Summary

Polymer science, as a discipline, delves into the complexities of macromolecular synthesis, chain architecture, self-assembly, and the dynamics that govern material properties. From the microcosm of monomers, repeating units, and chain conformations to the macrocosm of bulk plastics, elastomers, fibers, composites, and global polymer industries, these polymer concepts will unravel the threads that weave together the fabric of macromolecular science and engineering.

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Topic Review
Cotton Fabric
Cotton fabric is a woven or knitted textile built from twisted cellulose fibres, and it remains the most widely used apparel substrate. Its properties come from the fibre structure: the lumen and the convolutions give moisture uptake and a soft hand, while the crystalline cellulose provides strength [1]. The natural waxes and pectins on the raw fibre must be removed by scouring and bleaching before dyeing, and the finishing sequence determines the final whiteness and absorbency [2]. Functional finishing adds flame retardancy, antimicrobial behaviour, or water repellency, usually at the cost of tensile strength because the treatment also attacks the cellulose chain [3]. Grafting monomers onto the fibre surface is an alternative that leaves the bulk structure largely intact [4]. Durability of the finish to repeated laundering, rather than the initial performance, is the property that most often fails [5].
  • 18
  • 20 Oct 2026
Topic Review
Crystallite Size
Crystallite size is the mean extent of coherently diffracting domains within a powder or polycrystal, a quantity distinct from particle size because one particle may contain many such domains. Diffraction line broadening is the usual access route: the Scherrer relation converts peak width into a domain dimension, but the measured width also contains instrumental broadening and depends on crystallite shape through the Scherrer constant. Instrumental broadening should therefore be corrected using a suitable standard, LaB6 among them, or an appropriate profile model before a meaningful size is extracted. Extensions of the Scherrer analysis can, in favorable cases and with additional assumptions, yield a crystallite-size distribution rather than a single number; such distributions are not generally obtainable from peak widths alone and require suitable whole-profile or envelope-function treatments [1,2]. Size broadening overlaps with strain broadening in the same profile, so separating the two requires several orders of reflection or a full-profile treatment; established approaches include Williamson–Hall analysis and Warren–Averbach Fourier analysis [3]. Different routes to the same quantity give systematically different answers, as comparisons on hydroxyapatite show [4], and the same caution applies when the phase sits in a deformed matrix [5]. The resulting value is best regarded as an apparent domain size whose physical interpretation depends on how much of the profile has been modeled and on the corrections applied; it should not be equated with a unique physical dimension unless those effects are adequately treated. Machine-learning methods are also being explored for diffraction-data analysis and for assisting parameter extraction, but their predictions depend on training data and should be validated against physically based profile models rather than regarded as a substitute for instrumental corrections [6].
  • 20
  • 26 Oct 2026
Topic Review
Polyurethane Foam
Polyurethane foam is a cellular polymer formed by the reaction of a polyol with an isocyanate in which a blowing agent, whether produced by the reaction itself or added separately, expands the reacting mixture into a gas-filled structure. The properties follow from the cell size and from whether the cells are open or closed: closed-cell rigid foam carries load and insulates, while open-cell flexible foam recovers from compression. Both burn readily, and a large part of the literature concerns flame retardancy; a phosphorus-nitrogen intumescent system in rigid foam forms a char that shields the underlying polymer [1], and modifying the intumescent formulation changes how effective that char is [2]. Understanding how the intumescent layer works during a fire is what allows the formulation to be chosen rationally [3]. Building the flame-retardant moiety into the polymer backbone rather than adding it as a filler avoids the loss of mechanical properties that a high filler loading causes [4]. Surface coatings offer a way to keep the bulk formulation unchanged [5].
