Aims and Scope Porous materials with ultrahigh surface area have become of great importance in the domains of energy storage and environmental remediation in recent years. The book is an excellent guide to the subject of porous polymers, connecting the topics on design, preparation, properties and chemical modification of these materials. In addition, the author gives an overview of the main applications of porous materias as well as their future prospectives.
Institutional Price Campus-wide license. Their assembly in solution leads to an even richer variety of structures for example, disk-sphere, disk-cylinder, rectangular platelets, or quasicrystalline 14 — For example, hierarchical nanoporous particles and 3D films could be obtained by the addition of soluble additives during film formation 18 , 19 or by thermal CO 2 laser-induced patterned polymerization The porous structure is most commonly produced by the selective extraction of soluble components.
However, the generation of porous materials without etching or an extraction step has been much more restricted. A more frequently explored example is the preparation of 2D porous asymmetric architectures with regular hexagonally ordered pores 22 — 24 by self-assembly in solution and immersion in water. Expanding the structures from 2D to 3D could significantly broaden the possibilities for application.
For instance, it is known that the biological activity of cells is much higher if the cells are grown on 3D scaffolds To date, the use of polyHIPES porous emulsion-templated porous polymers synthesized within high internal phase emulsions has been an effective alternative method for one-pot preparation of monoliths with hierarchically isotropic pores with a diameter in the micrometer scale Analogous structures at the nanometer scale were only reported on the basis of breath figures 27 , applied to the amphiphilic polystyrene- b -poly N , N -dimethylacrylamide copolymer.
This method, however, requires a severe control of humidity and uses nonpolar solvents. We propose here a simple method to obtain flexible films with complex hierarchical and isotropic porous structures within 5 min. These films are constituted by micrometer-sized compartments, which are interconnected by long-range hexagonally ordered nanochannels Fig.
B Corresponding SEM cross-sectional image after 5 min of evaporation with details of a macrocavity and its fine mesoporous structure. The solution layer became turbid after 10 s of evaporation. This indicates that a macrophase separation initiates, with no further visual change observed after 5 min. The film was then immersed in water to extract the remaining solvent and to interrupt the phase separation after short evaporation times As shown by scanning electron microscopy SEM images Fig.
S1 , at the macroscale, spherical capsules of increasing size are formed as the evaporation time increases from 10 to 30 s, whereas at the mesoscale, hexagonal cylinders are simultaneously generated Fig. Taking into account the regularly spherical morphology of the capsules, we hypothesized that the phase separation follows the nucleation and growth NG mechanism. By increasing the evaporation time from 30 s to 1 and 5 min, we achieved a better long-range hexagonal order in bulk and at the surface fig. A Three-dimensional reconstruction of SEM images by serial block face.
B SEM surface. Full reconstruction macroscale and mesoscale of the 3D images enabled a better overview of the hierarchical structure. We combined two complementary advanced microscopy techniques: i serial block face SEM Fig. These compartments were highly interconnected, as shown by TEM tomography Fig. To gain insight into the mesoscale order formation in solution, we performed small-angle x-ray scattering SAXS. From the position of the first peak, the periodic distances between ordered domains were estimated as a function of concentration Fig.
C Periodic distance in solution as a function of copolymer concentration. In particular, the order on the surface is improved with DOX Fig. We observed a honeycomb architecture similar to that created by nature at the macroscale and mesoscale fig. S5 , indicating that our approach can precisely control the morphology at the mesoscale range. SAXS investigation confirmed that the mesoscale p6mm hexagonal order appears at higher evaporation time fig.
S4, A and B.go site
Emulsion-templated porous polymers: A retrospective perspective
We believe that the 3D hierarchical structure is formed by the co-occurrence of a macrophase separation following the NG mechanism Fig. The systems we present here are on the verge of thermodynamic instability with high block-solvent Flory-Huggins interaction parameters table S1 The Flory-Huggins interaction parameter depends on polymer concentration 31 , and it might even deteriorate as the solvent evaporates.
NG is promoted when the system is kept for some time under a thermodynamically metastable condition, which could be, in this case, induced when the solvent is partially evaporated, and the concentration of the copolymer simultaneously increases. In our investigated system, the nucleating phase is depleted of polymer and grows as time evolves. If a typical mechanism of NG is at work, the nuclei composition remains constant while their radius increases. When the polymer-depleted spherical nuclei continue to grow and come together, they flatten at the intersection if their size is practically equal.
Nuclei of different sizes might tend to coalesce because different curvatures would lead to different internal pressures according to Young-Laplace. In analogy to what happens in surfactant foams, hexagonal or heptagonal cells of similar size, separated by thin walls, are formed. As NG proceeds, the solution mass transfer inside these walls is directed to the intersection between three nuclei, the Plateau border red arrows in Fig.
