Heat Capacity Step Research Articles

Lysozyme-Sucrose Interactions in the Solid State: Glass Transition, Denaturation, and the Effect of Residual Water.

The freeze-drying of proteins, along with excipients, offers a solution for increasing the shelf-life of protein pharmaceuticals. Using differential scanning calorimetry, thermogravimetric analysis, sorption calorimetry, and synchrotron small-angle X-ray scattering (SAXS), we have characterized the properties at low (re)hydration levels of the protein lysozyme, which was freeze-dried together with the excipient sucrose. We observe that the residual moisture content in these samples increases with the addition of lysozyme. This results from an increase in equilibrium water content with lysozyme concentration at constant water activity. Furthermore, we also observed an increase in the glass transition temperature (Tg) of the mixtures with increasing lysozyme concentration. Analysis of the heat capacity step of the mixtures indicates that lysozyme does not participate in the glass transition of the sucrose matrix; as a result, the observed increase in the Tg of the mixtures is the consequence of the confinement of the amorphous sucrose domains in the interstitial space between the lysozyme molecules. Sorption calorimetry experiments demonstrate that the hydration behavior of this formulation is similar to that of the pure amorphous sucrose, while the presence of lysozyme only shifts the sucrose transitions. SAXS analysis of amorphous lysozyme-sucrose mixtures and unfolding of lysozyme in this environment show that prior to unfolding, the size and shape of lysozyme in a solid sucrose matrix are consistent with its native state in an aqueous solution. The results obtained from our study will provide a better understanding of the low hydration behavior of protein-excipient mixtures and support the improved formulation of biologics.

Step-scan differential calorimetry of protein denaturation: Modeling and experiment

Calorimetric step-scan curves of the reversible protein denaturation were modeled numerically. The quasi-equilibrium denaturation regime can be realized if the duration of isothermal steps is long enough so that the system is able to settle to equilibrium. We show the changes in the real and imaginary parts of the complex heat capacity during the denaturation process depending on the kinetic regime of denaturation. The practical application of the step-scan method for denaturation of lysozyme in water has revealed the negative temperature coefficient of the excess heat capacity of lysozyme. In the case of denaturation of lysozyme in glycerol studied by fast scanning calorimetry, the step-scan technique can be used to improve the quality of the baseline and reveal a heat capacity step after during denaturation.

Thermal shrinkage and heat capacity of monolithic polymeric physical aerogels

Monolithic physical aerogels based on semicrystalline linear polymers are suitable for molecular separation, catalysis, and thermal insulation. These low-density materials generally exhibit thermal shrinkage in their pre-melting region. Differential Scanning Calorimetry (DSC) shows that aerogel thermal shrinkages occur with relevant step decreases of heat capacity (ΔCp < 0). For physical aerogels based on the thermodynamically stable β form of syndiotactic polystyrene (sPS), a positive heat capacity step associated with glass transition (Tg) and a negative heat capacity step associated with thermal shrinkage are well separated. As for poly (2,6-dimethyl-1,4-phenylene)oxide (PPO), which exhibits the rather unique closeness of Tg and Tm, the two phenomena are superimposed and a regular increase of heat capacity with porosity, going from positive to progressively more negative values is observed. Negative heat capacity steps are not present for thermal shrinkage of polymer foams, which exhibit high porosity but the low surface area. On the basis of the present study, simple and fast DSC scans allow accurate evaluation of temperatures of thermal shrinkage of monolithic physical polymer aerogels.

Thermal and dielectric behavior of polyamide-6/clay nanocomposites

In this work, the influence of the incorporation of nanoparticles (organo-modified montmorillonite Cloisite 30B) in polyamide 6 (PA6) on rigid amorphous fraction (RAF) formation had been explored employing Differential Scanning Calorimetry (DSC), Flash Differential Scanning Calorimetry (Flash DSC) and Broadband Dielectric Spectroscopy (BDS) techniques. The existence of a RAF in PA6-montmorillonite nanocomposite films is available from specific heat capacity measurement at the glass transition region of the nanocomposites. It was shown that at high C30B content, this fraction becomes larger. Using Flash DSC, it was possible not only to measure the heat capacity step at the glass transition of the materials, but also to provide quantitative knowledge on the kinetics of crystallization and nucleation of PA6-based nanocomposites. The dielectric relaxation spectroscopy measurement was investigated, in the frequency range 0.1–106 Hz and varying temperature from 20 to 200 °C, which highlight different relaxation phenomena: the α dipolar relaxation, the αc relaxation and Maxwell–Wagner–Sillars (MWS) interfacial polarizations. As C30B content increases, a MWS relaxation emerges in the nanocomposites, thus revealing the increase of RAF in the nanocomposite with high C30B content.

