Sulfur-doped titania thin films with cubic mesostructures were prepared by dip coating via the evaporation induced self-assembly route. The effect of sulfur doping on structure, morphology, porosity, optical properties, and photocatalytic activity of the mesoporous films was studied. Compared to undoped titania films, the S-doped films showed better long-range ordering, bigger pore size, higher porosity, less shrinkage of the structure during calcination, a red-shift of the band gap, and a more hydrophilic surface. These characteristics led to an improved photocatalytic activity when the S-doped and undoped titania films were tested for degradation of methylene blue in aqueous solutions under the irradiation of 1 sun from a solar simulator. The photocatalytic activity of the sulfur doped titania film was stable during three consecutive experiments under solar light irradiation, confirming the mechanical stability and reusability of the doped nanostructured thin film photocatalysts.

Wide-angle neutron scattering experiments combined with empirical potential structural refinement modeling have been used to study the detailed structure of decyltrimethylammonium bromide micelles in the presence of acid solutions of HCl or HBr. These experiments demonstrate considerable variation in micelle structure and water structuring between micelles in the two acid solutions and in comparison with the same micelles in pure water. In the presence of the acids, the micelles are smaller; however, in the presence of HCl the micelles are more loosely structured and disordered while in the presence of HBr the micelles are more compact and closer to spherical. Bromide ions bind strongly to the micelle surface in the HBr solution, while in HCl solutions, ion binding to the micelle is similar to that found in pure water. The hydration numbers of the anions and extent of counterion binding follow the predictions of the Hofmeister series for these species.

Is hydration the solution to the viscosity of deep eutectic solvents (DESs)? In their Communication on page 9782 ff., K. J. Edler and co-workers determine the nanostructure of DES/water mixtures over a wide hydration range by neutron diffraction and atomistic modeling. The mixture retains the characteristics of the DES structure up to remarkably high water levels and is then converted into a state that is best described as a simple aqueous solution of the DES molecular components.

Ist Hydratation der Grund für die Viskosität von stark eutektischen Lösungsmitteln (DES)? In ihrer Zuschrift auf S. 9914 beschreiben K. J. Edler et al. die Bestimmung der Nanostruktur von DES-Wasser-Mischungen über einen großen Hydratationsbereich durch Neutronenbeugung und atomistische Modellierung. Die Mischung behält bis zu hohen Wasserbeladungen die charakteristische DES-Struktur und geht dann in einen Zustand über, der am besten als einfach wässrige Lösung der molekularen DES-Komponenten beschrieben wird.

Here, we present a new microwave-solvothermal method for the preparation of iron oxide nanostructures using deep eutectic solvents as a more sustainable reaction medium. By varying the synthesis temperature and solvent water fraction, the methodology offers control over iron oxide phase, size, and morphology, using efficient, rapid (10 minute) microwave heating. Synthesis with pure DES gives small (<5 nm) superparamagnetic samples of γ-Fe2O3 or α-Fe2O3, whereas hydrated DES yielded either nanoshards or large rhombohedral nanoparticles without the superparamagnetic response. Nanostructures were solution-cast onto F : SnO2 films. The photoelectrochemical response of the prepared photoanodes was assessed, with a maximum measured photocurrent response of 0.7 mA cm−2 at 1.23 V vs. RHE. We measured the solvent structure using synchrotron WAXS, demonstrating the differences between the dry and hydrated solvent before and after heat-treatment, and showing that the hydrated solvent is remarkably resilient to extensive degradation.

AbstractThe nanostructure of a series of choline chloride/urea/water deep eutectic solvent mixtures was characterized across a wide hydration range by neutron total scattering and empirical potential structure refinement (EPSR). As the structure is significantly altered, even at low hydration levels, reporting the DES water content is important. However, the DES nanostructure is retained to a remarkably high level of water (ca. 42 wt % H2O) because of solvophobic sequestration of water into nanostructured domains around cholinium cations. At 51 wt %/83 mol % H2O, this segregation becomes unfavorable, and the DES structure is disrupted; instead, water–water and DES–water interactions dominate. At and above this hydration level, the DES–water mixture is best described as an aqueous solution of DES components.

