In this review we introduce recent advances in the development of cellulose nanomaterials and the construction of high order structures by applying some principles of colloid and interface science. These efforts take advantage of natural assemblies in the form of fibers that nature constructs by a biogenetic bottom-up process that results in hierarchical systems encompassing a wide range of characteristic sizes. Following the reverse process, a top-down deconstruction, cellulose materials can be cleaved from fiber cell walls. The resulting nanocelluloses, mainly cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC, i.e., defect-free, rod-like crystalline residues after acid hydrolysis of fibers), have been the subject of recent interest. This originates from the appealing intrinsic properties of nanocelluloses: nanoscale dimensions, high surface area, morphology, low density, chirality and thermo-mechanical performance. Directing their assembly into multiphase structures is a quest that can yield useful outcomes in many revolutionary applications. As such, we discuss the use of non-specific forces to create thin films of nanocellulose at the air–solid interface for applications in nano-coatings, sensors, etc. Assemblies at the liquid–liquid and air–liquid interfaces will be highlighted as means to produce Pickering emulsions, foams and aerogels. Finally, the prospects of a wide range of hybrid materials and other systems that can be manufactured via self and directed assembly will be introduced in light of the unique properties of nanocelluloses.
The focus in the study of Pickering foams and emulsions has recently been shifting from using inorganic particles to adopting particles of biological origin for stabilization. This shift is motivated by the incompatibility of some inorganic particles for food and biomedical applications, as well as their poor sustainability. This review focuses on major developments in foams and emulsions stabilized by particles of biological origin from the last 5 years. Recent reports in the literature have demonstrated the ability of particles derived from cellulose, lignin, chitin, starch, proteins (soy, zein, ferritin), as well as hydrophobic cells to stabilize biphasic dispersions. We review the use of such nano- and micron-sized particles of biological origin for the stabilization of foams and emulsions, summarize the current knowledge of how such particles stabilize these dispersions, provide an outlook for future work to improve our understanding of bio-derived particle-stabilized foams and emulsions, and touch upon how these systems can be used to create novel materials.
Recent advances in the stabilization of emulsions and foams by particles of nanoscale and microscopic dimensions are described. Ongoing research in this highly active field is providing insight into (i) the molecular factors controlling particle wettability and adsorption, (ii) the structural and mechanical properties of particle-laden liquid interfaces, and (ii) the stabilization mechanisms of particle-coated droplets and bubbles. There is much potential for exploiting the emerging knowledge in new food product applications. The preparation of cheap and effective colloidal particles based on food-grade ingredients, especially proteins, is the key technological challenge.
Halloysite is natural tubular clay suitable as a component of biocompatible nanosystems with specific functionalities. The selective modification of halloysite inner/outer surfaces can be achieved by exploiting supramolecular and covalent interactions resulting in controlled colloidal stability adjusted to the solvent polarity. The functionalized halloysite nanotubes can be employed as reinforcing filler for polymers as well as carriers for the sustained release of active molecules, such as antioxidants, flame-retardants, corrosion inhibitors, biocides and drugs. The tubular morphology makes halloysite a perspective template for core-shell metal supports for mesoporous catalysts. The catalysts can be incorporated with selective and unselective metal binding on the nanotubes' outer surface or in the inner lumens. Micropatterns of self-assembled nanotubes have been realized by the droplet casting method. The selective modification of halloysite has been exploited to increase the nanotubes' ordering in the produced patterns. Pickering emulsions, induced by the self-assembly of halloysite nanotubes on oil-water interface, can be used for petroleum spill bioremediation and catalysis.
This review describes recent advances on the application of cellulose nanocrystals (CNCs) in selected applications. CNCs are produced via acid hydrolysis of cellulosic materials, such as wood, cotton, tunicate, or other biomass. It possesses many desirable properties, such as large surface area, high tensile strength and stiffness, excellent colloidal stability, and potential for modification due to the abundance of surface hydroxyl groups. By modifying its surface with small molecules, polymers, and nanoparticles, they can be utilized as a zero-dimension nanostructure for drug delivery, spun into 1-dimension fibers for enhanced strength, cast into 2-dimension films for flexibility, or molded into 3-dimension hydrogels and aerogels for compressibility or porous materials. The use and impact of CNCs in three industrial sectors: biomedical, wastewater treatment, energy and electronics are described and discussed, and we will offer our perspective on the future and new applications of this sustainable nanomaterial.