Morphology and molecular dynamics investigation of low molecular weight PDMS adsorbed onto Stöber, fumed, and sol-gel silica nanoparticles

Morphology, glass transition and molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto three types of silica nanoparticles, namely Stöber, fumed-pyrogenic, and silica gel, were studied employing scanning electron microscopy (SEM), isothermal nitrogen adsorption–desorption, calorimetry (DSC) and broadband dielectric spectroscopy (BDS) techniques. The initial Stöber particles (specific surface area SBET ∼240 m2/g) form a quite loose silica network with mainly textural pores of ∼12 nm in size. Fumed silica (SBET ∼260 m2/g) demonstrates denser aggregation and increased textural porosity (∼11 nm), while silica gel (SBET ∼850 m2/g) exhibits tremendous intraparticle porosity (tubular-like pores of ∼6 nm). On adsorption of PDMS (at ∼20 and ∼30 wt%), the glass transition temperature (Tg) decreases as compared to the bulk, while the glass transition step broadens. Results suggest loosened molecular packing of the polymer chains accompanied by a broadening of the range of relaxation times in the composites as compared to the neat polymer. On the other hand, the heat capacity step at glass transition is significantly suppressed in the composites, suggesting the formation of a rigid polymer fraction (RAF) at the interfaces with nanoparticles due to strong physical interaction (hydrogen bonding). RAF increases in the order Stöber < fumed (A300) < silica gel, this increase following that of SBET, in agreement with results in previous work on silica/PDMS systems. Next to the segmental dynamics (α relaxation) of the bulk-like polymer related to the glass transition, BDS allowed the detection of a separate segmental-like relaxation of the polymer in the interfacial silica-PDMS zone. In terms of timescale the interfacial relaxation is almost identical for Stöber and A300, and slightly faster for silica gel. Comparison of the results of the present work with previous results obtained with similar nanocomposites based on low molecular weight PDMS and silica, provides additional support to recently proposed ‘SBET–interfacial dynamics’ and ‘chain packing–polymer dynamics’ correlations.

Trend report: polyamide 6 and 66

In this work, the influence of the incorporation of nanoparticles (organo-modified montmorillonite Cloisite 30B) in polyamide 6 (PA6) on rigid amorphous fraction (RAF) formation had been explored employing Differential Scanning Calorimetry (DSC), Flash Differential Scanning Calorimetry (Flash DSC) and Broadband Dielectric Spectroscopy (BDS) techniques. The existence of a RAF in PA6-montmorillonite nanocomposite films is available from specific heat capacity measurement at the glass transition region of the nanocomposites. It was shown that at high C30B content, this fraction becomes larger. Using Flash DSC, it was possible not only to measure the heat capacity step at the glass transition of the materials, but also to provide quantitative knowledge on the kinetics of crystallization and nucleation of PA6-based nanocomposites. The dielectric relaxation spectroscopy measurement was investigated, in the frequency range 0.1–106 Hz and varying temperature from 20 to 200 °C, which highlight different relaxation phenomena: the α dipolar relaxation, the αc relaxation and Maxwell–Wagner–Sillars (MWS) interfacial polarizations. As C30B content increases, a MWS relaxation emerges in the nanocomposites, thus revealing the increase of RAF in the nanocomposite with high C30B content.

Linear baseline interpolation for single-process DSC data—Yes or no?