  • 15
  • 19 Oct 2026
Topic Review
Mechanical Stability
Mechanical stability is the ability of a material or a component to keep its structure, and therefore its properties, under mechanical load, deformation or repeated cycling. In electrochemical energy storage the term is taken more narrowly, for the ability of an electrode to survive the volume change that accompanies charging and discharging: active particles expand and contract, the coating swells and shrinks, and if the structure cannot accommodate the strain the coating cracks, particles lose contact with the current collector and the capacity fades. Porous and hierarchically structured electrodes accommodate that strain better than dense ones, which is why hierarchical porous carbons are reported with good rate behaviour and long life [1]. A flexible active material that deforms elastically with the substrate holds both its structure and its capacity over long cycling [2], and growing the active phase directly on a textile current collector removes the binder and the interface that usually fails first [3]. Conducting polymer composites with a two-dimensional inorganic phase combine electronic transport with mechanical compliance [4], and the same strategy has been taken into all-solid-state flexible devices where the electrode also has to survive bending [5]. Tests are rarely standardised, so cycling figures quoted under different mechanical conditions are not directly comparable.
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  • 19 Oct 2026
Topic Review
Anion Exchange Membrane
An anion exchange membrane is a polymer film bearing fixed cationic groups that conducts hydroxide or other anions while blocking the transport of cations and of the reactant gases. In a water electrolyser the membrane separates the two electrodes, carries the ionic current and sets the ohmic loss, so its conductivity and its stability in hot alkali largely determine how the cell performs; cationic head groups attached to an aryl-ether-free backbone resist the nucleophilic attack that degrades earlier materials [1]. Cross-linking two cationic sites into one polymer chain raises the ion content without the swelling that usually comes with it, and hence improves both conductivity and dimensional stability [2]. Carbonate formed when the cell is fed with air rather than pure oxygen lowers the conductivity, and models of the electrolyte composition quantify how large that penalty is [3]. Because reported performance depends strongly on cell hardware and test protocol, a standard test cell has been proposed for comparing membranes and catalysts [4]. The alkaline environment also widens the catalyst choice to nickel-based hydrogen evolution catalysts [5].
  • 14
  • 19 Oct 2026
Topic Review
Adhesion Strength
Adhesion strength is the resistance of an interface between a coating and its substrate to separation, and it is reported either as a stress at failure or, more often in practice, as the load at which damage appears in a standardised test. No single test measures an intrinsic interfacial property, because the quantity obtained depends on the stress state the test imposes and on the deformation of both layers. The scratch test is the most widely adopted: a loaded tip is drawn across the surface and the critical load at which the coating detaches is read from the acoustic or the frictional signal, and its interpretation has been examined in detail for a range of coating-substrate pairs [1]. Compressive stress in the coating contributes substantially to that critical load, so a mechanical model is needed to separate the residual stress from the true interfacial toughness [2]. Impact and pendulum variants load the interface in a different way and come into their own where the coating is too hard or too thin for a progressive scratch [3]. Combining scratching with acoustic microscopy lets the detached area be imaged rather than inferred [4], and in multilayer systems the same approach ranks the individual interfaces [5]. Values obtained with different methods are not directly comparable.
  • 10
  • 19 Oct 2026
Topic Review
Cellulose Nanocrystal
Cellulose nanocrystal is a rod-like crystalline nanoparticle obtained from cellulose, typically 3-20 nm in width and 100-500 nm in length, in which the chains are packed in a crystalline allomorph whose form depends on the source material and the hydrolysis route [1]. It is produced by hydrolysing native cellulose with mineral acid, most commonly sulfuric acid, which also esterifies part of the surface with sulfate half-esters and gives the particle a negative surface charge that stabilises aqueous suspensions [2]. The particles have a high aspect ratio, a density near 1.6 g cm-3, a Young's modulus on the order of 100-150 GPa and a low coefficient of thermal expansion, so they serve as a reinforcing nanofiller in polymers, films and hydrogels [3]. Above a critical concentration in water they self-assemble into a chiral nematic liquid crystal, and drying this phase leaves an iridescent film whose colour depends on the pitch and on the ionic strength of the medium [1]. The surface chemistry can be modified by oxidation, esterification or grafting to adjust compatibility with a given matrix, and carboxylated grades are prepared by TEMPO-mediated oxidation [4]. Limiting factors are the cost of the sulfuric-acid route and the sulfate-induced thermal instability it leaves behind, which restricts melt processing, together with the difficulty of drying the particles without irreversible aggregation [2]. Reported mechanical reinforcement depends on dispersion quality, and aggregation during drying or processing usually reduces the gain; the choice of polymorph has also been shown to affect processability and the properties of the resulting composite [5].