AbstractThe nanostructure of a series of choline chloride/urea/water deep eutectic solvent mixtures was characterized across a wide hydration range by neutron total scattering and empirical potential structure refinement (EPSR). As the structure is significantly altered, even at low hydration levels, reporting the DES water content is important. However, the DES nanostructure is retained to a remarkably high level of water (ca. 42 wt % H2O) because of solvophobic sequestration of water into nanostructured domains around cholinium cations. At 51 wt %/83 mol % H2O, this segregation becomes unfavorable, and the DES structure is disrupted; instead, water–water and DES–water interactions dominate. At and above this hydration level, the DES–water mixture is best described as an aqueous solution of DES components.

The liquid structure of the archetypal Deep Eutectic Solvent (DES) reline, a 1:2 molar mixture of choline chloride and urea, has been determined at 303 K. This is the first reported liquid-phase neutron diffraction experiment on a cholinium DES. H/D isotopic substitution is used to obtain differential neutron scattering cross sections, and an Empirical Potential Structure Refinement (EPSR) model is fitted to the experimental data. Radial distribution functions (RDFs) derived from EPSR reveal the presence of the anticipated hydrogen bonding network within the liquid, with significant ordering interactions not only between urea and chloride, but between all DES components. Spatial density functions (SDFs) are used to map the 3D structure of the solvent. Interestingly, choline is found to contribute strongly to this bonding network via the hydroxyl group, giving rise to a radially layered structure with ordering between all species. The void size distribution function calculated for reline suggests that the holes present within DESs are far smaller than previously suggested by hole theory. These observations have important implications in the future development of these ‘designer solvents’.

In recent years many studies into green solvents have been undertaken and deep eutectic solvents (DES) have emerged as sustainable and green alternatives to conventional solvents since they may be formed from cheap non-toxic organic precursors. In this study we examine amphiphile behaviour in these novel media to test our understanding of amphiphile self-assembly within environments that have an intermediate polarity between polar and non-polar extremes. We have built on our recently published results to present a more detailed structural characterisation of micelles of sodium dodecylsulfate (SDS) within the eutectic mixture of choline chloride and urea. Here we show that SDS adopts an unusual cylindrical aggregate morphology, unlike that seen in water and other polar solvents. A new morphology transition to shorter aggregates was found with increasing concentration. The self-assembly of SDS was also investigated in the presence of water; which promotes the formation of shorter aggregates.

We have investigated the properties in water of two tetraalkylammonium bromides (tetramethylammonium, TMA+, and tetrapropylammonium, TPA+), at 0.4 M, using neutron scattering coupled with empirical potential structure refinement to arrive at an atomistic description. Having both a polar and an apolar moiety, it is of interest to determine the strength of each moiety as a function of the alkyl chain length. TMA+ and TPA+, having different impact as structure directors in zeolite synthesis, were chosen for this study. Water arranges tetrahedrally around TMA+ and in an almost featureless manner around TPA+. TMA+ and TPA+ show an apolar hydration with TPA+ being slightly more apolar. TPA+ has a tendency to form small clusters of 2–4 molecules and to fold into a compact configuration. Both molecules correlate similarly with the bromide ion but do not dissociate completely at this concentration.

HypothesisOwing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants.ExperimentsStable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area.FindingsSulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to that seen for phospholipids.Figure optionsDownload full-size imageDownload high-quality image (103 K)Download as PowerPoint slide

•Soft matter systems require characterisation over many different length scales.•Small and wide angle scattering are now being combined to study such systems.•Recent studies of soft matter using small & wide angle scattering are reviewed.The characterization of structure over a wide range of length scales from atomic to microns is a common requirement for understanding the behaviour of many soft matter systems. In the case of self-assembling and colloidal materials, the final properties will depend sensitively on intermolecular as well as interparticle interactions. Experimental methods such as wide and small angle scattering, which, between them, cover a wide range of length-scales are therefore growing in importance to better understand and thus exploit these systems. This review covers the growing use of wide angle scattering, either in conjunction with small angle scattering, or applied to systems which have previously been studied using small angle scattering, in order to highlight the complementarity between these two techniques, and the areas where atomistic information has contributed to understanding of the behaviour of systems containing structure at much larger length scales.