Theoretical simulations were used to evaluate performance of the linear baseline interpolation for the consequent kinetic analysis of single processes under different circumstances including the effects of varying height of the heat capacity step between the reactants and products, or varying asymmetry of the interpolated kinetic peak. In general, height of the Cp step was found to have larger distorting influence than the peak asymmetry. The model-free kinetic methods were found to be robust enough not to be significantly affected by the distortions caused by using linear interpolation (the performance was compared to that of the most accurate and physically meaningful tangential area-proportional interpolation) – the largest errors in activation energy did not exceed approx. 3%. On the other hand, model-based analysis has shown that usage of the linear interpolation leads to a significant distortion of the shape of the kinetic peaks and large deviations in the integrated area of the kinetic peak (corresponding e.g. to specific heat associated with the process studied by differential scanning calorimetry). Distortions of the peak shape consequently led to often largely deviated values of kinetic exponents determined for the correctly preselected known kinetic models. Model-based kinetic analysis of real-life experimental data treated via linear interpolation could in such case lead even to a selection of an incorrect kinetic model.

The influence of the preparation conditions and filler content on thermal properties of poly-l -lactide and hydroxyapatite/poly-l -lactide nanocomposite

Poly-l-lactide (PLLA) and hydroxyapatite/poly-l-lactide (HAp/PLLA) are two widely used biomaterials for three-dimensional scaffolds, drug release matrices and implantable medical devices for reparation of bone tissue; diversity in the initial preparation and filler content has a significant influence on different properties such as morphology and crystallinity, thus playing a considerable role in most of these applications. For this reason, PLLA and HAp/PLLA samples with a large difference in crystallinity (from below 20% to over 70%) and filler content (up to 86 wt% of HAp nanoparticles with an average diameter of 80 nm) were prepared and consequent dissimilarities in morphology, crystallinity and thermal properties were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) measurements and Fourier transform infrared (FTIR) spectroscopy. Special attention was devoted to analyzing data obtained from thermal measurements. A three-phase model was employed in order to describe the heat capacity step decline in the nanocomposite; the evolution in different polymer fractions, the crystalline fraction and the mobile and rigid amorphous fractions, with filler content was determined. © 2017 Society of Chemical Industry

Effects of interfacial interactions and of crystallization on rigid amorphous fraction and molecular dynamics in polylactide/silica nanocomposites: A methodological approach

We employ a partly new experimental approach to polymer nanocomposites (PNCs) based on a semicrystalline matrix, in order to distinguish between phenomena affiliated, on the one hand, to interactions between polymer and nanoparticles, and, on the other hand, to polymer crystals. Thus, effects of silica nanoparticles and of crystalline fraction (CF) on glass transition and segmental dynamics in poly (l–lactic acid) were investigated by means of differential scanning calorimetry (DSC) and broadband dielectric relaxation spectroscopy (DRS). Analysis of results involves combination of measurements on initially amorphous and on semicrystalline (annealed) samples. No change in the glass transition temperature by the filler is observed by DSC, whereas the heat capacity step decreases in the PNCs. The segmental α relaxation (dynamic glass transition) in DRS becomes, however, faster and weaker in the PNCs. Results are rationalized in terms of the rigid amorphous fraction (RAF) due to filler (interfacial polymer, RAFfiller) and due to polymer crystals (RAFcrystal). RAFfiller and RAFcrystal were disentangled from the total RAF via two assumptions: (a) assuming the same RAFcrystal to CF ratio in the neat matrix and the PNCs, and (b) assuming the same RAFfiller in amorphous and semicrystalline samples. Changes of the various polymer fractions with composition show similar trends in DSC and DRS. RAFfiller was found to increase with filler fraction, with a saturation for the largest loading (20 wt%), assigned to filler aggregation confirmed by morphological characterization. Both RAFcrystal and mobile amorphous fraction, MAF, were found within experimental error almost constant with filler loading. The overall results suggest that interfacial interactions (RAFfiller) in combination with changes in semicrystalline morphology dominate polymer dynamics in semicrystalline PNCs.

Molecular Dynamics Study of Polyethylene under Extreme Confinement

We present results concerning the dynamics and the structure of adsorbed layers of molten polyethylene (PE) between two graphite surfaces. The molecular weight of the monodisperse PE chains reaches the entanglement regime. We study three cases of interwall distances, equal to two, three and four times the unperturbed radius of gyration (Rg) of PE chains. The confined system is equilibrated by use of efficient Monte Carlo (MC) algorithms. Conducting molecular dynamics (MD) simulations, we reveal the distribution of relaxation times as a function of distance from the graphite walls at the temperature of 450 K. From the atomic-level stresses we calculate a realistic estimate of the adhesion tension, which is not affected significantly by the width of the pore. Although the distance between the two walls is comparable to the width of the adsorbed layer, we do not record the formation of ‘glassy bridges’ under the studied conditions. The diffusion of polymer chains in the middle layer is not inhibited by the existence of the two adsorbed layers. Extreme confinement conditions imposed by the long range wall potentials bring about an increase in both the adsorption and desorption rates of chains. The presented results seem to cohere with a reduction in the calorimetric (heat capacity step) glass transition temperature (Tg).