In this paper, we focus on the recent advances on the physical chemistry of lignin. Emerging trends of incorporating lignin in promising future applications such as controlled release, saccharification of lignocelluloses, bioplastics, composites, nanoparticles, adsorbents and dispersants, in electro-chemical applications and carbon fibers, are also reviewed. We briefly describe the complexity of the lignin structure that influences the solution behavior, both as a macromolecule and a colloid, as well as the potential of being a renewable precursor in the development of high-value applications. Special attention is paid on summarizing the present knowledge on lignin colloidal stability and surface chemistry.
Harnessing the exceptional physical properties of graphene often requires its dispersion into aqueous or organic media. Dispersion must be achieved at a concentration and stability appropriate to the final application. However, the strong interaction between graphene sheets means it disperses poorly in all but a few high boiling organic solvents. This review presents an overview of graphene dispersion applications and a discussion of dispersion strategies: in particular the effect of shear, solvent and chemical modification on the dispersion of graphene (including graphene oxide and reduced graphene oxide). These techniques are discussed in the context of manufacturing and commercialisation.
Milk proteins are natural vehicles for bioactives. Many of their structural and physicochemical properties facilitate their functionality in delivery systems. These properties include binding of ions and small molecules, excellent surface and self-assembly properties; superb gelation properties; pH-responsive gel swelling behavior, useful for programmable release; interactions with other macromolecules to form complexes and conjugates with synergistic combinations of properties; various shielding capabilities, essential for protecting sensitive payload; biocompatibility and biodegradability, enabling to control the bioaccessibility of the bioactive, and promote its bioavailability. The review highlights the main achievements reported in the last 3 years: harnessing the casein micelle, a natural nanovehicle of nutrients, for delivering hydrophobic bioactives; discovering unique nanotubes based on enzymatic hydrolysis of α-la; introduction of novel encapsulation techniques based on cold-set gelation for delivering heat-sensitive bioactives including probiotics; developments and use of Maillard reaction based conjugates of milk proteins and polysaccharides for encapsulating bioactives; introduction of β-lg–pectin nanocomplexes for delivery of hydrophobic nutraceuticals in clear acid beverages; development of core-shell nanoparticles made of heat-aggregated β-lg, nanocoated by beet-pectin, for bioactive delivery; synergizing the surface properties of whey proteins with stabilization properties of polysaccharides in advanced W/O/W and O/W/O double emulsions; application of milk proteins for drug targeting, including lactoferrin or bovine serum albumin conjugated nanoparticles for effective drug delivery across the blood-brain barrier; beta casein nanoparticles for targeting gastric cancer; fatty acid-coated bovine serum albumin nanoparticles for intestinal delivery, and Maillard conjugates of casein and resistant starch for colon targeting. Major future challenges are spot-lighted.
Tailor-made microparticles and nanoparticles are finding increasing use in food products to alter their nutritional characteristics, flavor profile, appearance, rheology, stability, and processability. These particles are often fabricated from food-grade biopolymers, such as proteins and polysaccharides. Food biopolymers display a diverse range of molecular and physicochemical properties (e.g. molecular weight, charge, branching, flexibility, polarity, and solubility) which enables the assembly of colloidal particles that exhibit a broad range of functional attributes. By careful selection of appropriate biopolymers and assembly methods, biopolymer particles can be fabricated with tailored behaviors or features. In this article, we review recent developments in the design and fabrication of functional biopolymer nanoparticles and microparticles, and highlight some of the challenges that will be the focus of future research.