Poly(lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-PEG) nanoparticles are commonly used as drug carriers in controlled drug release and targeting. To achieve predictable and clinically relevant volumes of drug distribution, nanoparticle size, surface charge, and especially composition and structure must be controlled. Understanding the internal structures within the particles is fundamentally important to explain differences in drug loading and variations in drug release rate. We prepared nanoparticles from ester-terminated PLGA-PEG polymers via nanoprecipitation, and studied the effects of altering the solvent–water miscibility (THF, acetone, and acetonitrile). Morphology, size, polydispersity, and ζ-potential of PLGA-PEG nanoparticles were characterized. Small angle neutron scattering measurements and fitted models revealed the internal nanoparticle structure: PLGA blocks of 7–9 nm are encapsulated inside a fairly dense PEG/water network in a fractal geometry. Particles with a larger PLGA block volume and higher PEG volume fraction in the particle interior result in greater retention of the hydrophilic anticancer drug carboplatin.

Free-standing titania films were grown at the air–water interface, a novel method to synthesize robust TiO2 nanowire/nanoparticle composite films. The calcined films contain an anatase crystal phase and have a high surface area with a structure composed of one-dimensional long nanowires and mesoporous nanoparticle branches. These suggest a promising way to manufacture large areas of thick porous titania films for many applications. As one possible application, use of these films in a dye-sensitized solar cell demonstrates the potential of these materials.

The growth of free-standing surfactant-templated films of inorganic oxides at the air–solution interface is an attractive route to manufacture unsupported mesostructured membranes for a range of potential applications. So far this synthesis method has been relatively neglected due to the fragility of the initial films. More recent work to understand the mechanism of formation has led to development of thicker, more robust films, as well as providing new information on the general formation mechanisms of mesoporous materials whether in film or particulate form. This review describes the properties of silica and other inorganic oxide films templated by surfactants and grown at the air–solution interface, their formation mechanisms and implications for further development of these materials.

Self-assembly processes and corresponding phase boundaries depend on the structure of interacting molecules. We have studied the effect of surfactant head-group structure and counterion on the self-assembly processes occurring in aqueous mixtures of the cationic polymer polyethylenimine (PEI) and the cationic surfactants cetyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB) and cetylpyridinium chloride (CPC). Surface tension and conductometric methods were employed, as well as X-ray scattering and reflectometry techniques. The results indicate that the phase behaviour of PEI:cationic surfactant mixtures under dilute conditions can be tuned by altering head-group and counterion. The surfactant head-group exerts a greater influence overall, especially over micellization, since the counterion effect is screened at high polymer concentrations. Also, the self-assembly processes occurring at lower surfactant concentrations are not significantly affected by the counterion effect. The variation of surface tension with surfactant concentration shows a particular ‘well-like’ profile with a distinct break-point that can be directly related to the onset of film formation. Phase diagrams constructed using surface tension, conductivity and Brewster angle microscopy (BAM) data show three different regions where initial interactions, film formation and micellization take place, respectively, characterized by the two main self-assembly boundaries. Based on these results, we propose a molecular interpretation of the aggregation and film formation processes occurring in PEI:cationic surfactant mixtures under increasing surfactant concentrations within the dilute regime.

Polymer/silica composite films, stable to calcination, were produced using catanionic surfactant mixtures (hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS)) and polymers (polyethylenimine (PEI) or polyacrylamide (PAAm)) at the air/water interface. Film formation processes were probed by time-resolved neutron reflectivity measurements. Grazing incidence X-ray diffraction (GID) measurements indicate that the mesophase geometry of the interfacial films could be controlled to give lamellar, 2D hexagonal, and several cubic phases (Pn3̅m, Fm3̅m, and Im3̅m) by varying the polyelectrolyte molecular weight, polyelectrolyte chemical nature, or the cationic:anionic surfactant molar ratio. On the basis of GID results, a phase diagram for the catanionic surfactant/polyelectrolyte/TMOS film system was drawn. These films can be easily removed from the interface and mesoporous silica films which retain the film geometry can be obtained after calcination; moreover, this film preparation method provides a simple way to impart polymer functionality into the mesostructured silica wall, which means these films have potential applications in a variety of fields such as catalysis, molecular separation, and drug delivery.