Morphology and molecular dynamics investigation of PDMS adsorbed on titania nanoparticles: Effects of polymer molecular weight

Morphology, thermal transitions and molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto low specific surface area (25m2/g) spherical-like titania (TiO2) nanoparticles were studied employing adsorption–desorption nitrogen isotherms, morphology (SEM), calorimetry (DSC) and dielectric (BDS) techniques. The initial titania particles (crystallites of 40–140nm in diameter) were found to aggregate forming voids of a broad range. PDMS was adsorbed in the interior of voids in aggregates and onto external surfaces of the aggregates. With nanoparticles content increasing an increase in the glass transition temperature, Tg, is observed in DSC, accompanied by a broadening of the glass transition step and a decrease in the heat capacity step, ΔCp. According to BDS the interfacial polymer fraction is larger and exhibits slower dynamics (αint relaxation) in the case of shorter PDMS chains (∼22 monomers/chain) as compared to longer chains (∼105 monomers/chain). Changes in the interfacial polymer fraction correlate well with changes in the specific surface area of the aggregates, as recorded by gas molecules adsorption–desorption, and with morphology (SEM). Comparison with previous results obtained with PDMS-based nanocomposites suggests that interfacial polymer fraction and dynamics are dominated by the concentration of polymer–particle contact points (increased for shorter chains due to more free chain ends), rather than by the strength of polymer–filler physical bonds.

Glass transition and segmental dynamics in poly(l-lactic acid)/graphene oxide nanocomposites

Effects of graphene oxide (GO) and GO modified with dodecylamine (org-GO) on glass transition and segmental dynamics of poly(l-lactic acid) (PLLA) were investigated by differential scanning calorimetry (DSC) and two dielectric techniques, broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC) techniques. Measurements were performed on initially amorphous and on crystallization annealed samples. Isothermal crystallization in the neat matrix and the nanocomposites was followed by DSC and BDS with the same thermal protocol. No change in the glass transition temperature is observed by DSC, whereas the heat capacity step decreases in the nanocomposites. The segmental α relaxation becomes faster and broader in the nanocomposites and its dielectric strength decreases. The results were rationalized in terms of a fraction of interfacial polymer becoming immobilized in the nanocomposites. Changes of this interfacial polymer fraction with composition and functionalization show similar trends in DSC and BDS, absolute values are, however, larger by BDS.

Thermal aging and accelerated weathering of PVC/MMT nanocomposites: Structural and morphological studies

ABSTRACTThis work focuses on the influence of weathering factors—UV radiation, humidity, and temperature on the structure and morphology of poly(vinyl chloride)/montmorillonite (PVC/MMT) nanocomposites obtained by melt blending. It has been observed that organically modified MMT (OMMT) deteriorates the weathering resistance, the thermal behavior, as well as the long‐term stability of PVC. Decomposition of the organic modifier of MMT causes substantial color changes in the PVC nanocomposites as it facilitates the dehydrochlorination process of the polymer. However, the nonmodified MMT provides some stabilization during PVC weathering. The nanocomposites after annealing are characterized by higher glass transition temperature. The increase in heat capacity step (Δcp) during glass transition suggests that in the PVC composites with nonmodified MMT stronger molecular interactions between the polymer and clay platelets occur than in PVC/OMMT nanocomposites. The scanning electron microscopy images on the surface and the cross section show that thermal aging and weathering proceed by different mechanisms. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42090.

Structure-barrier property relationship of biodegradable poly(butylene succinate) and poly[(butylene succinate)-co-(butylene adipate)] nanocomposites: influence of the rigid amorphous fraction.