  • 12
  • 19 Oct 2026
Topic Review
Passive Film
A passive film is a thin, adherent, generally oxide-based layer that forms spontaneously on a metal or alloy surface under anodic conditions and that lowers the dissolution rate by several orders of magnitude relative to the bare metal [1]. On stainless steels the film is about 1–3 nm thick and consists mainly of chromium oxide or oxyhydroxide together with iron and nickel species, and its growth is usually described by a high-field mechanism in which ion migration through the film is rate-limiting [2]. The Point Defect Model expresses the same behaviour in terms of cation vacancies, anion vacancies, and cation interstitials that are generated and annihilated at the metal/film and film/solution interfaces, and it accounts for both steady-state growth and film breakdown [1][3]. Composition and structure are commonly probed by X-ray photoelectron spectroscopy, while the defect structure at atomic and nanometric scales is examined by scanning tunnelling and atomic force microscopy under electrochemical control [4]. Because the film behaves as a semiconductor, the donor or acceptor density obtained from Mott–Schottky analysis is often correlated with corrosion resistance [5]. Passivity is nevertheless lost in chloride-containing environments once the breakdown potential is exceeded, and the local chemistry that triggers pit initiation, together with the relative roles of film thinning, vacancy condensation, and chloride incorporation, remains debated [3][5].
  • 44
  • 19 Oct 2026
Topic Review
Chitosan Solvents
Chitosan Solvents are the liquid media capable of bringing chitosan, a partially deacetylated aminopolysaccharide obtained from chitin, into a molecularly dispersed or processable state. Because chitosan carries primary amino groups along its backbone, its solubility is governed largely by protonation: dilute aqueous acids convert the polymer into a cationic polyelectrolyte and dissolve it, whereas neutral water, alkaline media and most common organic solvents do not. Beyond this classical acid route, dissolution has been achieved in aqueous alkali–urea systems at low temperature, in dipolar aprotic solvents containing lithium salts, by salt formation in dimethyl sulfoxide, in ionic liquids, and in deep eutectic solvents. Each family offers a different balance of dissolving power, chain integrity, viscosity, cost and environmental profile, and each imposes different conditions on regeneration. The choice of solvent therefore determines not only whether chitosan dissolves, but also the molar mass it retains, the conformation it adopts in solution, and the morphology of the films, fibres, beads, gels and porous monoliths obtained after coagulation. This entry surveys the structural origins of chitosan solubility, the main solvent families and their dissolution mechanisms, criteria for solvent selection, and the material outcomes that follow from regeneration.
  • 64
  • 19 Oct 2026
Topic Review
Chitin Solvents
Chitin solvents are liquid media that break the dense hydrogen-bonded network of chitin and bring this otherwise intractable biopolymer into molecularly dispersed or colloidal solution. Chitin is a linear polymer of N-acetyl-D-glucosamine units joined by β-1,4-glycosidic bonds; it is the second most abundant biopolymer on Earth and the main organic constituent of crustacean shells, insect cuticles and fungal cell walls. It does not melt and is insoluble in water, dilute acids and bases, alcohols and almost all common organic solvents, so its shaping and chemical transformation generally require dissolution. Because the acetamido group at C2 is both a hydrogen-bond donor and an acceptor, chitin is markedly harder to dissolve than cellulose. Two strategies are used: derivatizing media, which convert the polymer temporarily into a soluble ester or ether that is cleaved on regeneration, and non-derivatizing media, which dissolve unmodified chitin directly—aqueous mineral acids, concentrated salt solutions and salt hydrates, alkali/urea mixtures, lithium chloride in N,N-dimethylacetamide, calcium chloride dihydrate in methanol, ionic liquids, deep eutectic solvents, and protic solvents such as hexafluoroisopropanol. Chitin solvents underpin regenerated chitin fibres, films, hydrogels, aerogels and nanofibres, and they enable homogeneous chemical modification, controlled deacetylation, molar-mass characterization and the valorization of seafood shell waste.
  • 44
  • 19 Oct 2026
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