Self-assembled Fibrillar Networks Research Articles

The striking influence of SWNT–COOH on self-assembled gelation

A miniscule amount of f-SWNTs remarkably improved (~17-fold) the gelation efficiency of amphiphilic molecules by triggering the formation of interconnecting self-assembled fibrillar networks (SAFIN) in supramolecular gelation.

Correlations of Properties and Structures at Different Length Scales of Hydro- and Organo-gels Based onN-Alkyl-(R)-12-Hydroxyoctadecylammonium Chlorides

The self-assembly and gelating ability of a set of N-alkyl-(R)-12-hydroxyoctadecylammonium chlorides (NCl-n, where n = 0-6, 18 is the length of the alkyl chain on nitrogen) are described. Several are found to be ambidextrous (gelating both water and a variety of organic liquids) and very efficient (needing less than ca. 0.5 wt % at room temperature). Structure-property correlations at different distance scales of the NCl-n in their hydro- and organo-gels and neat, solid states have been made using X-ray diffraction, neutron scattering, thermal, optical, cryo-SEM and rheological techniques. The self-assembled fibrillar networks consist of spherulitic objects with fibers whose diameters and degrees of twisting differ in the hydro- and organo-gels. Increasing n (and, thus, the molecular length) increases the width of the fibers in their hydrogels; an irregular, less pronounced trend between n and fiber width is observed in the corresponding toluene gels. Time-dependent, small angle neutron scattering data for the isothermal sol-to-gel transformation of sols of NCl-18/toluene to their gels, treated according to Avrami theory, indicate heterogeneous nucleation involving rodlike growth. Rheological studies of gels of NCl-3 in water and toluene confirm their viscoelastic nature and show that the hydrogel is mechanically stronger than the toluene gel. Models for the different molecular packing arrangements within the fibrillar gel networks of the hydro- and organogels have been inferred from X-ray diffraction. The variations in the fibrillar networks provide a comprehensive picture and detailed insights into why seemingly very similar NCl-n behave very differently during their self-assembly processes in water and organic liquids. It is shown that the NCl-n provide a versatile platform for interrogating fundamental questions regarding the links between molecular structure and one-dimensional self-aggregation, leading to gelation.

Spontaneous Orthogonal Self‐Assembly of a Synergetic Gelator System

Dedicated to ngel Guti rrez Ravelo on the occasion of his 68th birthday ACHTUNGTRENNUNG(Organo)gel materials have been exhaustively developed over the past two decades, however the recent interest for advanced functional nanomaterials has made this area of research particularly exciting. Organogels based on low molecular weight organic gelators (LMWOGs) are formed by self-assembled fibrillar networks (SAFINs), which are produced by a combination of weak non-covalent physical interactions including hydrogen bonding, p–p stacking, dipole–dipole or donor–acceptor interactions, metal coordination and van der Waals interactions. Gels based on strong chemical bonds cannot be redissolved and consequently, they do not show thermoreversible gel–sol transitions. The enhancement of the mechanical strength and thermostabilities of the gels has therefore become crucial for numerous applications in the area of material science. In view of some of the applications of gelator systems, we recently became interested in organic non-covalent interpenetrating polymer network (IPN) materials, more specifically, in the investigation of 3D organogel networks and their effects on the physico-chemical properties in the systems. Different groups have reported various examples of these innovative materials, which are synthesised under suitable conditions and characterised by a special network structure consisting of two types of morphologies of different physico-chemical nature. Van Esch and co-workers have recently reported that hydrogelators could undergo an orthogonal, independent selfassembly process in the presence of micellar and vesicular aggregates, with the subsequent coexistence of gel fibres within the formed nanostructures. Herein, we report the potential of two gelator systems (with different solvent-dependent abilities) to gel by self-assembly processes and their ability to spontaneously self-organise and simultaneously assemble into a novel nanomaterial containing two different interconnected porous and fibre-type domains. The final nanomaterial can remarkably improve the properties of related or similarly generated independent organogels. The multi-gelator gels comprise two different types of aggregates, which are spontaneously and simultaneously assembled. With this purpose, we employed a mixture of two different organogelators 1 and 2. Firstly, organogelator 1 is a synergistic multi-component organogelator liquid system, in which the gelation phenomenon of oxygenated solvents takes place at low temperature (after gentle heating of the isotropic solution). Organogelator 2 is an oligoamide, which exclusively produces stable organogels in chlorinated solvents upon cooling of the gently heated isotropic solution. The organogel properties of both gelator systems (1 and 2) have been reported previously.

