Silica Condensation Research Articles

Cell-Directed Integration into Three-Dimensional Lipid−Silica Nanostructured Matrices

We report a unique approach in which living cells direct their integration into 3D solid-state nanostructures. Yeast cells deposited on a weakly condensed lipid/silica thin film mesophase actively reconstruct the surface to create a fully 3D bio/nano interface, composed of localized lipid bilayers enveloped by a lipid/silica mesophase, through a self-catalyzed silica condensation process. Remarkably, this integration process selects exclusively for living cells over the corresponding apoptotic cells (those undergoing programmed cell death), via the development of a pH gradient, which catalyzes silica deposition and the formation of a coherent interface between the cell and surrounding silica matrix. Added long-chain lipids or auxiliary nanocomponents are localized within the pH gradient, allowing the development of complex active and accessible bio/nano interfaces not achievable by other synthetic methods. Overall, this approach provides the first demonstration of active cell-directed integration into a nominally solid-state three-dimensional architecture. It promises a new means to integrate "bio" with "nano" into platforms useful to study and manipulate cellular behavior at the individual cell level and to interface living organisms with electronics, photonics, and fluidics.

Ordered hexagonal mesoporous silica materials (SBA-15) with additional disordered large-mesopore networks formed by gaseous expansion

Ordered hexagonal mesoporous silica materials with additional disordered large-mesopore networks (DL-SBA-15s) have been prepared by one-pot process using urea as a producer of gas. Combined characterizations of XRD, SEM, and TEM techniques show that DL-SBA-15s not only have ordered 2D hexagonal mesopores (about 10 nm) similar to SBA-15, but also have another disordered large-mesopore network (about 20 nm) interconnected with hexagonal mesoporous channels, which are confirmed by nitrogen isotherms. The ordered hexagonal mesopores are templated by polymer surfactant micelle, and disordered large-mesopores are formed by gaseous expansion due to the decomposition of urea added in the silica gel. 29Si MAS NMR and FT-IR spectra show DL-SBA-15s have high degree of silica condensation and low silanols on the surface, compared with SBA-15. Furthermore, we have compared the adsorption capacity of myoglobin over conventional SBA-15 and DL-SBA-15 samples, and the results show that DL-SBA-15s exhibit much higher adsorption rate than conventional SBA-15 due to the presence of additional disordered large-mesopore networks and larger pore volume, which is potentially important for immobilization of enzymes on ordered mesoporous materials.

A Solution Study of Silica Condensation and Speciation with Relevance to in Vitro Investigations of Biosilicification

Requiring mild synthesis conditions and possessing a high level of organization and functionality, biosilicas constitute a source of wonder and inspiration for both materials scientists and biologists. In order to understand how such biomaterials are formed and to apply this knowledge to the generation of novel bioinspired materials, a detailed study of the materials, as formed under biologically relevant conditions, is required. In this contribution, data from a detailed study of silica speciation and condensation using a model bioinspired silica precursor (silicon catechol complex, SCC) is presented. The silicon complex quickly and controllably dissociates under neutral pH conditions to well-defined, metastable solutions of orthosilicic acid. The formation of silicomolybdous (blue) complexes was used to monitor and study different stages of silicic acid condensation. In parallel, the rates of silicomolybdic (yellow) complex formation, with mathematical modeling of the species present, was used to follow the solution speciation of polysilicic acids. The results obtained from the two assays correlate well. Monomeric silicic acid, trimeric silicic acids, and different classes of oligomeric polysilicic acids and silica nuclei can be identified and their periods of stability during the early stages of silica condensation measured. For experiments performed at a range of temperatures (273-323 K), an activation energy of 77 kJ.mol(-1) was obtained for the formation of trimers. The activation energies for the forward and reverse condensation reactions for addition of monomers to polysilicic acids (273-293 +/- 1 K) were 55.0 and 58.6 kJ.mol(-1), respectively. For temperatures above 293 K, these energies were reduced to 6.1 and 7.3 kJ.mol(-1), indicating a probable change in the prevailing condensation mechanism. The impact of pH on the rates of condensation were measured. There was a direct correlation between the apparent third-order rate constant for trimer formation and pH (4.7-6.9 +/- 0.1) while values for the reversible first-order rates reached a plateau at circumneutral pH. These different behaviors are discussed with reference to the generally accepted mechanism for silica condensation in which anionic silicate solution species are central to the condensation process. The results presented in this paper support the use of precursors such as silicon catecholate complexes in the study of biosilicification in vitro. Further detailed experimentation is needed to increase our understanding of specific biomolecule silica interactions that ultimately generate the complex, finely detailed siliceous structures we observe in the world around us.