Micron-thick hydrogel films with ordered 3D mesostructures form spontaneously at the interface of polyelectrolyte–surfactant solutions. Here we demonstrate that by rationally designing the micelle shapes it is possible to predict and so tailor the nanostructure formed within surfactant–polyelectrolyte films. Using quaternary ammonium surfactants with a range of packing parameters, we demonstrate that micelle shape in solution governs the ordered liquid crystalline phase found in the polymer-surfactant composite films. Such structural control allows modification of film properties to potentially enhance their effectiveness for applications such as inorganic templating, encapsulation and molecular sensing.

We have previously reported that robust mesostructured films will grow at the surface of alkaline solutions containing cetyltrimethylammonium bromide (CTAB), polyethylenimine (PEI), and silica precursors. Here we have used time-resolved small-angle X-ray scattering to investigate the structural evolution of the micellar solution from which the films form, at several different CTAB–PEI concentrations. Simple models have been employed to quantify the size and shape of the micelles in the solution. There are no mesostructured particles occurring in the CTAB–PEI solution prior to silica addition; however, after the addition of silicate species the hydrolysis and condensation of these species causes the formation of mesophase particles in a very short time, much faster than ordering observed in the film at the interface. The mesophase within the CTAB–PEI–silica particles finally rearranges into a 2D hexagonal ordered structure. With the aid of the previous neutron reflectivity data on films formed at the air/water interface from similar solutions, a formation mechanism for CTAB–PEI–silica films at the air/water interface has been developed. We suggest that although the route of mesostructure evolution of the film is the same as that of the particles in the solution, the liquid crystalline phase at the interface is not directly formed by the particles that developed below the interface.

Mesoporous titanium dioxide films have been produced via a self assembly pathway at the air–ethanol interface using partially fluorinated surfactants as structure directing agents. The high level of surface activity displayed by partially fluorinated compounds in alcohols has been used to generate an ordered film at the air–solution interface, as titanium oligomers condense into an ordered inorganic network. The minimisation and exclusion of water in these preparations directs structure formation at the interface and slows the titania polymerisation. X-ray scattering and Brewster angle microscopy techniques have been used to study the formation and structure of these materials.

We reveal a growth-collapse mechanism for self-assembled films of polyethyleneimine (PEI) and cetyltrimethylammonium bromide (CTAB) at the air–water interface. The work involved the quantification of film thickness on the micron scale through tracking oscillations in the amplitude and phase angles using single-angle, single-wavelength ellipsometry. Our results allow us to propose the following interfacial mechanism: film growth resulting from the association between trimethylammonium groups on surfactant micelles with lone pairs of electrons on the primary amine groups of long polymer chains, then arrest of the growth resulting from CO2 adsorption which increases the cationic charge density of the polyelectrolyte, followed by total film collapse resulting from its drying out and breakup into solid particles. We relate stages of the film development to the evolution of a Bragg peak using neutron reflectometry, where the highest degree of micellar ordering occurs just after the rapid growth stage and the loss of definition of the mesostructure is well correlated with the final collapse of the film. We also link the development to characteristic changes in the lateral film morphology using Brewster angle microscopy, including wrinkling during film growth and circular defects during collapse.