Self-Assembly Fibrillar Network Gels of Simple Surfactants in Organic Solvents

The self-assembled fibrillar network (SAFIN) organogels of a simple surfactant molecule, sodium laurate (C(11)H(23)COONa, SL), in organic solvents were investigated. The sol-gel transformation temperature depended on the SL concentration, the solvent, and the concentration of Na(+) was evaluated. An important finding is that Na(+) ions play an important role in forming organogels, which was regarded as the induction factor of gelation, but other cations, for instance, Li(+), K(+), Ca(2+), and Mg(2+), do not have this capability. The observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) proved that the organogels were network structures with fibers and ribbons by trapping a certain amount of organic solvent. High-resolution TEM (HR-TEM) images indicated that each of the fibers or ribbons was composed of cylindrical micelles. The X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra demonstrated that SL molecules in gels behave similarly to those in SL crystals. The mechanism of organogel formation was elaborated to provide a better understanding of fibrous surfactant gels in organic solvents.

Functional organogel based on a hydroxyl naphthanilide derivative and aggregation induced enhanced fluorescence emission

A new class of low molecular weight organogelator (LMOG) of hydroxyl naphthanilide moiety was suitably designed and synthesized and it forms gels through noncovalent interactions in hydrocarbon solvents. Self-assembly structure, hydrogen bonding interaction, and photophysical properties of organogelator 3-hydroxy-naphthalene-2-carboxylic acid (2-heptylcarbamoyl-phenyl)-amide ( 2) have been investigated by field emission scanning electron microscope (FE-SEM), FT-IR, UV–vis absorption and photoluminescence combined with theoretical studies by hybrid density-functional theory (DFT) B3LYP and semi-empirical calculations AM1 with CI methods. It was found that gelation is completely thermoreversible, and it occurs due to the aggregation of the organogelator resulting in the formation of a fibrous network due to the π–π stacking interaction complemented by the presence of both inter- and intra-molecular hydrogen bonding. The self-assembled fibrillar networks in the gels were distinctly evidenced by SEM observations. FT-IR studies confirm that the common driving force for aggregation in the organogels and microsegregation in the mesophase is the occurrence of a tight intermolecular hydrogen bonded network that does not persist in diluted solution. Gelator 2 is very weakly fluorescent in solution, but its intensity is increased by almost 30–32 times in their respective gelled state depending on the nature of the gelling solvents. The aggregation induced emission enhancement is ascribed to the formation of J-aggregation and inhibition of intramolecular rotation in the gel state.

Self‐Association of Bis‐Dendritic Organogelators: The Effect of Dendritic Architecture on Multivalent Cooperative Interactions

A series of bis-dendritic gelators consisting of a benzamide dendron and an alkyl dendron were synthesized to investigate the dendritic effect on self-assembly. The gelators with a first-generation benzamide (benzamide-G1) dendron or a first-generation alkyl (alkyl-G1) dendron formed stable gels in most aromatic solvents, and their self-assembled fibrillar networks were imaged by electron microscopy. The unbranched molecule (G0-G0) or the molecule possessing a second-generation benzamide (benzamide-G2) dendron did not form gels. Differential scanning calorimetry, powder X-ray diffraction, and Fourier transform IR studies revealed that introduction of a dendritic branch strongly affected the molecular packing as well as the strength of intermolecular interactions. Furthermore, concentration-dependent diffusion coefficient measurements and the evaluation of association constants by (1)H NMR spectroscopy indicated that bis-dendritic gelators with a benzamide-G1 dendron possessed high association constants and formed large aggregates, whereas molecules with a single benzamide formed dimers in chloroform. The formation of self-assembled fibrillar networks was driven by the multivalent and cooperative hydrogen bonding observed in the benzamide-G1 dendrons. Pi-pi stacking of aromatic groups and van der Waals interactions between alkyl chains also played roles in the self-assembly process, thus indicating that a spatial balance between two dendrons is important.