The main developments on nano-emulsion formation by low-energy methods in the last five years are reviewed. A general description on nano-emulsions, including issues such as size-range, terminology and classification of low-energy emulsification methods is given in the introduction. Low-energy methods, which use the internal chemical energy of the system to achieve emulsification, are classified depending on whether or not changes in the surfactant spontaneous curvature are produced during the process. Nano-emulsion formation triggered by the rapid diffusion of surfactant and/or solvent molecules from the dispersed phase to the continuous phase without involving a change in the spontaneous curvature of the surfactant is referred to as “self-emulsification”. When changes in the surfactant spontaneous curvature are produced during the emulsification process they are designated as “phase inversion” methods. These are classified as phase inversion temperature (PIT) and phase inversion composition (PIC) methods if emulsification is triggered by a change in temperature or composition, respectively. Investigations on nano-emulsion formation from O/W and W/O microemulsions using different dilution procedures has set light on the factors determining small droplet size and low polydispersity. Phase behaviour studies and characterization of the transient phases formed during the emulsification process have confirmed that the mechanism by which small droplets are formed is analogue in the PIT and PIC methods. Recent advances on nano-emulsion optimization and scale-up are also reviewed. ► Nano-emulsion formation by low-energy methods is reviewed. ► No changes in surfactant spontaneous curvature is involved in self-emulsification. ► Formation of low-polydisperse nano-emulsions can be achieved with either PIT or PIC. ► Nano-emulsion tunability and scale-up studies are necessary for industrial applications.
Low-salinity waterflooding is a relatively new method for improved oil recovery that has generated much interest. It is generally believed that low-salinity brine alters the wettability of oil reservoir rocks towards a wetting state that is optimal for recovery. The mechanism(s) by which the wettability alteration occurs is currently an unsettled issue. This paper reviews recent studies on wettability alteration mechanisms that affect the interactions between the brine/oil and brine/rock interfaces of thin brine films that wet the surface of reservoir rocks. Of these mechanisms, we pay particular attention to double-layer expansion, which is closely tied to an increase in the thickness and stability of the thin brine films. Our review examines studies on both sandstones and carbonate rocks. We conclude that the thin-brine-film mechanisms provide a good qualitative, though incomplete, picture of this very complicated problem. We give suggestions for future studies that may help provide a more quantitative and complete understanding of low-salinity waterflooding.
Emulsion science and technology has been used for many years to create a diverse range of commercial products, including pharmaceuticals, foods, agrochemicals, lubricants, personal care products, and cosmetics. The majority of these products are conventional emulsions consisting of droplets of one liquid dispersed in another immiscible liquid, , oil-in-water emulsions. Recently, there has been growing interest in extending the functional performance of emulsion-based products using structural design principles. This article reviews recent developments in the creation of structured emulsions, including multiple emulsions, multilayer emulsions, colloidosomes, microclusters, filled hydrogel microspheres, and hybrid systems. The structure, fabrication, properties, and potential applications of each type of structured emulsion are discussed. In addition, recent advances in the fabrication of emulsion droplets with specific properties (size, charge, interfacial properties, and physical state) are also reviewed, since these are the basic building blocks of structured emulsions. Examples of structured emulsions that can be created by structural design principles using emulsion droplets as a building block. ► Structural design principles can be used to improve the functionality of emulsions. ► A variety of structured emulsions have been developed based on layering, embedding and clustering. ► Examples include multiple emulsions, multilayer emulsions, colloidosomes, microclusters and filled hydrogel microspheres. ► The structure, properties, and applications of structured emulsions are reviewed.
Recent breakthroughs in colloidal synthesis allow the control of particle shapes and properties with high precision. This provides us with a constantly expanding library of new anisotropic building blocks, thus opening new avenues to explore colloidal self-assembly at a higher level of complexity. This article reviews the most recent advances in the preparation and self-assembly of colloids with well-defined anisotropic shapes. A particular emphasis is given to solution-based syntheses that provide micron-sized colloids in high yields, and to assembly schemes that exploit the shape anisotropy of the building blocks involved. ► We review recent synthetic strategies to fabricate colloids with well-defined shapes. ► Non-spherical colloids are used as building blocks for the assembly of new materials. ► Self-assembly schemes exploit shapes to program and regulate colloidal organization. ► Self-assembly toolbox: steric hindrance, depletion forces and topological defects.
