paper. Such paper is an attractive substrate for electronic devices because it is recyclable, compatible with biological objects, and easily biodegrades. [93]
As described above the properties of the nanocellulose makes an interesting material for reinforcing plastics. Nanocellulose can be spun into filaments that are stronger and stiffer than spider silk. [48] [107] Nanocellulose has been reported to improve the mechanical properties of thermosetting resins, starch-based matrixes, soy protein, rubber latex, poly(lactide). Hybrid cellulose nanofibrils-clay minerals composites present interesting mechanical, gas barrier and fire retardancy properties. [108] The composite applications may be for use as coatings and films, [109] paints, foams, packaging.
Nanocellulose can be used as a low calorie replacement for carbohydrate additives used as thickeners, flavour carriers, and suspension stabilizers in a wide variety of food products. [110] It is useful for producing fillings, crushes, chips, wafers, soups, gravies, puddings etc. The food applications arise from the rheological behaviour of the nanocellulose gel.
Applications in this field include: super water absorbent material (e.g. for incontinence pads material), nanocellulose used together with super absorbent polymers, nanocellulose in tissue, non-woven products or absorbent structures and as antimicrobial films.[ citation needed ]
Nanocellulose has potential applications in the general area of emulsion and dispersion applications in other fields. [111] [112]
The use of nanocellulose in cosmetics and pharmaceuticals has been suggested:
Nanocellulose can pave the way for a new type of "bio-based electronics" where interactive materials are mixed with nanocellulose to enable the creation of new interactive fibers, films, aerogels, hydrogels and papers. [114] E.g. nanocellulose mixed with conducting polymers such as PEDOT:PSS show synergetic effects resulting in extraordinary [115] mixed electronic and ionic conductivity, which is important for energy storage applications. Filaments spun from a mix of nanocellulose and carbon nanotubes show good conductivity and mechanical properties. [116] Nanocellulose aerogels decorated with carbon nanotubes can be constructed into robust compressible 3D supercapacitor devices. [117] [118] Structures from nanocellulose can be turned into bio-based triboelectric generators [119] and sensors.
In April 2013 breakthroughs in nanocellulose production, by algae, were announced at an American Chemical Society conference, by speaker R. Malcolm Brown, Jr., Ph.D, who has pioneered research in the field for more than 40 years, spoke at the First International Symposium on Nanocellulose, part of the American Chemical Society meeting. Genes from the family of bacteria that produce vinegar, Kombucha tea and nata de coco have become stars in a project — which scientists said has reached an advanced stage - that would turn algae into solar-powered factories for producing the “wonder material” nanocellulose. [9]
Cellulose nanocrystals have shown the possibility to self organize into chiral nematic structures [120] with angle-dependent iridescent colours. It is thus possible to manufacture totally bio-based pigments and glitters, films including sequins having a metallic glare and a small footprint compared to fossil-based alternatives.
Nanochitin is similar in its nanostructure to cellulose nanocrystals but extracted from chitin.
A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized:
Cellulose is an organic compound with the formula (C
6H
10O
5)
n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms. Cellulose is the most abundant organic polymer on Earth. The cellulose content of cotton fibre is 90%, that of wood is 40–50%, and that of dried hemp is approximately 57%.
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At the lowest range, metal particles smaller than 1 nm are usually called atom clusters instead.
Electrospinning is a fiber production method that uses electrical force to draw charged threads of polymer solutions for producing nanofibers with diameters ranging from nanometers to micrometers. Electrospinning shares characteristics of both electrospraying and conventional solution dry spinning of fibers. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suited to the production of fibers using large and complex molecules. Electrospinning from molten precursors is also practiced; this method ensures that no solvent can be carried over into the final product.
In materials science, the sol–gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon (Si) and titanium (Ti). The process involves conversion of monomers in solution into a colloidal solution (sol) that acts as the precursor for an integrated network of either discrete particles or network polymers. Typical precursors are metal alkoxides. Sol–gel process is used to produce ceramic nanoparticles.
In physics, a "coffee ring" is a pattern left by a puddle of particle-laden liquid after it evaporates. The phenomenon is named for the characteristic ring-like deposit along the perimeter of a spill of coffee. It is also commonly seen after spilling red wine. The mechanism behind the formation of these and similar rings is known as the coffee ring effect or in some instances, the coffee stain effect, or simply ring stain.
Nanofibers are fibers with diameters in the nanometer range. Nanofibers can be generated from different polymers and hence have different physical properties and application potentials. Examples of natural polymers include collagen, cellulose, silk fibroin, keratin, gelatin and polysaccharides such as chitosan and alginate. Examples of synthetic polymers include poly(lactic acid) (PLA), polycaprolactone (PCL), polyurethane (PU), poly(lactic-co-glycolic acid) (PLGA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(ethylene-co-vinylacetate) (PEVA). Polymer chains are connected via covalent bonds. The diameters of nanofibers depend on the type of polymer used and the method of production. All polymer nanofibers are unique for their large surface area-to-volume ratio, high porosity, appreciable mechanical strength, and flexibility in functionalization compared to their microfiber counterparts.