A molecular insight into the nature of crystallographic mismatches in self-assembled fibrillar networks under non-isothermal crystallization conditions

The lengths of the 12-hydroxystearic acid (12HSA) fibers are influenced by crystallographic mismatches resulting from the incorporation of 12HSA monomers into the crystal lattice in an imperfect manner. On a molecular level, this can be differentiated using synchrotron Fourier transform infrared (FTIR) spectroscopy by monitoring the change in area of the 1700 cm−1 and 3200 cm−1 peaks, corresponding, respectively, to the dimerization of the carboxylic acid groups and hydroxyl non-covalent interactions, during crystallization. The crystallographic mismatch is attributed to a plateau in the apparent rate constant for the dimerization of the carboxylic acid head groups while the hydroxyl interactions linearly increase as a function of cooling rate (ϕ). The rate constant for hydroxyl interactions linearly increases as a function of cooling rate while a plateau is observed for the rate of dimerization at cooling rates between 5 and 7 °C min−1. At cooling rates greater than 5 to 7 °C min−1 12HSA monomers do not effectively dimerize before being incorporated into the crystal lattice causing crystal imperfections impeding linear epitaxial crystal growth and produces branched fibers. At slow cooling rates (i.e., less than 5 to 7 °C min−1), long fibers are produced with a fractal dimension between 0.95 and 1.05 and for rapid cooling rates (i.e., greater than 5 to 7 °C min−1) short branched fibers are produced with a fractal dimension between 1.15 and 1.32.

Unraveling the packing pattern leading to gelation using SS NMR and X-ray diffraction: direct observation of the evolution of self-assembled fibers

A detailed understanding of the mode of packing patterns that leads to the gelation of low molecular mass gelators derived from bile acid esters was carried out using solid state NMR along with complementary techniques such as powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarizing optical microscopy (POM). Solid state 13C{1H} cross polarization (CP) magic angle spinning (MAS) NMR of the low molecular mass gel in its native state was recorded for the first time. A close resemblance in the packing patterns of the gel, xerogel and bulk solid states was revealed upon comparing their 13C{1H}CPMAS NMR spectral pattern. A doublet resonance pattern of 13C signals in 13C{1H}CPMAS NMR spectra were observed for the gelator molecules, whereas the non-gelators showed simple singlet resonance or resulted in the formation of inclusion complexes/solvates. PXRD patterns revealed a close isomorphous nature of the gelators indicating the similarity in the mode of the packing pattern in their solid state. Direct imaging of the evolution of nanofibers (sol–gel transition) was carried out using POM, which proved the presence of self-assembled fibrillar networks (SAFINs) in the gel. Finally powder X-ray structure determination revealed the presence of two non-equivalent molecules in an asymmetric unit which is responsible for the doublet resonance pattern in the solid state NMR spectra.

Tunable Mechanics of Peptide Nanofiber Gels

The mechanical properties of self-assembled fibrillar networks are influenced by the specific intermolecular interactions that modulate fiber entanglements. We investigate how changing these interactions influences the mechanics of self-assembled nanofiber gels composed of peptide amphiphile (PA) molecules. PAs developed in our laboratory self-assemble into gels of nanofibers after neutralization or salt-mediated screening of the charged residues in their peptide segment. We report here on the gelation, stiffness, and response to deformation of gels formed from a negatively charged PA and HCl or CaCl(2). Scanning electron microscopy of these gels demonstrates a similar morphology, whereas the oscillatory rheological measurements indicate that the calcium-mediated ionic bridges in CaCl(2)-PA gels form stronger intra- and interfiber cross-links than the hydrogen bonds formed by the protonated carboxylic acid residues in HCl-PA gels. As a result, CaCl(2)-PA gels can withstand higher strains than HCl-PA gels. After exposure to a series of strain sweeps with increasing strain amplitude HCl- and CaCl(2)-PA gels both recover 42% of their original stiffness. In contrast, after sustained deformation at 100% strain, HCl-PA gels recover nearly 90% of their original stiffness after 10 min, while the CaCl(2)-PA gels only recover 35%. This result suggests that the hydrogen bonds formed by the protonated acids in the HCl-PA gels allow the gel to relax quickly to its initial state, while the strong calcium cross-links in the CaCl(2)-PA gels lock in the deformed structure and inhibit the gel's ability to recover. We also show that the rheological scaling behaviors of HCl- and CaCl(2)-PA gels are consistent with that of uncross- and cross-linked semiflexible biopolymer networks, respectively. The ability to modify how self-assembled fibrillar networks respond to deformations is important in developing self-assembled gels that can resist and recover from the large deformations that these gels encounter while serving as synthetic cell scaffolds in vivo.