Synthesis of MFI zeolites with improved crystallization rate and mesoporosity in the presence of CO 2-in-water emulsions

In this work, we demonstrate a novel and efficient route for fast crystallization of MFI zeolites of silicalite-1 and ZSM-5 with enhanced silica condensation in the presence of CO 2-in-water microemulsions. Compared to the conventional synthesis method, this new technique needs a very short time for the crystallization of MFI zeolites (4–8 h) in the presence of compressed CO 2. Furthermore, the synthesis of MFI zeolites containing mesoporosity (mesoporous MFI zeolites) under compressed CO 2 condition does not require any organotemplate, which is of great economic importance to industrial application. Interestingly, ZSM-5 synthesized in the presence of compressed CO 2 possessed uniform chain-like crystal morphology, while silicalite-1 synthesized in the presence of compressed CO 2 exhibited monodispersed crystals as characterized by scanning electron microscopy (SEM). We have extended the CO 2-in-water microemulsions route to synthesize other zeolites such as TS-1, Beta and Y. This newly developed method opens a new avenue for the fast synthesis of template-free mesoporous zeolites.

Oxidation reactions using air as oxidant thanks to silica nanoreactors containing GOx/peroxidases bienzymatic systems

A new kind of enzymes encapsulation method is presented. It combines the sol–gel method with a templating process using bilayers of phospholipids to provide an organized network of phospholipids inside the silica and in the same time protect the embedded enzymes, as if they were entrapped in a biological membrane supported on silica. This brings a porosity control to the classical sol–gel encapsulation and therefore increases the accessibility of the substrates to a maximum of enzymes. A first family of hybrid phospholipids–silica materials, named Sponge mesoporous silica (SMS), has been synthesized, which features a sponge-like structure. The formation of a negative curvature in the rigid phospholipid bilayers was induced by adding ethanol (>50%) to the aqueous medium, which provokes the separation of the head groups and the undulations of the lipid bilayers. Dodecylamine added to stabilize this structure acts as a catalyst for silica condensation. Lactose was added to avoid direct interaction of the enzymes with the silica at the interface with the lipids bilayer. Lipase was encapsulated in SMS and shows higher activity for ester hydrolysis compared to commercial immobilized-lipase. An experiment design plan was carried out to optimize SMS synthesis using hemoglobin (Hb) as biocatalyst for oxidation reactions using H 2O 2. As a result, a new structure was identified, formed by the aggregation of nanoporous silica capsules, named NPS, with a higher activity compared to SMS biocatalysts. These new biological nanoreactors were used to encapsulate simulteanously Hb and glucose oxidase, to produce in situ H 2O 2 from air, and perform oxidation reactions. This system was used for the elimination of the carcinogenic polycyclic aromatic hydrocarbon pollutants from water.

Study of [Dy(η 6- p-xylene)(GaCl 4) 3]-incorporated polyhedral silica nanofoam

Preparation and characterization of organometallic dysprosium complex embedded polyhedral silica nanofoam (PNF-SiO 2) is reported. The nanoporous solid was obtained via a sol–gel process involving precipitation of polymer micelles, hydrolysis and condensation of silica by swelling of triblock copolymer template micelles of PEO–PPO–PEO at acidic pH using high oil concentration and fast stirring. Metal-complex incorporation was performed via wet impregnation (WI) at higher temperature, where the dysprosium complex is chemically bound to the silanol groups of the silica foam surface. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) revealed that the particles of the organometallic complex are evenly distributed on the walls of the polyhedral cells, while nitrogen adsorption/desorption measurements (BET) verified that the characteristic meso- and macrocell structure of PNF-SiO 2 composed of polyhedral cells of silica joined at mesosized windows are preserved also after incorporation.