Nanofoams are a class of nanostructured, porous materials (foams) containing a significant population of pores with diameters less than 100 nm. Aerogels are one example of nanofoam.
Self-assembling peptides are a category of peptides which undergo spontaneous assembling into ordered nanostructures. Originally described in 1993, these designer peptides have attracted interest in the field of nanotechnology for their potential for application in areas such as biomedical nanotechnology, tissue cell culturing, molecular electronics, and more.
Within surface science, a quartz crystal microbalance with dissipation monitoring (QCM-D) is a type of quartz crystal microbalance (QCM) based on the ring-down technique. It is used in interfacial acoustic sensing. Its most common application is the determination of a film thickness in a liquid environment. It can be used to investigate further properties of the sample, most notably the layer's softness.
Bacterial cellulose is an organic compound with the formula (C
6H
10O
5)
n produced by certain types of bacteria. While cellulose is a basic structural material of most plants, it is also produced by bacteria, principally of the genera Komagataeibacter, Acetobacter, Sarcina ventriculi and Agrobacterium. Bacterial, or microbial, cellulose has different properties from plant cellulose and is characterized by high purity, strength, moldability and increased water holding ability. In natural habitats, the majority of bacteria synthesize extracellular polysaccharides, such as cellulose, which form protective envelopes around the cells. While bacterial cellulose is produced in nature, many methods are currently being investigated to enhance cellulose growth from cultures in laboratories as a large-scale process. By controlling synthesis methods, the resulting microbial cellulose can be tailored to have specific desirable properties. For example, attention has been given to the bacteria Komagataeibacter xylinus due to its cellulose's unique mechanical properties and applications to biotechnology, microbiology, and materials science.
Ultralight materials are solids with a density of less than 10 mg/cm3, including silica aerogels, carbon nanotube aerogels, aerographite, metallic foams, polymeric foams, and metallic microlattices. The density of air is about 1.275 mg/cm3, which means that the air in the pores contributes significantly to the density of these materials in atmospheric conditions. They can be classified by production method as aerogels, stochastic foams, and structured cellular materials.
Hydrogel from wood-based nanofibrillated cellulose (NFC) is used as a matrix for 3D cell culture, providing a three-dimensional environment that more closely resembles the conditions found in living tissue. As plant based material, it does not contain any human- or animal-derived components. Nanocellulose is instead derived from wood pulp that has been processed to create extremely small, nanoscale fibers. These fibers can be used to create a hydrogel, which is a type of material that is made up of a network of cross-linked polymer chains and is able to hold large amounts of water.
Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid with extremely low density and extremely low thermal conductivity. Aerogels can be made from a variety of chemical compounds. Silica aerogels feel like fragile styrofoam to the touch, while some polymer-based aerogels feel like rigid foams.
There are many water purifiers available in the market which use different techniques like boiling, filtration, distillation, chlorination, sedimentation and oxidation. Currently nanotechnology plays a vital role in water purification techniques. Nanotechnology is the process of manipulating atoms on a nanoscale. In nanotechnology, nanomembranes are used with the purpose of softening the water and removal of contaminants such as physical, biological and chemical contaminants. There are variety of techniques in nanotechnology which uses nanoparticles for providing safe drinking water with a high level of effectiveness. Some techniques have become commercialized.
Bio-inspired photonics or bio-inspired optical materials are the application of biomimicry to the field of photonics. This differs slightly from biophotonics which is the study and manipulation of light to observe its interactions with biology. One area that inspiration may be drawn from is structural color, which allows color to appear as a result of the detailed material structure. Other inspiration can be drawn from both static and dynamic camouflage in animals like the chameleon or some cephalopods. Scientists have also been looking to recreate the ability to absorb light using molecules from various plants and microorganisms. Pulling from these heavily evolved constructs allows engineers to improve and optimize existing photonic technologies, whilst also solving existing problems within this field.
Perovskite nanocrystals are a class of semiconductor nanocrystals, which exhibit unique characteristics that separate them from traditional quantum dots. Perovskite nanocrystals have an ABX3 composition where A = cesium, methylammonium (MA), or formamidinium (FA); B = lead or tin; and X = chloride, bromide, or iodide.
Emily D. Cranston is a Canadian chemist who is a professor at the University of British Columbia and President’s Excellence Chair in Forest Bioproducts. She investigates nanocellulose and hybrid bio-based materials. Cranston is an NSERC E.W.R. Steacie fellow and was awarded the Kavli Emerging Leader in Chemistry lectureship in 2018 and the Tappi NanoDivision Technical Award in 2021.
Stephen James Eichhorn FRSC FInstP FIMMM CEng is Professor of Materials Science and Engineering at the University of Bristol.
Passive daytime radiative cooling (PDRC) is the use of unpowered, reflective/thermally-emissive surfaces to lower the temperature of a building or other object.