Composites composed of polyesters, poly(butylene succinate) (PBS) or poly[(butylene succinate)-co-(butylene adipate)] (PBSA), and 5 wt% of montmorillonite (CNa) or organo-modified montmorillonite (C30B) were melt-processed and transformed into films by either compression-molding or extrusion-calendering. XRD, rheological measurements and TEM images clearly indicated that films containing CNa are microcomposites, while nanocomposites were observed for those containing C30B. Using Flash DSC, it was possible, for the first time, not only to measure the heat capacity step at the glass transition of these two materials in their amorphous state, but also to investigate whether the preparation technique influenced the Rigid Amorphous Fraction (RAF) in our PBS- and PBSA-based nanocomposites. In this work, we have successfully shown the correlation between the microstructure of the films and their barrier properties, and especially the role played by the RAF. Indeed, the lowest permeabilities to gases and to water were determined in the films containing the highest RAF in both PBS- and PBSA-based materials.

Field Test and Sensitivity Analysis of a Sensible Heat Balance Method to Determine Soil Ice Contents

Soil ice content impacts winter vadose zone hydrology. It may be possible to estimate changes in soil ice content with a sensible heat balance (SHB) method, using measurements from heat pulse (HP) sensors. Feasibility of the SHB method is unknown because of difficulties in measuring soil thermal properties in partially frozen soils. The objectives of this study were (i) to examine the SHB method for determining in situ ice content, and (ii) to evaluate the required accuracy of HP sensors for use in the SHB method. Heat pulse sensors were installed in a bare field to measure soil temperatures and thermal properties during freezing and thawing events. In situ soil ice contents were determined at 60‐min intervals with SHB theory. Sensitivity of the SHB method to temperature, heat capacity, thermal conductivity, and time step size was analyzed based on numerically produced soil freezing and thawing events. The in situ ice contents determined with the SHB method were sometimes unrealistically large or even negative. Thermal conductivity accuracy and time step size were the key factors contributing to SHB errors, while temperature and heat capacity accuracy had less influence. Ice content estimated with a 15‐min SHB time step was more accurate than that estimated with a 60‐min time step. Sensitivity analysis indicated that measurement errors in soil temperature and thermal conductivity should be less than ±0.05°C and ±20%, respectively, but the error in the soil heat capacity could vary by ±50%. Thus, improving the accuracy of thermal conductivity measurements and using short time steps are required to accurately estimate soil ice contents with the SHB method.

Dielectric properties of epoxy/montmorillonite nanocomposites and nanostructured epoxy/SiO2/Montmorillonite Microcomposites

Composites reinforced with microparticles using a polymer matrix reinforced by nanoparticles represent a new emerging class of materials. Epoxy composites have been prepared using quartz as microfillers and organically modified Montmorillonite as nanofillers in order to study the dielectric properties of such new materials. The structure of the composites as determined by transmission electron microscopy, is neither exfoliated nor intercalated, although the thickness of C30B stacks is in the nanometric range. The influence of nano‐ and microparticles on epoxy matrix amorphous structure has been highlighted through Differential Scanning Calorimetry experiments. C30B has not effect on glass transition temperature but a drastic from 357 K to 325 K decrease is observed with the addition of microparticles. Heat capacity step remains unchanged, except for the microcomposite. And finally, Broadband Dielectric Spectroscopy has been used to characterize the dielectric properties at different temperatures. The spectra have been fitted with Havriliak–Negami equation to extract the relaxation times and the dielectric strengths associated with local β and γ relaxations and the main α relaxation. POLYM. COMPOS., 115–124, 2016. © 2014 Society of Plastics Engineers

The effect of rigid polymeric particles addition on the local dynamic heterogeneity and the ultrasound attenuation of butyl acrylate-methyl methacrylate copolymers

The effect of rigid poly(styrene-co-acrylonitrile) nano and micro-particles on the dynamic heterogeneity of poly(butyl acrylate-co-methyl methacrylate) (BM) matrices and the ultrasound attenuation in the corresponding composite systems were studied. The loss of local segmental mobility in the matrix chains located within an interfacial layer around the rigid nanoparticles and its consequent influence on the macroscopic response of the filled copolymers was investigated by dynamic mechanical (DMA), differential scanning calorimetry (DSC), and solid-state NMR methods. Upon comparison with the neat copolymers, no significant changes in the peak temperature and width of the matrix glass transition were observed in the DMA and the DSC data of the composites. The 1H transverse relaxation and dipolar filtering experiments of the matrix phase gave similar results for both the neat copolymers and the composite samples. In alignment with the NMR results, the weight fraction of the vitrified chains segments, obtained from heat capacity step at Tg, was found to be only around 2% of the matrix phase. The insensitivity of the applied experimental techniques to the presence of the interfacial layer was also verified by calculating the thickness and weight fraction of this layer in a weakly interacting nanocomposite. Furthermore ultrasound attenuation of the neat and filled BM copolymers was described in terms of viscoelastic loss in the matrix phase and contributions from wave scattering from the rigid particles.