Physicochemical Characterization and Surface Acid Properties of Mesoporous [Al]-SBA-15 Obtained by Direct Synthesis

In this work, [Al]-SBA-15 samples were prepared by three different direct synthesis methods and one postsynthesis procedure, aiming to study the influence of the preparation procedures on their structural, textural, and physicochemical features. To this aim, samples were investigated by combining different experimental techniques (XRD, N(2) physisorption, (27)Al-MAS NMR, and IR spectroscopy). All preparation methods led to the formation of aluminum-containing SBA-15 samples. Nevertheless, depending on the preparation procedure, samples exhibited different structural, textural, and surface characteristics, especially in terms of Brønsted and Lewis acid sites content. [Al]-SBA-15(1) was synthesized by the pH-adjusting method and presented the lowest surface area and pore volumes. Its surface displayed three families of medium and one family of high strength Brønsted acid sites. The Brønsted/Lewis ratio was 3.49. [Al]-SBA-15(2) and [Al]-SBA-15(3) were synthesized by prehydrolysis of the silica and the aluminum precursors. In [Al]-SBA-15(2), ammonium fluoride was used as silica condensation catalyst. These two materials presented similar surface area, pore diameters and volumes, and Brønsted acidity. The Brønsted/Lewis acid sites ratio were 3.07 and 2.15 for [Al]-SBA-15(2) and [Al]-SBA-15(3), respectively. The [Al]-SBA-15(P) obtained by postsynthesis alumination displayed surface area similar to that of [Al]-SBA-15(3), Brønsted/Lewis acid sites ratio of 2.75, and Brønsted acidity similar to that of [Al]-SBA-15(1). The presence of extra-framework aluminum oxide was identified only on [Al]-SBA-15(3) and [Al]-SBA-15(P).

One step room temperature synthesis of ordered mesoporous silicaSBA-15 mediated by cellulose nanoparticles

Well ordered SBA-15 mesoporous silicas are prepared using a simple room temperature procedure made possible by the addition of small amounts of cellulose nanoparticles to a synthesis gel containing Si, water, ethanol, HCl, and P123 co-polymer. The presence of the cellulose nanoparticles enhances the level of silica condensation, in addition to improving the mesostructural ordering and results in SBA-15 materials with very low microporosity. The cellulose acts by reducing the solubility of the P123 co-polymer and also segregates the hydrophilic ethylene oxide segments of the co-polymer from the forming silica framework. These actions are conducive for the formation and phase separation of the P123–silica mesophase. Small amounts of cellulose-related organics are retained in the SBA-15 mesophase, although the pores are templated by P123 co-polymer.

Study of the Pluronic−Silica Interaction in Synthesis of Mesoporous Silica under Mild Acidic Conditions

The interaction between silica and poly(ethylene oxide) (PEO) in water may appear trivial and it is generally stated that hydrogen bonding is responsible for the attraction. However, a literature search shows that there is not a consensus with respect to the mechanism behind the attractive interaction. Several papers claim that only hydrogen bonding is not sufficient to explain the binding. The silica-PEO interaction is interesting from an academic perspective and it is also exploited in the preparation of mesoporous silica, a material of considerable current interest. This study concerns the very early stage of synthesis of mesoporous silica under mild acidic conditions, pH 2-5, and the aim is to shed light on the interaction between silica and the PEO-containing structure directing agent. The synthesis comprises two steps. An organic silica source, tetraethylorthosilicate (TEOS), is first hydrolyzed and Pluronic P123, a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer, is subsequently added at different time periods following the hydrolysis of TEOS. It is shown that the interaction between the silica and the Pluronic is dependent both on the temperature and on the time between onset of TEOS hydrolysis and addition of the copolymer. The results show that the interaction is mainly driven by entropy. The effect of the synthesis temperature and of the time between hydrolysis and addition of the copolymer on the final material is also studied. The material with the highest degree of mesoorder was obtained when the reaction was performed at 20 degrees C and the copolymer was added 40 h after the start of TEOS hydrolysis. It is claimed that the reason for the good ordering of the silica is that whereas particle formation under these conditions is fast, the rate of silica condensation is relatively low.