Preface to the Molecular and Polymer Gels; Materials with Self-Assembled Fibrillar Networks Special Issue

Preface to the Molecular and Polymer Gels; Materials with Self-Assembled Fibrillar Networks Special Issue

Hydrogen-Bonding Density of Supramolecular Self-Assembled Fibrillar Networks Probed Using Synchrotron Infrared Spectromicroscopy

We employed synchrotron infrared spectromicroscopy to provide new insights into the development of self-assembled fibrillar networks. The noncovalent interactions responsible for the occurrence of transient junction zone in 12HSA arise because of hydroxyl−hydroxyl hydrogen bonding. This may result from the preferential arrangement of carboxylic acid groups to dimerize within the fiber, resulting in a reduction of the fiber−solvent interfacial tension. As well, synchrotron infrared spectromicroscopy indicates that the crystallization process of SAFiNs efficiently displaces solvent from the interface of the growing crystals contributing to the epitaxial growth into axially symmetric elongated aggregates. The periodicity in the density of hydrogen bonding resolves the supramolecular chirality of 12HSA fibers.

Switchable Perfomance of an l-Proline-Derived Basic Catalyst Controlled by Supramolecular Gelation

An L-proline-derived low molecular weight gelator forms gels in nitromethane and nitroethane and acts as a basic catalyst for the Henry nitroaldol reaction of these solvents with 4-nitrobenzaldehyde and 4-chlorobenzaldehyde. The reported catalyst is efficient only upon aggregation into self-assembled fibrillar networks. The formation of the gels is associated to a basicity boost of the L-proline residues. Gel dissociation blocks the catalytic efficiency for the nitroaldol reaction but enhances a reaction pathway leading to alkenes. Because of the reversible nature of supramolecular gels, subtle temperature changes allow for a reversible sol-gel transition associated to an activation of the catalyst. The catalytic gel from nitroethane is significantly more active than the one from nitromethane probably because of its different structure as revealed by X-ray diffraction and thermal stability studies. The results shown indicate that in solution the L-proline moiety catalyzes the reaction of nitroalkanes with aldehydes via iminium intermediates while efficient nitroaldol reactions are promoted in the gel phase through an ionic pair type mechanism. The fact that upon aggregation the amino acid-based molecule used as gelator plays both a structural (gel formation) and catalytic role is interesting for the point of view of life origin studies.

Engineering Molecular Self-Assembled Fibrillar Networks by Ultrasound

The architecture of self-organized three-dimensionally interconnected nanocrystal fibrillar networks has been achieved by ultrasound from a solution consisting of separate spherulites. The ultrasound stimulated structural transformation is correlated to the striking ultrasonic effects on turning nongelled solutions or weak gels into strong gels instantly, with enhancement of the storage modulus up to 3 magnitudes and up to 4 times more gelling capability. The basic principle involved in the ultrasound-induced structural transformation is established on the basis of the nucleation-and-growth model of a fiber network formation, and the mechanism of seeding multiplication, aggregation suppressing, and fiber distribution and growth promotion is proposed. This novel technique enables us to produce self-supporting gel functional materials possessing significantly modified macroscopic properties, from materials previously thus far considered to be “useless”, without the use of chemical stimuli. Moreover, it provides a general strategy for the engineering of self-organized fiber network architectures, and we are consequently able to achieve the supramolecular functional materials with controllable macroscopic properties.