Study of dielectric relaxation of epoxy composites containing micro and nano particles

The influences of micro and nanoparticles on relaxation kinetics were studied using Differential Scanning Calorimetry and Dielectric Spectroscopy. The samples are composed of Quartz and/or Organically Modified Montmorillonite dispersed in an epoxy matrix. The heat capacity step, normalized to epoxy quantity, did not show significant variations, contrary to the glass transition temperature, which decreased for the nanostructured microcomposite. The main α relaxation parameters, fragility index and relaxation time at the glass transition temperature combined to show that, even though molecular movements are hindered by the presence of particles acting as obstacles, the global mobility of the molecular chains is increased because reticulation of the epoxy has been prevented. The local β relaxation, associated with crankshaft motions of the hydroxylether groups, is not affected by micro and nanoparticles. The modification of the γ relaxation associated with the ending epoxy groups suggests that different interfacial interactions occur with nanoparticles/epoxy and microparticles/epoxy. The relaxation parameters will be situated in the context of the dielectric breakdown results. Dielectric breakdown strengths are more modified by inhomogeneity in sample preparation than by addition of organically modified Montmorillonite to the composite material.

Gradient of molecular dynamics at the glass transition of PETg–Montmorillonite nanocomposites

Temperature Modulated Differential Scanning Calorimetry (TMDSC) is used to estimate Cooperative Rearranging Region (CRR) average sizes for polymer/clay nanocomposites, obtained by mixing polyethylene 1,4-cyclohexylenedimethylene terephthalate glycol (PETg) filled and organically modified nanoclay (C15A) following a master-batch process. Two different basal distances are obtained. It is shown that the greater the basal distance and the nanofiller content, the lower the heat capacity step at the glass transition temperature Δ Cp( T g ), and the lower the CRR volume. It is also shown that the evolution of the CRR volume is consistent with the evolution of the fragility index obtained by DSC and Broadband Dielectric Spectroscopy (BDS) when the nanofiller content changes. The fragility index and the CRR size decreases can be correlated to nanofiller presence, hindering the molecular movements. From the Vollenberg and Heikens [34] approach, this behaviour can also be interpreted through the existence of an interfacial bilayer. This interfacial bilayer is composed by a zone, which is next to the nanofiller, with a density higher than the matrix one, followed by a more expanded zone with a density lower than the matrix one.

Immobilized Polymer Fraction in Hyperbranched Polymer/Silica Nanocomposite Suspensions

The glass transition behavior of hyperbranched polymer (HBP) molecules with suspensions of silica and glass particles up to the concentrated regime (25 vol %) was analyzed by modulated differential scanning calorimetry (MDSC). The reversing and nonreversing components of the MDSC signal were measured on suspensions of untreated and silylated particle of size in the nanometer and micrometer ranges. The heat capacity step (ΔCp) at the glass transition of the HBP was found to be independent of silica loading for microparticles, whereas it decreased with increasing particle amount in the case of nanoparticles. A similar behavior was observed for the enthalpy relaxation. These changes in chain dynamics and the progressive suppression of aging were attributed to immobilization effects of the HBP at the surface of the particles, which became detectable only in the case of a very high specific surface. The immobilized HBP fraction was assumed to form a shell of constant thickness around individual particles and was calculated from the ΔCp at the transition. In the case of untreated particles with a silanol surface, the immobilized shell was formed by HBP molecules H-bonded to the particles. The thickness of the shell was found to be equal to 1.9 nm, which corresponded to half the size of the HBP. In the case of methacrylsilane-treated silica, the immobilized shell thickness was found to be equal to 1.3 nm, which corresponded to a monolayer of covalently bound silane. © 2010 American Chemical Society.