Bioinspired Silicification of Functional Materials: Fluorescent Monodisperse Mesostructure Silica Nanospheres

Herein we demonstrate a simple but versatile bioinspired polyamine-catalyzed silicification route to synthesizing functional materials which is monodisperse, mesoporous, and spherically uniform having nanosizes under extremely mild conditions similar to the biosilicification processes. Employing the principles learned from nature and in particular from diatom biomineralization to integrate the functions required for silica condensation and self-assembly leads to the formation of such functional materials. Importantly, the integration of such functions requires the presence of suitable multivalent counteranions, whose interaction is structure specific while facilitating the mineralization process to form these unique silica structures under the green conditions of aqueous medium, neutral pH, and room temperature. The versatility of the method is exemplified in controlling the size, uniformity, and the nanoarchitectural features of the silica obtained within a very short time frame of 30 min. A wide variety of techniques (fluorescence imaging, live confocal imaging, dynamic light scattering, MAS 29Si NMR, N2 sorption, X-ray diffraction, FT-IR, thermo-gravimetric analysis, scanning and transmission electron microscopy) have been used to study the formation process and characterization of the materials.

Temperature dependence of CO 2 concentration gradient within polymer films as determined by reactive templating

The swelling of thin polymer films by supercritical carbon dioxide has been shown to exhibit an anomalous maximum in the sorption isotherms. This swelling maximum occurs when the activity of the fluid phase approaches unity and the extent of the swelling increases as the critical temperature is approached. Using an in situ selective reactive templating approach based upon silica condensation within hydrophilic domains of an amphiphilic polymer film, the CO 2 distribution within the polymer film is elucidated from the pore sizes generated by hydrophobic domains upon removal of the amphiphile. The origin of the maximum in the swelling of the thin films is demonstrated to be concentration gradients that extend from both interfaces of the film; as the temperature approaches the critical temperature, the local swelling at both interfaces increases progressively. However, the pressure range over which gradients in CO 2 concentration occurs decreases as the critical temperature for CO 2 is approached.

Dual‐Tone Patterned Mesoporous Silicate Films Templated From Chemically Amplified Block Copolymers

AbstractDirectly patterned mesoporous silicate films are prepared using positive‐ and negative‐tone strategies by performing phase selective silica condensation within lithographically exposed poly(styrene‐b‐tert‐butyl acrylate) (PS‐b‐PtbA) templates containing photoacid generators. The use of supercritical fluid as a process medium enables rapid diffusion of the silicate precursor within the prepatterned block copolymer template film without disrupting its morphology. Template exposure through the mask triggers area selective generation of acid, which in turn both deprotects the poly(tert‐butyl acrylate) block to yield a poly(acrylic acid) block and provides a catalyst for silica precursor condensation yielding pattern formation at the device level. Because the acid generated in the UV exposed field preferentially segregates into hydrophilic poly(acrylic acid) domains of the phase segregated, deprotected block copolymer, precursor condensation is simultaneously controlled at nanoscopic length scales via templating by the underlying block copolymer morphology. The ability of PS‐b‐PtbA to undergo chemical transformation in two stages, deprotection followed by crosslinking, enables precise replications of the photomask in positive and negative tones. Detemplating via calcination yields patterned mesoporous silicate films without etching. Template formulations are optimized using infrared spectroscopic studies and the silicate films are characterized using electron microscopy and scanning force microscopy.

Immobilization and activity of Rhizomucor miehei lipase. Effect of the matrix properties prepared from nonionic fluorinated surfactants

We report the immobilization of Rhizomucor miehei lipase ( RmL) onto mesoporous silica materials, in particular the investigations concerning the effects of the level of silica condensation and of the pore size on the enzyme activity. The efficiency of the immobilization was revealed by FTIR spectroscopy. Infrared was also used to determine the quantity of adsorbed enzyme. Immobilization efficiency increased when the RmL concentration in the buffer solution was changed from 2 to 10 mg/mL. Nevertheless, while upon enzyme immobilization the mesopore ordering was sustained for the support recovered after hydrothermal treatment at 100 °C, a structure collapse occurred for the one prepared at 80 °C. The difference in behavior is attributed to the lower hydrothermal stability of this material, which reflects the lower level of silica condensation. The enzyme-containing mesostructured silica was effectively used to catalyze the model esterification reaction of lauric acid with 1-propanol, as the immobilized lipase retained its catalytic activity. A linear relationship was observed between the reaction rate and the amount of catalyst. RmL immobilized on mesoporous materials presented a satisfactory reusability, while the remaining activity of RmL after 4 months of storage was 47% of the initial one.