Self-Assembly of Esters of Arjunolic Acid into Fibrous Networks and the Properties of their Organogels

Nine esters of a naturally occurring triterpenoid, arjunolic acid (from Terminalia arjuna), with alkyl chains have been synthesized, and their self-assembly has been studied in organic liquids. All of the esters examined were found to be excellent gelators. No birefringence was detected in optical micrographs of the transparent toluene gels with 5% (w/w) ethyl arjunolate or 5% (w/w) p-nitrobenzyl arjunolate as the gelator, but a spherulitic-type pattern was seen for a gel of 1.2% (w/w) p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane. Electron microscope images revealed self-assembled fibrillar network (SAFIN) structures with right-handed helical ribbons in some gels. With increasing concentration of the gelators, the gel-to-sol transition temperature (T(gel)) increased and then approached plateau values. Differential scanning thermograms demonstrated that the heats for transition from transparent gels to sols of ethyl arjunolate or p-nitrobenzyl ajunolate in toluene are very small. Powder X-ray diffractograms revealed that the molecular packing in the SAFIN of the 5% (w/w) ethyl aijunoate in the toluene gel was amorphous and similar to the diffractogram recorded for the neat gelator. Although the diffractogram of neat p-nitrobenzyl arjunolate consisted of broad peaks, suggesting disordered packing, the low-angle peaks of the corresponding toluene gel were much sharper; these results indicate more crystalline packing in the SAFIN than in the neat gelator. The kinetics and growth of the transformation of sols of p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane to their gels have been investigated at different incubation temperatures by circular dichroism spectroscopy. The data have been analyzed to probe the mechanism of SAFIN formation and the relationship between the molecular structures of the esters of arjunolic acid and their abilities to function as gelators of a wide variety of organic liquids.

Robust Organogels from Nitrogen-Containing Derivatives of (R)-12-Hydroxystearic Acid as Gelators: Comparisons with Gels from Stearic Acid Derivatives†

Thirteen members of a new class of low molecular-mass organogelators (LMOGs), amides, and amines based on (R)-12-hydroxystearic acid (HSA; i.e., (R)-12-hydroxyoctadecanoic acid) and the properties of their gels have been investigated by a variety of structural and thermal techniques. The abilities of these LMOGs, molecules with primary and secondary amide and amine groups and the ammonium carbamate salt of 1-aminooctadecan-12-ol, to gelate a wide range of organic liquids have been ascertained. Their gelating efficiencies are compared with those of HSA and the corresponding nitrogen-containing molecules derived from stearic acid (i.e., HSA that lacks a 12-hydroxyl group). Several of the HSA-derived molecules are exceedingly efficient LMOGs, with much less than 1 wt % being necessary to gelate several organic liquids at room temperature. Generally, the self-assembled fibrillar networks of the gels consist of spherulitic objects whose dimensions depend on the protocol employed to cool the precursor sol phases. X-ray studies indicate that the LMOG molecules are packed in lamellae within the fibers that constitute the spherulites. In addition, some of the organogels exhibit unusual thixotropic properties: they recover a large part of their viscoelasticity within seconds of being destroyed by excessive strain shearing. This recovery is at least an order of magnitude faster than for any other organogel with a crystalline fibrillar network reported to date. Correlations of these LMOG structures (as well as with those that lack a hydroxyl group along the n-alkyl chain, a headgroup at its end, or both) with the properties of their gels, coupled with the unusual theological properties of these systems, point to new directions for designing LMOGs and organogels.

Rapid and Reversible Gel−Sol Transition of Self-Assembled Gels Induced by Photoisomerization of Dendritic Azobenzenes

An asymmetric bis-dendritic gelator (1) consisting of an azobenzene dendron and an aliphatic amide dendron was synthesized to achieve a photoresponsive self-assembly. The compound gelled in a wide range of organic solvents, even at concentrations as low as 0.02% (w/v) in cyclohexane. The self-assembled fibrillar network structure was confirmed by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analyses. The rapid and reversible gel-sol transition by irradiation with UV and visible light was investigated by UV-vis and Fourier transform infrared (FT-IR) spectroscopy, FE-SEM, and XRD analyses. Upon irradiation of the gel with UV, trans-to-cis isomerization of the azobenzene groups occurred, and the gel turned into a sol state. The gel was recovered immediately by the reverse cis-to-trans isomerization after the exposure to visible light. The trans-to-cis isomerization of the azobenzenes disrupted the hydrogen bonding of azobenzene amide groups, together with the hydrogen bonding in the aliphatic amide dendron. This facile communication between the two amide dendrons leads to the dissociation of the gel fibers and collapse of the gel.