We have prepared self-supporting, free-standing titania-surfactant mesostructured films via spontaneous growth on the surface of ethanolic solutions, as an alternative synthetic route to evaporation induced self-assembly. The initial stages of surfactant templating and interfacial film formation in alcoholic solutions of titania with a polyethylene−poly(ethylene glycol) surfactant have been observed by small angle neutron scattering and Brewster angle microscopy. Variation of parameters including the titania precursor concentration, acid concentration, and surfactant concentration allowed formation times and pathways to be probed. These time-resolved observations of titania development represent a novel achievement in formation studies and have allowed a formation mechanism for titania−surfactant films to be proposed. Micelles in solution undergo an initial slow accumulation of titania, followed by rapid growth of a titania shell, followed again by a slow growth period, and these species accumulate at the solution interface to form the film via a phase transition driven by evaporation from the solution surface. This mechanism shows no solution aggregation in early developmental stages and is significant in understanding early solution phase development and for developing new materials based on evaporation induced self-assembly processes as well as for spontaneous growth of films at interfaces.

Mesoporous silica vesicles (MSV) with a hierarchical structure were developed using triblock copolymer Pluronic P103 and anionic surfactant sodium dodecyl sulfate (SDS) as a co-surfactant in the present of an inorganic salt, sodium fluoride (NaF). To some extent, variation in the particle size and vesicle cavity diameter can be achieved by adjusting the anionic–nonionic surfactant molar ratio. An onion-like vesicle morphology was obtained by changing the inorganic salt concentration. Based on the fitting of small angle neutron scattering data, a formation mechanism has been proposed. This work opens up a new way to synthesize mesoporous silica vesicles with controllable hierarchical structure using nonionic surfactant P103 and anionic surfactant SDS.

We have investigated the spontaneous self-assembly of solid, mesostructured films that form at the air−solution interface on solutions containing a neutral water-soluble polymer and catanionic surfactant mixtures of hexadecyltrimethylammonium bromide (CTAB) and sodium dodecylsulphate (SDS). The formation processes and structures were probed using neutron reflectivity, X-ray reflectivity, off-specular time-resolved scattering, and grazing incidence diffraction. The mesostructures of films prepared with polyethylene oxide, polyethylenimine, and polyacrylamide at various cationic/anionic surfactant molar ratios are compared. The results suggest that polymers having a weak interaction with the surfactants cause a depletion aggregation process that results in a lamellar phase, whereas polymers having a stronger interaction with the surfactants produce more complex mesostructures in the films.

Spontaneous growth of non-ionic surfactant-templated thin films at the air–water interface was investigated using three techniques: Brewster angle microscopy (BAM), time-resolved off-specular X-ray reflectivity and grazing incidence X-ray diffraction (GIXD). Experiments were also carried out to study the evolution of micelles in the subphase solution using small-angle neutron scattering (SANS). Films were prepared in acidic conditions using octaethylene glycol mono-n-hexadecyl ether (C16EO8) as the surfactant and tetramethyloxysilane (TMOS) as the silica precursor. Three different TMOS–C16EO8 molar ratios (3.5, 7.1 and 10.8) were studied. Variation of the silica-precursor concentration causes a significant effect on the film-formation time, the solution and film-growth mechanisms and the final film structure.

Mesostructured thin films are known to form at the interface between either air or a solid surface and a dilute acidic solution containing the silica precursor, and surfactant template. These films are transparent, and, when grown at the air/solution interface, self-supporting. We have been studying the formation processes of these films to try to understand and thus control the formation of both the mesoscale and the macroscale structure. The films are characterised using a variety of in situ methods including X-ray reflectivity techniques and Brewster angle microscopy, to study both the large and small scale structure development processes. As a result of our investigations we have suggested a coacervation driven mechanism for film growth and application of this understanding now drives our further development of these films. Here we present results concerning the effect of surfactant headgroup type, structure and counterions on the development of well-organised mesostructures, and also on the macroscopic film characteristics.

Substitution of a polyelectrolyte for silica during formation of surfactant-templated films produces similar nano- and macroscale structures confirming that silica acts as a polyelectrolyte during thin film self-assembly.