At the same time, solvent transfer continues to occur from the already polymer-concentrated phase to the depleted nuclei. This flow blue arrows in Fig. As a result, channels connecting the adjacent spherical compartments are formed. As more solvent leaves the wall, the mobility of the polymer system decreases, and the system gels. In addition, breath figures are favored in the presence of nonpolar solvents and not in the presence of highly polar solvents such as DMF, which we used for this method Breath figures mostly lead to regular porosity only on the upper layers of films.
We have shown that this new approach could be extended to different PS- b -PtBA molecular weights fig. S7 , and we expect to obtain similar structures with other copolymer systems close to a metastable condition. Scheme of NG development: Nuclei growth and simultaneous solvent flow from the polymer-rich matrix to the polymer-depleted nuclei blue arrows ; solvent flow in the Plateau border between nuclei red arrows. The morphology and porosity scale of these films are very convenient for air purification filters, which target the elimination of viruses, such as echovirus or rhinovirus, or pollution particles with a size in the range of 20 to 30 nm Particles of this size should be removed by the mesoporous structure, as shown in Fig.
Because these pores cover the walls of all compartments, which are distributed in the whole film, the particles can repeatedly be excluded with high efficiency when flowing through the porous structure. On the other hand, the large compartments make the films less dense and decrease the resistance to air flow.
E Remaining inorganic structure after polymer dissolution. S8 , making this system a starting platform for other applications, such as adsorption and removal of heavy metals 35 , 36 , which require hydrophilic materials or further functionalization. Because of the presence of carboxylic groups and the unique morphology, a targeted application could be to use the now converted PS- b -PAA isotropic film as a scaffold to grow porous inorganic materials As a proof of concept, we grew porous calcium carbonate CaCO 3 , which is known as a bioinspired material for bone regeneration After the copolymer dissolution, a very porous CaCO 3 skeleton is left Fig.
In conclusion, we propose a new and versatile method to obtain well-defined 3D hierarchical structures that have tunable compartments and interconnected hexagonally ordered nanochannels at the macroscale and mesoscale. These structures are formed by solution NG and block copolymer self-assembly. We anticipate that this class of materials could be used for storage, catalysis, transport, and drug delivery, and as air purification filters and scaffolds to design bioinspired materials.
The polydispersity values were 1. All chemicals were used as received. Synthesis of isotropic films with a 3D hierarchical structure. After 10 s of evaporation, the cast solution started to become turbid. After 5 min, no visual change was observed. To quench the phase separation after short evaporation times or to extract the remaining solvent, the system was immersed in water. Afterward, the film was washed five times with water.
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To prove that the hydrolysis took place, we performed nuclear magnetic resonance NMR spectroscopy and Fourier transform infrared FTIR spectroscopy fig. S8, A and B. The system was allowed to react for 5 days to obtain porous CaCO 3. Afterward, the template was removed by washing gently with water and ethanol for 24 hours.
The morphology of the 3D hierarchical structures was investigated by SEM via Nova Nano and Magellan microscopes using an accelerating voltage of 2 to 5 kV and a working distance of 1. The samples were coated before measurement with iridium or with platinum using a Quorum QTES equipment. The samples for cross section were stained with RuO 4 before they were fractured in liquid nitrogen.
The bulk morphology was also studied by TEM. The 3D reconstruction of the macroscale structure was carried out using serial block face SEM. Small pieces of Ru-red—stained films were embedded in epoxy resin for serial block face cross-sectional imaging. The microscope was operated at an accelerating voltage of 2.
A solid-state backscatter detector was used to acquire serial section images stacks of , , and sections from three regions of interest. Three-dimensional segmentation and reconstruction of the film were performed using Avizo Fire 8. In addition, we performed the 3D reconstruction of the mesoscale structure by using TEM tomography. Xplore 3D tomography software FEI Company was used to acquire the tilt series for tomographic reconstruction. The tomograms were generated using a back projection algorithm as implemented in the IMOD software. To count the pores and to estimate the average pore size, we used the ImageJ software.
The x-ray wavelength was 0. Plots of intensity versus scattering vector q were obtained by the radially integrated 2D patterns after normalization to the intensity of the primary beam and subtraction of the background. The position of the scattering peaks was obtained by fitting the data with a sum of Lorentz functions using Igor Pro 6.
POPs – International Symposium on Porous Organic Polymers
The effective area of the film was approximately 2. Hierarchical structure of PS - b -PtBA films obtained after evaporation times varying from 10 to 30 s, before immersion in the nonsolvent bath. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license , which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited. NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail.
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Science Advances 11 May : eaat We report a simple method for rapid replication of hierarchical, isotropic porous materials that mimic complex living structures. Table of Contents. All rights reserved.