There is a great deal of interest in the Food Industry in the use of polysaccharides and proteins to stabilise oil-in-water emulsions and there is a particular interest nowadays in the use of polysaccharide–protein complexes. There are three classes of complexes namely; (a) naturally-occurring complexes in which protein residues are covalently attached to the polysaccharide chains as is the case, for example, with gum Arabic; (b) Maillard conjugates, which are formed by interaction of the reducing end of a polysaccharide with an amine group on a protein forming a covalent bond; and (c) electrostatic complexes formed between a polysaccharide and a protein with opposite net charge. This review sets out our current understanding of the nature of these different polysaccharide–protein complexes and their ability to stabilise oil-in-water emulsions.
Several forms of cellulose nanomaterials, notably cellulose nanocrystals and cellulose nanofibrils, exhibit attractive properties and are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, basis for low-density foams, additive in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic, and medical products. This entry focuses on cellulose materials as filler in polymer nanocomposites. The ensuing mechanical properties obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials that has not yet been properly resolved and remains a challenge.
This paper provides a review of superhydrophobicity and related phenomena (superoleophobicity, omniphobicity, self-cleaning) induced by surface micro- and nanostructuring. The classical approaches to superhydrophobicity using the Young, Wenzel, and Cassie–Baxter models for the contact angle (CA) are presented. After that, the issues that are beyond the Wenzel and Cassie–Baxter theories are discussed, such as multiscale effects, 1D vs. 2D interactions, the effects of contact line, size of roughness details, curvature, and CA hysteresis dependence on roughness. New potential applications of superhydrophobicity are reviewed, such as new ways of energy transition, antifouling, and environment-friendly manufacturing.
Texture and mouthfeel arising from the consumption of food and beverages are critical to consumer choice and acceptability. While the food structure design rules for many existing products have been well established, although not necessarily understood, the current drive to produce healthy consumer acceptable food and beverages is pushing products into a formulation space whereby these design rules no longer apply. Both subtle and large scale alterations to formulations can result in significant changes in texture and mouthfeel, even when measurable texture-related quantities such as rheology are the same. However, we are only able to predict sensations at the initial stages of consumption from knowledge of material properties of intact food. Research is now on going to develop strategies to capture the dynamic aspects of oral processing, including: from a sensory perspective, the recent development of Temporal Dominance Sensation; from a material science perspective, development of new in vitro techniques in thin film rheology and tribology as well as consideration of the multifaceted effect of saliva. While in vivo, ex vivo, imitative and empirical approaches to studying oral processing are very insightful, they either do not lend themselves to routine use or are too complex to be able to ascertain the mechanism for an observed behaviour or correlation with sensory. For these reasons, we consider that fundamental in vitro techniques are vital for rational design of food, provided they are designed appropriately to capture the important physics taking place during oral processing. We map the oral breakdown trajectory through 6 stages and suggest a dynamic multi-scale approach to capture underlying physics. The ultimate goal is to use fundamental insights and techniques to design new food and beverages that are healthy yet acceptable to consumers.
Cellulose is a polymer so widely abundant and versatile that we can find it almost everywhere in many different forms and applications. Cellulose dissolution is a key aspect of many processes; the present treatise reviews the main achievements in the dissolution area. In particular, the main solvents used and underlying mechanisms are discussed. As is described, cellulose solvents are of highly different nature giving great challenges in the understanding and analyzing the subtle balance between different interactions. Recent work has much emphasized the role of cellulose charge and the concomitant ion entropy effects, as well as hydrophobic interactions.
During the last ten years significant progress has been made in the understanding of specific ion effects. On the one hand new ideas about the origin of these effects came up, and on the other hand new experimental techniques were developed so that now even the ion concentration profile near surfaces can be measured with some confidence. In the present review some of the most important new progresses are summarised and critically discussed, especially in the context of colloidal and biological systems.