Organo- and hydrogels derived from cyclo(L-Tyr-L-Lys) and its ε-amino derivatives

Cyclo(L-Tyr-L-Lys) (1) and its e-amino derivatives (2a–2g) were synthesized and investigated as organo- and hydrogelators. Although 1 precipitates in water, it enables the gelation of a number of polar organic solvents including DMF and DMSO. Ultrasound promotes 1 to form a hydrogel when cooling its aqueous solution. Even at 56 °C the hydrogelation still occurs when its concentration reaches 1.5 wt% under the assist of sonication. Moreover, after N-acylation of 1 with alkyl carboxylic acids and anhydrides, 2a–2g exhibit chain length dependent hydrogelation ability. 2a–2c with short alkyl tails yield hydrogels at around 1.0 wt%. Rheological results showed that a robust thermoreversible hydrogel is created from 2b at 2.5 wt%. The self-assembled fibrillar networks in the gels were distinctly evidenced by TEM and SEM observations. 1H NMR analyses suggested that intermolecular hydrogen-bonding between diketopiperazine rings plays an essential role in the self-aggregation of these gelators. Based on X-ray powder diffraction data, a possible molecular packing model was deduced for the xerogel of 1. Also the interdigitated bilayer structure was proposed for the self-assembly of 2a–2g in ethanol.

Solvent-free construction of self-assembled 1D nanostructures from low-molecular-weight organogelators: sublimation vs. gelation

The formation of self-assembled fibrillar networks in the absence of solvent is reported for a whole family of amino acid derived gelators containing nicotinoyl and isonicotinoyl terminal groups. Fibrillar networks can be formed easily by a sublimation process (vapor–solid method). In this work is reported an unprecedented comparison of the microfibrillar structures formed by organogelators within a solvent (acetonitrile and toluene) and in the absence of solvent. The use of different techniques such as scanning electron microscopy (SEM), wide-angle X-ray diffraction or FT-IR revealed that, for these compounds, the solvent did not influence significantly the intrinsic tendency of these molecules to form 1D nanostructures. However, SEM revealed that solvent effects were evident at higher levels of organization in connection with phenomena as fibril–fibril fusions and at the molecular level by the stabilization of different polymorphs.

Post-crystallization increases in the mechanical strength of self-assembled fibrillar networks is due to an increase in network supramolecular ordering

Fibre–fibre interactions strongly influence the elastic properties of an organogel and are of critical importance to the ability of the network to entrain liquid oil. At 30 °C, there was a significant decrease in the storage modulus in time due to a decrease in the amount of crystalline material (i.e. a decrease in the free induction decay (FID) amplitude) and order of crystalline material (i.e. an increase in the FID T2 relaxation time (i.e. a measure of proton mobility)). Conversely, at 5 °C, there was an increase in G′ in time but no changes were observed in both the amount of crystalline material and its order. This increase in G′ was accompanied by a significant increase in the enthalpy of melt and the melting temperature, which translated to a significant increase in the entropy of melt of the system. This decrease in the absolute entropy of the system in time probably arose due to an increase in the number of van der Waals interactions between 12-hydroxystearic acid fibres. Hence the increased order of the system is due to the fibre–fibre interactions which results in a significant increase in G′ in time at 5 °C.

Use of Fluorescence Spectroscopy To Study Polymeric Materials with Porous Structure Based on Imprinting by Self-Assembled Fibrillar Networks

Different polymeric materials have been prepared from the organogels formed by a polymerizable methacrylic mixture (methyl methacrylate/ethylene glycol dimethacrylate, 1:1, w/w) and the macrocyclic pseudopeptide 1. The use of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide as a very efficient radical initiator allows polymeric materials in which the structure of the fibrils formed by self-assembly of the organogelator 1 is truly preserved to be obtained. Removal of the pseudopeptidic molecule provides materials with a porous structure reflecting that of the original self-assembled fibrils. The use of fluorescent probes such as rhodamine B and pyrene greatly facilitate the study of the porous structures formed and, accordingly, that of the morphology of the original fibrils. Those studies reveal the presence of a permanent porosity and the organization of the substructures as a porous network. This confirms the existence of a nucleation and growth mechanism for the generation of the fibrils, giving rise to the formation of spherulitic structures. Those spherulites are additionally linked by connections of variable size. A series of diffusion experiments allowed establishment of a direct dependence of the inner porosity of the materials on the amount of self-organizing template used for their preparation.