We have examined the effect of the different components in the spontaneous formation of surfactant-templated mesostructured silicate films grown at the air/solution interface. The rate of film formation shows differing dependencies on the concentrations of the silica precursor, tetramethoxysilane, the surfactant template, cetyltrimethylammonium bromide (CTAB), water and the solution pH. Further, we relate the nature of the film formation to the properties of the dried film using small angle scattering methods. From this data a general formation mechanism for the interaction between silica and surfactant micelles in this system is proposed. The polymerising silica can be considered as a cationic polyelectrolyte which interacts with the positively charged CTAB micelles through the bromine anion of the surfactant and via adsorption of the micelles as the polymer becomes more hydrophobic. This polyelectrolyte–surfactant system undergoes a liquid–liquid phase separation (coacervation) at a critical point dependant on the charge and molecular weight of the polymer and the charge on the surfactant micelle.

Growth of a mesostructured silica thin film at the air/water interface was observed in situ using Brewster angle microscopy and surface pressure measurements allowing real time observation of nucleation of the film and its rapid growth to full surface coverage at the end of the induction period.

Spontaneous growth of non-ionic surfactant-templated thin films at the air–water interface was investigated using three techniques: Brewster angle microscopy (BAM), time-resolved off-specular X-ray reflectivity and grazing incidence X-ray diffraction (GIXD). Experiments were also carried out to study the evolution of micelles in the subphase solution using small-angle neutron scattering (SANS). Films were prepared in acidic conditions using octaethylene glycol mono-n-hexadecyl ether (C16EO8) as the surfactant and tetramethyloxysilane (TMOS) as the silica precursor. Three different TMOS–C16EO8 molar ratios (3.5, 7.1 and 10.8) were studied. Variation of the silica-precursor concentration causes a significant effect on the film-formation time, the solution and film-growth mechanisms and the final film structure.

We have investigated the properties in water of two tetraalkylammonium bromides (tetramethylammonium, TMA+, and tetrapropylammonium, TPA+), at 0.4 M, using neutron scattering coupled with empirical potential structure refinement to arrive at an atomistic description. Having both a polar and an apolar moiety, it is of interest to determine the strength of each moiety as a function of the alkyl chain length. TMA+ and TPA+, having different impact as structure directors in zeolite synthesis, were chosen for this study. Water arranges tetrahedrally around TMA+ and in an almost featureless manner around TPA+. TMA+ and TPA+ show an apolar hydration with TPA+ being slightly more apolar. TPA+ has a tendency to form small clusters of 2–4 molecules and to fold into a compact configuration. Both molecules correlate similarly with the bromide ion but do not dissociate completely at this concentration.

Mesoporous titanium dioxide films have been produced via a self assembly pathway at the air–ethanol interface using partially fluorinated surfactants as structure directing agents. The high level of surface activity displayed by partially fluorinated compounds in alcohols has been used to generate an ordered film at the air–solution interface, as titanium oligomers condense into an ordered inorganic network. The minimisation and exclusion of water in these preparations directs structure formation at the interface and slows the titania polymerisation. X-ray scattering and Brewster angle microscopy techniques have been used to study the formation and structure of these materials.

In recent years many studies into green solvents have been undertaken and deep eutectic solvents (DES) have emerged as sustainable and green alternatives to conventional solvents since they may be formed from cheap non-toxic organic precursors. In this study we examine amphiphile behaviour in these novel media to test our understanding of amphiphile self-assembly within environments that have an intermediate polarity between polar and non-polar extremes. We have built on our recently published results to present a more detailed structural characterisation of micelles of sodium dodecylsulfate (SDS) within the eutectic mixture of choline chloride and urea. Here we show that SDS adopts an unusual cylindrical aggregate morphology, unlike that seen in water and other polar solvents. A new morphology transition to shorter aggregates was found with increasing concentration. The self-assembly of SDS was also investigated in the presence of water; which promotes the formation of shorter aggregates.

The growth of free-standing surfactant-templated films of inorganic oxides at the air–solution interface is an attractive route to manufacture unsupported mesostructured membranes for a range of potential applications. So far this synthesis method has been relatively neglected due to the fragility of the initial films. More recent work to understand the mechanism of formation has led to development of thicker, more robust films, as well as providing new information on the general formation mechanisms of mesoporous materials whether in film or particulate form. This review describes the properties of silica and other inorganic oxide films templated by surfactants and grown at the air–solution interface, their formation mechanisms and implications for further development of these materials.