Synthesis and Characterization of Biocompatible and Size-Tunable Multifunctional Porous Silica Nanoparticles

In this work, size-controlled multifunctional mesoporous silica nanoparticles having large surface areas, embedded luminescence, high magnetization, and excellent aqueous dispersity have been successfully prepared by using a simple one-pot synthesis. The size and pore ordering of these particles can be easily controlled based on the number density of Fe3O4 nanoparticle nucleation sites introduced during the silica condensation reaction. Dissolution of the embedded Fe3O4 nanoparticles yields hollow mesoporous silica nanoparticles as well. These multifunctional porous nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, nitrogen adsorption−desorption behavior, dynamic light scattering, zeta potential, magnetic susceptibility, and photoluminescence. Furthermore, in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) and hemolysis assays were performed to evaluate any unintended cytotoxicity. The biocompatibility of the multifunctional nanoparticles, e...

Direct Preparation of Thermally Stable Sn-Incorporated SBA-15 Mesoporous Materials in the Self-Generated Acidic Environment

Highly ordered Sn-incorporated SBA-15 mesoporous materials with Sn loading up to 10 mol % were prepared in one pot using P123 triblock copolymer as the template in a self-generated acidic environment with the aid of NaCl. The acidity of the synthesis solution generated by hydrolysis of Sn precursor was found suitable not only for the self-assembly of P123 micelles and tetraethyl othorsilicate (TEOS) but also to incorporate the Sn ions into the SBA-15 materials. Prehydrolysis of TEOS in the synthesis solution containing P123, NaCl, and H2O prior to adding Sn precursor was essential to reduce the strong interference from the Sn ions in the self-assembly process. A well-ordered 2D hexagonal p6mm pore arrangement was observed in the Sn-SBA-15 materials with Sn/Si ratios of 0.01−0.10, while tetragonal SnO2 nanocrystallites were observed when the Sn/Si ratio was higher than 0.07. In situ small-angle X-ray scattering showed that a worm-like pore arrangement appeared at the beginning of the self-assembly process. As the reaction period prolonged, further condensation of silica and rearrangement of pore structure resulted in a well-ordered 2D hexagonal p6mm mesostructure. For the Sn-SBA-15 materials with Sn/Si ratios of 0.07−0.1, it was noticeable that two sets of 2D hexagonal pore arrangements with slightly different d spacings were present. One set of larger d spacing formed by incorporation of very small tin oxide species at the interface of P123 micelles and silicate appeared faster than the other of smaller d spacing. When the Sn/Si ratio was smaller than 0.05, Sn was probably incorporated in the SBA-15 framework as isolated ions. Beyond this loading, tetragonal SnO2 nanocrystallites (∼4.7 nm) aggregated into rod- or tube-like morphologies of 5−10 nm in diameter and 20−50 nm in length were formed inside the mesochannels. The mesostructure of Sn-SBA-15 was thermally stable up to 1000 °C, which is superior to pure siliceous SBA-15. Moreover, the SnO2 nanocrystallites confined inside the mesochannels did not sinter into large SnO2 crystals even after calcination at 1000 °C.

Effect of Counter Ions on the Silica Oligomerization Reaction

The silicate oligomerization reaction is key to sol-gel chemistry and zeolite synthesis. Numerous experimental and theoretical studies have addressed the physical chemistry of silicate oligomers in the prenucleation stage of siliceous zeolite formation. Here we report a study of a silica condensation reaction in aqueous solution in the presence of counter ions (Li(+) and NH(4)(+)). Ab-initio molecular dynamics simulations have been used to construct reaction energy diagrams including transition state free energies. Contact with Li+ as well as NH(4)(+) increases the activation energies of the dimerization step compared to the situation in the absence of counterions. The presence of NH(4)(+) has no effect on consecutive oligomerization steps. Hence NH(4)(+) will increase the relative formation rate of larger oligomers.

Formation of hybrid nano-crystals in organic–inorganic films from a basic sol

Organic–inorganic films containing hybrid nanocrystals have been prepared by sol–gel processing in controlled conditions. We have systematically changed the temperature and the aging time of a precursor sol containing an organically modified alkoxide bearing an epoxy group, 3-glycidoxypropyltrimethoxysilane, to obtain a controlled crystallization of hybrid layered structures in hybrid films. The precursor sol has been aged at different temperatures, from 5 to 60 °C, and for 1, 2 or 3 days; the films have been deposited from the aged sol and immediately after characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. We have observed that the formation of the hybrid crystals can be obtained only when at least 50% of the epoxies are opened and a larger silica condensation is achieved. These conditions are reached after aging at 60 °C for 1 day, or at longer aging times when the sol is aged at lower temperatures. Transmission electron microscopy and optical polarized images have confirmed the formation of the hybrid crystals.

Impact of thickness on CO2 concentration profiles within polymer films swollen near the critical pressure

Abstract The isothermal swelling of polymer thin films by a supercritical fluid does not increase monotonically with increasing chemical potential (pressure), but rather a maximum in swelling is generally observed near the critical pressure. A reactive templating approach utilizing the condensation of silica within hydrophilic domains of a swollen amphiphilic polymer film enables visualization of the qualitative concentration profile of CO2 by the changes in the size of hydrophobic domains (pores) with cross sectional TEM microscopy; specifically, isothermal swelling of poly(ethylene oxide-propylene oxide-ethylene oxide) films by CO2 at 60 °C is examined. Films that contain thickness gradients are used to avoid any uncertainties in the impact of thickness due to variations in the temperature or pressure during the silica modification. A uniform pore size (local swelling) is observed for all film thicknesses when the pressure is outside of the anomalous maximum in the film swelling, except for a small increase at the buried interface due to preferential adsorption of CO2 to the native silicon oxide surface of the substrate. However at this swelling maximum, a gradient in the pore size is observed at both interfaces. These swelling gradients at interfaces appear to be responsible for the anomalous maximum in thin films. As the film thickness increases beyond 350 nm, there is a decrease in the maximum swelling at the free interface.

Enzyme-modified nanoparticles using biomimetically synthesized silica

The entrapment of enzymes within biomimetic silica nanoparticles offers unique and simple immobilization protocols that merge the stability of proteins confined in solid phases with the high loading and reduced diffusion limitations inherent to nano-sized structures. Herein, we report on the biomimetic silica entrapment of chemically derivatized horseradish peroxidase for amperometric sensing applications. Scanning electron microscopy shows evidence of the formation of enzyme-modified nanospheres using poly(ethylenimine) as a template for silicic acid condensation. When these nanospheres are directly deposited on graphite electrodes, chemically modified anionic peroxidase shows direct electron transfer at 0 mV vs Ag|AgCl. Microgravimetric measurements as well as SEM images demonstrate that negatively charged peroxidase is also entrapped when silica precipitates at gold electrodes are modified with a self-assembled monolayer of poly(ethylenimine). Electrostatic interactions may play a crucial role for efficient enzyme entrapment and silica condensation at the PEI template monolayer. The in-situ biomimetically synthesized peroxidase nanospheres are catalytically active, enabling direct bioelectrocatalysis at 0 mV vs Ag|AgCl with long-term stability.

Morphological Changes from Silica Tubules to Hollow Spheres Controlled by the Intermolecular Interactions within Block Copolymer Micelle Templates

The morphological changes from tubules to large hollow spheres to (micelle-sized) small hollow-spherical silica were realized by polystyrene-block-poly(vinylpyridine) (PS-b-PVP) block copolymer micelle templates by controlling the intermolecular interactions with the corona chains. PS-b-PVP with weak intermolecular interactions among PVP corona chains yields the coexistence of tubules, large hollow spheres, and small hollow spheres. The coexistence of the three phases arises from the direct aggregation of block copolymer micelles during hydrolytic condensation of a silica precursor (tetraethylorthosilicate), as evidenced by transmission electron microscopy. When the degree of intermolecular interactions within the PVP corona blocks is increased by a change in either the degree of quaternization of the PVP blocks or the dielectric constant of the medium, small hollow spherical silica, with size equivalent to the block copolymer micelles, were solely obtained. We believe that this morphological change is due to the fact that the dipole-dipole interactions among quaternized PVP blocks physically cross-link the PVP coronas in micelles resisting the curvature change during the silica condensation.